Download Unit 2 Summary Notes Cells, tissues and organs

Unit 2 Summary Notes
Cells, tissues and organs
Multicellular organisms contain many different types of cells, which are specialised to carry
out particular functions. A large number of specialised cells together make up tissues and
various tissues together make up an organ.
Specialised animal cells
There are numerous specialised cells in animals which perform particular functions.
Some examples of specialised animal cells and their functions are described below.
Muscle cells
These are long, thin cells which contract to cause movement. The cells contain a large
number of mitochondria to produce the large amount of energy required for this contraction.
Sperm cells
A sperm cells particular function is to fertilise an egg cell. It has a specialised tail to allow it
to swim towards an egg and the head of the sperm cell contains enzymes to digest the
exterior of the egg, which allows the sperm to enter the egg and fuse
with it.
Tail
Head contains
nucleus and enzymes
Projection to connect
Nerve cells
with other cells
These cells form connections with other nerve cells to create a huge network which is used
to transmit impulses throughout the body; this allows us to co-ordinate movement and
thoughts. They have long projections which allow them to make connections with other cells;
these connections can be made with cells some distance away.
Blood cells
Red blood cells are small and have a ‘bi-concave’ shape to increase their
surface area and to allow them to squeeze through tiny blood capillaries. Their
function is to transport oxygen around the body; to achieve this, they contain
a pigment called haemoglobin which binds with oxygen and they lack a nucleus to maximise
the amount of pigment they can carry.
White blood cells fight infection in the body. They have an irregular shape to squeeze
through blood vessels and their shape allows them to surround a microbe; they also contain
enzymes which digest the microbe into harmless waste substances.
Specialised plant cells
Phloem cells
These cells are involved in the transport of sugar in plants; they have
perforated end walls which allow sugars to be transported to the next phloem
cell. They also possess companion cells with a large nucleus to control the
phloem cells.
Root hair cells
These cells are responsible for absorbing water (for
photosynthesis) from soil around the roots. Each cell has a large
surface area to maximise the volume of water it can absorb.
Palisade mesophyll cells (leaf cells)
These are found in the upper layer of a leaf and have the main function of carrying out
photosynthesis; they contain a very large number of chloroplasts to maximise
photosynthesis.
Tissues
Tissues are groups of specialised cells which will carry out a particular function.
Examples of animal tissues include:
-Muscle
-Blood
-Nerves
Examples of plant tissues include:
-Vascular tissue (i.e. transport tissues such as xylem and
phloem)
-Palisade tissue (layer of palisade cells within the leaf)
-Root tissue
Organs
Organs are made up of several types of tissue grouped
together, for example, the small intestine is made up of muscle
tissue, connective tissue, epithelial lining tissue and also nerve
tissue to control its action. Organs can carry out specific
function due to the large variety of specialised cells within
them.
Other examples of animal organs include:
-Heart (pumps blood around the body)
-Lungs (site of gas exchange)
-Eyes
Examples of plant organs include:
-Leaves
-Reproductive organs (e.g. anther)
Examples of the link between cells, tissues and organs are shown below:
Muscle cells
Cell
Nerve cells
Cell
Muscle tissue
Heart
Tissue
Organ
Nerve tissue
Brain
Tissue
Organ
2.2 - Stem cells and meristems
Part a: Stem cells
Stem cells are unspecialised cells which are found in all multicellular
organisms. Stem cells have the potential to become many different types
of cells and so are described as the site of production of specialised
cells. As with other body cells, stem cells undergo mitosis and therefore
increase the number of cells in an organism; specialised cells produced by
division of stem cells can be used for growth or repair.
The diagram shows a few of the possible cell types
which can be produced by stem cells.
Potential uses of stem cells
Stem cells are currently being used after cancer treatment to restore destroyed stem cells;
bone marrow (which contains stem cells) is transplanted into a patient and the cells it
contains will begin to produce blood cells.
Due to the unspecialised nature of stem cells, they could potentially be used to cure or
repair damage caused by a wide range of conditions.
Stem cell technology could be used to:

repair damaged heart tissue after a heart attack

grow new skin cells to repair skin damage after burns

grow complete organs (removing the need for waiting lists for transplants)
Stem cell technology is a promising but ethically controversial procedure due to the source
of some stem cells; stem cells can be derived from adult tissues (and other sources) or they
can be sourced from embryos. The use of embryonic stem cells has been criticised by many
groups due to the ethics of creating, using and destroying potential embryos.
Part b: Meristems
Within plants, only particular areas can undergo mitosis and therefore contribute to growth,
these areas are called meristems. Meristems produce non-specialised cells in plants and
these non-specialised cells can potentially become any type of plant cell (e.g. leaf mesophyll
cells, phloem cells etc).
Root tip
Shoot tip
Areas which undergo growth, such as root tips and shoot tips, will contain meristems.
2.2. - Propagating and Growing Plants Summary
Growing Plants from Seed
Types of Seeds
Type of seed
Method of sowing
Advantage
Large seeds
Individually
Reduces competition
(e.g. broad bean)
spread out
for light, water,
space and minerals
Mixed with sand
Helps to sow the
seeds more evenly
Very small seeds
Pelleted (enclosed
Seeds are easier to
in a ball of clay)
handle and can be
sown more evenly
Chitted seeds
Individually
Seed coat split to
(pre-germinated)
spread out
allow germination
before sowing
Sowing Seeds
Seeds must be sown in a particular way to allow the best chance of growth. They must:

Be spread evenly

Watered regularly

Be maintained at an appropriate temperature (using a thermostat) and humidity.
Vegetative Propagation
Vegetative propagation is a form of asexual reproduction used by plants which produces clone
offspring. There are many methods of vegetative reproduction, examples of which are outlined below.
Bulbs and Tubers
Bulbs store food. They have buds which produce flowers or daughter bulbs. Since these are produced
from one parent, this is a method of vegetative propagation.
The food store allows bulbs to withstand winter conditions and to grow early in the spring before
seeds germinate.
a daffodil bulb
Tubers are another example of a food storage organ e.g. potato
Attached Offspring
Some plants produce miniature plants called plantlets attached to the parent.
The plantlets obtain food from the parent plant until they have produced roots and can absorb water
and minerals from the soil.
1. Production of Plantlets from Runners
In the case of Spider Plant and Mother of Thousands, the plantlet forms at the end of a runner (a
horizontal stem).
The plantlet can be 'pegged down' into a small pot of compost using wire.
When roots are established, the runner is cut close to the new plant and the wire removed.
Strawberry plants can also be propagated by this method.
parent plant
parent plant
runner
young
plant
Spider Plant
runner
cut after
rooting
young plant
Mother of Thousands
2. Production of Leaf Plantlets
The Mexican Hat Plant produces large
numbers of small plantlets along the
leaf edges. These can be detached from
the leaf and grown in pots of compost.
plantlet
s
The Piggy -back Plant produces plantlets in the
middle of its leaves.
plantlet
3. Production of Plants from Offsets
Some plants, for example Mother-in-Law’s Tongue, produce offsets.
Offsets are small plantlets produced as side shoots at the base of the
parent plant.
These can be detached from the parent plant and grown separately.
offset
Artificial Propagation
Artificial propagation is a method of propagating plants which is carried out by humans; this type of
propagation is not a natural method used by plants. Artificial propagation means that part of a plant,
for example a stem or leaf, is cut off from its parent and treated so that it grows into a new plant.
This method is quicker than waiting for the parent plant to produce seeds and all new plants will be
exactly like the parent plant e.g. same colour of flower and leaves.
Methods of artificial propagation are described below.
1. Taking Stem Cuttings
Nodes are points on a plant's stem where new growth occurs. When a plant stem is wounded, for example by
cutting below a node, the stem produces roots. Rooting powder can also be used which speeds up root growth
Cuttings are placed in propagators, these have electrical cables that supply heat to the cuttings to
encourage root growth.
If too much heat is supplied, the plant will wilt as it loses too much
water. This can be prevented by reducing the leaf surface area by
removing some of the lower leaves or by increasing the humidity by
placing the cutting in a propagator or covering it with a polythene bag.
Commercial plant growers use mist propagation to maintain a high level of humidity in the air around
the cuttings by continually spraying a very fine mist of water into the air.
Taking a Cutting
Step 1 A diagonal cut is made in the stem
just below a node (i.e. where leaf
joins the stem).
Step 2
Remove the lower leaves of the
cutting to reduce water loss.
Step 3
Dip the cut end of the stem into rooting
powder to encourage the growth of roots.
Step 4 Carefully place the cutting into a hole in the
centre of compost in a plant pot. Gently firm the compost by
pressing down around the cutting.
Step 5 Water the compost.
Step 6 Place the potted cutting in a propagator with a lid to
increase humidity and reduce water loss from the cutting.
2. Layering
Layering is a method of propagating plants which have long flexible stems.
When the stem is still attached to the parent plant, it is 'pegged down' into a pot of rooting compost
or into the soil if it is an outdoor plant. Often the stem is wounded by cutting below a 'node' (point
where leaves are attached) and dusted with rooting powder to encourage root growth.
When roots develop, the stem is cut to separate the new plant from the parent plant.
stem of parent
The advantage of 'layering' is that the new plant
plant
new plant
is supplied with water, food and minerals from the
parent plant. This means that many plants which
are difficult to raise from cuttings can be
propagated by this method. The plants produced
are also larger.
Protected Cultivation
Protected cultivation involves growing plants in a sheltered enclosure (e.g. a greenhouse) in which the
environment can be controlled.
1. Greenhouses and Polythene Tunnels
Greenhouses and polythene tunnels protect plants from cold, wind, rain and frost.
polythene tunnel
greenhouse
Heating Greenhouses
To control the temperature in a greenhouse, the electricity supply is connected to a
thermostat. When the temperature falls below a fixed temperature the thermostat
switches the heating on and switches it off when a fixed upper temperature is reached.
The advantage of heating is that it prevents frost damage and encourages plant growth.
The disadvantage is that the plant may lose too much water and wilt.
Ventilation of Greenhouses
Ventilation means providing fresh air. Stale moist air provides ideal conditions for the spread of
disease for example grey mould (mildew).
Ventilation is also important in controlling temperature and humidity (how much moisture is in the
air).
To provide the best conditions for plant growth, automatic ventilation is essential. Automatic
systems work without anyone being there to operate them. The two main automatic systems for
controlling ventilation are automatic window openers and thermostatically controlled electric fans.
2. Floating Fleece and Cloches
Floating fleece and cloches also protect plants from the weather.
Cloches are tent-like structures made from glass, plastic or polythene.
Plastic or polythene cloches are the most common type nowadays being
cheaper and less likely to break than glass.
Floating fleece is a light material which allows the plants to grow
under it, protecting the plants from frost while still allowing water and
light to pass through.
Commercial uses of plants
Plants are used for many different things and have become an enormous industry, on which
the entire world depends.
Some of the most common uses for plants are:

Food

Raw materials

Medicine

Fuels
Food
Agriculture or the production of plants for use as a food stuff, vital industry for all people in
the world. Of the land on planet earth, almost 40% is currently used for the production of
crops for food and there is the potential for even more land to be used in this way.
Corn – A staple food for the majority of sun-Saharan Africa, corn is both easily grown and is
edible with very little preparation.
Wheat – Covers more of the earth than any other crop and grows well in almost all climates
making it a better general crop than rice or corn. Wheat is also the major source of
vegetable protein for humans
Rice – A staple crop for the majority of Asia and is more important than corn as rice’s sole
use is as a food (corn has other used which will be discussed later). Rice accounts for 1/5 of
all the calories consumed by humans.
Raw Materials
The most obvious use of plants as raw materials is Timber wood, used to make frames for
buildings, buildings themselves, boats and any number of smaller items made from wood. Oils
extracted from plants (sunflower oil) can be used for things such as cooking. One of the
most used plants is the cotton plant, which is used to make clothes for people all over the
world.
Medicines
Another common commercial use for plants is in medicine. Some of the most well-known
medicines are mass produced in this way, for example:
Willow trees are used to produce Aspirin for helping with pain (among other things).
Opium poppies are used to produce morphine, a very strong pain killer.
Quinine made from the bark of Cinchona tree, is used to treat malaria.
Fuels
Corn is mass produced to make ethanol, which when mixed with gasoline, is used as gasohol.
Sugar cane is also grown for this use, in particular in South America and Australia.
The increasing population of the world has put greater demand on the production of plants in
particular the use of plants as food stuffs is incredibly important. As the population
increases, more forward planning and attention must be paid to the conservation and
management of plant species.
Pharming techniques
Pharming techniques involve the genetic modification of plants in order to improve the plant
yields or the development of new products.
This process involves the inserting of a gene into an existing plant species in order to create
an improved variety of that species. An example of this is the insertion of pesticide
resistance into oil seed rape plants, therefore less plants will be lost as waste.
In short: The DNA for the gene
that is looking to be expressed, is
extracted and inserted into the
plant by using enzymes
Once the plant is fully grown, the
product is extracted and sterilised
then is used in the form of a
medicine
The most used role of pharming is in the insertion of genes used to produce medicines; this
allows pharmaceuticals to be produced at a lower cost and in greater numbers. Some
examples of medicines currently being produced in this way are: Hormones, antibodies and
vaccines.
There are however, disadvantages of producing plants in this way, some of which are:

The potential transfer of inserted genes (i.e. disease resistance) into wild
varieties of plant

The lack of information on how GM foods affect human health

Unexpected toxin could be produced by these plants

The development of GM crops is expensive
Reproduction
All living things must reproduce in order to produce offspring similar to themselves. This is
essential for their survival. If they were unable to reproduce they would decrease in
number and become extinct.
Asexual Reproduction
In single-celled organisms, cell division allows them to reproduce. The cell simply divides into
two identical, but smaller, cells when it is fully grown.
Daughter
cell
growth
cell division
young
cell
mature
cell
Daughter
cell
This type of reproduction only requires one parent and is called asexual reproduction.
All offspring produced by asexual reproduction are genetically identical to each other and
are called clones.
An example of an organism that reproduces asexually is yeast.
Yeast reproduce by a process called budding.
Bud forming on
the single celled
yeast
Asexual Reproduction in Multicellular Organisms
Organisms such as some plants can reproduce asexually. There are various structures
produced by plants to allow them to reproduce by this method such as runners (strawberry
plants), tubers (potato plants) and bulbs (daffodils).
Sexual Reproduction in Multicellular Organisms
In plants sexual reproduction results in the production of seeds which develop into new
plants.
Embryo
Seed Coat
Food Store
Name of Part
Food Store
Function
Provides material and energy for growth of new plant
Embryo
Grows into a new plant
Seed Coat
Protects the seed
The male sex cells in plants are called pollen grains and produced by the anthers and the
female gametes are called ovules and produced by the ovary.
Structure of a flowering plant
anther
stigma
stamen
ovary
ovules
Name of Structure
Function of Part
Stamen
Male part of flower made up of the filament and the anther
Anther
Produces pollen grains, which contain the male gamete.
Stigma
Ovary
Female part of the flower.Traps pollen grains on its sticky
surface.
Produces ovules
Ovules
Contain the female gametes
Pollination and Fertilisation
Pollination
Pollination is the transfer of pollen from the anther to the stigma. This can be performed by either wind
or insects.
In wind pollinated flowers
 Flowers are small without bright petals, scent or nectar
 Anthers hang outside flower so that pollen is blown away by wind
 Feathery stigmas hang outside flower so that they can catch pollen blown in the
wind
 Pollen grains are light and smooth so that they are blown easily away
In insect pollinated flowers
 Flowers large with bright petals, scent and nectar to attract insects
 Anthers and sticky stigma inside flower so that insect brushes against them
 Pollen grains are rough or sticky to catch onto insect.
Fertilisation
When a pollen grain lands on the stigma during pollination a sugary substance
on the surface causes it to grow a pollen tube.
The pollen tube grows down into the ovary. The male sex cell nucleus then leaves the pollen grain and
travels down the pollen tube into the ovary to reach the female sex cell nucleus.
male sex cell nucleus
female sex cell nucleus
The fusion of the nuclei from the male and female sex cell is called fertilisation. The fertilised egg is
zygote which is referred to as a seed. The zygote is diploid.
Sexual Reproduction in Animals
In mammals, the male gametes (sperm) which are haploid are produced in the testes and female
gametes (eggs) which are also haploid are produced in the ovaries.

