Download Calderglen High School Biology Unit 2 Multicellular Organisms

Multicellular Organisms
Calderglen High School
Biology Unit 2
Multicellular Organisms
1
Multicellular Organisms
Cells are the basic unit of live. Living organisms are composed of cells. Some
organisms consist of one cell - unicellular organism. Multicellular organisms consist
of many cells are more complex.
Unicellular organisms
Unicellular organisms include
bacteria, some algae, some fungi
and a group of organisms called
protozoa.
A unicellular organism called an Amobea bbc bitesize
Multicellular Organisms
These organisms are composed of many. The individual cells require food, oxygen
and the removal of waste products such as carbon dioxide. However, a division of
labour occurs amongst the cells. This means every cell does not carry out every
function, specific cells become specialised to perform a particular function.
Cell organisation
The cells are organised as shown below
Cells
Tissues
Eg
muscle
and
bone.
Organs
Eg liver,
eye or
stomach
Systems
Eg
circulatory
system,
digestive
system
Organisms
2
Multicellular Organisms
Examples of Specialisation of Animal Cells
Motor Neuron
Image BBC
Bitesize
 They have a long “tail” ideal for the transmission of nerve impulses.
 This ensures connections can be made with other cells.
 A protective sheath allows the nerve impulse to travel quickly from one end
of the cell to the other.
Sperm Cell
Produced by male
The cell has three parts. The head
contains the nucleus, the mid- area
contains many mitochondria and the
tail allows the sperm to swim.
Image BBC Bitesize
Red Blood Cell
Specialisation of Red blood cells which transport oxygen around the body.
Scran image
 The cell produces haemoglobin
 The nucleus breaks down, leaving
more space in the cell for the
transport of oxygen.
 The cell has a large surface area to
allow faster uptake of oxygen.
Plants are organised in a similar way, examples of plant organs include leaves and
flower.
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Multicellular Organisms
Examples of Specialisation of Plan Cells
Plant Cells are organises in a similar way, examples of plant organs include leaves
and flower.
Examples of Specialisation of Plant Cells
It consists of a companion cell and a sieve tube cell which transports sugar in the
plant. The sugar produced by photosynthesis can transported to all parts of the
plant in the companion cell.
Phloem Tissue
Sieve cell
Sieve plate
Companion
cell
These cells are adapted to their function
because;
 Sieve plates (perforations) formed in the
cell wall
 Phloem contains companion cells which
control the activity of the sieve tube
because the sieve tube does not contain a
nucleus.
Image BBC Bitesize
Palisade Mesophyll Cell
These cells are involves with photosynthesis and they form a continuous layer of
cells near the leaf surface.
These cells have become adapted for their function;
 The cells are column shaped
 The cells contain many chloroplasts to allow maximum photosynthesis
Palisade mesophyll cell in a
leaf
Image – BBC Bitesize
Image – BBC Bitesize
4
Multicellular Organisms
A Root Hair Cell
Root hairs absorb water and mineral salts form the soil. These substances move up
the plant in the xylem. Root hairs are adapted for their function because they are
Root hair cell
Image – BBC Bitesize
 Lacking in chloroplasts because
root hairs are underground in the
soil.
 The shape of the cell ensures a
large surface area for absorption
of water and mineral salts.
 The presence of the vacuole in the
extended section of the root hair
gives rise to absorption of mineral
salts and the movement of water
into the hair by osmosis.
5
Multicellular Organisms
Stem Cells and Meristems
The cells of an organism contain 2 sets of chromosomes (except sex cells) for
example human cells contain 2 sets of 23 chromosomes making 46 in total.
However some genes on a chromosome will be switched on or off to form
specialised cells in different tissues, organs and systems. This happens early in the
cells development and is irreversible. The cells specialised cells originate from are
called stem cells and these can become any type of cell e.g. red blood cell, nerve
cell or bone cell. Stem cells are needed as an organism grows and to replace
damaged cells.
Liver
Image
BBC
Bitesize
Bone
Nerve
Red blood cell
Stem cells can be extracted from early human embryos or from bone marrow or
the blood circulation. Using tissue culture techniques they can be induced to form
differentiated cells. Recent research has also found ways to reverse some
specialised adult cells back to stem cells.
