Download Topic 1 Patterns in Nature

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Biology
Preliminary Course
Stage 6
Patterns in nature
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Number: 43209
Title: Patterns in nature
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Photographs courtesy of the Australian Key Centre for Microscopy and Microanalysis,
University of Sydney
Part 1 pp 8, 18, Part
4 pp 5, 6, 9, 11
Photographs courtesy of Jane West
Part 1 pp14-16,
Part 5 p 9,
Part 8 pp 9, 10
Diagram of a cross-section of a leaf, Messel, H (Chair) (1963) Science for high school students.
University of Sydney
Part 5 p 12
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© State of New South Wales, Department of Education and Training 2008.
Contents
Module overview
Outcomes ............................................................................................ iv
Indicative time...................................................................................... iv
Resources............................................................................................ iv
Icons ................................................................................................... vii
Glossary............................................................................................. viii
Part 1: Chemicals in cells ...................................................1–17
Part 2: Osmosis and diffusion .............................................1–23
Part 3: Cell theory and the light microscope........................1–26
Part 4: Electron microscopes and cell organelles ...............1–25
Part 5: Obtaining and transporting materials in plants ........1–40
Part 6: Obtaining materials in animals ................................1–15
Part 7: Transporting materials in animals ...........................1–21
Part 8: Growth and repair....................................................1–18
Student evaluation of the module
Introduction
i
ii
Patterns in nature
Module overview
Living things use raw materials in different ways to construct new living
tissues and repair existing tissues. All living organisms carry out similar
processes to form the structures that make up their bodies. To carry out
these processes, raw materials need to be obtained. The types of raw
materials and the way in which these raw materials are obtained differ
between living organisms. There are more similarities than differences
in the overall processes involved, the elements used and the molecules
made.
Intake of the materials required by all living organisms and the removal
of waste products are influenced by the surface areas of membranes
through which these nutrients and waste products must pass. In large
multicellular forms, complex organ systems with large surface area to
volume ratios, have evolved to allow movement of material across the
membranes. These organs are concerned with specialised functions in
the bodies of large multicellular organisms.
In this module you will be learning about the structure and function of
cells in plants and animals.
In order to make the most of this information the following assumed
knowledge is required.
Introduction
•
Diffusion involves random movement of particles.
•
Systems in multicellular organisms serve the needs of cells.
•
Systems in multicellular organisms supply the needs of cells.
•
Word equations can be used to describe a range of reactions.
•
The role of cell division in growth, repair and reproduction in
multicellular organisms.
•
Information is transferred as DNA on chromosomes when cells
reproduce.
•
Genes consist of DNA.
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Outcomes
This module increases students’ understanding of the history, nature and
practice of biology and current issues, research and developments in
biology.
Indicative time
This module is designed to take forty indicative hours. The module is
divided into eight parts, each approximately five hours of work.
Resources
The following materials will be required for each part. You may wish to
read through the list and plan ahead to ensure you have what you need
when you get to each activity. Alternative activities are given.
For Part 1 you will need:
•
Tes-tape® (can be purchased at the chemist)
•
iodine (use antiseptic preparation such as Betadine® from the
chemist)
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brown paper, such as the kind used for baking or as lunch bags
For Part 2 you will need:
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•
a packet of jelly crystals or
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potassium permanganate
•
two 12 cm lengths of dialysis tubing. Dialysis tubing is selectively
permeable. You could substitute cellophane wrapping paper.
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glucose powder, a sugar
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two small glass jars of the same size and shape
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4 pieces of strong cotton or thread
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some fine plastic (cling wrap) for covering jars
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a piece of Tes-tape® about 5 cm long, cut into three equal lengths
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a spoon or spatula for stirring or mixing
Patterns in nature
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waterproof pen.
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calcium hydroxide (about 1/4 tsp)
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phenolphthalein (about 1/4 tsp)
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powdered gelatine or yellow jelly crystals. Do not use any other
coloured jelly crystals.
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a jug or measuring cylinder for measuring 150 mL of boiling water.
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a small mixing bowl or 250 mL beaker. The bowl should have
straight sides.
•
some vinegar. Vinegar is an acidic solution containing acetic acid.
•
a refrigerator to set your jelly.
For Part 3 you will need:
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microscope lamp (if the microscope does not have one built into
the unit)
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clean glass slides and coverslips
•
dropper
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onion, moss or very soft fleshy plant stem
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meat blood (obtained by collecting the liquid remaining after frozen
goods are defrosted)
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iodine (or an antiseptic preparation containing iodine such as
Betadine®)
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blade or small vegetable knife
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cutting board.
Alternative exercises are provided if you do not have access to a
microscope.
For Part 5 you will need:
• 1 large beaker or saucepan
• 1 small beaker or glass jar
• Bunsen burner or hot plate
• tripod and gauze (if using Bunsen)
• 250 mL water
• 50 mL methylated spirit
• a few soft fleshy leaves such as a geranium
• aluminium foil
• a variegated leaf plant
Introduction
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iodine solution
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stick of celery
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glass of water with food colouring (red/blue works best)
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knife, small kitchen type
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hand lens or microscope with lamp
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glass slides and cover slips if using microscope
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thin glass tubing or clear plastic tubing
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Vaseline® or petroleum jelly
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soft, fleshy plant stem eg. Impatiens
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marker pen or sheet of graph paper
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scissors
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retort and clamp or similar
For Part 6 you will need:
• mortar and pestle or a suitable grinding tool and vessel
• petri dish or small plate
• Bunsen burner or hotplate
• 3 test tubes or similar
• sand
• small quantity of liver from a butcher
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hydrogen peroxide (this can be purchased at a pharmacist)
For Part 8 you will need:
•
microscope and lamp
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two slides and a cover slip
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onion with fresh roots (you need to soak onion base in water at least
a week in advance)
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methyl green pryonin or aceto-orcein stain.
Alternatively use prepared slides of a root tip (if available).
If you do not have access to a microscope or prepared slide, use the
photographs provided.
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Patterns in nature
Preparing resources
Some activities have alternative suggestions. You may wish to skim
through the parts to decide which activities you will be doing.
Where preparation is required, the instructions have been included in the
activity outline.
Icons
The following icons are used within this module. The meaning of each
icon is written beside it.
The hand icon means there is an activity for you to do. It
may be an experiment or you may make something.
You need to use a computer for this activity.
Discuss ideas with someone else. You could speak with
family or friends or anyone else who is available. Perhaps
you could telephone someone?
There is a safety issue that you need to consider.
There are suggested answers for the following questions at
the end of the part.
There is an exercise at the end of the part for you to
complete.
Introduction
vii
Glossary
The following words, listed here with their meanings, are found in the
learning material in this module. They appear bolded the first time they
occur in the learning material.
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alimentary canal
tube through which food passes between the
mouth and anus
amino acid
nitrogen containing basic building block
molecule of proteins
antibodies
a type of protein that reacts in with a specific
antigen, part of the body defence mechanism
aqueous
used to describe substances that contain water
biconcave
concave shape on either side of a lens
bond
something that combines or holds things
together
Brownian motion
describes a pattern of random movement of
particles in liquids or gases
cloaca
the terminal part of the gut in most vertebrates
except the higher mammals
compound
a pure substance composed of two or more
elements
desiccation
the drying out or removal of moisture
disaccharide
a molecule with double units of sugar
distended
enlarged, stretched or swollen
enzyme
a highly specialised cellular protein that
reduces the amount of energy required to
initiate a chemical reaction, thereby
increasing the speed of reaction
flaccid
limp
guard cells
pair of specialised cells in a plant epidermis
forming a pore or stomate
haemoglobin
a protein molecule found in red blood cells
that transport oxygen
histologist
a person who studies detailed or microscopic
tissue structure
hypertonic
higher solute concentration than another fluid
hypotonic
lower solute concentration than another fluid
Patterns in nature
Introduction
ion
an atom that carries a charge due to loss or
gain of electrons
isotonic
similar solute concentration as another fluid
lenticel
pore found on stems and roots in higher plants
for gas exchange
lignin
thickening substance found in cell walls of
plants
lymph glands
organs in the body that produce lymph or
interstitial fluid which is clear and assists in
the bodies defence system
magnification
to increase the size of something
mangroves
vegetation found in estuarine areas
metabolism
describes the chemical reactions occurring
within an organism
monosaccharide
a molecule with single unit of sugar
multicellular
organisms composed of more than one cell
nectar
a sugars secretion of a plant that attracts birds
and insects
organelle
any part of a cell that has a specific functional
role
organism
any living plant or animal
orifice
a tube like opening
oxidation reaction
a chemical reaction in which the proportion of
oxygen in the molecule is increased
plasma membrane
also called cell membrane, the outer boundary
of a cell
polysaccharides
a molecule with multiple units of sugar
precipitate
a solid formed from the reaction of two liquid
substances
prion
an infectious particle composed of protein,
containing no genetic material
radioisotope
natural or artificial isotope exhibiting
radioactivity, used as a source for medical or
industrial purposes
resolution
the ability of optical instruments to produce
separate images of close objects
respiration
the process by which carbohydrates and
oxygen are combined to release energy,
carbon dioxide and water
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x
saturated
maximum uptake of a substance has been
achieved
secrete
to produce and pass through a membrane out
of a cell
stomata
a pore through which gas exchange takes
place, usually located on a leaf
translucent
diffuse transmission of light through a surface
that is not smooth
tripe
lining of a ruminant stomach
turgid
describes the swollen or distended state of a
cell
unicellular
describes organisms composed of only one
cell
vesicles
a small sac like structure
villi
finger like growth on the inside wall or lining
of the small intestine
virus
disease causing microscopic organism
composed of nucleic acid surrounded by a
protein coat, dependent on the metabolic and
reproductive processes of the cell they invade
viscosity
the tendency of a material to resist movement
through it
Patterns in nature
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 1: Chemicals in cells
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Contents
Introduction ............................................................................... 2
Chemicals in cells...................................................................... 4
Organic compounds in cells.................................................................5
Inorganic compounds in cells ............................................................10
Testing for chemicals in cells.............................................................11
Suggested answers................................................................. 13
Exercises – Part 1 ................................................................... 15
Part 1: Chemicals in cells
1
Introduction
In this part you are going to investigate the major groups of chemicals
found in cells and carry out some simple tests for these chemicals.
In this part you will be given opportunities to learn to:
•
identify the major groups of substances found in living cells and
their uses in cell activities
In this part you will be given opportunities to:
•
plan, choose equipment or resources and perform a first–hand
investigation to gather information and use available evidence to
identify the following substances in tissues:
–
glucose
–
starch
–
lipids
–
proteins
–
chloride ions
–
lignin
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board's website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
This version November 2002.
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There are some practical experiments to do in this part of the module.
Alternative exercises are given wherever possible. To do all of the
practical exercises you will need the following items.
•
Tes–tape®
•
iodine
•
brown paper
Part 1: Chemicals in cells
3
Chemicals in cells
Chemical compounds are substances consisting of two or more
elements chemically combined in a definite proportion. Water is a
compound composed of the elements hydrogen and oxygen. Sucrose (a
type of sugar) is a compound composed of the elements carbon,
hydrogen and oxygen.
Chemical compounds can be divided into two groups, inorganic and
organic compounds. Organic compounds have a structure based on
carbon atoms which are often linked to form carbon chains. Examples
of organic compounds include carbohydrates, lipids, proteins and
nucleic acids.
Inorganic compounds may or may not contain carbon. They may be
found in living and non–living things. Examples of inorganic
compounds are water, carbon dioxide and salts eg. sodium chloride
(common salt) and calcium phosphate (found in bone).
The most abundant inorganic compound in our body is water (H2O);
about 70% of our body is water. Many chemicals dissolve in water to
form ions. Ions are charged particles. For example, sodium chloride,
found in our blood and body fluids exists as sodium ions (Na+) and
chloride ions (Cl–).
1
What is the difference between an organic and an inorganic substance?
_____________________________________________________
_____________________________________________________
_____________________________________________________
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2
Complete the table below by listing the organic and inorganic
substances mentioned in the previous information.
Organic substances
Inorganic substances
Check your answers.
Membranes around cells provide separation from and links to the
external environment.
Organic compounds in cells
Now you have some background information you will focus on the main
organic compounds that are found in cells–carbohydrates, lipids,
proteins, nucleic acids, lignin and vitamins.
Carbohydrates
Carbohydrates are organic compounds commonly found in food as
starches and sugars.
1
Make a prediction about which elements are present in carbohydrates.
_____________________________________________________
2
You may have heard the word carbohydrate used in association with
diets and training in the media. Name some common foods that contain
carbohydrates.
_____________________________________________________
_____________________________________________________
Check your answers.
Part 1: Chemicals in cells
5
Carbohydrates are organic compounds. Therefore they contain carbon.
This is indicated by the carbo part of carbohydrate. The hydr part
indicates hydrogen while the ending ate indicates oxygen.
Carbohydrates are important sources of energy in cells. Carbohydrates
are broken down into glucose during the process of digestion. Glucose is
required by all cells for the process of respiration which provides energy.
If we eat more carbohydrate than the body needs, the excess is stored as
fat. It may be stored under the skin or around the internal organs.
There are three groups of carbohydrates:
•
monosaccharides
•
disaccharides
•
polysaccharides.
Monosaccharides (mono–sack–ah–rides) are the simplest carbohydrates.
They are single sugar units such as glucose. Glucose is found in all cells.
It is the main source of energy. Other monosaccharides are fructose
(fruit sugar) and ribose a sugar in nucleic acids (acids such as RNA).
Disaccharides (di–sack–ah–rides) are double units of sugars.
An example is sucrose or table sugar which comes from sugar cane
and sugar beet. Sucrose is made when a glucose molecule and a
fructose molecule are bonded together. A molecule of water is lost in
this reaction.
Polysaccharides are complex carbohydrates consisting of multiple sugar
units which form huge molecules. Examples are starch and cellulose.
cellulose
starch
Cellulose and starch molecules.
One starch molecule consists of two to three thousand glucose molecules
joined together. Cellulose is the main component of plant cell walls.
It consists of more than two thousand glucose molecules joined together.
The previous illustrations show small sections of a cellulose and starch
molecule. Both are insoluble in water.
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Testing for carbohydrates
Sugars (reducing type that contain certain disaccharides and
monosaccharides) can be identified by using Benedict’s solution.
Benedict’s solution is blue–green in colour. The solution changes to an
orange–red when heated in the presence of sugars such as glucose.
Glucose can also be tested for by using Tes–tape®. The paper tape
changes from a yellow to a green colour in the presence of glucose.
Starches can be tested for using iodine solution, which turns a dark
blue–black colour in the presence of starch.
Cellulose can be tested for by adding iodine solution then concentrated
(70%) sulfuric acid. When iodine is placed on cellulose it remains
brown. After a few drops of acid are added, the iodine changes colour to
purple or black if cellulose is present.
Lipids
Lipids include fats, oils, waxes and steroids. Lipids are found in both
plant and animal cells.
Excess lipids are stored in the body as fat in animals. Lipids are used to
store energy. This fat store also provides protection around vital organs.
Some large mammals such as whales, seals and polar bears use fat to
insulate them from extreme temperatures.
Lipids, like carbohydrates, contain the elements carbon, hydrogen
and oxygen. However, the hydrogen and oxygen are not in a 2:1 ratio.
Simple fats consist of three fatty acids combined with one
glycerol molecule.
Two types of lipids exist, those that have single bonds between the
carbon atoms. These are most often the animal fats such as lard and
butter. They are called the saturated lipids. Unsaturated lipids have
some carbon atoms that have two bonds. These are the vegetable oils
which are liquid at room temperature. You may have heard these terms
used when referring to margarine products.
Lipids can be tested for with a piece of thin brown paper such as that
used as a lunch bag. If fat is present a translucent stain or smear appears
on the paper.
Name some examples of lipids used in the home.
_________________________________________________________
Check your answers.
Part 1: Chemicals in cells
7
Proteins
Proteins are another important group of organic compounds. Proteins are
used for growth and development and form part of many important
substances in the body such as enzymes and antibodies.
There are about 2000 different proteins in any human cell.
Proteins contain the elements carbon, hydrogen, oxygen and nitrogen.
Sometimes they contain sulfur and phosphorus.
Proteins, like polysaccharides, are large molecules built from the linking
of many smaller molecules. The small molecules in this case are amino
acids. The bonds between the amino acids are peptide bonds. There are
commonly 20 different amino acids and they can join in any order.
The order determines the type of protein formed.
1
List some food which are high in protein.
_____________________________________________________
_____________________________________________________
2
Why are proteins important in our diet?
______________________________________________________
______________________________________________________
Check your answers.
Testing for proteins
The Biuret test is used to test for the presence of protein. To carry out
the test a few drops of sodium hydroxide are combined with dilute
copper sulfate and heated in a water bath. If protein is present a purple
colour is produced.
Nucleic acids
Nucleic acids are commonly found in the chromosomes of the nucleus of
a living cell. Two nucleic acids are commonly found in the nucleus.
These nucleic acids are deoxyribose nucleic acid (DNA) and ribose
nucleic acid (RNA).
DNA is formed from building blocks called nucleotides
(new–klee–oh–tides). Each nucleotide itself is formed from three parts,
sugar, phosphate unit and a base. The sugar is called deoxyribose sugar.
It is ribose sugar with one less atom of oxygen.
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The bases are adenine (add–en–een),
guanine (gwar–nene), thymine
(thigh–meen) and cytosine
(site–oh–seen).
A
T
C
G
C
G
sugar
nitrogen base
T
A
C
G
phosphate unit
T
A
A
Nucleotide unit.
T
C
G
Nucleotide units combine to form part
of a DNA molecule.
A
T
C
The structure of this molecule is like a
ladder. The sides are formed from the
sugar and phosphate groups. The rungs
are formed from the bases.
The bases bond in such a way that
adenine pairs with thymine (A–T), and
cytosine pairs with guanine (C–G).
The order of the these pairs is the
genetic code for an organism.
G
G
A
C
C
T
G
DNA double helix.
Testing for nucleic acids
The presence of nucleic acids is indicated by using aceto–orcein.
When a few drops are added to nucleic acid a blue green colour
is produced.
Lignin
Lignin forms much of the wood in trees. It enables cells to become rigid
and provide support and protection.
The presence of lignin can be tested by the addition of a solution of
toluidine blue on fresh plant material. Lignin will stain green–blue while
unlignified parts will be pink–purple.
Part 1: Chemicals in cells
9
Vitamins
Vitamins are organic compounds needed in very small quantities for
normal growth and health of organisms. Their main functions are in the
enzyme systems in the body, without them, enzymes would not function.
Most vitamins are obtained directly from food although some are formed
in the body. For example, carotene (the yellow–orange pigment in
carrots and other yellow or orange vegetables and fruits) is changed into
vitamin A in the body. As well, a substance in our skin is changed to
vitamin D when our skin is exposed to sunlight.
Complete Exercise 1.1.
Inorganic compounds in cells
By far the most abundant substance in our bodies is water (between 60%
and 70%). Expressed another way, a typical 70 kg person would have
42 L of water in the body. While people can survive several weeks
without food, they can last only a few days without water. Plants also
contain large amounts of water. What happens to a pot plant if it is not
watered regularly?
Other inorganic substances found in cells are mineral salts. These are
simple chemical compounds that exist as ions when dissolved in water.
For example, common table salt (sodium chloride) NaCl, becomes Na+
and Cl– ions when dissolved in water.
Mineral ions are essential for many body processes, the amount of each
type varying over the lifespan of the organism.
Other mineral ions required by the body are listed below.
10
•
Calcium essential for bone development and blood clotting.
•
Iron which is used for the formation of haemoglobin in red blood cells.
•
Chlorine required for water balance as well as acid–base balance in
the blood and formation of hydrochloric acid (HCl) in the stomach.
Chlorine is present as chloride ions (Cl-). The presence of chloride
ions can be detected by using silver nitrate solution. A white
precipitate results when chloride ions are present.
•
Sodium is required for water balance and is essential for the nervous
system. Sodium is present as ions (Na+).
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•
Potassium is involved in muscle contraction which is essential for
movement. It is present as ions (K+). The ratio of sodium and
potassium ions controls the nervous system.
•
Phosphorus is an important component of the chemicals involved in
energy transformations around the body.