The sperm cell consists of a head, which contains a nucleus and a tail to allow it to swim.
A large number of sperm cells are produced.
 The egg cell is larger than the sperm and has a food store, it is unable to move on its own.
It also contains a nucleus.
The human reproductive organs are shown below;
oviduct
Female Reproductive Organs
Name of Structure
Function of Part
Ovary
Produces egg cells
Fallopian tube / oviduct
Site of fertilisation in mammals
Uterus
Where the embryo develops
Vagina
Where sperm cells are deposited
uterus
ovary
Name of Structure
Function of Part
Testis
Produces sperm cells
Sperm duct
Passes sperm from testis to
penis
Urethra
Tube which carries sperm cells
(and urine) out of body
Penis
Passes sperm cells into vagina
Male Reproductive Organs
Sperm
duct
Urethra
Testis
Penis
Fertilisation in animals
To increase the number of organisms in a population depends on the process of fertilisation.
Fertilisation is when the nucleus of the male sex cell fuses with the nucleus of the female
sex cell.
Sperm cell
Egg cell
(Male sex cell)
(Female sex cell)
Fertilisation
Fertilised Cell
There are two methods of fertilisation – internal, mainly used by land animals, and external
used by aquatic animals. Internal fertilisation is where the sperm and egg join inside the
female. With external fertilisation the sperm and eggs are released into the surrounding
water where they join.
Examples of animals that use external
fertilisation are fish and amphibians.
Examples of animals that use internal
fertilisation are birds and mammals.
Development
In mammals internal development occurs, which means that the
embryo develops inside the female’s reproductive system.
Compared with bird development this has a number of advantages
such as the developing embryos are kept warm, fed and protected
by one or both parents.
In birds their eggs have to be incubated because they need to be
kept warm for the embryos to develop. After the eggs hatch, parental care of the young is
essential because they cannot fly or feed themselves at first.
In trout the fertilised eggs begin to develop and when they hatch the trout fry feed on food
from their yolk sac. Once they are free-swimming and the mouth has developed they feed
on small aquatic animals.
yolk sac
Increasing Chances of Survival
Animals which have external fertilisation, e.g. trout and frogs, produce a great many more
eggs than animals which fertilise internally, e.g. birds and mammals.
With internal fertilisation there is a greater chance of sperm reaching the eggs and
fertilisation taking place. There is also less chance of the gametes becoming diseased. With
external fertilisation many of the eggs will get eaten by predators or will not get fertilised
as the sperm and eggs drift away from each other. As there is a greater chance of survival
with internal fertilisation, it is possible to produce fewer eggs.
Land animals need to use internal fertilisation so that the sperm can swim to the egg or, as in
the case of amphibians, return to the water to breed.
As mammals also have internal development and look after their young after birth, this
means that they can produce even fewer eggs than other groups of animals.
The number of young surviving can be calculated using the following formula:
Number of
young surviving
= fertilised eggs – (diseased eggs + eggs eaten + young eaten)
The percentage of the young surviving can be calculated using the following formula:
% =
Total young surviving
Total number of eggs produced
x 100
Examples of the survival chances of different species
Species
Total no.
eggs
produced
No. of
eggs
fertilised
Rabbit
Trout
Human
Pheasant
8
3000
1
15
8
2000
1
12
No. of
fertilised
eggs
diseased
0
200
0
2
No. of
fertilised
eggs
eaten
0
800
0
2
No. of
young
eaten
Total
young
surviving
% survival
4
850
0
3
4
150
1
5
50
5
100
33
Variation and Inheritance
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 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
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 or
inability to roll the tongue is an example of single gene inheritance. In pea plants, the
possession of lilac or white flowers is an example of single gene inheritance. 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
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 controlled in this way by more than one gene is said to show polygenic
inheritance
Phenotypes and Dominant Genes
For every characteristic we have 2 genes- one from our mother the other from our
father. These genes are part of our chromosomes. Each characteristic is controlled by
two forms of a gene, one from each parent carried in a gamete (sperm or egg cell).
Differing forms of a gene are called ALLELES. For example , the alleles for the gene
for eye colour are blue, green ,brown etc. The phenotype is the physical appearance
results from this inherited information e.g. Someone with blue eyes has the
phenotype blue eyes. The combination of alleles that causes this phenotype is called
the genotype. 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 is therefore represented by 2 letters (one letter for each gene)