Possible uses of stem cells include the treatment of diabetes and cancer. Repair
to body organs including bone and the windpipe or even the growth of organs for
transplant such as liver and skin. Another area of possible use is stem cells could
be used to grow tissues to test the effect of toxins such as pesticides sprayed on
crops.
The problem is how to make the undifferentiated stem cells into the specialised
cells required. Scientists are making big steps in this area but work still needs to
be done.
Stem cells that turn into blood cells are called haematopoietic stem cells and can
be used to form red blood cells, white blood cells or platelets.
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Multicellular Organisms
A specific example of stem cell use
Brain diseases – stem cells from embryo‟s have been programmed to form brain
cells that can replace damaged ones. This could help diseases such as Parkinson‟s
where damage to nervous tissue leads to muscle spasms caused by continual
muscle contraction. Replacement cells could also be used for Alzheimer‟s disease
where damaged brain cells cause memory loss and confusion.
Ethical Issues
Some people object to the use of embryos on moral or religious grounds arguing
this is a loss of potential human life. This has to be balanced against the
prevention and release from suffering the stem cells could bring. Some religions
are strongly against the use of stem cells
Meristems
Plants contain regions of undifferentiated cells (non-specialised cells) in regions
called Meristems. These Meristems are the only region in plants where cell division
occurs (by mitosis). They have the potential to become any type of cell and they
contribute to plant growth.
The cells in the meristem become elongated (longer) and vacuolated (vacuoles
appear) and then differentiated.
Differentiation is when the unspecialised cells become specialised, e.g. they may
become long hollow tubes called xylems that carry water upwards from the roots
in plants.
7
Multicellular Organisms
Control and Communication
In a multicellular organism, cells communicate using nerve impulses or hormones.
The central nervous system produces electrical impulses for rapid communication
between different parts of the body.
Nervous control
The brain and spinal cord are made of neurons. The brain and the spinal cord
make up the central nervous system (CNS).
Many nerves join with the CNS. They bring messages as nerve impulses from
sensory organs which contain cells called receptors.
The CNS sorts this information and processes it.
To trigger a response, a different group of nerves are used to carry messages from
the CNS to effectors which are usually muscles.
image bbc bitesize
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Multicellular Organisms
The Brain
The brain plays a very important part in the way you respond to any factors that
may affect your body. Just to read this page, millions of nerve messages are
zipping around within your own brain.
The brain itself is made up of several different parts or regions, each with its own
specialised function.
image bbc bitesize
Part of the brain
Function
Cerebrum
Controls conscious actions, as well
as reasoning and learning.
Cerebellum
Balance and muscle co-ordination
Medulla
Controls the rate of breathing and
heartbeat.
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Multicellular Organisms
Nerve pathways
It involves three types of nerve cell or neurons. Neurons are highly specialised
because they carry electrical impulses, they do not come in contact with one
another:
 A sensory neuron which carries electrical impulses from a sense organ to the
CNS.
 A relay neuron which is located in the brain or spinal cord. It receives
electrical impulses from the sensory neuron and transmits them to other nerve
cells involved in the response.
 A motor neuron which receives electrical impulses from relay nerve cells and
transmits them to a muscle or gland which will carry out the response.
When stimulated by an electrical impulse, muscles respond by contract and
glands by releasing chemicals. Muscle responds more rapidly than glands.
 Reflex actions are fast responses that do not normally involve conscious
thought. They usually protect your body from harm. Examples of reflex actions
include sneezing when foreign particles enter the nose, withdrawal of a hand
from a hot object, blinking when an object moves near the eye.
 The circuit of the neurons that act to produce the reflex action is called the
reflex arc (refer to the diagram on the next page)
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Multicellular Organisms
Image from BBC Bitesize
Relay neuron
Sensory neuron
Motor neuron
muscle
Burning candle
Reflex arc
 The transmission of a nerve impulse through a reflex arc is called a reflex
action. In the example above the sensory neuron in the hand detects the heat
and this initiates an electrical impulse which travels towards the relay nerve.