Testing for chemicals in cells
The substances you need to know tests for are glucose, starch, lipids,
proteins, chloride ions and lignin.
Read the information in this section again to identify the tests used to detect
the presence of the substances listed here. Complete the table below.
Chemical compound
Test
Indication
glucose
starches
chloride ions
protein
lipids
lignin
Check your answers.
In this activity you will be carrying out some tests on substances found in
tissues.
To do this experiment you will need to obtain the following materials.
•
Tes–tape® (this can be obtained at a pharmacy)
•
Iodine (this can be substituted by using a preparation such as
Betadine®, from a pharmacy)
•
Brown paper (use a brown paper lunch bag)
Part 1: Chemicals in cells
11
Testing for glucose
Glucose is a chemical widely distributed in cells. Glucose is the organic
compound usually involved in respiration. It is the compound from
which we obtain energy. All cells need energy, so we would expect to
find glucose in cells.
The test for glucose is simple with Tes–tape®. All you have to do is to
press the yellow paper tape, Tes–tape®, against the cells or tissue being
tested. If you want to test some potato for glucose, cut a fresh section
and press the Tes–tape® against it. Leave the paper for several minutes
and note any colour change. If testing a liquid produced by cells, such as
milk, dip the Tes–tape® in the liquid, then remove it. Wait for a few
minutes to see if there is a colour change. A colour change from yellow
to green indicates glucose.
Test any three tissues for glucose. Any skin on plant foods needs to be
removed. Record your test on a sheet of paper. Suggested tissues are
potato, celery and any fruit.
Complete Exercise 1.2.
Testing for starch
Starch is a polysaccharide carbohydrate. It is the form in which plants
store excess sugar (in animals, excess sugar is usually stored as fat). To
test plant cells or tissue for starch, you add a few drops of iodine to a
freshly cut section. A colour change from yellow–brown to blue–black,
indicates that starch is present. Remember that iodine is a chemical used
to stain cells so that their organelles can be more easily seen.
Test any three tissues for starch eg. seeds (such as rice), banana, potato.
Complete Exercise 1.3.
Testing for lipids
Lipids can be found in common foodstuff such as butter or oil. To carry
out the test, you will need to get a brown paper bag (lunch bag) and rub
the test sample on the paper and look for the translucent smear or stain.
Try rubbing butter, margarine or oil onto a brown paper bag.
Complete Exercise 1.4.
To finish this part visit the LMP science online site for links to view
animations of food tests. www.lmpc.edu.au/science
12
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Suggested answers
Types of chemical compounds
1
Organic compounds all contain carbon. Many are found in living
things. Inorganic compounds don’t necessarily contain carbon and
are found in both living and non–living things.
2
Organic substances
Inorganic substances
carbohydrates
water
lipids
carbon dioxide
proteins
sodium chloride
nucleic acids
calcium phosphate
Carbohydrates
1
Carbohydrates contain the elements carbon, hydrogen and oxygen.
2
Examples of foods high in carbohydrates include cereals, bread,
pasta, potato and rice.
Lipids
Lipids in the home include lard, dripping, oil, cream, butter and
margarine products. Foods such as nuts and grains are high in lipids.
Proteins
1
Food high in proteins include: peanuts, meat, fish, cheese, eggs.
2
Proteins are used for growth and repair in the body.
Part 1: Chemicals in cells
13
Testing for chemicals in cells
14
Chemical compound
Test
Indication
glucose
Testape®
paper tape changes from
yellow to green on drying
starches
iodine solution
yellow solution changes to
purple or black
chloride ions
add a few drops of silver
nitrate solution
a grey/white precipitate
results if chloride ions are
present
protein
Biuret test. Add a few drops
of sodium hydroxide solution
then dilute copper sulfate
a purple colour is produced
lipids
rub sample with brown paper
a translucent stain on paper
is produced
lignin
toluidine blue
green–blue colour
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Exercises - Part 1
Exercises 1.1 to 1.4
Name: _________________________________
Exercise 1.1: Chemicals in cells
a)
Identify the major groups of substances found in living cells.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Fill in the table below showing the uses in cell activity of the
substances listed.
Substance
Uses in cell activity
Carbohydrates
Lipids
Proteins
Nucleic acids
Lignin
Vitamins
Part 1: Chemicals in cells
15
Exercise 1.2: Testing for glucose
a)
Name the tissues you tested for glucose.
______________________________________________________
______________________________________________________
b) Explain what you did and describe the results.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c)
What are your conclusions?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 1.3: Testing for starch
a)
Record your observations of iodine on food products.
______________________________________________________
______________________________________________________
b) Explain what you did and describe the results.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c)
What are your conclusions?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
16
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Exercise 1.4: Testing for lipids
a)
Name the foods you tested for lipids.
_____________________________________________________
_____________________________________________________
b) Explain what you did and describe the results.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
What are your conclusions?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 1: Chemicals in cells
17
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 2: Osmosis and diffusion
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Contents
Introduction ............................................................................... 2
Membrane structure .................................................................. 4
Movement across a membrane................................................. 5
Investigating diffusion...........................................................................6
Investigating osmosis...........................................................................7
Active transport ..................................................................................11
Why are cells so small?........................................................... 13
Surface area to volume ratio..............................................................14
Suggested answers................................................................. 19
Exercise–Part 2 ....................................................................... 21
Part 2: Osmosis and diffusion
1
Introduction
In this part you are going to investigate the role of membranes in cells
and how they separate the internal chemicals of the cell and also act as a
link to the outside environment.
In this part you will be given opportunities to learn to:
•
identify that there is movement of molecules into and out of cells
•
describe the current model of membrane structure and explain how it
accounts for the movement of some substances into and out of cells
•
compare the processes of diffusion and osmosis
•
explain how the surface area to volume ratio affects the rate of
movement of substances into and out of cells.
In this part you will be given opportunities to:
•
perform a first–hand investigation to model the selectively
permeable nature of a cell membrane
•
perform a first–hand investigation, to demonstrate the difference
between osmosis and diffusion
•
perform a first–hand investigation to demonstrate the effect of
surface area to volume ratio on rate of diffusion.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board's website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
This version November 2002.
2
Patterns in nature
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There are some practical experiments to do in this part of the module.
Alternative exercises are given wherever possible. To do all of the
practical exercises you will need the following items.
•
a packet of jelly crystals or
•
potassium permanganate
•
two 12 cm lengths of dialysis
tubing. Dialysis tubing is
selectively permeable. You
could substitute cellophane
wrapping paper.
•
glucose powder, a sugar
•
two small glass jars of the
same size and shape
•
4 pieces of strong cotton or
thread
•
some fine plastic (cling wrap)
for covering jars
•
a piece of Tes–tape® about 5
cm long, cut into three equal
lengths
•
a spoon or spatula for stirring
or mixing
•
waterproof pen.
Part 2: Osmosis and diffusion
•
calcium hydroxide (about 1/4
tsp)
•
phenolphthalein (about 1/4 tsp)
•
powdered gelatine or yellow
jelly crystals. Do not use any
other coloured jelly crystals.
•
a jug or measuring cylinder for
measuring 150 mL of boiling
water.
•
a small mixing bowl or 250
mL beaker. The bowl should
have straight sides.
•
some vinegar. Vinegar is an
acidic solution containing
acetic acid.
•
a refrigerator to set your jelly.
3
Membrane structure
Cells are bound by a plasma membrane. Although not visible even
under the strongest light microscope, its existence has been verified in
the last three decades. The cell membrane separates the contents of the
cell from its surroundings providing a barrier to its external environment.
Water, gases, ions and other small molecules are able to move through
the membrane, while other substances are not. This ability to allow some
substances through and not others means that the membrane is selectively
permeable (also known as semipermeable or differentially permeable).
The current model of plasma membrane structure was proposed by
Singer and Nicholson in 1972. They described it as a ‘fluid mosaic
model’ in which a double layer of lipid molecules has proteins and
glycoproteins embedded within it. The layers have tiny pores or
openings that allow the movement of materials in and out of the cells.
protein
double
lipid
layer
glycoprotein
molecule
cholesterol
Fluid mosaic model of the structure of a plasma membrane.
4
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Movement across a membrane
All matter consists of atoms, ions and molecules. In liquids and gases
these molecules are not fixed in position–they are moving at random.
Substances move in and out of cells in solution, this means that the
substance is dissolved in a liquid (usually water). The cell membrane
allows some substances to pass across it but not others depending on the
size of the particles or molecules. Molecules that can move across such a
selectively permeable membrane include glucose, oxygen and carbon
dioxide. Starch and protein are too large.
The kinetic theory of matter provided some qualitative explanations for
the motion of particles in solution toward the end of the 19th century.
This described particles in the various states of matter in a constant state
of motion depending on the temperature of the matter. The higher the
temperature, the faster the motion.
solid
liquid
gas
Particles in solids, liquids and gases are in a constant state of motion.
This movement of particles results in collisions. Each collision changing
the particle’s velocity by a small amount, resulting in a random motion of
the particles.
1
What happens to the motion of the particles in a solid if it is heated?
_____________________________________________________
Part 2: Osmosis and diffusion
5
2
If a gas is cooled, describe the effect that this would have on the
motion of its particles.
______________________________________________________
3
Can you predict the effect a temperature change might have on the
diffusion of particles within a liquid in a cell?
______________________________________________________
Check your answers.
Investigating diffusion
Diffusion is the random movement of particles from regions where they
are in a high concentration to regions of lower concentration.
This produces a uniform distribution.
You have experienced diffusion when a bottle of perfume is opened in
one part of a room. After a while, you can smell it across the room.
The perfume, as a gas, has diffused across the room. After a while the
smell of the perfume is all over the room.
Diffusion is important in living things as it allows organisms to take in
materials that they need and lose waste material. This process is a
passive process as it requires no energy from an organism. It occurs
because of the random movement of particles.
Materials required:
•
two glass jars
•
two crystals of potassium permanganate or one packet of coloured jelly
crystals
•
one cup of cold water
•
one cup of hot water
Method
6
1
Pour a cup of cold water into a glass jar.
2
Drop one crystal of either potassium permanganate or jelly into the
water.
3
Observe the crystal as it sinks to the bottom of the jar and then
continue to watch for two to three minutes. Answer the questions
below. Then repeat the procedure, using hot water.
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a) What happens to the crystal as it drops to the bottom of the jar?
_________________________________________________
b) Explain using your knowledge of particle movement during
diffusion, what is occurring as the crystal remains in the water
for 2–3 minutes.
_________________________________________________
_________________________________________________
_________________________________________________
c) What was the most significant difference in your observations
when the procedure was repeated using hot water?
_________________________________________________
_________________________________________________
Investigating osmosis
Osmosis is a special case of particle movement as it describes the
movement of water across a selectively permeable membrane from an area
where there is more water (less concentrated or dilute) to an area that has
less water solution (more concentrated) to achieve a uniform distribution.
selectively permeable membrane
solute less
concentrated
(more water)
solute more
concentrated
(less water)
net movement of water molecules
water
solute
Osmosis occurs when water moves across a selectively permeable membrane
from a region where the solute is less concentrated to a region where the solute
is more concentrated.
Part 2: Osmosis and diffusion
7
same concentration
Osmosis results in solutions of the same concentration either side of a
selectively permeable membrane.
Aim: To investigate the process of osmosis.
Material needed:
•
glucose powder (a sugar)
•
two 12 cm lengths of dialysis tubing. Dialysis tubing is selectively
permeable. You could substitute cellophane wrapping paper.
•
two small glass jars of the same size and shape
•
4 pieces of strong cotton or thread
•
some fine plastic (cling wrap) for covering jars
•
a piece of Tes–tape® about 5 cm long, cut into three equal lengths
•
a spoon or spatula for stirring or mixing
•
waterproof pen.
Method
1
Run water over the dialysis tubing and rub it firmly with your thumb
and forefinger to open it up. Take care not to put a hole in it.
2
Use the thread to tie one end of the dialysis tubing. This must be
very firm so no liquid can seep through it.
If using cellophane, cut a square shape and bring the four corners
together. The solution can be poured into this and tied up using
string or thread.
8
3
Mix the glucose in about 50 mL of water to dissolve it. Dip a small
piece Tes–tape® into the glucose solution and then remove it.
Notice its colour as it dries.
4
Pour the glucose solution into the dialysis tubing until it is about half
full.
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5
Firmly tie another piece of thread around the other end of the
dialysis tubing, making a bag. Ease out some of the air as you
do this.
6
Wash the bag thoroughly to remove any glucose solution which may
be on the outside.
7
Half fill one small glass jar with water. Using a waterproof pen,
mark the level of the water on the outside of the jar.
Note: you need to mark this level very accurately.
8
Put the same amount of water in the other jar and mark the level, as
you did for the first jar. This container will be the control as you
will compare what happens in this container with what happens in
the container with the bag of glucose solution.
9
Put the bag of glucose solution in one of the jars of water. Immerse
it as much as possible.
10 Prepare another dialysis tubing bag and this time half fill it with
water only. Immerse it in the second jar of water. You have now set
up the control.
11 Cover both jars with plastic (such as gladwrap) and leave overnight.
Both set ups are now similar in all ways except there is glucose in
the bag in one jar and water only in the bag in the other.
Remember that the water levels in the two jars were the same before
the bags were added.
12 Next day lift the bag of glucose solution and let the water drip off it
into its jar.
What do you notice about the water level in this jar now?
13 Lift the bag of water and let the water drip off it into its jar.
Compare the water level in this control jar with the level in the first
jar.
14 Check whether the glucose molecules moved through the dialysis
tubing by dipping some Tes–tape® into the water in both jars.
Remember to let the Tes–tape® dry for a while before making a
decision.
Results
The level of water in the control beaker remained the same while the
level in the experimental beaker has gone down. The dialysis tubing
from the experimental beaker is more taut than at the beginning.
The dialysis tubing from the control experiment has remained the same.
Part 2: Osmosis and diffusion
9
Experiment
Control
mark water level
Experiment
Control
mark water level
glucose
solution
water
dialysis tubing
Next day remove the bagsof dialysis tubing
Experiment
Control
water level
change
In Exercise 2.1 write a brief conclusion to the experiment.
10
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Active transport
Active transport is required when materials required by the cell are in a
lower concentration surrounding the cell. This can occur, for example,
when the concentration of dissolved ions in root cells is higher than in
the surrounding soil water.
In active transport molecules, within the membrane itself, attach to a
substance and pull it across the membrane against the concentration
gradient. These are called carrier molecules. In the diagram below
potassium ions (K+) are being actively transported across a membrane
with the aid of carrier (transporter) molecules.
outside cell
cell membrane
inside cell
transporter
molecule
Active transport across a selectively permeable membrane.
Active transport requires energy to move materials across the membrane,
usually against the diffusion gradient.
Some materials still cannot move across the membrane. The reasons for
this include size, solubility, or they are not able to bind with the proteins
in the membranes in order to carry them through.
A summary to learn
•
Water enters cells across selectively permeable membranes from an
area that has more water (dilute or less concentrated) to an area that
has less water (more concentrated solution). This process is called
osmosis and is an example of passive transport as energy is not
required.
Part 2: Osmosis and diffusion
11
•
Differences in concentration are called a concentration or diffusion
gradient.
•
Solutes such as sodium or calcium ions enter plant cells by diffusion
from a region of low concentration of solute to a high concentration.
This is against the concentration gradient and so requires energy. It
an example of active transport.
•
A selectively permeable membrane is one that allows some, but not
all, substances to pass through it.
Diffusion
Osmosis
Movement of particles from a region of
high concentration to a region of low
concentration.
A special type of diffusion.
Movement of water across a
selectively permeable membrane from
a region of high concentration of water
to a region of low concentration of
water.
Complete Exercise 2.2 now.
12
Patterns in nature
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Why are cells so small?
Have you ever wondered why cells are so small? What is the advantage
to being small?
The answer lies in the relationship between volume (the amount of space
occupied) and surface area.
All cells need to take in substances from their surroundings and release
wastes. These substances must pass through the physical boundary
separating the inside of the cells from the outside. The larger the size of
this boundary, compared to the size or volume of the cell, the more
efficient this process is.
The following two shapes are both cubes. They are different sizes.
1 cm cube
2 cm cube
If these shapes represented sponges, which one would become saturated first
when placed in a puddle of water? Suggest a reason for your answer.
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Part 2: Osmosis and diffusion
13
Surface area to volume ratio
A ratio is a proportional relationship between two quantities. In this
case it is the relationship between volume and surface area.
To understand how this relationship affects movement of materials
across a membrane you will now use a model.
In this model consider ‘cells’ of three different sized cells:
•
a cell with sides measuring 3 cm
•
a smaller cell with sides measuring 2 cm
•
and a model of an even smaller cell with sides measuring 1 cm.
To calculate the ratio of the surface area to volume, you need to find both
the surface area and volume of each ‘cell’.
Surface area
The surface area is the sum of the total area (length ¥ width) of all sides.
There are six faces on a cube. Area is calculated by multiplying the
length by width.
•
The area of one face of the large cell is 3 cm ¥ 3 cm (9 cm2)
•
The area of one face of the medium cell is 2 cm ¥ 2 cm (4 cm2).
•
The area of one face of the smallest cell is 1 cm ¥ 1 cm (1 cm2).
The total surface area of each cell is multiplied by six since a cube has
six faces. The total surface area of each cell is calculated as follows.
•
Total surface area of large cell is 9 cm2 x 6 = 54 cm2
•
Total surface area of medium cell is 4 cm2 x 6 = 24 cm2
•
Total surface area of small cell is 1 cm2 x 6 = 6 cm2
Volume
Volume of a cube is calculated by multiplying the
length ¥ width ¥ depth. Here is how you calculate the volume for each
of the model cells.
14
•
The volume of the large cell is 3 cm x 3 cm x 3 cm = 27 cm3.
•
The volume of the medium cell is 2 cm ¥ 2 cm x 2 cm = 8 cm3.
Patterns in nature
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•
The volume of the smallest cell is 1 cm ¥ 1 cm x 1 cm = 1 cm3.
You can express the surface area (SA) and volume (V) as a ratio (SA:V).
•
SA:V (large cell) = 54:27 = 2:1
•
SA:V (medium cell) = 24:8 = 3:1
•
SA:V (small cell) = 6:1
You can see that the smaller the cell, the higher the surface area to
volume ratio. Check that this is true by doing some calculations yourself.
1
Calculate the surface area to volume ratio of a model cell of sides
4 cm x 4 cm x 4 cm.
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
Calculate the surface area to volume ratio of a model cell of sides
0.1 cm x 0.1 cm x 0.1 cm.
_____________________________________________________
_____________________________________________________
_____________________________________________________
3
How does the surface area to volume ratio change as the cell
becomes smaller?
_____________________________________________________
Check your answers.
A small cell has relatively more surface area to absorb substances.
This means that small cells have an advantage over large cells when
materials are moving in and out. Therefore, there is an advantage in
small size.
Part 2: Osmosis and diffusion
15
Advantage of small size investigation
The experiment outlined on the next page will help you to verify your
ideas on how size affects the movement of substances.
Aim: To demonstrate the advantage of small size, or a large surface area to
volume ratio in a model cell.
Background information:
In this experiment, you will make three model cells out of jelly.
The cells will be made alkaline by using calcium hydroxide (an alkali).
You will be colouring your cells pink by using phenolphthalein.
Phenolphthalein turns pink in alkaline solution.
During your experiment, you will put your alkaline, pink cells in some
acid. When an acid reacts with an alkali, it neutralises it. As the acid
diffuses into your model cells, the acid will neutralise the alkali and
the pink colour will disappear leaving the model cells colourless or
pale yellow.
From this observation you will be able to make inferences about the
movement of acid into your model cells. Then you may be able to
extrapolate and draw a conclusion about the movement of materials into
cells and the effect size has on this process.
Note: If you cannot obtain any calcium hydroxide or phenolphthalein, it
is possible to do the same exercise using potato cubes and a solution of
iodine. The iodine can be purchased in the form of antiseptic
preparations such as iodine tincture or iodine paint.
What you need:
16
•
calcium hydroxide (about 1/4 tsp)
•
phenolphthalein solution (about 1/4 tsp)
•
powdered gelatine or yellow jelly crystals. Do not use any other
coloured jelly crystals.
•
a jug or measuring cylinder for measuring 150 mL of boiling water.
•
a small mixing bowl or 250 mL beaker. The bowl should have
straight sides.