BB has the 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 is said to have a HETEROZYGOUS genotype
bb has the phenotype white and is said to be HOMOZYGOUS recessive.
Genetic Crosses
A genetic cross is laid out as follows:
Example
 A pea plant which produces round pea seed is crossed with a pea plant which produces
wrinkled peas seeds.
 All the offspring are round.
1. Which is the dominant allele of the gene?
2. What is the genotype and phenotype of the parents and F1.
3. What is the genotype and phenotype of the F2?
4. What is the ratio of phenotype in F2?
Turn over to see this example.

The phenotype ratio when 2 heterozygous individuals cross is always 3:1

The actual ratio may differ from the expected ratio since fertilisation is a random
process. An element of chance is involved.
Family Trees
A family tree can be used to show the links between all the members of a family
Example

It is possible to work out the genotypes of the individuals in a family tree. Always start with
the individuals who show the recessive phenotype.
The need for Transport
A unicellular organism has a large surface area: volume ratio and can therefore gain or lose
all materials by diffusion through its surface.
As an organism grows larger its surface area: volume ratio decreases. This means it can’t gain
or lose materials fast enough for it to survive.
A large multicellular organism therefore, needs a specialised transport system to transport
materials quickly from one part of the organism to another.
Materials transported include:
Water
Oxygen
Carbon dioxide
Plant Transport
1. Need for Water
Plants require water for the following reasons:
• Photosynthesis
• Transporting materials
2. Movement of Water through a Plant
Water enters the plant via the roots. The roots are adapted for
this role by having root hair cells which increases the surface area
for absorption.
Food
Xylem
Water moves into the root hairs,
through the root cells and into the
xylem vessels by osmosis. Water and
minerals are transported up through
the stem in xylem. Xylem cells are
lignified to withstand the pressure
changes as water moves through the
plant
Once in the leaves, water moves from cell to cell by osmosis. Water is used by mesophyll
cells for photosynthesis and is also lost from the leaf by evaporation through tiny pores
called stomata ( singular = stoma)
The loss of water through leaves is called TRANSPIRATION
Section through a leaf
Stomata
Stomata open during the day to allow gas exchange for photosynthesis. This allows water to be lost by
evaporation from the leaf. The opening and closing of stomata is controlled by guard cells, which are found
in the leaf epidermis. The guard cells take in water by osmosis, swell and become turgid, opening the pore.
The guard cells shrink when they lose water. This causes the pore to close.
3. Transport of Sugar
Sugar is transported up and down the plant in living phloem cells.
Animal Transport
1. Circulatory System
The circulatory system consists of
i.
Blood
ii.
Blood vessels
iii.
The heart
In mammals, nutrients, oxygen and carbon dioxide are transported in the blood. The blood
travels round the body inside blood vessels. The blood is pumped round the body by the
heart. There is a pathway of blood through heart, lungs and body.
Blood
Blood vessels
There are three types of blood vessel;
Arteries
Capillaries
Valves
Veins
The Heart
The heart is a muscular pump which has four chambers: Left Atrium, Left Ventricle, Right
Atrium, Right Ventricle. Like veins, it has valves to prevent backflow of blood.