The impulse is transferred to the rely nerve which passes on the impulse to the
motor nerve. The nerve impulse travels along the motor nerve to the muscle
which brings about a muscle contraction and the hand is withdrawn from the
heat.
 The neurons do not touch, there is a small gap called a synapse between
neurons which allows chemicals to transfer from one neuron to another.
Sensory neuron
Relay neuron
Motor neuron
Synapse (gap
Synapse (gap
between neurons)
between neurons)
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Multicellular Organisms
Hormonal control
Hormones are made up of proteins. They are chemical messengers which pass on
information to target tissues which have special receptor cells sensitive to that
specific hormone. Only some tissues are affected by specific hormones. Glands
which release hormones into the bloodstream are known as endocrine glands.
Endocrine system
Image from BBC Bitesize
Pancreas
Liver
Testes
(male)
Ovary
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Multicellular Organisms
Regulation of Blood Glucose Level in the Blood
Cells are constantly using up glucose
present in the bloodstream for energy.
A rise in blood glucose concentration is
detected by cells in the pancreas. These
cells produce the hormone insulin. This
hormone is transported in the blood to
the liver where it activates glucose to be
converted to glycogen. This brings blood
glucose concentration down to around its
Scran image
normal level.
If the blood glucose concentration drops a different set of cells in
the pancreas detect this change and release the hormone glucagon
into the bloodstream. This second hormone is transported to the
liver and activates the conversion of glycogen to glucose. The blood
glucose concentration therefore rises to its normal level.
Regulation of Blood Glucose levels
Insulin produced when blood glucose
level is above the normal level
blood glucose
level
Glycogen in
the liver
Glucagon is produced when the
blood glucose level falls below the
normal level
13
Multicellular Organisms
Diploid Cells




After fertilisation, a zygote (fertilised egg) is formed.
The cell is DIPLOID
A diploid cell has 2 sets of chromosomes (in humans this is 46 chromosomes).
One set has come from the male parent and one set has come from the
female parent.
 Every body cell has a copy of the chromosomes that was in the zygote.
 Therefore, every body cell is a diploid cell.
 The diploid number in humans is 46.
Haploid Cells






Eventually, the adult will produce sex cells.
Another name for the sex cells is GAMETE.
Gametes will only have one set of chromosomes.
A HAPLOID cell has only one set of chromosomes
The haploid number in humans is 23.
Fertilisation
 If a haploid gamete from a male meets a haploid gamete from a female, a
diploid zygote is formed.
Haploid
Haploid
Gamete eg
Gamete eg
sperm
egg
Fertilisation
produces a
diploid
zygote
14
Multicellular Organisms
Gamete Production in Animals




Like plants, animals produce gametes in sex organs.
In human males, SPERM are produced in the TESTES.
In human females, EGGS (ova) are produced in the OVARIES.
Millions of sperm cells are produced in the testes and are able to swim in
fluid using their long tails.
 Egg cells are the largest human cells because of the large food store in the
cytoplasm.
Sperm (male gamete)
Egg (female gamete)
head
tail
Cell membrane
nucleus
Cytoplasm
containing a
food store
Scran
images
15
Multicellular Organisms
Animal Reproductive System
Male reproductive system image bbc bite size
sperm duct
penis
Testes
Female reproductive system
image bbc bitesize
testes
ovary
womb
Sexual Reproduction in Plants
 Flowers are the organs of sexual reproduction in plants.
 The flower contains both the male and female parts.
 The ANTHER and FILAMENT together is known as the STAMEN. This is the
male parts of the flower.
 The male anther is the site of gamete production. The diploid anther cells
produce the haploid pollen grains, which contain the male gametes.
 The OVARY is the female part of the flower.
 The female ovary is the site of gamete production. The diploid ovary cells
produce haploid eggs (the female sex cell or gamete).
16
Multicellular Organisms
Variation
 A characteristic shows DISCRETE VARIATION if it can be used to divide up
the members of a species into two or more distinct groups.