•
some vinegar. Vinegar is an acidic solution containing acetic acid.
•
a refrigerator to set your jelly.
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What to do:
1
Put 6 tsp of gelatine powder in a small mixing bowl (or 250 mL
beaker). Add 150 mL of boiling water.
Stir well until all the gelatine is dissolved.
If you are using jelly crystals, use half the packet of crystals with
150 mL of boiling water.
2
Add about 1/4 tsp of calcium hydroxide and 2 drops of phenolphthalein.
Do not handle these chemicals. Use a spoon.
3
Stir well to mix thoroughly. A bright pink should be produced. Add a
little extra calcium hydroxide if the pink colour does not appear.
4
Put the pink jelly in the refrigerator for about an hour to set firmly.
Make sure you warn family members that the jelly is for an
experiment. Do not eat. Place a warning sign on the jelly.
5
When the pink jelly has set, remove it intact from the beaker or
bowl. Run a knife around the sides, invert it and tap the bottom to
free it.
6
Use your knife and ruler to make three different sized cubic cells:
–
a large one with sides 3 cm
–
a medium–sized one with sides 2 cm
–
a small one with sides 1 cm.
Make the sizes of the cubes as accurate as possible. Plan your
cutting areas before you start, otherwise you may find yourself short
of jelly. Your mixing bowl must be a shape that allows you to cut
out the three ‘cells’ with the volumes indicated.
4
Put your three model cells into the empty beaker or bowl. Cover
them with vinegar.
5
Leave until the small one has just lost all its pink colour. Remove
the cells from the vinegar immediately using a spoon.
6
Slice each of the larger cubes in half and quickly measure in
centimetres the width of the pink centres. Make your measurements
as accurate as possible.
For the alternate version cut your cubes out of potato and immerse
in a solution of iodine.
Complete Exercise 2.3.
Part 2: Osmosis and diffusion
17
18
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Suggested answers
Movement across the membrane
1
The particles in a solid speed up and move apart when heated.
2
Particles in a gas that has been cooled would slow down and move
closer together (condense).
3
Diffusion could occur faster in cells at a higher temperature
compared to those at a lower temperature.
Why are cells so small?
The smaller sponge would become saturated first.
Surface area to volume ratio
1
Surface area = 42 x 6 = 96 cm2
Volume = 4 x 4 x 4 = 64 cm3
SA:V = 96:64 = 1.5:1
2
Surface area = 0.12 x 6 = 0.06 cm2
Volume = 0.1 x 0.1 x 0.1 = 0.001 cm3
SA:V = 0.06:0.001 = 60:1
3
The smaller the cell, the higher the surface area to volume ratio.
Part 2: Osmosis and diffusion
19
20
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Exercises – Part 2
Exercises 2.1 to 2.3
Name: _________________________________
Exercise 2.1: Investigating osmosis
Write a brief conclusion for your experiment.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 2.2: Osmosis and diffusion
Compare the differences between diffusion and osmosis. The word
compare can be defined as ‘show how things are similar or different’. In
this case there are both similarities and differences between diffusion and
osmosis. Write your answer with the definition of compare in mind.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 2.3: Advantage of small size
a)
Use the results from your experiment to complete the table
following. If you were unable to do the experiment use the answers
supplied to answer the questions.
Part 2: Osmosis and diffusion
21
22
Patterns in nature
1x1x1
2x2x2
Your results
3x3x3
Worked examples only
3x3x3
2x 2 x 2
1x1x1
Dimensions of the
model cells (cm)
2.53 or 15.6 cm3
1cm3
0cm3
2.5 cm
1cm
0cm
0
(Assume it is
perfectly cubic…this
will be the
measurement in the
previous column
cubed.) (A)
(Use a decimal point
giving as accurate a
measurement as
possible)
0
Volume of coloured
centre.
Width of the
coloured centre in
centimetres
1 cm3
27 cm3
8cm3
1 cm3
(Use the first
column.) (B)
Volume of the
whole cube—the
entire ‘cell’.
1 cm3
11.4 cm3
7cm3
1 cm3
This will be (B—A)
Volume of the
uncoloured part of
the cell.
100%
11.4/27 x100= 42%
7/8 x100= 87.5%
1/1 x100= 100%
(This is the
measurement in the
previous column
divided by the total
volume (B) multiplied
Percentage of the
cell which is
uncoloured
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b) The last column of the table represents the percentage of each cell
which was colourless.
Why was this part of the cell colourless?
_____________________________________________________
_____________________________________________________
c)
i)
If the jelly blocks were living cells, and the acid was a normal
nutritional requirement of a cell, which block would be supplied
most efficiently by diffusion?
_________________________________________________
_________________________________________________
_________________________________________________
ii) Why is this cell supplied most efficiently with ‘nutrients’?
Refer to the surface area and volume in your answer.
_________________________________________________
_________________________________________________
_________________________________________________
c)
Explain the advantage to cells of small size or a large surface area to
volume ratio.
_____________________________________________________
_____________________________________________________
_____________________________________________________
d) Explain how the SA:V affects the rate of movement of substances
into and out of cells.
_____________________________________________________
_____________________________________________________
_____________________________________________________
e)
Can you think of other examples where SA:V in living things has a
significant effect? Hint: think about adaptations to the surrounding
environment.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 2: Osmosis and diffusion
23
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 3: Cell theory and the light microscope
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Contents
Introduction ............................................................................... 2
What is cell theory? ................................................................... 4
The historical development of the cell theory .....................................4
Evidence to support the cell theory .....................................................6
Problems with the cell theory...............................................................6
The microscope......................................................................... 7
The light microscope ............................................................................8
Cell organelles ........................................................................ 11
Using a light microscope....................................................................11
Summary................................................................................. 17
Suggested answers................................................................. 21
Exercises–Part 3 ..................................................................... 23
Part 3: Cell theory and the light microscope
1
Introduction
Organisms are made of cells which have similar structural characteristics.
In this part you will be given opportunities to learn to:
•
outline the historical development of the cell theory, in particular,
the contributions of Robert Hooke and Robert Brown
•
describe evidence to support the cell theory
•
discuss the significance of technological advances to developments
in cell theory
•
identify cell organelles seen with current light microscopes
In this part you will be given opportunities to:
•
use available evidence to assess the impact of technology, including
the development of the microscope on the development of the cell
theory
•
perform a first–hand investigation to gather first–hand information
using a light microscope to observe cells in plants and animals and
identify nucleus, cytoplasm, cell wall, chloroplast and vacuoles.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board's website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
This version November 2002.
2
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There is a practical activity in this part that requires the use of a
microscope and the following equipment:
•
microscope lamp (if the microscope does not have one built into
the unit)
•
clean glass slides and coverslips
•
dropper
•
onion, moss or very soft fleshy plant stem
•
meat blood (obtained by collecting the liquid remaining after frozen
goods are defrosted)
•
iodine (or an antiseptic preparation containing iodine such as
Betadine®)
•
blade or small vegetable knife
•
cutting board.
Alternative exercises are provided if you do not have access to a
microscope.
Part 3: Cell theory and the light microscope
3
What is cell theory?
You have previously studied cells and you know that living things are
made of cells and that cells share similar structural characteristics.
But did you know that the existence of cells had to wait for the historical
development of the microscope for their discovery? To examine this
history you need to look at the contributions of a range of scientists
including, Robert Hooke and Robert Brown.
The historical development of the
cell theory
Before looking at the historical development of the cell theory it is
useful to be clear about what the cell theory means. The cell theory was
proposed by Scheilden and Swann in 1839 and added to by Virchow
in 1858.
In summary the cell theory states that:
•
cells are the basic units of life and reproduction
•
most organisms consist of a cell or cells and cell products
•
all cells come from pre–existing cells.
Most cells are so small that they are invisible to the naked eye.
This meant that the discovery of cells had to wait until there were
magnifiers to see them. The simplest magnifiers are single lenses such as
those used in a magnifying glass. The development of the cell theory
depended on the manufacture and use of lenses and magnifying devices
such as microscopes as well as the combined investigation efforts of
many scientists. This occurred over a period of 300 years.
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Robert Hooke
In 1665 Robert Hooke, an English scientist, used a compound
microscope to observe the cellular nature of cork. (A compound
microscope consists of two or more lenses which are positioned inside a
tube.) Hooke’s microscope magnified objects about 270 times (x270)
their normal size.
Hooke's microscope.
Hooke's drawing of cork cells.
He called the structures seen in the cork, cells because they reminded
him of the small rooms (cells) that monks lived in.
Anton van Leewenhoek
A few years later in 1676 Anton van Leeuwenhoek
(lay–van–hook), a Dutchman made amazing
discoveries of unicellular organisms like bacteria.
Leeuwenhoek used, not compound microscopes,
but single lens microscopes. These magnified
about 250 times (x250).
Van Leeuwenhoek was a master lens grinder.
Unfortunately, he was extremely secretive about his
method of grinding lenses and didn’t pass on his
Van Leeuwenhoek's
knowledge and skills.
microscope.
Part 3: Cell theory and the light microscope
5
Robert Brown
Robert Brown (1773–1858) was a Scottish botanist who accompanied
Matthew Flinders to Australia in 1801. As well as identifying new
genera of plants in Australia, he is known for discovering Brownian
movement and the cell nucleus.
Evidence to support the cell theory
The main evidence for the cell theory occurred when the theory of
spontaneous generation was disproved. This theory stated that life arose
from non–living matter such as piles of rubbish and organisms such as
rats and flies were produced by rotting meat. Francesco Redi
(1626–1697) showed that maggots only arose from meat that flies had
visited and Louis Pasteur (1822–1888) showed that micro–organisms
only come from other micro–organisms. The work of these two
scientists convinced people that living things are made of cells and that
all cells come from pre–existing cells. This led to important changes in
hygiene and medical practices.
Problems with the cell theory
Since the time when the cell theory was proposed, viruses and prions
have been identified.
How do viruses and prions fit into the cell theory? They do not
structurally resemble cells. They are much smaller than cells. They do
not have a nucleus, cell membrane or cytoplasm.
Viruses consist mainly of a core of deoxyribose nucleic acid (DNA) and
a protein coat. Prions are an infectious protein particle that causes
various nervous diseases in mammals. Mad cow disease is an example
of a disease caused by a prion. Prions do not contain any genetic
material. While viruses often appear to be non–living, they can
reproduce when they are within a living cell. So, they pose a problem.
Are they living or non–living? Many people regard viruses as living, but
they differ from other living things in that they are not cellular.
Complete Exercise 3.1.
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The microscope
The development of the cell theory was closely related to the
technological advances that occurred with the development of
improved lenses.
As well as the improvement in microscopes, other technological
advances have occurred. These include machines called microtomes that
are capable of cutting ultra–thin sections of material. Also the ability to
use different chemicals as staining agents. Some stains are taken up
selectively by different materials and can be used to identify chemicals
such as starch or different structures within the cell. Examples of
commonly used stains are iodine, toluidine blue and eosin.
When looking at microscopes there are two factors that are important,
magnification and resolution.
Magnification is the amount that the object is magnified or how much
larger the object appears. A light microscope magnifies up to 1000
times. The new generation of microscopes are the electron microscopes,
the first of which was built in 1933 by Ernst Ruska. The magnification
of an electron microscope is about one million times the normal size.
Resolution (resolving power) is the ability of a microscope to distinguish
two or more points together, as discrete objects. If the resolution of a
microscope is poor you can continue magnifying an object but it just
appears to be more blurred and bigger.
The magnification of an electron microscope can be up to one million
times with a resolving power of up to 0.0002 µm (micrometres).
The light microscope can only resolve up to 0.2 µm. This is about 500
times more than the human eye can resolve.
Part 3: Cell theory and the light microscope
7
The light microscope
The light microscope passes a beam of light through a specimen which is
magnified by the objective lens. The light then travels up the body of the
microscope and is then magnified again as it is passes through the lens in
the eyepiece.
Light microscope.
© Australian Key Centre for Microscopy.
In this activity you have to use available evidence to assess the impact of
technology, including the development of the microscope on the
development of the cell theory..
To do this look for information from a range of resources including popular
scientific journals, CD–ROMs and the Internet.
Illustrate the trends and patterns by creating a table such as the one below
that shows the development of the microscope. Look for a logical
progression of ideas as technological advances lead to the development of
the cell theory.
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There are some useful starting points on the LMP Science Online site,
http://www.lmpc.edu.au/science.
Also try the interactive activities dealing with the microscope.
1590
Father and son team, Hans and Zacharias Janssen, construct the first
compound microscope.
1665
Robert Hooke using a compound microscope observed cork.
1672
Marcello Malpighi (1628–1699) discovered capillaries.
1676
Anton van Leeuwenhoek (1632–1723) described unicellular organisms.
His great skill was in producing outstanding lenses that had a better
resolution than any other lenses of the time.
1824
Rene Dutrochet (1776–1847) was he first to state that all animals and
plants are made of cells.
1831
Robert Brown (1773–1858) named the nucleus and found it was
present in both plants and animal cells.
1839
Mathias Schleiden (1804–1881) and Theodor Schwann (1810–1882)
were given credit for the cell theory.
1855
Rudolf Virchow (1821–1902) added the third statement of the cell
theory that all cells come from pre–existing cells.
1880
Walther Flemming (1843–1905) described cell division or mitosis from
observations on living and stained cells.
1932
Ernst Ruska built the first electron microscope.
Today
The best light microscopes today have a magnification of 1500x.
Electron microscopes can have a magnification of up to one million
times and high resolving power.
Part 3: Cell theory and the light microscope
9
1
List the main features of the cell theory.
• ____________________________________________________
• ____________________________________________________
• ____________________________________________________
2
Use the information in the table on the previous page to answer the
following questions.
a) Who observed that plant and animal cells have a nucleus?
_________________________________________________
b) Who are given credit for the cell theory?
_________________________________________________
c) Who stated that cells come from pre–existing cells?
_________________________________________________
3
Complete the following sentences.
a) Hooke’s compound microscope magnified objects about ____ X.
Van Leeuwenhoek’s microscopes magnified object about ___ X.
A modern compound microscope can magnify about ______ X.
b) The different microscopes were developed as a result of _____
changes.
c) One important improvement in microscopes has been that they
have increased the __________________________ of objects.
Check your answers.
Do Exercise 3.2 now.
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Cell organelles
Within a cell there are structures that are common to many cells.
These are called organelles. All cells are held together as a unit by the
cell membrane (also called the plasma membrane). In plant cells, the cell
membrane is surrounded by a cell wall composed of cellulose.
Common organelles that you may have heard of include the nucleus,
mitochondria, chloroplasts and ribosomes. Some cell organelles are
visible using a light microscope; more are seen with an electron
microscope. You will look firstly at the organelles that are visible under
a light microscope.
Using a light microscope
The table below shows the cell structures that can be seen when using a
light microscope to examine plant and animal cells.
Animal cells
Plant cells
nucleus
nucleus
cell membrane
cell membrane
cytoplasm
cytoplasm
nuclear membrane
nuclear membrane
cell wall
chloroplasts
vacuole
Part 3: Cell theory and the light microscope
11
The cell wall and chloroplasts of some plant cells can be clearly seen.
The chloroplasts in plant cells show up clearly because they are green.
This is due to the presence of the green pigment, chlorophyll.
Vacuoles can be large in mature plant cells but very small in animal cells,
if it is present at all.
Observing plant and animal cells
The following activity will help you identify structures in some cells.
You will be observing plant and animal cells using a light microscope.
You can revise how to use and set up the microscope in the Science resource
book or if you have access to the Internet the following web site will provide
you with an address.
http://www.lmpc.edu.au/science.
If you do not have access to a microscope to carry out the activity, you
can use the light microscope photographs on the following pages to
answer the questions in this section.
Materials:
•
microscope
•
microscope lamp (if the microscope does not have one built into
the unit)
•
clean glass slides and coverslips
•
dropper
•
onion, moss or very soft fleshy plant stem
•
meat blood (obtained by collecting the liquid remaining after frozen
goods are defrosted)
•
iodine (or an antiseptic preparation containing iodine such as
Betadine®)
•
blade or small vegetable knife
•
cutting board.
Method:
1
Prepare a very thin section of specimen.
Use the blade to cut a very thin section of the plant material.
Caution: Always cut away from your fingers.
2
12
Prepare a wet mount of each specimen for investigation under the
microscope.
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To make a wet mount use the dropper to place a drop of water onto
the clean glass slide. Place the thin section of plant material onto the
drop of water and gently lower the cover slip. If onion is being used,
a drop of iodine can be added to the slide to provide a greater
contrast. (Iodine will stain any starch present.) Gently lower a cover
slip using the techniques illustrated below.
The blood can be placed directly onto the slide and smeared thinly.
Lower the coverslip gently onto the smear.
Cut a thin section, place a drop of water on the slide,. add the section and then
cover with a coverslip.
3
Place the slide on the microscope stage and use the coarse focus to
move the objective as close as possible to the slide while watching
from the side. Then whilst looking through the eyepiece move the
coarse focus away from the slide until the image is focused.
If the image does not appear ecogni, then repeat the steps again
(more slowly), making sure that the objective is once again lowered
whilst watching from the side to ensure that the slide and objective
are not accidentally damaged.
For more detail rotate the objective stage so that the high power
objective is being used to bring your specimen into clear view.
If you have a fine focus knob it should only be used when looking
through the high power objective.
4
Draw a ecogni diagram of each of the specimens observed in the
spaces on the following pages. Label any of the structures you were
able to identify.
Remember when drawing diagrams:
•
use pencil for the drawing
•
make the diagrams at least a half page in size
•
use a heading and label any structures you ecognize.
Part 3: Cell theory and the light microscope
13
Photograph of human blood viewed through a light
microscope. The larger cell is a white blood cell
showing the lobed nucleus. The rest are red blood
cells with no nucleus. (Photo Jane West)
Drawing showing the biconcave shape
of red blood cells.
Your drawing of human blood cells.
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Human cheek cells as seen through a light
microscope.(Photo Jane West)
Drawing of an animal cell as seen through a light
microscope.
Your drawing of animal cells.
Part 3: Cell theory and the light microscope
15
Photograph of a plant epidermis viewed through a
light microscope under high magnification. (Photo
Jane West)
A drawing of a plant cell. You may notice that it is difficult to
see the chloroplasts and vacuole in the photograph.
Your drawing of plant cells.
Do Exercise 3.3 now.
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Summary
Use this self–correcting summary to check your knowledge of the cell
theory and the technology that has led to the discovery of cell organelles.
1
What are the three main generalisations in the cell theory?
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
Which type/s of technology has made it possible for us to know that
cells exist?
_____________________________________________________
_____________________________________________________
_____________________________________________________
3
Outline one improvement in microscopes following Hooke’s early
discoveries.
_____________________________________________________
_____________________________________________________
_____________________________________________________
4
Study the photograph of the light (optical) microscope on the next
page.
a) Identify the parts labelled and state a function of each part.
Do this by using a table with the three headings: Letter, Name of
part, and Function on your own paper. You may need to refer to
the Science resource book if you were unable to use a
microscope.
Part 3: Cell theory and the light microscope
17
Light microscope.
© Australian Key Centre for Microscopy.
b) Explain briefly how you would prepare a wet mount.
__________________________________________________
__________________________________________________
__________________________________________________
c) Name one chemical that can be used to stain cells.
__________________________________________________
d) Why are stains useful when examining cells using the
microscope?
__________________________________________________
__________________________________________________
__________________________________________________
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e) Briefly outline the steps involved in observing a specimen using
the low power of a light (optical) microscope.
_________________________________________________
_________________________________________________
f)
What is the term used to describe the ability to see fine details
clearly?
_________________________________________________
Check your answers.
Part 3: Cell theory and the light microscope
19
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Suggested answers
The microscope
1
Life and reproduction is not possible without cells.
Living things are made up of cells.
Cells are produced from other cells.
2
a) Robert Brown
b) Schleiden and Schwann
c) Rudolf Virchow
3
a) Hooke’s compound microscope magnified objects about 270 X.
Van Leeuwenhoek’s microscopes magnified object about 250 X.
A modern compound microscope can magnify about 1000 X.
b) The different microscopes were developed as a result of
technological changes.
c) One important improvement in microscopes has been that they
have increased the magnification of objects.
Summary
1
Cells are the basic units of life and reproduction.