 Humans can be split up into two groups depending on their ability to roll
their tongue and into four groups based on blood group types A, B, AB and O.
 Data obtained from a survey of a characteristic that shows discrete variation
is represented by a bar chart
Discrete variation graph
Image bbc bitesize
 Some characteristics are controlled by the alleles of a single gene – they are
expressed as clear-cut PHENOTYPIC groups showing discrete variation.
 In humans, the ability to roll the tongue is an example of the single gene
inheritance.
 In pea plants, the possession of lilac or white flowers is an example of single
gene inheritance.
17
Multicellular Organisms
Continuous Variation
 A characteristic shows continuous variation when it varies amongst the
members of a species in a smooth, continuous way from one extreme to
another and does not fall into distinct groups.
 CONTINUOUS VARIATION can be represented by a normal DISTRIBUTION
CURVE (the curve would be bell shaped).
Image bbc bitesize
 Few individuals show values close to the extremes of the range.
 Most individuals show values close to the middle of the range (also known as
the average).
 Some characteristics are controlled by the alleles of several genes.
 This results in the characteristic being expressed as a range of PHENOTYPES
e.g. Human height.
 A characteristic showing CONTINUOUS VARIATION controlled in this way by
more than one gene is said to show polygenic inheritance.
18
Multicellular Organisms
Phenotypes and Dominant Genes
 For every characteristic we have 2 genes – one from our mother and one
from our father.
 Genes are part of chromosomes.
 Each characteristic is controlled by two forms of a gene.
 Each parent contributes one form of the gene.
 Each gamete (sex cell) carriers one of the two forms of the gene.
 Differing forms of a gene are called ALLELES.
 Example – The alleles for the gene for eye colour are blue, brown, green,
etc.
 PHENOTYPE – this is the physical appearance resulting from the inherited
information.
 Example – Someone with blue eyes has the phenotype blue eyes.
 Genes or alleles can be said to be DOMINANT (shows up in the phenotype) or
RECESSIVE (hidden when it is present along with the dominant gene).
 GENOTYPE – this is the combination of genes in a gene pair.
 Genotype is represented by 2 letters (one letter for each gene).
Note – the phenotype of this
individual is Black Hair
Dominant
black gene
Recessive
white gene
 If the 2 alleles that an organism possesses for a characteristic are identical,
the organism is said to be HOMOZYGOUS for the characteristic.
 BB has a phenotype black it is said to have a HOMOZYGOUS genotype.
 Homozygous is often called „pure breed‟ or „true breeding‟.
 Bb has the phenotype black but it is said to have a HETEROZYGOUS
genotype.
 If the 2 alleles that an organism possesses for a characteristic are different,
the organism is said to be HETEROZYGOUS for that characteristic.
 bb has the phenotype white and is said to be HOMOZYGOUS recessive.
19
Multicellular Organisms
Genetic Crosses
A genetic cross is laid out as follows:
 A pea plant which produces round pea seeds is crossed with a pea plant
which produces wrinkled pea seeds.
 All the offspring are round.
R:
Round
r: Wrinkled
Parents Phenotype (P)
Round
Parents Genotype (P)
RR
Gametes
X
Wrinkled
X
R
X
First Generation (F1) Genotype
Rr
First Generation (F1) Phenotype
Round
F1 X F1 =
Rr
Gametes
R,r
Genotype
RR
Rr
X
Rr
rr
r
Rr
R, r
rr
Second Generation (F2)
Phenotype
Round
Round
Round
Wrinkled
Second Generation (F2)
F2 Phenotypic ratio
3
:
1
The actual ratio may differ from the expected ratio since fertilisation is a random
process. An element of chance is involved.
20
Multicellular Organisms
Need for Transport systems in Plants
As an object increases in size the surface area to volume ratio decreases. This
means a larger object has to be supplied with nutrients using a transport system
Transport of water in plants
Root Hair Cell
Image BBC Bitesize
The root hair is an extension of the root cell and water is taken in by osmosis
through the cells selectively permeable membrane. When this cell has taken on a
reasonable amount of water it will have a higher water concentration than the
next cell and so water will pass to this next cell by osmosis. This process continues
until the water reaches specialised water transport vessels called xylem.
Image – BBC Bitesize
Root
epidermal
Xylem
cell
vessel
Water travels across the root cortex cells by
osmosis and then enters the xylem vessels.
21
Multicellular Organisms
Xylem
Water and minerals are transported from
the roots upwards to the leaves. Xylem
forms when the nucleus and end walls of
the cells disintegrate forming long
hollow lignified tubes. Xylem is a nonliving material.
Rings of lignin
(give plant
support)
Image – BBC Bitesize
Water movement in xylem vessels
Transpiration is the evaporation of water from the mesophyll cells in the leaves of
plants. Water evaporates through stomata whose opening and closing is controlled
by guard cells, which are found in the leaf epidermis (outer layer of cells). In order
to replace this lost water, water is pulled up through the xylem vessels
(transpiration stream). Mesophyll cells in the leaf require water for photosynthesis
and this is delivered via the xylem vessels.
Section of leaf
Mesophyll
cell in the
leaf
Air space in
Xylem
leaf
Lower
epidermis
Stoma
Guard cell
Image – BBC Bitesize
22
Multicellular Organisms
Factors affecting transpiration
The following factors affect the rate of transpiration; temperature, humidity, air
movement and light. These factors are known as abiotic factors.
Abiotic factor
Transpiration rate
Temperature
Light intensity
Air movement
Humidity
An increase in any of these factors will
result in an increase in the rate of
transpiration
An increase humidity will result in
decrease in
the rate of transpiration
Opening and closing of stomata
When the guard cells become turgid this forces the stoma open. When the guard
cells are flaccid the stoma closes.
guard
cells
stoma
epidermis
Stoma open
Stoma closed
Images – BBC Bitesize
23
Multicellular Organisms
Diagram of a leaf showing the position of the stoma.
Image BBC Bitesize
stoma
Transport of sugar in plants
Sugar is transported up and down the plant in living phloem cells.
Sieve plate
Image -BBC Bitesize
Companion cell
Sieve cell
Differences between Xylem and phloem
Xylem
Phloem
Transports water and minerals
dead
lignified
No companion cell
No sieve plates
Transports sugar
living
Not lignified
Companion cell
Sieve plates
24
Multicellular Organisms
Transport Systems in Animals
Blood consist of two parts
Plasma
Other blood cells
The role of blood
Blood consists of blood cells and
the fluid that surrounds them
called plasma.
Many substances are transported
dissolved in plasma including
glucose and amino acids.
Red blood cells
Red blood cells transport oxygen from the lungs to body cells. The pigment
haemoglobin found in the red cells reacts with oxygen at the lungs to form
oxyhaemoglobin. At the tissues the oxygen is released to diffuse into the cells.
Red blood cells have no nucleus In order to
maximise the space available to carry
oxygen. They are very small to fit through
the smallest blood vessels and have a
biconcave shape that increases their
surface area.
Image source
SCRAN
Red blood cells
In mammals the main transport system is the circulatory system, comprising of the
heart and associated blood vessels. The heart is a muscular pump, pumping blood
around the body to deliver nutrients and oxygen as well as dispose of carbon
dioxide and waste. The wall of the left ventricle is thicker than that of the right
because it has to pump blood all round the body.
25
Multicellular Organisms
Structure of the heart
Valve at exit to
Valve at exit to
pulmonary artery
aorta
Right atrium
Left atrium
Right ventricle
Left ventricle
Image from BBC Bitesize
Valves between atria
and ventricles
Valves in the heart and in veins prevent the backflow of blood
26
Multicellular Organisms
Circulation
Pulmonary
vein
aorta
Pulmonary
artery
Image from BBC Bitesize
Vena cava
Deoxygenated blood
Oxygenated blood
The Coronary artery
The first branch of the aorta
leaving the heart is the coronary
artery and this supplies the heart
muscle with oxygenated blood.
The diagram on the right also
shows how a build up of lipid
material called plaques can lead to
a coronary heart attack.