Most organisms consist of a cell or the products of cells.
All cells come from pre–existing cells.
2
Magnifiers and microscopes make it possible for us to know that
cells exist.
3
The grinding of lenses for single lens microscopes.
Part 3: Cell theory and the light microscope
21
4
4
a)
Letter
Name
Function
e
eyepiece
magnification lens
o
objective
magnification lens
c
condenser
focuses light from mirror onto specimen
s
stage
support for specimen
l
light
light source
f
focus knob
moves the stage to focus image
b) A wet mount is made by placing a thin section of a specimen
into a drop of water on a clean slide. This is covered with a
coverslip. A stain may be added to the specimen if required.
c) Examples of stains are iodine, toluidine blue and eosin
d) Stains are useful because they make the image easier to see by
increasing the contrast between structures. They are also useful
because they can indicate the presence of different types of
compounds for example iodine turns blue–black in the presence
of starch.
e) Direct lamp or light source into microscope using the mirror.
Place slide on the stage.
Lower low power objective whilst looking from the side.
Look down eyepiece and slowly wind the coarse focus knob up,
until the image comes into focus.
f)
22
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Exercises – Part 3
Exercises 3.1 to 3.3
Name: _________________________________
Exercise 3.1: What is cell theory?
a)
What are the three main generalisations of the cell theory?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) What was the contribution of the following two scientists to the cell
theory.
Robert Hooke
_____________________________________________________
_____________________________________________________
_____________________________________________________
Robert Brown
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
Outline the theory of spontaneous generation. Name two scientists
whose work disproved the theory of spontaneous generation and
gave support to the cell theory.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 3: Cell theory and the light microscope
23
Exercise 3.2: The microscope
a)
Complete the sequence scaffold below highlighting the historical
developments in the establishment of technology in developing the
cell theory.
The first one has been done for you.
24
Date
Event
1590
Father and son team, Hans and Zacharias Janssen,
construct the first compound microscope .
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1665
1676
circa 1900
circa 1933
b) The diagram above shows the development of the microscope.
These technological advances were important in the development of
the cell theory. Discuss the significance of technological advances
to developments in cell theory.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 3.3: Cell organelles
a)
Compare and contrast plant and animal cells. This means that you
must look at the similarities and differences between the two types
of cells.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 3: Cell theory and the light microscope
25
b) Draw a diagram in the space below of a generalised plant and animal
cell as seen through a light microscope, labeling the structures
identified.
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Biology
Preliminary Course
Stage 6
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Part 4: Electron microscope and cell organelles
2
0
0
In
r2
e
b S
o
t
c NT
O
ng DM E
i
t
ra E N
o
rp A M
o
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Contents
Introduction ............................................................................... 2
The electron microscope ........................................................... 3
Using an electron microscope .............................................................4
Structure and function..........................................................................5
Tissues, organs and organ systems........................................ 14
Summary................................................................................. 15
Suggested answers................................................................. 17
Exercises–Part 4 ..................................................................... 21
Part 4: Electron microscope and cell organelles
1
Introduction
Plants and animals have specialised structures to obtain nutrients from
their environment. You may recall that plants and animals obtain
nutrients differently. Plants rely on the Sun to manufacture food by a
process called photosynthesis. Plants are autotrophic organisms.
Animals cannot manufacture their own food; they consume or eat other
organisms in order to gain the nutrients they require for life processes.
Animals are heterotrophic organisms.
Plants and animals have specialised cells, tissues and organs to obtain the
nutrition they require and carry out their body processes. Some of these
will be investigated in this part.
In this part you will be given opportunities to learn to:
•
identify cell organelles seen with an electron microscope
•
describe the relationship between the structure of cell organelles and
their function
•
identify some examples that demonstrate the structural and
functional relationships between cells, tissues, organs and organ
systems in multicellular organinsms
In this part you will be given opportunities to:
•
process information from secondary sources to analyse electron
micrographs of cells and identify mitochondria, chloroplasts, Golgi
bodies, lysosomes, endoplasmic reticulum and cell membranes.
Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board’s website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.
This version November 2002.
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The electron microscopes
There are two main types of electron microscopes:
•
the transmission electron microscope and
•
the scanning electron microscope.
Unlike light microscopes that use a beam of light passing through the
specimen electron microscopes use a beam of electrons.
The transmission electron microscope uses the electrons that pass
through very thin specimens, to show detailed images of internal
structures. The scanning electron microscope produces images of the
surface features of objects, often coated with a very thin layer of metal
atoms to enhance the image.
One disadvantage of using electron microscopes is that the preparation of
specimens is very expensive. For example, the specimen must be kept in
a vacuum to avoid scattering the electron beam or it must be fixed in
heavy metal compounds eg. gold. This means that it is not possible to
view live specimens, also a disadvantage. It is unclear whether such
harsh treatment of specimens might actually distort the true nature of the
structure of the cells.
An electron microscope
Part 4: Electron microscope and cell organelles
3
The advantage of the electron microscope is that the magnification
(x 1 million) and the resolution (0.0002 micrometre) are very high.
Do Exercise 4.1 now.
Using an electron microscope
Under a light microscope there is a limit to the organelles that are visible
even with the latest technology. The story is different however, under an
electron microscope where there are many more organelles visible.
The table below lists the cell structures that are visible with an
electron microscope.
4
Cell structure
Animal cells
Plant cells
nucleus
present
present
nucleolus
present
present
cell membrane
present
present
cytoplasm
present
present
nuclear membrane
present
present
mitochondria
present
present
Golgi bodies
present
present
ribosomes
present
present
endoplasmic reticulum
present
present
lysosomes
present
absent
cell wall
absent
present
chloroplasts
absent
present
vacuole
absent
present
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Structure and function
The nucleus
The nucleus is usually large and spherical. The nucleus is enclosed by a
double membrane. This membrane has pores that allow fairly large
molecules to move in and out of the nucleus.
The nucleus often contains a nucleolus which is involved in the
manufacture of proteins in the cell. (Refer to the electron micrograph
below showing the nucleus and other organelles.)
Nucleus in a rat intestinal wall. (g—Golgi bodies, m—mitochondrion,
nu—nucleolus, n—nucleus, rer—rough endoplasmic reticulum)
© Australian Key Centre for Microscopy.
The nucleus controls the activities of the cell. It does this largely by
controlling the formation of proteins in the cell. The nucleus contains the
chromosomes, which carry the genes. Genes are units of inheritance and
determine which types of proteins are formed.
Part 4: Electron microscope and cell organelles
5
What sort of structural feature/s does the nucleus have that makes it suited
for its function?
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Plastids and chloroplasts
Plastids are oval–shaped organelles. Some store substances such as food
made by plants eg. starch. Other plastids contain pigments such as the
green pigment, chlorophyll. Plastids that contain chlorophyll are
called chloroplasts.
Chloroplast in soybean leaf. (g — granum, r — ribosomes, s — starch grains)
© Australian Key Centre for Microscopy.
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Look at the three dimensional drawing of a chloroplast below.
Note that it has, like a nucleus, a double membrane. Within a chloroplast
is a membrane known as the lamella. In some areas, the lamella is
densely packed into grana (singular granum). These resemble stacks of
coins and increase the surface area. The grana are embedded in a
colourless substance called the stroma.
ring of DNA
double membrane
starch grain
stroma
or
lamella
ribosome
stack of grana
(thylakoids)
Photosynthesis occurs in chloroplasts. So, essentially, the chloroplasts
are the food–making organelles of plants. The chlorophyll is contained
in the grana. It is the chlorophyll that absorbs light energy which makes
the process of photosynthesis possible.
Describe how the structure of a plastid such as a chloroplast assists the
process of photosynthesis in plant cells.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
The cell membrane
The cell membrane, also known as the plasma membrane, surrounds all
cells. It is a physical barrier but it is thin and contains pores that allow
selected materials to pass through. In plant cells the cell membrane is
surrounded and protected by the cell wall.
The function of the cell membrane, apart from keeping the cell together,
is to regulate the flow of substances into and out of the cell.
The membrane is described as selectively permeable. This means it
allows some substances to pass through while stopping other substances.
Part 4: Electron microscope and cell organelles
7
Describe how the structure of the cell membrane enables it to carry out the
function described here.
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
A summary
Following is a summary of important points so far. Fill in the missing
words as you read this summary.
1
The _____________ is a large spherical organelle that controls the
activities of the cell. This organelle is surrounded by a
_____________ membrane that has _____________ in it.
2
Chloroplasts are one type of _____________. They are green coloured
because they contain the green pigment, _____________. Like the
nucleus, the chloroplast is surrounded by a _____________ membrane.
Chloroplasts absorb _____________ energy, which drives the
food–making process called _____________.
3
The cell or plasma membrane keeps the cell intact. It allows some
substances to enter and leave while preventing others from entering or
leaving. It is therefore described as _____________ permeable.
Check your answers.
Mitochondria
Cells may contain several or hundreds of mitochondria. The more active
a cell is, the more mitochondria there are.
1
Make a prediction to explain why there are more mitochondria in an
active cell than one not involved in activity.
_____________________________________________________
_____________________________________________________ .
A mitochondrion is surrounded by a double membrane.
Look at the photomicrograph on the next page, which shows some
mitochondria. You can see that the inner membrane is highly folded.
Folded membranes like this provide a very large surface within a
small space.
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Mitochondria in unicellular algae.
© Australian Key Centre for Microscopy.
Mitochondria are the organelles in which the final stages of cellular
respiration occur. They are the organelles in which the energy produced
is released by cellular respiration. The wastes from this process, carbon
dioxide and water, are also formed in these structures. Mitochondria are
often referred to as the powerhouses of the cell because they are the
organelles which provide energy for the cell.
2
How does the structure of a mitochondrion support its function?
_____________________________________________________
_____________________________________________________
Check your answers.
Golgi bodies
A Golgi body was first observed and identified as an organelle by
Camillo Golgi (1844–1926), an Italian histologist. Hence, Golgi is
always spelt with a capital letter. We are inclined to get the impression
that these not so well known organelles were discovered when the
electron microscope came into use. This is not so.
Part 4: Electron microscope and cell organelles
9
The Golgi body was actually discovered when Golgi used an optical
microscope and a dye containing a silver compound. There was
originally much argument as to whether or not it was a new organelle or
simply a product of the staining technique he used. The matter was not
resolved for about 60 years when electron microscopes verified
Golgi’s claims.
Find the Golgi body in the electron micrograph below. Note that the
Golgi body consists of stacks of membranes which bulge out in places to
travel through the cell.
Small Golgi body in a grass leaf cell. (g — Golgi body, rer — rough
endoplasmic reticulum, cw — cell wall)
© Australian Key Centre for Microscopy.
The Golgi body has been found in nearly all types of cells, but is
particularly abundant in cells that secrete substances eg. the
salivary glands.
The Golgi apparatus can absorb amino acids and sugars and use them to
synthesise more complex proteins and carbohydrates. These chemicals
are contained in the vesicles, which become detached from the Golgi
apparatus. These vesicles appear to move away from the Golgi apparatus
across the cytoplasm to the cell membrane. Finally, the small vesicles
fuse with the cell membrane and the protein–carbohydrate substances are
discharged (secreted) from the cell.
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So, the Golgi body prepares and secretes various chemicals for use either
within or outside the cell.
How is the function of a Golgi body supported by its structure?
_________________________________________________________
_________________________________________________________
Check your answer.
Ribosomes
Compared to the nucleus, mitochondria, chloroplasts and Golgi body,
ribosomes are very small indeed. They are tiny, spherical organelles
which are found throughout the cell.
Ribosomes are found within other organelles such as the nucleus and
chloroplasts. They are also found attached to a membrane system known
as the endoplasmic reticulum.
Rough endoplasmic reticulum in rat intestine. (Arrowheads indicate ribosomes
attached to the surface of the rough endoplasmic reticulum).
© Australian Key Centre for Microscopy.
Part 4: Electron microscope and cell organelles
11
Ribosomes are the organelles where proteins are made. They are most
numerous in cells that produce proteins. The small size of ribosomes
gives a high surface area to volume ratio.
How does the structure of a ribosome enable it to produce proteins?
_________________________________________________________
_________________________________________________________
Check your answer.
Endoplasmic reticulum
The endoplasmic reticulum is a network of membranes that run through
the cytoplasm. The rough endoplasmic reticulum looks rough because
there are ribosomes attached to it. Smooth endoplasmic reticulum has no
ribosomes on it. The endoplasmic reticulum is an intricate combination
of canals.
Rough endoplasmic reticulum in mouse intestine. Parallel sheets of rough
endoplasmic reticulum can be seen surrounding the nucleus. (n — nucleus,
nu — nucleolus, m — mitochondria, rer — rough endoplasmic reticulum)
© Australian Key Centre for Microscopy.
The endoplasmic reticulum forms a complex system of canals or
channels along which substances are transported throughout the cell.
Smooth endoplasmic reticulum is involved in the formation of lipids
(fats). It also helps inactivate some drugs.
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How does the structure of endoplasmic reticulum relate to its function?
_________________________________________________________
_________________________________________________________
Check your answer.
Lysosomes
Lysosomes were first described in the 1950s. They are smaller than
mitochondria and are enclosed by single membranes. The membrane
does not permit the movement of enzymes from within and is capable of
resisting their digestive action. Lysosomes are more commonly found in
animal cells.
The lysosome is thought to contain enzymes that take in and break down
older cell organelles. If a lysosome should rupture (break) the enzymes
would break down and destroy the cell.
How is the structure of a lysosome relevant for the function it performs?
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
You will need to look carefully at the micrographs throughout the module
and familiarise yourself with them, as you may be required to identify such
pictures/diagrams at a later stage. Use other secondary sources of electron
micrographs to identify mitochondria, chloroplasts, Golgi body, lysosomes,
endoplasmic reticulum and cell membranes. Use the electron micrographs
on the previous pages and the LMP Science webpage for more sources of
pictures. Make sure you can identify the above cell organelles.
Complete Exercise 4.2.
Part 4: Electron microscope and cell organelles
13
Tissues, organs and organ systems
Cells are not a disorganised mass of matter. Instead cells are grouped
together to form tissues, tissues make up organs and organs make up
organ systems. The table below summarises this information.
Definition
Animal example
Plant example
tissue
a group of cells of the same type
with the same function
blood
phloem
organ
part of an animal or plant forming a
structural and functional unit which
is made up of one or more tissues
heart
leaf
organ system
a group of organs that function
together as a unit
blood system
vascular system
Explain the difference between tissues, organs and organ systems.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Do Exercise 4.3 to complete this part.
In the next part you will go on to investigate how specialised structures
are used by organisms to obtain nutrients from their surroundings.
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Summary
Self–correcting summary.
1
a) What are two advantages of using electron microscopes over
light microscopes?
_________________________________________________
_________________________________________________
b) In what way is the use of the electron microscope limited?
_________________________________________________
c) Which organelles would you be able to see using an electron
microscope that were not visible using a compound or light
microscope?
_________________________________________________
2
Complete the summary of cell organelle structure and function
following by filling in the missing words.
a) Mitochondria (singular ________________ ) are organelles with
a double ________________. The inner membrane is highly
________________ producing a large surface area.
Mitochondria are described as the powerhouses of cells because
they provide cells with ________________ to do work. The
final stages of the energy–releasing change called
________________ occur in these organelles.
b) A Golgi body consists of ________________. These
membranes bulge out to form ________________. These
vesicles contain various chemicals which are used whether
within the cell or ________________ by the cell for use
elsewhere.
c) ________________ are small, spherical structures which are the
site of protein synthesis.
Part 4: Electron microscope and cell organelles
15
d) The endoplasmic reticulum is a network of ________________
which form canals or passageways. The canals
________________ a variety of substances throughout the cell.
Endoplasmic reticulum with ribosomes attached is called
________________ endoplasmic reticulum.
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Suggested answers
The nucleus
The nucleolus is involved in the formation of proteins which controls the
activities of the cell. Substances are able to move in and out of the cell
through the pores in the nuclear membrane.
Plastids and chloroplasts
The stack of grana in chloroplasts increases the surface area available
within the chloroplast for photosynthesis.
Chloroplasts contain chlorophyll which absorbs light energy and makes
photosynthesis possible.
The cell membrane
The cell membrane is a physical barrier, it is thin and contains tiny pores
to enable the diffusion of matter across it.
A summary
1
The nucleus is a large spherical organelle which controls the
activities of the cell. This organelle is surrounded by a double
membrane that has pores in it.
2
Chloroplasts are one type of plastid. They are green coloured
because they contain the green pigment, chlorophyll. Like the
nucleus, the chloroplast is surrounded by a double membrane.
Chloroplasts absorb light energy, which drives the food–making
process called photosynthesis.
3
The cell or plasma membrane keeps the cell intact. It allows some
substances to enter and leave while preventing others from entering
Part 4: Electron microscope and cell organelles
17
or leaving. It is therefore described as selectively (or semi)
permeable.
Mitochondria
1
Active cells require large amounts of energy. Energy in cells is
provided by the process of respiration. Mitochondria might be the
site where respiration occurs, therefore providing the energy needed.
2
The highly folded inner membrane increases the surface area for
respiration. The large surface area provided by a folded membrane
provides more places for respiration to occur. So, respiration can
occur on a large–scale.
Golgi body
The Golgi consist of stacks of membranes which increase the surface
area for diffusion and synthesis of complex molecules. The vesicles
function is transporting these molecules to the cell membrane.
Ribosomes
The large surface area to volume ratio enables efficient movement of
materials across the ribosome’s membrane.
Endoplasmic reticulum
The large surface area enables the endoplasmic reticulum to efficiently
transport materials around the cell.
Lysosome
The semipermeable nature of the membrane prevents the enzymes
escaping into the cell and destroying it.
Tissues, organs and organ systems
Cells are fundamental units that make up a living thing. Similar cells
work together to form tissues and different tissues work together in
an organ.
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Summary
1
a) Greater magnification and resolution
b) Specimens are killed in the process of preparation for viewing
with an electron microscope. No guarantee that the resulting
images are true representations of the original living tissue. The
cost of electron microscope technology is very high.
c) Nucleolus, Golgi, endoplasmic reticulum (rough and smooth),
lysosome, mitochondria, ribosomes.
2
a) Mitochondria (singular mitochondrion) are organelles with a
double membrane. The inner membrane is highly folded
producing a large surface area. Mitochondria are described as
the powerhouses of cells because they provide cells with energy
to do work. The final stages of the energy–releasing change
called respiration occur in these organelles.
b) A Golgi body consists of membranes. These membranes bulge
out to form vesicles. These vesicles contain various chemicals
which are used whether within the cell or secreted by the cell for
use elsewhere.
c) Ribosomes are small, spherical structures which are the site of
protein synthesis.
d) The endoplasmic reticulum is a network of membranes, which
form canals or passageways. The canals transport a variety of
substances throughout the cell. Endoplasmic reticulum with
ribosomes attached is called rough endoplasmic reticulum.
Part 4: Electron microscope and cell organelles
19
20
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Exercises – Part 4
Exercises 4.1 to 4.3
Name: _________________________________
Exercise 4.1: The electron microscope
a)
Identify two types of electron microscopes.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b)
Describe two disadvantages of using an electron microscope.
_____________________________________________________
____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
What magnification and resolution are available with an electron
microscope?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 4: Electron microscope and cell organelles
21
Exercise 4.2: Observing plant and animal cells
The following diagrams show the structure of a generalised plant and
animal cell, as viewed with an electron microscope.
cytoplasm
Golgi apparatus
plasma membrane
cell wall
ribosomes
chloroplast
vacuole
nucleus
nucleolus
mitochondrion
endoplasmic reticulum
Plant cell (as seen with an electron microscope).
mitochondrion
nucleus
Golgi apparatus
nucleolus
smooth
endoplasmic
reticulum
plasma membrane
lysosome
rough
endoplasmic
reticulum
Animal cell (as seen with an electron microscope).
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a) Which structures are you able to see with an electron
microscope that are not possible to see with a light microscope?
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
b) Identify differences between plant and animal cells.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
c) You are a biologist working in a research laboratory comparing
plant and animal cells. Prepare a comparison of the two types of
cells, their structure and function.
You may find it more convenient to put this information into a
table. A suggested table with headings is provided here for you.
You may select headings of your own.
For each organelle state how the structure enables it to carry out
its specific function.
Part 4: Electron microscope and cell organelles
23
Organelle structure
24
Function
Found in
animal cells
Found in
plant cells
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Exercise 4.3: Tissues, organs and organ systems
a)
Define the following terms
tissues _______________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
organs _______________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
organ systems _________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Organ systems in multicellular organisms supply the needs of cells.
For example, the circulatory system transports oxygen from the
lungs to the cells. Outline how one other organ system supplies the
needs of cells.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 4: Electron microscope and cell organelles
25
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 5: Obtaining and transporting materials in plants
2
0
0
In
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b S
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Contents
Introduction ............................................................................... 2
Autotrophic and heterotrophic cells ........................................... 4
Obtaining nutrients in plants...................................................... 5
Photosynthesis .....................................................................................5
Function of leaves ..............................................................................11
The stem.............................................................................................13
Roots...................................................................................................16
Transport systems in plants .................................................... 18
Xylem ..................................................................................................19
Phloem................................................................................................28
Gas exchange in plants........................................................... 30
Suggested answers................................................................. 37
Exercises–Part 5 ..................................................................... 39
Part 5: Obtaining and transporting materials in plants
1
Introduction
Plants have specialised structures to obtain nutrients from their
environment. You may recall that plants and animals obtain nutrients
differently. Plants rely on the Sun to manufacture food by a process
called photosynthesis. Plants are autotrophic organisms. Animals cannot
manufacture their own food; they consume or eat other organisms in
order to gain the nutrients they require for life processes. Animals are
heterotrophic organisms.
Plants and animals have specialised cells, tissues and organs to obtain the
nutrition they require and carry out their body processes. Some of these
will be investigated in this part.
In this part you will be given opportunities to learn to:
2
•
distinguish between autotrophs and heterotrophs in terms of nutrient
requirements
•
identify the materials required for photosynthesis and its role in
ecosystems
•
identify the general word equation for photosynthesis and outline
this as a summary of a chain of biochemical reactions
•
explain the relationship between the organisation of the structures
used to obtain water and minerals in a range of plants and the need to
increase the surface area available for absorption
•
explain the relationship between the shape of leaves, the distribution
of tissues in them and their role
•
outline the transport system in plants including:
–
root hair cells
–
xylem
–
phloem
–
stomates and lenticels
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In this part you will be given opportunities to:
•
plan, choose equipment or resources and perform first–hand
investigations to gather information and use available evidence to
demonstrate the need for chlorophyll and light in photosynthesis
•
perform a first–hand investigation and gather first–hand data to
identify and describe factors that affect the rate of transpiration
•
perform a first–hand investigation of the movement of materials in
xylem or phloem.
Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board’s website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.
This version November 2002.
To complete the practical activities in this part you will require the
following equipment. Alternative exercises have been included.
•
•
•
•
•
•
•
•
•
•
1 large beaker or saucepan
1 small beaker or glass jar
Bunsen burner or hot plate
tripod and gauze (if using
Bunsen)
250 mL water
50 mL methylated spirit
a few soft fleshy leaves such as a
geranium
aluminium foil
a variegated leaf plant
iodine solution
Part 5: Obtaining and transporting materials in plants
•
stick of celery
•
glass of water with food colouring
(red/blue works best)
•
knife, small kitchen type
•
hand lens or microscope with lamp
•
glass slides and cover slips if using
microscope
•
thin glass tubing or clear plastic
tubing
•
Vaseline® or petroleum jelly
•
soft, fleshy plant stem eg.
Impatiens
•
marker pen or sheet of graph paper
•
scissors
•
retort and clamp or similar.
3
Autotrophic and heterotrophic cells
Cells can be classified as either autotrophic or heterotrophic depending
on how nutrition is obtained.
Autotrophic cells are those which can make their own food
(auto = self; trophic = feeding). Plant cells with chloroplasts are
autotrophic. The Sun’s energy is used to combine simple substances like
carbon dioxide and water. These two raw materials are used to make
glucose. Glucose can be changed into starch and other more complex
substances like cellulose.
Heterotrophic cells are those which cannot make their own food
(hetero = other). Heterotrophs depend on food made by others.
Heterotrophic cells include animal cells, fungal cells and some
bacterial cells.
Examples of autotrophic cells are:
_________________________________________________________
Examples of heterotrophic cells are:
_________________________________________________________
Check your answers.
Complete Exercise 5.1.
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Obtaining nutrients in plants
Photosynthesis
Plants carry out the food–making process called photosynthesis. In this
process plants convert the Sun’s energy into chemical energy stored in
sugars such as glucose. To do this, plants must have access to materials
such as carbon dioxide and water. Oxygen and water are also produced
in the process.
Inputs
carbon dioxide
water
light
Outputs
oxygen
water
sugars
What do you remember about photosynthesis?
1
Where does photosynthesis take place in a plant?
_____________________________________________________
2
Name the cell organelle where photosynthesis takes place.
_____________________________________________________
Part 5: Obtaining and transporting materials in plants
5
3
Describe the conditions necessary for photosynthesis to take place.
______________________________________________________
______________________________________________________
Check your answers.
Plants are producers as they make their own food. Plants are the first
step in a food chain. They use light energy to produce carbohydrates like
glucose. These carbohydrates are eaten by animals (herbivores and
omnivores). In turn, herbivores are eaten by carnivores and so on
through the food chain. So, in an ecosystem photosynthesis is an
important step in the flow of energy.
The phases of photosynthesis
There are two main stages or phases in the photosynthetic process.
These are called the light and dark phases.
The light phase
During this phase, light is absorbed by chlorophyll and the splitting of
water molecules occurs. Water molecules are split to form oxygen and
hydrogen ions. Light acts on the chlorophyll. The energy is converted
from light to chemical energy. These reactions take place in the grana of
the chloroplast. Many enzymes are used to carry out the process.
light
chlorophyll a
ENERGY
oxygen
released
splits
H2O
H+
to the second phase
Simplified light phase of photosynthesis.
6
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The dark phase
The dark phase is often called the fixation of carbon phase.
Carbon dioxide is fixed into glucose molecules using hydrogen ions and
energy obtained during the light phase.
energy
from light
phase
hydrogen
from light
phase
H+
+
5C sugar
CO2
many steps
Simplified dark phase of photosynthesis.
This phase also involves a number of steps in the reaction where specific
enzymes are required. This series of reactions occur in the colourless
fluid of the chloroplast called the stroma that surround the grana.
Light is not required for these reactions. Glucose is synthesised during
the dark phase.
1
Outline what happens in the light phase of photosynthesis.
_____________________________________________________
_____________________________________________________
2
Outline what happens in the dark phase of photosynthesis.
_____________________________________________________
_____________________________________________________
Check your answers.
Word equations are used to describe reactions. They can also be used as
a summary for complex pathways. The general word equation for
photosynthesis is shown below.
light energy
carbon dioxide + water
sugar + oxygen
chlorophyll
You can see from the previous diagrams that photosynthesis is a complex
process. So, this equation is a summary of the biochemical reactions that
make up the process of photosynthesis. You do not need to learn these
biochemical reactions.
Part 5: Obtaining and transporting materials in plants
7
A general equation for photosynthesis is:
6CO2 +6 H2O
C6H12O6 + 6O2
Radioactive tracing has shown that a more correct equation for
photosynthesis is:
6CO2 +12 H2O
C6H12O6 +6O2 + 6H2O
Complete Exercise 5.2.
Why do most plants appear green?
Photosynthetic pigment is a mixture of a number of different pigments,
including chlorophyll. Chlorophyll absorbs mostly blue–violet and red
light and reflects green. This characteristic of reflecting green light is
why most leaves appear green in colour.
Engelmann’s experiment
Thomas Englemann was a German biologist who investigated the
wavelength of light used by plants during photosynthesis. He used
bacteria to detect the presence of oxygen by observing the change in
bacteria numbers in different light environments. The environments
were created by projecting the whole spectrum onto a filament of algae.
The results indicated that red and violet wavelengths are absorbed by
chlorophyll pigments, resulting in the increased production of oxygen
and increased numbers of bacteria in the corresponding regions.
The need for chlorophyll and light in photosynthesis
In this activity you will be investigating the need for chlorophyll and light in
photosynthesis.
The first experiment examines the production of starch as an indicator
that photosynthesis has occurred in parts of a leaf.
The second experiment focuses on the production of starch in areas of
leaves that do not contain chlorophyll.
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Variegated leaves have areas that do not contain chlorophyll (Photo J West).
Aim
The aim of this experiment is to demonstrate the need for chlorophyll and
light in photosynthesis.
Materials required:
•
1 large beaker or saucepan
•
1 small beaker or glass jar
•
Bunsen burner or hot plate
•
tripod and gauze (if using Bunsen)
•
250 mL water
•
50 mL methylated spirit
•
a few soft fleshy leaves such as a geranium
•
aluminium foil
•
a variegated leaf plant (leaves with a mixture of colours – choose
one that is a mixture of yellow and green)
•
iodine solution.
Method:
1
Place aluminium foil over one half of your leaf on the plant, secure
with paperclips and leave overnight.
Part 5: Obtaining and transporting materials in plants
9
2
Place in direct sunlight for several hours.
3
Place your variegated plant in sunlight for several hours.
4
Pick the leaves from both plants and place the leaves in a beaker
with the water. Remove the foil from the soft leaf. Heat the water
and leaves gently, until they go very limp.
5
Turn off the heat source.
6
Remove the leaves from the water and place into the small beaker or
jar with the methylated spirit.
Care should be taken using methylated spirit, as it is a flammable
substance. Avoid contact with a naked flame. Even methylated spirits
vapours are flammable.
10
7
Place the small beaker or jar into the hot water and allow to stand for
approximately five minutes. The green pigment should be extracted
from the leaves after this time. If the methylated spirit has not become
very dark green, stir the leaves and leave for a few extra minutes.
8
After there has been sufficient chlorophyll extracted, remove the
leaves and wash them in water.
9
Now place your two leaves onto a white surface and flood them with
iodine. Remember that iodine turns blue–black in the presence of
starch and starch is produced in areas that are actively
photosynthesising.
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Results
In the areas that produce starch and are carrying out photosynthesis the
iodine will turn blue–black or purple. In the yellow areas of variegated
plants there is no chlorophyll so these areas should not be coloured.
In the leaf that was covered with aluminium foil the light would not have
got under the foil and photosynthesis would not have occurred.
Conclusion
The experiment demonstrated that photosynthesis does not occur unless
there is both light and chlorophyll present.
Do Exercise 5.3 now.
Function of leaves
Go outside into the garden or take a walk to a park. Look at the leaves on
the plants and sketch three different ones on your own paper.
Note, on your drawings, three similarities and three differences in the
leaves you selected.
You will have noticed that most leaves are thin and flat. There are a
large range of leaf shapes. Being thin and flat means that leaves have a
large surface area to volume ratio which is important for the absorption
of light, oxygen and carbon dioxide.
Part 5: Obtaining and transporting materials in plants
11
epidermis
cuticle
cells containing chloroplasts
palisade
mesophyll
layer
spongy
mesophyll
stomate
air space
xylem
phloem
cell wall
vascular bundle
Cross–section of a leaf. Source: Messel, H (chair). (1963.) Science for high
school students. The Foundation for Nuclear Energy. University of Sydney.
The chloroplasts are located in the mesophyll (middle leaf) region of the
leaf. Gases enter and leave the leaf through the stomates. Therefore, the
structure of the leaf ensures that the photosynthetic cells that contain
chlorophyll are close enough to the top of the leaf to receive light and
close enough to the stomates to gain the gases they require.
1
Outline the features of leaves.
_____________________________________________________
_____________________________________________________
2
Identify the major role of leaves.
______________________________________________________
______________________________________________________
12
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3
a) Identify the tissue where photosynthesis occurs in leaves. How
does the location of this tissue assist in photosynthesis?
_________________________________________________
_________________________________________________
b) Xylem carries water up through the plant. How does the
location of this tissue help in photosynthesis?
_________________________________________________
_________________________________________________
c) Xylem is associated with phloem in plants. Predict a role
related to photosynthesis for phloem in plants.?
_________________________________________________
_________________________________________________
4
Can you suggest a reason why leaves are thin and flat? (Hint: Think
about the effects of the SA:V.)
_____________________________________________________
_____________________________________________________
Check your answers.
The stem
You have looked at the structure of leaves. This is where photosynthesis
occurs. But how does the products of photosynthesis get to the other
parts of the plants. To answer that question you need to look at the
structure of the stem.
Sketch a plant from your garden and label the stem, leaves, flowers and
buds. Use your own paper.
Stems can be recognised because they have leaves and buds. Most stems are
above ground, forming part of the shoot system of plants. Some plants have
underground stems and their leaves may be reduced to scales.
Although the arrangement varies with different types of plants, stems
usually form a complex branching pattern. The leaves are spaced along
them to gain maximum exposure to sunlight.
Part 5: Obtaining and transporting materials in plants
13
Tissues in stems
Stems are usually green when young and can carry out photosynthesis.
They may become woody when older. At the tip of each stem is a
terminal bud, a growing point for the plant. Stems also support the
flowers and fruit of the plant.
One of the main functions of stems is transport. Internally, stems contain
tubes of conducting tissue, the xylem and phloem. This vascular tissue
carries materials between the shoot and root systems. The conducting
tissue is arranged in a ring or scattered throughout the stem tissue.
The outer covering of stems, the epidermis, forms an impermeable layer
protecting the inner cells and preventing water loss. There are stomates
for the exchange of gases on young green stems and lenticels which
serve the same purpose on woody stems.
Cells in the cortex and pith usually store food but may also contain
chloroplasts and photosynthesise. There are air spaces between cells for
the circulation of gases. Some stems are hollow with little or no pith.
Cross–section of a stem showing vascular bundles. (Photo Jane West)
14
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Close–up of a vascular bundle showing xylem, cambium and phloem
(Photo Jane West)
Vascular bundles
Vascular bundles are groups of conducting tissue in a stem. Each bundle
contains three types of tissue: xylem, phloem and cambium.
Xylem forms long tubes up to 1 m in length. They are dead cells
(they have no nucleus). These long tubes are known as xylem vessels.
Xylem vessels are thickened with woody material, with cross walls that
have broken down. Xylem gives support, strength and rigidity to the
stem, and transports water and mineral ions upwards from the roots to the
leaves. Note; Water and mineral ions travel only in one direction in the
xylem–upwards.
Phloem consists of living sieve–tube cells forming long columns.
There are perforations in the cell walls so that the cytoplasm of the cells
connects along the tubes. Associated with the sieve–tube cells, are
companion cells and other supporting tissue. Organic materials including
sugars, amino acids and hormones are transported by the living
Part 5: Obtaining and transporting materials in plants
15
sieve–tube cells of phloem tissue. This movement is called translocation.
Materials move both up and down through the plant in the phloem.
The movement is too fast to be caused only by diffusion. There are
several theories suggesting possible forces involved but the exact
mechanism remains unknown.
Cambium cells are capable of cell division. They divide to form cells
which become new xylem and phloem tissue. In older stems division of
the cambium cells results in a continuous ring of vascular tissue.
Roots
You have now read about how and why plants transport water. Have you
asked yourself where they get the water? Roots do not photosynthesise
but grow through the soil anchoring the plant and supplying the plant
with water and mineral ions. To do this roots have to have an extensive
surface area to be able to absorb water. The drawing below shows a
young root covered in root hairs. The root hairs greatly increase the
surface area of the root so that water can pass from the soil into the plant.
As well as root hairs plants have different types of roots. The two main
types of roots are fibrous roots and tap roots.
16
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fibrous
taproot
1
Outline the differences between taproots and fibrous root systems.
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
What structures of root systems increase surface area to improve
water uptake?
_____________________________________________________
3
Explain how the large surface area of roots assists in the survival of
plants in dry weather.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Complete Exercise 5.4.
Part 5: Obtaining and transporting materials in plants
17
Transport systems in plants
You have already looked at some of the structures involved in the
transport system of plants. Answer these questions below for revision.
1
What is the role of the root, stem and leaf in flowering plants?
_____________________________________________________
_____________________________________________________
2
Plants have a system of vascular bundles to transport sugars, gases
and water within the plant. The term vascular bundle is used to
describe the conducting tissue in a stem.
What type of tissue is found in a vascular bundle?
______________________________________________________
______________________________________________________
Check your answers.
xylem tubes move water
up the plant from the roots
phloem tubes move sugars
dissolved in water throughout
the plant
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Like all multicellular organisms, plants need to transport materials from
one place to another. Sugars are produced by the process of
photosynthesis in the leaves. Every cell in a plant requires sugars for
respiration. So, sugars are transferred from where they are produced to
where they are needed.
The same is true for water and minerals. These are taken into the plant
through the root hairs and are needed by every cell in the plant.
This transport function is carried out by xylem tissues (for water and
minerals) and phloem (for sugars).
Cambium cells are capable of cell division. They divide to form cells,
which become new xylem and phloem tissue. In older stems, division of
the cambium cells results in a continuous ring of vascular tissue.
Xylem
Xylem forms long tubes up to one metre in length. They are made up of
dead cells, thickened with woody material (lignin), the cross walls have
broken down. They are known as xylem vessels. Xylem gives support,
strength and rigidity to the stem, and transports water and mineral ions
upwards from the roots to the leaves. Note: water and mineral ions travel
only in one direction in the xylem–upwards.
Movement of water and dissolved chemicals takes place in xylem vessels
which form part of the vascular bundles within roots, stems and leaves.
Detailed information on the processes involved in the movement of
substances through the xylem can be found in the Additional resources
section of this part.
Stems can be recognised because they have leaves and buds.
Most stems are above ground, forming part of the erect shoot system of
plants. Some plants have underground stems and their leaves may be
reduced to scales.
Stems are usually green when young and can carry out photosynthesis.
They may become woody when older. At the tip of each stem is a
terminal bud, a growing point for the plant. Stems also support the
flowers and fruit of the plant.
Part 5: Obtaining and transporting materials in plants
19
In this activity you will be investigating the movement of water through the
plant.
Materials required:
•
stick of celery
•
glass of water with food colouring (red/blue works best)
•
knife, small kitchen type
•
hand lens or microscope with lamp
•
glass slides and cover slips if using microscope.
What you will do:
1
Place a stick of celery into the glass of coloured water for a few
hours.
Place the celery into the glass. (Photo: J West)
2
20
Remove celery from water and cut in half, carefully, cutting away from
fingers. Using the hand lens, examine the stem and the location of the
coloured water.
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Cut across the stem. (Photo: J West)
The coloured liquid is seen in the xylem. (Photo: J West)
4
Where in the stem is the coloured water located?
_____________________________________________________
5
Name the tissue in which the water is located.
_____________________________________________________
Part 5: Obtaining and transporting materials in plants
21
6
Draw a sketch of your observations.
If you have access to a microscope, prepare a slide of a cross–section of
the celery stem. Observe this specimen under the microscope and look at
it. (A cross–section is produced by cutting across, not lengthways.).
Water enters the plant through the roots. The roots are covered by fine
root hairs which increase the surface area for absorption of water.
The root hairs are single celled extensions of the root epidermis (surface
or outer layer of the root).
Water enters the root hair by diffusion. The concentration of solutes in
the soil water is lower than inside the root hair cells. Water will move
from an area of high water concentration (in the soil) to an area of low
water concentration (within the root hair cells).
root hair
soil particles
water
Water moves into the plant from the soil through the root hairs.
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One of the main functions of stems is transport of substances around the
plant. Stems contain tubes of conducting tissue or vascular bundles,
which consist of the xylem and phloem, that carry materials between the
shoot and root systems. The conducting tissue is arranged in a ring or
scattered throughout the stem tissue.
Transpiration
When stomates are open gases including carbon dioxide can diffuse into
a plant. At the same time, however, water molecules can diffuse into the
air because of the higher water concentration inside the plant.
Water evaporates from the cell surfaces, diffuses through the intercellular
spaces and out through the stomates. This diffusion of water from a plant
is called transpiration.
Water loss by transpiration is unavoidable by a plant with the stomates
open. The water lost needs to be replaced by uptake through the roots.
There is a constant upward flow of water through a plant. This is known
as the transpiration stream.
If water loss exceeds water intake, the stomates close and cells lose their
turgidity. The stems and leaves wilt and the plant may die.
Transpiration is an important part of the mechanism by which water and
mineral ions are transported from the roots to the stems and leaves.