A heart
Coronary
artery
27
Multicellular Organisms
Blood Vessels
Arteries carry blood away from the heart. They have a thick muscular wall and a
narrow central channel. The blood in arteries is under high pressure.
Veins carry blood towards the heart they have a thinner muscular wall than
arteries and a wider central channel. The blood in veins is under low pressure and
they contain valves to prevent backflow.
Artery
Vein
Thin muscular
Valve
wall
Thick
muscular
wall
Wide
Direction of
central
blood flow
channel
Capillary
Thin central
channel
Capillaries are exchange vessels. Their
walls are only one cell thick to allow
materials to cross from tissues to
capillaries easily. There is a dense
network of capillaries giving a large
surface area. Examples of materials that
cross capillary walls are oxygen and
glucose into cells and carbon dioxide and
urea from cells to the capillary.
28
Multicellular Organisms
The Lungs
Function of the lungs
The lungs are organs of gas exchange. Blood from the body is pumped from the
heart to the lungs via the pulmonary artery. This blood is rich in carbon dioxide
and low in oxygen (deoxygenated). At the lungs gas exchange takes place carbon
dioxide diffuses from capillaries into the alveoli and oxygen diffuses from the
alveoli into the capillaries. This oxygenated blood is then returned to the heart via
the pulmonary vein. From the left ventricle it is then distributed round the body
via the aorta.
The Lungs
trachea
rings of cartilage
lung
airways inside the
lungs
alveoli
Deoxygenated
blood
Air in
Air out
Oxygenated
blood
Alveolus and the large capillary network
29
Multicellular Organisms
An alveolus showing gas exchange
Image from scran
deoxygenated blood
oxygenated blood
O2
Red blood cell
Feature of a gas exchange surface
Feature
large surface area
moist surface
thin lining
surrounded by large capillary
network
CO2
moisture layer
Function
to absorb oxygen
allows oxygen to dissolve
eases diffusion of oxygen into blood
to pick up and transport oxygen
30
Multicellular Organisms
Function of rings of cartilage
The incomplete rings of cartilage in the bronchi and trachea ensure they remain
permanently open at all times.
Function of cilia and mucus
The trachea and bronchi are lined with tiny hairs called cilia and glandular cells
that secrete stick mucus. The cilia beat rhythmically sweeping mucus with
trapped micro-organisms upwards into the larynx from where they pass into the
stomach via the oesophagus, to be destroyed by stomach acid.
cilia
Image BBC Bitesize
31
Multicellular Organisms
Digestive System
The digestive system includes the alimentary canal running from the mouth to the
anus and associated organs including the liver, pancreas, salivary glands gall
bladder.
oesophagus
liver
stomach
pancreas
large intestine
small intestine
anus
Image from SCRAN
32
Multicellular Organisms
Peristalsis
Food moves through the digestive system by a method called peristalsis. This
involves circular muscles behind the food bolus contracting while those in front of
the food relax and the food is pushed forward.
Once food has passed down the oesophagus it enters the stomach. Churning now
occurs- this involves stomach wall muscles mixing food
with digestive juices.
Food is released from the
stomach and passes into the
Muscles
small intestine where
contract
absorption takes place.
Ball of
oesophagus
food
Muscles in front
of the food relax
and the ball of
food moves
forward
Image BBC Bitesize
The small intestine has
several features facilitating
absorption.
 It is very long
 The internal surface is folded and has thousands of finger like projections
called villi. (The small intestine has a large surface area for the absorption
of food).
 The small intestine has a good blood supply to carry away the products of
digestion.
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Multicellular Organisms
Structure of a villus
Thin wall of the villus
Blood capillary absorbs
glucose and amino
acids
Lacteal –
Absorbs the products of
fat digestion called fatty
acids and glycerol
Image from
SCRAN
Image Scran
The villi in the small intestine are adapted for the absorption because they are
 thin walled
 a large surface area
 good blood supply
The villus wall consists of a one cell thick layer of epithelial cells so the end
products of digestion can easily pass through. Glucose and amino acids pass into
the blood capillaries and the products of fat digestion enter the lacteal.
34