The evaporation of water has a cooling effect on the plant, particularly
the leaves.
Factors affecting transpiration
The structure of the plant has an effect on the transpiration rate.
Stomates may be open or closed. When they are closed the transpiration
rate drops and diffusion occurs at a much slower rate through the cuticle.
Normally, stomates are open during the day for the exchange of gases in
photosynthesis and closed at night.
Some plants have special features (adaptations) to reduce the
transpiration rate. Structural features may include a very thick cuticle,
sunken stomates, hairs on the leaf or a reduction in leaf surface area.
Physiological features may include the closure of the stomates or rolling
up of the leaf to reduce surface area, during the day when the temperature
is high.
There are a number of external (environmental) factors that affect
transpiration in a plant. These are temperature, humidity, wind, light
and soil.
Part 5: Obtaining and transporting materials in plants
23
•
In high temperatures, diffusion is more rapid (warm air holds more
water than cold air).
•
If the atmosphere is saturated with water vapour (conditions of high
humidity) transpiration is decreased.
•
Moving air increases the transpiration rate. Water vapour is carried
away from the leaf and a high diffusion gradient maintained.
•
Light intensity affects stomate opening and this in turn affects the
transpiration rate.
•
The water content of the soil and the solute concentration affect the
rate at which water can be taken up by a plant.
Measuring transpiration
A potometer is an instrument which can be used to measure the rate of
transpiration. There are several varieties of potometers. In a potometer,
water is run into the apparatus through a glass funnel.
A soft, fleshy twig or branch is pushed into the tubing which must be
completely filled with water (it may assist to colour the water so that the
movement can be easily seen).
This must be a tight fit, otherwise water will run out of the capillary tube
and the instrument will not function correctly. The area around the neck
of the tubing where the plant has been inserted needs to be sealed, using
Vaseline® or petroleum jelly.
soft fleshy plant
funnel or well
water
base
very thin gradated glass tubing
Experimental set up to measure the rate of transpiration.
24
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As time passes, the thin thread of water moving along the capillary tube
towards the plant will be visible. A scale fitted behind the capillary tube
helps in the measurement of the rate of transpiration. It is possible to
accelerate the process by changing the environmental conditions of the
plant. For example, by using a fan it is possible to simulate windy
conditions. Other variables (factors) such as temperature can be
investigated for their effect on the rate of transpiration.
The effect of the environment on transpiration
Optional activity
If you have access to the equipment below then carry out the experiment.
If not, answer the questions at the end of the experiment in the results
section.
The aim of this experiment is to compare the rate at which a leaf loses
water, that is, transpires, under different conditions.
Materials required:
•
thin glass tubing or clear plastic tubing (look at the diagram to see
what it could look like)
•
Vaseline® or petroleum jelly
•
soft fleshy plant stem eg. Impatiens
•
marker pen or sheet of graph paper
•
scissors
•
retort and clamp or similar.
What you will do:
1
Fill the funnel with water.
2
Insert the soft, fleshy branch into the tubing
3
Smear Vaseline®, paraffin or fat around the join between the stalk
and the tubing. This join must be airtight when removed from the
water.
4
Check that there is no water leaking from your potometer at any
point. Water is most likely to escape in the area where the stalk is
placed into the tubing.
5
Set up a second potometer in the same way, but this time omit the
leafy branch. The second potometer is used as the control.
What is the function of a control?
_____________________________________________________
Part 5: Obtaining and transporting materials in plants
25
6
7
26
Expose the potometer and the control to the following conditions and
measure the time taken for the water to move 2 cm along the glass
tube. Conditions to which the experiment and control and to be
exposed are:
•
cool and shady (in a room away from a window or draught)
•
cool and windy (use a fan for creating ‘wind’)
•
hot and shady (use a radiator)
•
hot and windy (use a radiator plus a fan).
Draw up a table of results on your own paper and enter your
measurements.
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Results:
1
Outline the conditions where you would expect the transpiration rate
to be greatest.
_____________________________________________________
_____________________________________________________
2
Which type of conditions causes plants to wilt?
_____________________________________________________
_____________________________________________________
3
Why do people need to top up the water in vases with cut flowers?
_____________________________________________________
_____________________________________________________
4
Not all the water lost from vases of flowers is taken up by the plants.
Explain.
_____________________________________________________
_____________________________________________________
Conclusion
Transpiration rate is affected by different external conditions.
For each of the conditions below describe the rate of transpiration (fast,
medium, slow).
•
cool and shady ________________________________________
•
cool and windy ________________________________________
•
hot and shady _________________________________________
•
hot and windy ________________________________________
Explain briefly how nutrients are obtained and transported around plants.
Your answer should include the names of the main structures and processes
involved.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Part 5: Obtaining and transporting materials in plants
27
Summary of processes of water transport
Several processes appear to be involved in the upward movement of
water in plants.
•
Adhesion: forces of attraction between different particles are called
forces of adhesion. The cellulose cell walls in plants soak up water
by this process, in much the some way as a blotter soaks up water.
•
Capillarity: capillarity is the rise of water in thin tubes by forces of
adhesion and cohesion. The water rises up thin tubes because of
attraction between the particles of the plant and water particles
(adhesion) and because of the attraction between the water particles
themselves (cohesion).
•
Root pressure: this refers to the upward movement of water caused
by the pressure from water moving into the root as a result of
osmosis.
•
Transpiration–cohesion: the transpiration cohesion theory proposes
that the loss of water molecules from the leaves, that is,
transpiration, results in the upward movement of more water
molecules since these molecules are attracted to each other by forces
of cohesion.
•
Guttation: is the loss of water in the form of a liquid from openings
on the leaves.
Phloem
Phloem tissue like xylem tissue, consists of tube–like cells. In phloem
these cells are called sieve cells and they form long columns.
When these cells mature they lose their nuclei. There are perforations in
the cell walls at the end so that the cytoplasm of the cells can connect
along the tubes. These are called sieve plates. Associated with the sieve
tube cells are companion cells (which retain their nuclei and cytoplasm)
and other supporting tissue.
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Phloem tube.
Translocation
Organic materials including sugars, amino acids and hormones are
transported by the living sieve tube cells of the phloem tissue.
This movement is called translocation.
The material that flows through phloem is called sap. The approximate
composition is 30% plant sugars and 70% water.
Materials move both upwards and downwards through the plant.
The movement is too fast to be caused only by diffusion. There are
several theories suggesting possible forces involved however the exact
mechanism remains unknown. Probably the most widely accepted
explanation for the mechanism of phloem translocation is the pressure
flow hypothesis of Ernst Much, which was proposed in 1930.
Leaves and roots can be sources of nutrients; nutrients are unloaded into
stem apexes, flowers, fruits and roots.
Movement of sap through the phloem results in pressure within the cells.
When aphids stick a feeding tube into the phloem, the sap is forced
through the aphid’s body.
Complete Exercise 5.4.
Part 5: Obtaining and transporting materials in plants
29
Gas exchange in plants
Like multicellular animals, multicellular plants usually have specialised
tissues for gas exchange. You will look mainly at angiosperms
(flowering plants) and algae (seaweeds and their relatives) in this section.
Respiration is the process by which energy is released for use by the cell.
All plant cells respire. Plant cells respire aerobically (most of the time).
This means that they use oxygen gas in the process and release carbon
dioxide gas as a waste product.
Some plant cells produce glucose by the process of photosynthesis.
During photosynthesis carbon dioxide is used and oxygen is released.
During daylight a plant respires as well as carrying out photosynthesis.
In sunlight, plants:
•
release more oxygen from photosynthesis than their cells use in
respiration
•
use all the carbon dioxide released by their cells in respiration in
photosynthesis
•
take in additional carbon dioxide from the atmosphere to satisfy the
needs of photosynthesis.
At night, plants:
•
do not photosynthesise
•
take in oxygen gas from the atmosphere for respiration.
•
release carbon dioxide gas as a product of respiration.
Overall plant metabolism results in the release of more oxygen than
carbon dioxide.
If a plant was placed in a sealed container for several days and nights the
composition of air in the container would change. Even though plants do
not photosynthesise at night, they still release more oxygen during
photosynthesis than they absorb by respiration.
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So, what is the evolutionary significance of plants releasing more oxygen
than carbon dioxide?
Prior to the evolution of photosynthesising organisms, the Earth’s
atmosphere was significantly different as it contained no free oxygen gas.
It probably contained gases like methane as well as higher levels of
carbon dioxide than today. As free oxygen, produced by photosynthesis,
became available it could react with the methane to produce carbon
dioxide. That carbon dioxide was then available for photosynthesis.
Since photosynthesis produces a net amount of oxygen, the atmospheric
oxygen levels were able to gradually increase.
Photosynthesis has changed the composition of the atmosphere of the
planet. This must surely be one of the most significant change made by
living things on the planet.
1
Imagine that you have placed a plant into an airtight container.
There is air in the container, but it cannot escape from the container.
The container is placed outside and left in sunlight for eight hours.
What would you expect to happen to the composition of the air in
the container?
_____________________________________________________
_____________________________________________________
2
Return to the plant in the sealed container. What would happen to
the composition of the air in the container at night?
_____________________________________________________
_____________________________________________________
Check your answers.
Gas exchange in leaves
Green plants require gas exchange for two purposes:
•
provision of carbon dioxide gas for photosynthesis
•
provision of oxygen gas for respiration.
When these gases are not available within the cells of a plant then the
gases need to be brought in from the surrounding atmosphere.
The leaf is one of the most important gas exchange sites. Cells in leaves
respire and are also some of the most important cells involved in the
process of photosynthesis.
Part 5: Obtaining and transporting materials in plants
31
You will already know that the outer surface of a leaf has a waxy
covering (cuticle). The cuticle is a most unsatisfactory surface for gas
exchange. However, it does prevent excessive water loss.
Gases enter the leaf through tiny holes called stomates. Cells in the
interior of a leaf do not have a waxy covering.
In most plants, there are more stomates on the underside of the leaf than
on the upper surface. This reduces the amount of water that can be lost
through the stomatal openings. Look at the diagram of a cross–section of
a leaf following.
cuticle
epidermal cell
palisade mesophyll
many chloroplasts
in cytoplasm of cell
xylem and phloem cells
in leaf vein
spongy mesophyllwith fewer
chloroplasts in cytoplasm
air space
epidermis
cuticle
The stomate is shown on the lower surface of the leaf. The two guard
cells of a stomate surround a pore. When the guard cells are turgid
(full of fluid) they are curved like a banana. The curve of the two turgid
guard cells creates the opening that allows gases into and out of the leaf.
When the guard cells are flaccid they collapse, sealing the stomate.
When stomates are closed, water vapour and gases cannot pass into or
out of the leaf.
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Leaf epidermis. Note the stomates are all open.
Many consider stomate closure to be an adaptation to prevent desiccation or
drying out. Explain.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Where does gas exchange occur?
Gas exchange in plants occurs on the surface of each cell in the leaf.
Moisture on the outside of the cells allows gases to dissolve into fluid.
Once dissolved, gases can diffuse into the cell.
Wastes are removed by a similar method. The waste gases diffuse to the
moisture on the outside of each cell and from there to the gases in the
cavities within the leaf.
For cells that are not immediately adjacent to a leaf cavity, gases are
passed by diffusion from cell to cell to deliver gases to cells deeper in the
leaf. Stomates open into cavities and there are considerable air spaces
within the leaf.
Because the cells within the leaf are so tiny, the surface area to volume
ratio is high for each cell adjacent to a leaf cavity. Just as in lungs, gills
and insect tracheoles a high surface area to volume ratio is important for
gas exchange in plants.
Part 5: Obtaining and transporting materials in plants
33
Gas exchange is required for all plant cells, even the ones that are not
photosynthesising.
Gas exchange in stems
As stems are often thick, a different structure is required to allow gases to
pass through outer coverings such as bark. This structure is the lenticel.
Lenticels are a loose association of cells with many intercellular spaces
between them. These spaces allow oxygen to pass from the atmosphere
to the respiring cells within the stem. Lenticels also allow waste carbon
dioxide to leave the plant.
lenticels
Lenticels can be found on a woody stem.
lenticel
Lenticels allow gas exchange to occur.
Root hairs are sufficiently moist, small and thin to allow adequate gas
exchange between the gases in the soil air and the roots.
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1
With the aid of examples, explain why gas exchange surfaces have a
high surface area to volume ratio.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
Outline the role of stomates in:
a) gas exchange
_________________________________________________
b) prevention of desiccation.
_________________________________________________
3
A number of plants growing in arid parts of Australia close their
stomates during the heat of the day. Their stomates are only opened
during the evening, early morning and late afternoon.
Make a hypothesis to explain these observations.
_____________________________________________________
_____________________________________________________
Check your answers.
Complete Exercise 5.5.
Part 5: Obtaining and transporting materials in plants
35
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Suggested answers
Autotrophic cells and heterotrophic cells
Autotrophic cells include plant cells and some bacterial cells.
Heterotrophic cells include animal cells, fungal cells and some
bacterial cells.
Photosynthesis
1
Photosynthesis takes place in the green parts of plants, especially the
leaves.
2
Photosynthesis occurs in the chloroplasts.
3
Light provides the energy that drives the process, photosynthesis.
Chlorophyll (in the chloroplasts), carbon dioxide and water are
necessary materials.
The phases of photosynthesis
1
Light is absorbed by chlorophyll and water molecules are split into
hydrogen and oxygen.
2
Carbon fixation and glucose is synthesised in the dark phase of
photosynthesis.
Function of leaves
1
Leaves are mostly green, thin and flat. They have a network of
veins.
2
The major role of leaves is to provide the plant with food.
Photosynthesis occurs mainly in the leaves.
3
a) Photosynthesis occurs in mesophyll (spongy and palisade).
The mesophyll is located between the layers of epidermis.
Mesophyll has access to carbon dioxide that enters through the
stomata.
Part 5: Obtaining and transporting materials in plants
37
b) Xylem provides water for photosynthesis.
c) Phloem transports the products of photosynthesis to the rest of
the plant.
4
The flat shape increases the SA:V ratio. This means there is a large
surface area available for light absorption for photosynthesis.
Because leaves are thin, the mesophyll is close to the epidermis.
So, carbon dioxide can easily absorb to the mesophyll for the
process.
Roots
1
Tap roots have a main central root from which the root hairs grow.
Fibrous roots do not have a central root, but simply a collection of
fine roots spreading out.
2
Roots have root hairs on their surface that increase the surface area.
3
The increased surface area enables the plants to spread out within the
soil to gather available moisture and dissolved nutrients. This aids in
the survival of the plants, particularly in times/areas when there may
be a water shortage.
Transport systems in plants
1
Roots absorb water and dissolved nutrients from the soil.
The stem supports the plant and the leaf is the site of photosynthesis.
2
Each vascular bundle contains three types of tissue: xylem, phloem
and cambium. (Note: cambium is not a conducting tissue.)
The effect of the environment on transpiration
Nutrients are absorbed through the root hairs on the root system of a
plant. They are transported via the xylem by adhesive and cohesive
forces, to the leaves. The movement of water upward through the
plant is called transpiration. From the leaves, the products of
photosynthesis are transported via the phloem to the rest of the plant.
The movement of sugars around the plant is called translocation.
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Exercises – Part 5
Exercises 5.1 to 5.5
Name: _________________________________
Exercise 5.1
Outline the main difference between autotrophs and heterotrophs.
_________________________________________________________
_________________________________________________________
Exercise 5.2: The phases of photosynthesis
a)
Write down the general word equation for photosynthesis.
b) Explain why this equation can be thought of as a summary of a chain
of biochemical reactions.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 5.3: Photosynthesis
a)
List the materials required for photosynthesis.
_____________________________________________________
_____________________________________________________
b) What is the role of photosynthesis in the ecosystem?
_____________________________________________________
_____________________________________________________
Part 5: Obtaining and transporting materials in plants
39
Exercise 5.4: Absorption of water and minerals in
plants
Plants obtain water and minerals through their root systems. Roots are
generally long and thin. Root hairs are found along the tips of growing
roots. How does the structure of the root system affect a plant’s ability to
obtain water and minerals?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 5.5: Transport systems in plants
a)
Multicellular plants and animals have transport systems. Why is this
necessary?
______________________________________________________
______________________________________________________
b) Describe the movement of water through a plant starting with root
hairs and finishing with the water leaving the plant.
______________________________________________________
______________________________________________________
______________________________________________________
c)
You have learned that materials move upwards in xylem.
Substances move upward and downward in the phloem.
How do we know this? Briefly describe the evidence for movement
of substances in the xylem or the phloem.
You may need to consult a biology textbook and another source such
as the Internet.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
40
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 6: Obtaining materials in animals
2
0
0
In
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b S
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Contents
Introduction ............................................................................... 2
Obtaining nutrients in animals ................................................... 4
Increased surface area in animals ......................................................4
Digestion in grazing herbivores ...........................................................6
Digestion in carnivores.........................................................................8
Nectar feeders ....................................................................................10
Suggested answers................................................................. 13
Exercises–Part 6 ..................................................................... 15
Part 6: Obtaining materials in animals
1
Introduction
Animals have specialised cells, tissues and organs to obtain the nutrition
they require and carry out their body processes. Some of these will be
investigated in this part.
In this part you will be given opportunities to learn to:
•
describe the role of teeth in increasing the surface area of complex
foods for exposure to digestive chemicals
•
explain the relationship between the length and overall complexity
of digestive systems of a vertebrate herbivore and a vertebrate
carnivore with respect to:
–
the chemical composition of their diet
–
the functions of the structures involved.
In this part you will be given opportunities to:
•
perform a first–hand investigation to demonstrate the relationship
between surface area and rate of reaction
•
identify data sources, gather, process, analyse and present
information from secondary sources and use available evidence to
compare the digestive systems of mammals, including a grazing
herbivore, carnivore and a predominantly nectar feeder.
Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board’s website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.
This version November 2002.
2
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To complete the practical activities in this part you will require the
following equipment. Alternative exercises have been included.
•
•
•
•
•
•
mortar and pestle or a suitable grinding tool and vessel
petri dish or small plate
Bunsen burner or hotplate
3 test tubes or similar
sand
small quantity of liver from a butcher
•
hydrogen peroxide (this can be purchased at a pharmacist)
Part 6: Obtaining materials in animals
3
Obtaining nutrients in animals
You have seen that plants have structures such as root hairs that increase
surface area for absorption. Animals have increased surface area for the
absorption of nutrients, as well.
Food and water are taken in through the mouth and pass through the
alimentary canal. The nutrients are digested and absorbed along the way.
The physical breakdown in the mouth by the teeth increases the surface
area for chemical digestion in the stomach and the small intestine.
The lining of the intestines is made of folded membranes called villi that
increase the surface area for the absorption of nutrients.
Increased surface area in animals
The following activity will help you demonstrate how increased surface
area assists the digestive process in the body. If you grind up a substance
you produce a much larger surface area for any reaction to occur.
This is what happens in your mouth when you chew on your food.
You increase the surface area for enzymes to work on the food.
In this experiment you will compare the rate of reaction of a whole piece
of liver and one that has been ground up. The whole piece of liver will
have a smaller SA:V than the equal size piece of ground liver.
Hydrogen peroxide is broken down by an enzyme found in the liver.
This produces oxygen which can be seen as bubbles in the container.
Materials required:
4
•
mortar and pestle or a suitable grinding tool and vessel
•
petri dish or small plate
•
3 test tubes or similar
•
Bunsen burner or hotplate
•
sand
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•
small quantity of liver from a butcher
•
hydrogen peroxide (this can be purchased at a chemist)
Procedure
1
Divide the liver into two equal quantities.
2
Place a small quantity of clean sand into a test tube or onto a dish or
plate.
3
Take one piece of liver and grind it together with the sand and place
into test tube or onto dish.
4
Place one piece (whole) into a test tube or onto dish.
5
Add an equal volume of hydrogen peroxide to each of the four test
tubes and observe carefully.
Observations
1
Describe what is seen in each of the test tubes by completing the
table below.
2
A control is used in an experiment to ensure that a fair test is being
carried out. Which test tube is the control in this experiment?
_____________________________________________________
Results
Sample
Description of reaction
Amount of gas produced
sand only
fresh liver ground with
sand
whole piece of liver
Conclusion
What can you say about surface area and rate of reaction from this
experiment?
_________________________________________________________
_________________________________________________________
Part 6: Obtaining materials in animals
5
Digestion in grazing herbivores
Digestion begins in the mouth. The shape of the teeth give a clue to the
type of food eaten by an animal. Herbivores have large grinding molars
that crush the food to increase the surface area for digestion.
incisors
molars
Herbivore teeth.
Herbivores have diets high in complex carbohydrates. These complex
carbohydrates such as cellulose and lignin require a complex digestive
system.
The ruminant digestive system. Can you identify the components?
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Patterns in nature
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Grazing herbivores use micro–organisms contained within their digestive
systems to break down complex carbohydrates such as cellulose.
The process of cellulose digestion is called fermentation. This may occur
before or after the stomach.
Many farm animals like sheep, cattle, goats and camels are foregut
fermenters. The have complex digestive systems with three or four
stomach compartments to deal with their diet. The largest of these
stomach compartments is called the rumen, so they are called
ruminant animals.
Cattle, for example, have a stomach that is made of four compartments
called the rumen, reticulum, omasum and abomasum. It is the special
ruminant bacteria that are located in the rumen that carry out the majority
of the fibre digestion.
oesophagus
reticulum
omasum
rumen
abomasum
duodenum
small
intestine
caecum
large
intestine
Organs of the ruminant digestive system.
Ruminant animals require water, carbohydrates, proteins, fats, vitamins
and minerals in their diet.
Part 6: Obtaining materials in animals
7
Animals use carbohydrates to provide energy. All animals can make
use of sugars and starches in food, but only ruminants such as sheep
and cattle can make full use of the complex carbohydrate, cellulose.
The great benefit of the ruminant digestive system is that it can
decompose cellulose through the activity of micro–organisms in
the rumen.
Proteins are the basic structural material of many parts of an animal and
its products. In the rumen the protein that an animal eats is altered.
The protein requirements of grazing animals are mostly supplied from
the pasture they graze. However, ruminants are able to make their own
proteins through the action of micro–organisms.
Cell contents also contain minerals. These are chemical substances
needed by all animals for proper growth and development.
Most ruminant animals live in sunlight and have access to green feed,
so they usually do not suffer from a shortage of vitamins. Ruminant
animals have an inbuilt supply of the B group vitamins, which are
synthesised by micro–organisms in the rumen.
The other main group of grazing herbivores are the hindgut fermenters.
Examples of this group are horses, rabbits and possums. They carry out
cellulose digestion in an organ after the stomach called the caecum.
In rabbits the caecum has the capacity ten times the stomach and it fills
most of the abdomen.
Digestion in carnivores
Carnivore teeth are adapted to catching and holding prey and then
ripping it to pieces. They have large canines. Examples of carnivores
are dogs, cats and the Tasmanian devil.
incisors
canines
molars
Carnivore teeth.
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The digestive systems of carnivores are the simplest among mammals.
The large intestine of carnivores is relatively shorter than herbivores.
The food source for carnivores is animal cells eg. muscle cells. These do
not have a cell wall and so they can be digested rapidly. Muscle cells in
meat are high in protein so carnivores do not need to eat large amounts of
food to gain the same amount of nutrients that a herbivore requires.
Muscle cells are also higher in energy content and take less energy to
digest than the food of herbivores.
The differences in food eaten are reflected in the different structures in
the digestive systems of herbivores and carnivores. Herbivores have to
take in a large amount of food that requires complex digestion.
They have large specialised digestive systems. Carnivores take in a
smaller amount of high energy food and have smaller and less complex
digestive systems.
stomach
small intestine
dog
(Canis familiaris)
10 cm
(for a 80 cm
length dog)
rectum
colon
Digestive system of a dog.
1
What type of teeth is used for eating meat? Can you suggest a reason
for their special shape?
_____________________________________________________
_____________________________________________________
2
What type of teeth is used by animals that eat only plants? Can you
suggest why they have a different shape to that of the meat eaters?
_____________________________________________________
_____________________________________________________
3
What type of teeth do humans have? How does this reflect the type
of food eaten?
_____________________________________________________
_____________________________________________________
Part 6: Obtaining materials in animals
9
4
Carnivores do not possess a four chambered stomach. They do not
have a use for fibre digestion, as they consume only meat.
Carnivorous animals have only one stomach chamber.
How many stomach chambers do humans have? Can you suggest a
reason for this?
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Nectar feeders
The length and structure of the intestines will vary according to the diet
of the organism. The more complex the substances that enter the
intestines the longer they are. Organisms such as nectar feeders that eat
simple carbohydrates will have a shorter digestive tract overall compared
to that of the animals that eat complex carbohydrates such as the
herbivores and carnivores. This is due to the fact that their primary food
source is simple sugars which are easily digested or broken down.
stomach
honey possum
(Tarsipes rostratus)
small intestine
1 cm
rectum
colon
The honey possum – an example of a nectar feeder.
Comparison of different digestive systems
You have seen from the previous information that the digestive systems
of different species have different structures that reflect their food source.
Each has structural differences that allow the animal to obtain the
appropriate nutrients. The table on the next page summarises this
information.
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Patterns in nature
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Feature
Herbivore
Carnivore
Nectar feeder
major chemical
composition of
diet
complex
carbohydrates
including
cellulose
proteins, fats
simple sugars,
protein
teeth
large grinding
molars to crush
food
sharp canines
and molars for
catching and
holding prey
few teeth
time in mouth
chewed for a long
period of time
rapidly swallowed
rapidly swallowed
time spent eating
most of the day
short feeding
period
Honey possums
can drink up to
20% of their body
mass in minutes
stomach
foregut
fermenters
(ruminants eg.
cattle) have a four
chambered
stomach for break
down of cellulose
small, one
chambered
stomach
two chambered
stomach, one
may be for nectar
storage
intestines
hindgut
fermenters have
an enlarged
caecum for break
down of cellulose
short and
unspecialised
large and small
intestines
indistinguishable,
no caecum
You will need to gather, process and analyse information from secondary
sources to carry out the following task.
Suggested places to look for information include Internet, journal articles,
and text–books. There is also some information above. Make sure your
source is reliable by checking it against other sources. A table such as the
one above is a good way of presenting information.
You need to identify your data source and present information to compare
the digestive systems of mammals, including a grazing herbivore, carnivore
and a nectar feeder There are some good starting points on the LMP website.
http://www.lmpc.edu.au/science
Complete Exercise 6.1.
Part 6: Obtaining materials in animals
11
12
Patterns in nature
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Suggested answers
Digestion in grazing herbivores
1
Canines and incisors for cutting and tearing the meat, molars for chewing.
2
Incisors for cutting and molars for chewing or grinding.
3
Humans have an omnivorous diet and so have incisors for cutting,
canines for tearing and molars for chewing.
4
Humans have one stomach. They do not eat significantly high
proportions of fibre compared to herbivores and do not have the
ruminant bacteria for this purpose.
Part 6: Obtaining materials in animals
13
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Patterns in nature
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Exercises – Part 6
Exercise 6.1
Name: _________________________________
Exercise 6.1: Obtaining nutrients in animals
a)
Describe the role of teeth in increasing the surface area of food for
the exposure to digestive enzymes.
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Prepare a table to summarise the differences between the digestive
tract of vertebrate herbivores, carnivores and nectar feeders.
Organise your answers into the columns shown in the table below.
Type of
vertebrate
Chemical
composition of
diet
Structures of the
digestive system
Function of
structure
herbivore
carnivore
nectar feeder
Part 6: Obtaining materials in animals
15
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 7: Transporting materials in animals
2
0
0
In
r2
e
b S
o
t
c NT
O
ng DM E
i
t
ra E N
o
rp A M
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Contents
Introduction ............................................................................... 2
Transport systems in animals.................................................... 3
Respiratory system ..............................................................................3
Circulatory system................................................................................3
Excretory system..................................................................................4
Circulatory systems ................................................................... 5
Gas exchange in animals .......................................................... 8
Insects...................................................................................................8
Fish .....................................................................................................10
Frogs...................................................................................................11
Mammals ............................................................................................12
Investigative technology .......................................................... 16
Exercises–Part 7 ..................................................................... 19
Part 7: Transporting materials in animals
1
Introduction
In plants and animals transport systems and gaseous exchange move
chemicals through the internal environment as well as the external
environment.
In the previous parts you have identified the nutrients required by living
things and how they are obtained form the surroundings. In this part you
will be looking at how these nutrients are transported around animals.
In this part you will be given opportunities to learn to:
•
compare the roles of the respiratory, circulatory and excretory
systems
•
identify and compare the gas exchange surfaces in an insect, a frog, a
fish and a mammal
•
explain the relationship between the requirements of cells and
transport system in multicellular organisms
•
compare open and closed circulatory systems using one vertebrate
and one invertebrate as examples
In this part you will be given opportunities to:
•
use available evidence to discuss, using examples, the role of
technologies, such as the use of radioisotopes in tracing the path of
elements through living plants and animals.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board's website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
This version November 2002.
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Transport systems in
animals
In animals there are three systems that move materials around the body
and between the body and the surrounding environment.
These systems are:
•
respiratory system
•
circulatory system
•
excretory system.
Respiratory system
The respiratory system is responsible for the movement of gases
throughout the body. Oxygen is required for every cell in the body and
carbon dioxide must be removed from every cell in the body.
The respiratory system performs this function. Organs that are part of
the respiratory system of animals are lungs, gills and spiracles in insects.
Circulatory system
The circulatory system transports food, oxygen and wastes throughout
the body. Every cell has requirements for nutrients and must get rid of
poisonous waste materials. This is the role of the circulatory system.
Organs of circulatory systems are heart, veins, arteries, capillaries and
the haemocoel in insects. Circulatory systems may be open or closed.
Part 7: Transporting materials in animals
3
Excretory system
All animals need to excrete wastes produced from metabolic processes in
their cells. A build–up of wastes can produce unwanted effects and
many substances such as urea can become toxic in excess qualities.
Wastes substances that have to be remove include water, carbon dioxide
and nitrogenous compounds. Organs of excretion include kidneys, lungs,
skin and malpighian tubules in insects.
Comparison of the systems
All three systems have different tasks but they share common features
and common roles. The circulatory system has a role in the other two
systems because the blood vessels move materials to the organs of
respiration and excretion. Organs of the respiratory system such as the
lungs have a function in excretion of carbon dioxide. All three systems
work together to transport nutrients and waste products from where they
enter the body to where they leave the body.
The table below summarises this information.
Respiratory system
Circulatory system
Excretory system
Organs
Lungs, gills, skin,
spiracles
Heart, blood vessels,
lymph, haemocoel
Kidneys, lungs, skin,
malpighian tubules
Function
Movement of gases
through the body
Transport nutrients and
waste products around the
body
Rid the body of
waste materials,
water balance
Complete Exercise 7.1.
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Patterns in nature
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Circulatory systems
All multicellular plants and animals require a transport mechanism to
move nutrients, gases and wastes to and from cells. These materials need
to be moved around an organism’s body efficiently. This to ensure that
all cells obtain the appropriate materials to maintain function and any
products and wastes are removed.
Both plants and animals have methods of transporting materials within
the body. However, the transport of materials occurs in different ways.
In this section you will focus on transport in animals.
The circulatory system transports oxygen, food material and wastes to
and from cells. The movement of the blood through an organism
depends on the action of a heart.
All vertebrates and some invertebrates such as earthworms have a closed
circulatory system. This means that blood is transported around an
organism within muscular tubes or blood vessels.
The diagram following shows the movement of blood through the human
circulatory system.
Invertebrates such as arthropods have an open circulatory system.
A pool of blood is circulated by the action of a heart, there are no
specialised vessels for transporting blood.
An insect’s blood is in direct contact with its body cells–blood is not
contained in blood vessels as such. The internal space of an insect’s body
can be considered as a single blood vessel called the haemocoel.
This name comes from Greek words: haima (blood) and koilia (hollow).
An insect’s circulation system is in fact not entirely ‘open’ as they have
pumping vessels to promote the flow of blood.
Part 7: Transporting materials in animals
5
anterior
vena cava
capillaries
in arms and
head
capillaries
in lungs
capillaries
in lungs
posterior
vena cava
pulmonary
artery
right
atrium
pulmonary
vein
left
atrium
right
ventricle
left
ventricle
hepatic
portal vein
hepatic
artery
capillaries
in liver
mesenteric
vein
capillaries in
stomach and
small intestine
renal
vein
mesenteric
artery
capillaries
in kidneys
renal
artery
capillaries in
legs and
abdominal organs
oxygenated blood
de-oxygenated blood
Human circulatory system – a closed system.
accesory pump
haemocoel
pumping vessel
brain
gut
Insect circulatory system – partially open system.
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Patterns in nature
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A closed circulatory system ensures that there is one pathway ensuring
tissues are supplied with blood. It relies on a central heart to pump the
blood around within the specialised blood vessels. These require large
amounts of energy. All vertebrates have a closed circulatory system.
Open circulatory systems do not require the large amounts of energy
required by closed circulatory systems. They suit smaller animals that do
not make rapid movements.
Complete Exercise 7.2.
Part 7: Transporting materials in animals
7
Gas exchange in animals
All animal cells respire. Animal cells respire aerobically (most of the
time). They use oxygen gas in the process and release carbon dioxide
gas as a waste product. Animal cells do not photosynthesise.
In this section you will investigate and compare gas exchange surfaces of
an insect, a fish, a frog and a mammal. The gas exchange tissues and
organs of major groups of multicellular animals are often different.
In this section you will examine those differences.
Insects
Insects do not have lungs or gills. Insects exchange gases with the
atmosphere using trachea, tracheoles and spiracles.
longitudinal
trachea
spiracle
tracheoles
Structures used in gas exchange in an insect.
8
Patterns in nature
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Insects carry out gas exchange through a series of internal tubes (trachea)
that connect to the outside through holes (spiracles) located at various
points on the insect body.
The trachea branch into smaller and smaller tubes (tracheoles).
Tracheoles are very tiny (about one micron in diameter). The branching
into many tiny tubes has two advantages for the insect.
•
Because the tracheoles are extensively branched throughout the
insect, most cells are close to specialist gas exchange surfaces.
•
The branching and the small size of the tracheoles greatly increases
the surface area to volume ratio of the gas exchange surfaces.
Fluid collects in the ends of the tracheoles and it is into this fluid that
gases dissolve before diffusing into the surrounding cells.
The tracheoles are close to body cells. When waste gases eg. carbon
dioxide concentrations are higher in the cell than the neighbouring
trachea, then the waste gases diffuse out of the cell. When oxygen levels
are higher in the trachea than the surrounding cells oxygen will diffuse
into the cells.
The spiracles connect the trachea to the atmosphere surrounding the
insect. When the insect uses its muscles the trachea are compressed
and this causes gases to be pushed out of the spiracles. When the
muscles relax the trachea are not compressed and gases flow back into
the trachea.
Spiracles are able to close to help reduce water loss. Because the internal
parts of the body are very humid it is possible for water be removed as a
vapour from the body.
Spiracles also have fine hair–like structures to prevent dust entering the
system. If dust were to enter, the tracheoles could become blocked and
this would reduce the efficiency of the gas exchange surfaces.
Part 7: Transporting materials in animals
9
Fish
Most fish use gills for gas exchange. Gills are external structures–they
hang outside the main body cavity and often have a protective cover over
them. Gills have a large surface area because they are thin and
highly folded.
water from
mouth
gill raker
gill arch
cartilage
water flows out
behind operculum
lamella
water
primary filaments
operculum
Gas exchange in fish
Water enters a fish’s mouth and passes over the gills. When most fish
are stationary they gulp water to maintain the flow over the gills.
This also explains why so many fish (sharks included) swim with their
mouth open–this allows the water to pass into the mouth and over the
gills without the need to gulp water.
Gases are exchanged between the surrounding water and the fish on the
gill surface. The gases enter the circulatory system where they are
transported to cells throughout the body. The main blood vessels
entering the gills branch into tiny tubes called capillaries.
The capillaries are very close to the gill surface. It is the colour of the
blood in the capillaries that makes gills appear red. Capillaries being tiny
and numerous make the surface area to volume ratio for diffusion of
gases very high in the gills.
10
Patterns in nature
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Frogs
Frogs have two methods of gas exchange: gas exchange via the lungs and
gas exchange via the skin. The diagram below shows the structures
involved.
lungs
diffusion in moist skin
Frogs exchange gases through their lungs and moist skin.
Gas exchange via the lungs
Lungs are internal organs involved in gas exchange. The gas exchange
surfaces of terrestrial organisms are usually internal to prevent
desiccation (drying out). You will have noticed that the gas exchange
surfaces of insects (also terrestrial) are internal too.
Frogs ventilate their lungs by positive pressure breathing. This means
that they force air into the lungs. This method of breathing is very
different to the negative pressure breathing seen in mammals. You will
look at negative pressure breathing later.
Unlike human nostrils, which stay open all the time, frogs are able to
open and close their nares (nostrils). To breathe, a frog
•
closes its mouth and opens its nares
•
lowers the floor of the mouth causing air to be ‘sucked’ into the
mouth cavity
•
closes the nares (nostrils)
•
raises the floor of the mouth.
This forces the air in the mouth into the lungs.
Part 7: Transporting materials in animals
11
Lung structure of a frog
The internal structure of a frog lung is not too dissimilar to a human lung.
Air enters the lungs and then moves through a series of branching tubes.
The tubes become smaller and smaller as they branch (this is becoming a
familiar theme for gas exchange). The finest tubes are in close
association with capillaries (small blood vessels). Gases diffuse into and
out of the blood at these sites.
Like the fish, the circulatory system delivers gases to the cells.
The circulatory system also receives the waste gases from cells and
delivers them to the lungs. You will take a much closer look at the
structure of lungs in the next section.
Gas exchange via the skin
The skin of a frog is thin and kept moist by the habitats in which the frog
lives. The skin is permeable to water (unlike human skin).
Frogs dehydrate rapidly if they are not kept in a moist environment.
This is why you find frogs in moist locations.
Gases from the atmosphere dissolve into the moisture on the skin.
From there the gases can diffuse into the capillaries beneath the skin.
The skin does not exchange sufficient gases for all of a frog’s needs.
However, the gas exchange is important and allows the frog to remain
submerged for longer than if it had to depend on lungs alone.
While submerged, gaseous exchange occurs on the frog’s skin.
Mammals
Mammalian lungs are internal. This helps to reduce the loss of water
and heat through these structures that have a high surface area to
volume ratio.
To get air into the lungs the mammal lowers the air pressure in the lungs.
When the air pressure in the lungs is lower than the surrounding
atmosphere, air enters via the nose.
To remove air from the lungs, mammals increase the pressure of the air
in the lungs. When air pressure in the lungs is higher than the
surrounding atmosphere air moves out of the lungs.
The structure of the human respiratory system is shown on the diagram
on the following page.
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Patterns in nature
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nose
nasal cavity
trachea wall
magnified
epiglottis
cilia
to the stomach
trachea
bronchus
bronchiole
rib
right lung
showing
lobes
left lung
dissected to
show
internal
diaphragm
from pulmonary
artery
air
to pulmonary
vein
cluster of
alveoli
capillaries
Structures involved in the exchange of gases in humans.
Air enters the body through the nostrils. The nasal cavity warms the air,
filters it and removes dust. The air then moves into the throat region or
pharynx (pronounced farrinks). It enters the largest air tube–the trachea
(pronounced track–ee–ah) through the opening called the glottis.
The epiglottis is a flap of tissue that closes over the glottis and stops food
going down the wrong way when we swallow.
The trachea branches into two bronchi (pronounced bron–key).
Each bronchus (singular) branches into smaller air passages called
bronchioles (bron–key–oles) and these end in very thin–walled alveoli
(pronounced al–vee–oh–lie), singular alveolus. Blood capillaries are
wrapped closely around the alveoli.
It has been estimated that the total surface area of the alveoli of an adult
male is about one third the area of a tennis court. A large surface area
obviously allows for a greater quantity of gases to be exchanged.
The thinness of the walls of the alveoli allows for rapid diffusion of
oxygen into the blood and carbon dioxide out of the blood. The moisture
in the alveoli walls allows gases to dissolve.
Part 7: Transporting materials in animals
13
blood from body
(low in oxygen, high in carbon dioxide)
blood capillary
wall of alveolus
air inhaled
air exhaled
carbon dioxide
oxygen
blood cell
blood to rest of body
(high in oxygen,
low in carbon dioxide)
Movement of material in an alveolus.
Composition of inhaled and exhaled air is shown in the table below.
Gases
Percentage in inhaled air
(%)
Percentage in exhaled air
(%)
oxygen
21
16
0.04
4
about 80
about 80
varies according to the
humidity of the air
more than in inhaled air
carbon dioxide
nitrogen
water vapour
Air passages
Rings of cartilage keep the trachea and bronchi open and prevent them
closing when the air pressure inside the body falls. The lining cells of
the air passages have numerous cilia (sill–ee–ah). These are minute
hair–like projections that sweep to and fro.
Mucus is secreted by special gland cells, also present in the lining or
epithelial (ep–e–theel–e–al) cells. Dust particles and bacteria in the air
are trapped by the mucus film. The movements of the cilia sweep them
14
Patterns in nature
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away in the mucus to the larynx and the mucus is swallowed or
coughed up.
The nose hairs and mucus also trap dust and foreign particles.
Around the lungs is a membrane, the pleural (ploo–ral) membrane, which
covers the outside of the lungs and the inside of the chest cavity.
It contains a fluid that lubricates the surface so that there is no friction
between the tissues during breathing movements.
The mechanism of breathing
In mammals, breathing refers to the movements of the chest that result in
air entering and leaving the lungs.
The movement of air in and out of our chest is bought about by changes
in the pressure of the air in the chest cavity. This pressure varies because
the volume of the chest cavity varies. The chest cavity is airtight and
enclosed by ribs with intercostal (inter–cos–tal) muscle between them.
At the base of the chest cavity is the diaphragm (die–ah–fram).
The diaphragm is the muscular sheet separating the chest (also called
thorax) and abdomen.
At rest, the diaphragm is curved upwards. The intercostal muscles relax
at the same time and the ribs move downwards and inwards.
These collapsing movements reduce the size of the chest cavity, increase
the pressure of the air in the lungs and thus force it out.
During inhalation, the diaphragm contracts and flattens, being more taunt
or tight in this state. At the same time, the intercostal muscles contract
and move the rib cage up and outwards. This increases the volume of the
chest cavity and reduces the pressure of the air in it. Air thus moves into
the lungs. You can check these movements by placing your fingers over
your rib cage as you inhale and exhale.
Complete Exercise 7.3.
Part 7: Transporting materials in animals
15
Investigative technology
Much of what is known about the structure and function of living
things has been directly associated with the improvements in
technology available.
New technology is increasing the range of investigative methods in
research laboratories, industry, environmental management and in the
medical profession. The use of radioisotopes have improved productivity
and gained information that cannot be obtained in any other way.
Radioisotopes produce radioactive emissions that can be easily detected.
This property makes radioisotopes very useful as tracers.
Radioactive materials can be tracked through a process, system or
organism. Examples of use include mapping pathways of nutrients and
toxins through ecosystems, absorption of nutrients by plants and tracing
metabolic pathways. Increasingly medical diagnosis is making use of
tracers for organ and tissue function.
Many chemical elements have isotopes. (Isotopes have the same number
of protons but a different number of neutrons in the nucleus of an atom.)
Some isotopes are unstable and emit alpha or beta particles and
sometimes gamma radiation.
Tracers can be used to follow movement of substances in large amounts
or at molecular or even atomic levels. The observations are made by
measuring the radioactivity or by measuring the relative abundance of the
stable isotopes. The instruments used for detecting the tracers pathway
include electroscopes, scintillation counters, the Geiger–Müller counter
and the mass spectrometer.
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Radioactive tracers
Radiation is used in nuclear medicine to diagnose the functioning of
organs such as the liver and kidneys. Radioactive tracers are used which
emit gamma rays for very short periods of time. Radioactive materials
are introduced into the body orally, by injected or they are inhaled.
An image of the organ showing the location of the radioisotope is used in
diagnosis. An unusual pattern indicates a malfunction in the organ.
Bone and other tissue can be seen much more clearly using these imaging
techniques than by x–rays.
Blood flow to the brain, liver and kidney function and bone growth can
be diagnosed using radioisotopes as tracers. The amount of radioisotope
given to patient is a very small dose, only enough to obtain an image for
diagnosis.
Technetium–99 is a very common isotope used in medicine.
It has a half–life of six hours. Technetium–99 emits low energy gamma
rays so the patient receives only a very low radiation dose.
Geiger counters
A Geiger counter is a machine that measures radioactivity.
In the experiment on the following page radioactive carbon was taken in
by the leaves through the process of photosynthesis. The Geiger counter
was used to measure the amount of radioactive carbon in the leaves and
in the fruit. The next day the readings showed that the radioactive carbon
had moved from the leaf to the fruit.
Part 7: Transporting materials in animals
17
Day 1
sugar with radioactive carbon on scraped leaf
Geiger counter
HIGH
tomato fruit
Geiger counter
LOW
Day 2
sugar with radioactive carbon on scraped leaf
Geiger counter
LOW
tomato fruit
Geiger counter
HIGH
Gather information from secondary sources on the use of radioisotopes in
tracing the path of elements through living plants and animals.
You will need to carry out a search of secondary information sources such as
contacting research institutions such as ANSTO, CSIRO or the Internet.
Conventional sources such as libraries will have many references you can
use and may be a good place to start.
Process the information by answering the questions in Exercise 7.4.
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Exercises - Part 7
Exercises 7.1 to 7.4
Name: _________________________________
Exercise 7.1: Transport systems in animals
Compare the roles of the excretory, respiratory and circulatory systems in
the body. systems
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Exercise 7.2: Circulatory systems
a)
What is the role of the circulatory system in humans?
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Part 7: Transporting materials in animals
19
b) What is the difference between open and closed circulatory systems?
Give examples.
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c)
Which system is more efficient – open or closed circulatory system?
Give reasons.
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Exercise 7.3: Comparison of gas exchange
Identify and compare the gas exchange surfaces in an insect, a frog a fish
and a mammal by filling in the table below.
Organism
Name of gas
exchange structures
insect
frog
Surface Area/Volume
ratio
Gas exchange
structures
internal/external
high
skin
low
lungs
high
external
fish
mammal
20
internal
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Exercise 7.4: Radioactive tracers
Discuss the role of radioisotopes as tracers in medicine. What are the
issues? Provide points for and against the use of radioactive materials in
medicine.
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Part 7: Transporting materials in animals
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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 8: Growth and repair
2
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In
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b S
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Contents
Introduction ............................................................................... 2
Cell division ............................................................................... 3
Sites of mitosis .....................................................................................4
What happens during mitosis? ............................................................6
Mitosis in plant cells .............................................................................7
Cytokinesis .........................................................................................11
Additional resources................................................................ 12
Suggested answers................................................................. 15
Exercises–Part 8 ..................................................................... 17
Student evaluation of module
Part 8: Growth and repair
1
Introduction
Maintenance of organisms requires growth and repair.
In this part you will be given opportunities to learn to:
•
identify mitosis as a process of nuclear division and explain its role
•
identify the sites of mitosis in plants, insects and mammals
•
explain the need for cytokinesis in cell division
•
identify that nuclei, mitochondria and chloroplasts contain DNA.
In this part you will be given opportunities to:
•
perform a first–hand investigation using a microscope to gather
information from prepared slides to describe the sequence of changes
in the nucleus of plant or animal cells undergoing mitosis
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board's website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html
This version November 2002.
Materials required:
•
microscope and lamp
•
two slides and a cover slip
•
onion with fresh roots (you need to soak onion base in water at least a
week in advance)
•
methyl green pryonin or aceto–orcein stain.
Alternatively use prepared slides of a root tip (if available).
If you do not have access to a microscope or prepared slide, use the
photographs provided.
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Cell division
A multicellular organism such as a human, begins life as a single cell
formed from the union of two sex cells. From this microscopic beginning
the organism grows to become an adult. This is achieved by the process
of cell division. One cell divides forming two cells and then each of these
cells divide forming more cells to continue the process of cell division.
Mitosis is a type of cell division that results in the replication of identical
cells. Meiosis is another type of cell division which produces gametes or
sex cells. Meiosis produces cells that have half the number of
chromosomes of the parent cell.
Mitosis results in growth of an organism, is involved in the healing of
wounds and the replacement of cells eg. red blood cells and skin cells.
With the exception of gametes (ova and sperm), all the body cells or
somatic cells come from pre–existing cells by mitosis.
1
Write a definition, in your own words, for mitosis.
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2
How is mitosis different from meiosis?
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3
What is the role of cell division in multicellular organisms?
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Check your answers.
Part 8: Growth and repair
3
Sites of mitosis
Mitosis occurs in areas of rapid growth in organisms. These sites are in
different places in different types of organisms. This is usually due to the
need for rapid replication such as growth points or sites where repair to
damaged tissue is required. Multicellular organisms may also have stages
in their life cycle during which mitosis may occur at a greater rate such as
within a developing foetus.
Plants
Mitosis in plants occurs in special cells called meristematic cells and in
the layer of cells in the stem called cambium. These cells are responsible
for the growth in length and width.
In the root there is a protective area called the root cap. Behind this area
is the apical meristem where active cell division is occurring. This is
followed by an area of elongation where the newly formed cells increase
in size.
cortex
growth zone
xylem
cell
division
phloem
cell
elongation
root hair
root cap
Diagram of a root tip showing the growth zone.
In the stems, secondary growth occurs in the cambium. The vascular
cambium forms phloem and xylem cells.
At the tip of the shoots there is the apical meristem where mitosis is
occurring rapidly forming new cells. Buds are another structure that
contain meristematic tissue which is capable of rapid growth.
4
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Insects
Insects have a multiple staged life cycle. During a larval stage the
organism increases in size. This is due to cell enlargement and not cell
division. Increased rates of mitosis occur in the epidermal cells before a
moult during the pupal stage. Metamorphosis results in the breakdown of
the larval tissue and the development of the adult insect.
Mammals
In mammals mitosis is occurring in many parts of the body. Skin, hair
and nails are continually growing. Blood cells are made daily to replace
those that have died. Any injury results in rapid mitosis to repair the
damage. Young mammals are growing rapidly and at this stage of life
mitosis rates are high.
1
Complete the following table by matching the sites of mitosis in either
plant or mammal.
Site of mitosis
Plant/animal
root tip
skin
digestive tract
shoot tip
bone marrow
hair and nails
stems
2
Explain why mitosis is important to insects during metamorphosis.
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Check your answers.
Complete Exercise 8.1.
Part 8: Growth and repair
5
What happens during mitosis?
When a cell divides, a series of changes occur in the nucleus of cells.
The most important parts of the nucleus involved in the process are the
chromosomes. Chromosomes determine the characteristics of an
organism. Genes are found along chromosomes and consist of sections of
DNA (deoxyribose nucleic acid). Most of the DNA in a cell is found in
the nucleus.
1
What is DNA? Why is it important?
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2
The DNA part of chromosomes carries the genetic code as genes.
Each time a cell divides by mitosis, new daughter cells end up with
chromosomes, and hence DNA, which is identical to those of the
original parent cell.
The discovery of the structure of DNA and the way it is replicated
during cell division, has been one of the most exciting and important
events in 20th century biology. Mitosis is essentially the replication
of chromosomes and their separation into daughter cells.
What major developments in technology do you think assisted in the
identification of DNA?
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Check your answers.
Self replicating organelles
Plastids and mitochondria are self–replicating organelles. This means
that when mitosis is occurring these organelles reproduce independently
of the nuclear division.
Chloroplasts (a type of plastid) and mitochondria both posses genetic
material (DNA) that enables them to replicate. It is thought that they may
be descendants of ancient procaryotic cells that have since become part of
other cells.
1
List the cell organelles that contain DNA.
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2
Most of the cell’s DNA is present in the nucleus. What parts of the
nucleus are made of DNA?
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3
What is the role of DNA in the cell?
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Check your answers.
Complete Exercise 8.2.
Mitosis in plant cells
The process of mitosis in plants is similar to that in animals. However,
there are two differences:
•
there are no centrioles in most plants
•
the cell does not become constricted in the last stage of the process.
In plant cells, the partition usually starts in the centre of the cell and
grows outwards to meet the existing right cell wall.
1
Why do cells undergo mitosis?
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2
What are the differences between the parent cells undergoing mitosis
and the resulting daughter cells?
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3
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What is the significance of division after replication for a cell?
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Check your answers.
Part 8: Growth and repair
7
Microscopic examination of mitosis in plant cells
As you have already read the root tip is a site of rapid mitosis in plants.
In this experiment you will examine a root tip for the stage of mitosis.
Materials required:
•
microscope and lamp
•
two slides and a cover slip
•
onion with fresh roots (you need to soak onion base in water at least a
week in advance)
•
methyl green pryonin or aceto–orcein stain.
Alternatively use prepared slides of a root tip (if available).
If you do not have access to a microscope or prepared slide, use the
photographs provided following.
Procedure:
1
Remove a new root from the base of the onion and place it in the
centre of a clean slide (only the top portion is required if it is very
long).
2
Place another slide on top and gently squash the two slides together.
This should grind the root tip.
3
Remove the top slide, ensuring the squashed material remains on the
lower slide.
4
Add one drop of stain to the material and cover with the cover slip.
5
Allow to stand for about 20 minutes and then examine under the
microscope.
Observe the cells in the slide of the root tip. You are looking for the
different stages of mitosis.
8
6
Identify cells that have undergone mitosis.
7
Draw diagrams showing the stages in mitosis.
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Slide of root tip showing various stages of mitosis. How many stages can you
pick out? (Photo Jane West)
Interphase (animal
cell)
Interphase plant cell
Your drawing of a plant cell
nucleus
Part 8: Growth and repair
9
10
Prophase (animal
cell)
Prophase plant cell
Your drawing of a plant cell
Metaphase (animal
cell)
Metaphase plant cell
Your drawing of a plant cell
Anaphase (animal
cell)
Anaphase plant cell
Your drawing of a plant cell
Telophase (animal
cell)
Telophase plant cell
Your drawing of a plant cell
Patterns in nature
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Cytokinesis
Mitosis refers to the changes involving the chromosomes during cell
division. Cell division, however, usually includes the division of the
cytoplasm and certain organelles within the cytoplasm. The division of
the cytoplasm is called cytokinesis.
In animal cells cytokinesis is usually achieved by the formation of a
cleavage furrow which deepens to constrict the two parts. In plant cells, a
cell wall forms across the middle, separating the two parts.
1
At what point in mitosis does cytokinesis occur?
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2
Why is cytokinesis important in cell division?
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Check your answers.
Complete Exercise 8.3.
You have come to the end of the module Patterns in nature. You will
have come to recognise that there are patterns in living things as they
adopt similar methods of solving the problems of surviving.
Part 8: Growth and repair
11
Additional resources
Phases in mitosis
You do not need to learn the names of the stages of mitosis.
1
Interphase
This stage is sometimes misleadingly called the ‘resting’ stage.
In fact, the cell is very active. It is during this stage that each
chromosome becomes replicated. A cell with four chromosomes would
end up with eight at this stage. Cells with 46 chromosomes (a human
cell) would end up with 92 and so on.
Organelles, such as mitochondria, ribosomes (and chloroplasts in plants)
are also replicated although how they are replicated is not clearly
understood. As well, the centrioles, which are outside the nucleus, begin
to separate. In most of the more complex plants there are no centrioles.
2
Prophase
During this stage, the chromosomes are visible, first as long, thin strands.
As the process continues, the chromosomes become shorter and thicker.
Each chromosome and its replica are held together by a structure called
the centromere. The identical chromosomes at this stage are called
chromatids. The centrioles move to opposite ‘poles’ of the cell and
spindle fibres start to form. This stage ends with the breakdown of the
nuclear membrane.
3
Metaphase
The spindle consists of long molecules of protein lying across the cell
from pole to pole. The chromosomes move through the cytoplasm to the
spindle and become fastened to it by their centromere. The centromere
becomes attached along a plane about halfway between the poles.
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This plane is called the equator. At this middle stage the chromosomes
are in the middle of the cell.
4
Anaphase
The centromeres divide so that each chromatid has its own centromere.
Each chromatid now is a daughter chromosome. The daughter
chromosomes move apart, each member of a pair moving to opposite
poles of the cell. Each group of daughter chromosomes forms a densely
packed group at each pole. Remember: at anaphase the chromosomes are
moving apart. Notice that four chromosomes move to opposite parts
(poles) of the cell. Notice also that the cells start to become constricted in
the centre.
5
Telophase
Nuclear membranes form around each group of daughter chromosomes.
The chromosomes uncoil to become slender threads. A new cell
membrane forms at the equator. The cytoplasm divides and two new
daughter cells now exist, where there was originally only one parent cell.
Part 8: Growth and repair
13
2 early prophase
1 interphase
3 late prophase
nucleus
chromatid
centromere
4 metaphase
spindle
6 telophase
5 anaphase
Mitosis in an animal cell with two chromosomes.
14
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Suggested answers
Cell division
1
Mitosis is a type of cell division resulting in the replication of
identical cells.
2
Meiosis produces cells that have half the number of chromosomes
compared to the parent cell. This process produces the gametes or
sex cells.
3
Cell division is responsible for growth, repair and reproduction of
multicellular organisms.
Sites of mitosis
1
2
Site of mitosis
Plant/animal
root tip
plant
skin
animal
digestive tract
animal
shoot tip
plant
bone marrow
animal
hair and nails
animal
stems
plant
Cells need to be produced rapidly when undergoing metamorphosis
compared to other stages in which no mitosis occurs.
Part 8: Growth and repair
15
What happens during mitosis?
1
DNA makes up the material of inheritance or the genetic material in
a cell. Every cell needs to have its own DNA code for its specific
structure and function.
2
The development of the electron microscope and staining techniques.
Self replicating organelles
1
The nucleus, chloroplasts and mitochondria all contain DNA.
2
The chromosomes in the nucleus are made of DNA. A section of
DNA with specific information is called a gene. Genes are part of
chromosomes.
3
DNA contains information that is transferred when cells replicate.
Mitosis in plants
1
Cells undergo mitosis for growth and repair of body tissue.
2
The parent cells are usually larger than daughter cells initially.
3
Cells must divide after replication otherwise they would end up with
double the amount of genetic material.
Cytokinesis
16
1
After the chromosomes have separated into two nuclei the cytoplasm
divides so that the cells are able to enter interphase.
2
Cytokinesis is important because after mitosis the nucleus has
divided and separate nuclear membranes of the daughter cells have
formed. Then the cytoplasm must divide (cytokinesis) to produce
two new cells.
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Exercises - Part 8
Exercises 8.1 to 8.3
Name: ________________________
Exercise 8.1: Mitosis
Mitosis is a very significant process in any living thing.
Write a short report to explain the significance of the process of mitosis
for plants and animals.
Your report should include reference to:
•
the role of cell division in multicellular organisms
•
the activities of chromosomes during mitosis (describe the sequence
of change)
•
where mitosis occurs in plants, mammals and insects.
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Part 8: Growth and repair
17
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Exercise 8.2: What happens during mitosis?
Identify the parts of a cell that contain DNA.
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_________________________________________________________
Exercise 8.3: Cytokinesis
Explain the importance of cytokinesis.
_________________________________________________________
_________________________________________________________
_________________________________________________________
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18
Patterns in nature
Student evaluation of the module
Name: ________________________
Location: ______________________
We need your input! Can you please complete this short evaluation to
provide us with information about this module. This information will
help us to improve the design of these materials for future publications.
1
Did you find the information in the module clear and easy to
understand?
_____________________________________________________
2
What did you most like learning about? Why?
_____________________________________________________
_____________________________________________________
3
Which sort of learning activity did you enjoy the most? Why?
_____________________________________________________
_____________________________________________________
4
Did you complete the module within 35 hours? (Please indicate the
approximate length of time spent on the module.)
_____________________________________________________
5
Do you have access to the appropriate resources? eg a computer, the
internet, scientific equipment, chemicals, people that can provide
information and help with understanding science
_____________________________________________________
_____________________________________________________
Please return this information to your teacher, who will pass it along to
the materials developers at OTEN – DE.
BIOPRE 43209 Patterns in nature
Learning Materials Production
Open Training and Education Network – Distance Education
NSW Department of Education and Training