The right side of the heart collects deoxygenated blood (no oxygen) returning from the
body and pumps it to the lungs to pick up a fresh supply of oxygen.
The left side of the heart collects oxygenated blood (has oxygen) returning from the lungs
and pumps it out to the body to supply the cells with oxygen.
The Major Blood Vessels of the Heart
Path that blood takes through the heart
The Coronary Arteries
The Coronary Arteries supply the heart
muscle with food and oxygen. They
branch off from the aorta.
The Respiratory System
The lungs are the gas exchange
surfaces of the body. Oxygen
(O2) and Carbon dioxide (CO2) are
exchanged between the blood and
the air.
The rings of cartilage keep the
airways open.
Inhaled air (high in O2, low in CO2) passes down the trachea, bronchi, bronchioles and finally
reaches the tiny alveoli (singular- alveolus).
Exhaled air (low in O2, high in CO2) passes out of the lungs in the reverse direction.
The Alveoli
Oxygen and carbon dioxide are exchanged in the alveoli. Each alveolus has a layer of fluid
lining it. Oxygen from the air in the alveolus dissolves in the fluid and diffuses rapidly into
the blood through the single celled walls of the alveolus and blood capillary. Carbon dioxide
diffuses out of the blood and into the air in the alveolus.
Gas exchange is efficient because;
FEATURE
1. Large Surface Area
PROVIDED BY
Millions of alveoli in lungs
ADVANTAGE
Increases surface area for
diffusion to take place
2. Good Blood Supply
3. Alveoli have very thin walls
Alveoli surrounded by dense
Large volumes of O2 and CO2
capillary network
can be exchanged
Wall made of only a single
Gases only have to diffuse a
layer of cells
short distance
Mucus and Cilia
The air we breathe in contains dust, dirt and microorganisms which could damage our lungs or
cause infections.
To prevent this, special cells lining the trachea and bronchi produce sticky mucus which traps
anything harmful, preventing it from entering.
Others are covered in tiny hair-like structures called cilia, which then moves the dirty mucus upwards to
the throat to be swallowed.
The Digestive System
The digestive system is where digestion takes place. Digestion breaks down large insoluble
food molecules into small soluble ones which can be absorbed into the bloodstream.
Food enters the digestive system through the mouth and travels down through the
oesophagus and stomach and into the small intestine. On its journey it is broken down by
enzymes.
The products of digestion are absorbed into the bloodstream from the small intestine. The
remaining material passes into the large intestine where water is absorbed, leaving material
which becomes faeces. Faeces is stored in the rectum and then expelled through the anus.
Enzymes are released by the salivary glands, stomach, pancreas and the small intestine. The
gall bladder releases bile which is not an enzyme but helps to break down fat.
Peristalsis
Food is moved through the digestive system by a process called peristalsis. During peristalsis, the muscles
behind the food contract, at the same time as the muscles in front of the food relax. This pushes the food
forward.
Villi
The absorption of small soluble molecules occurs in the small intestine.
The small intestine is adapted for maximum absorption in the following ways;
1. The inner lining is covered in projections called villi that provide a large surface area for absorption.
2. Each villus has a very thin wall which allows molecules to diffuse quickly into the bloodstream.
3. Villi have a good blood supply to aid absorption of glucose and amino acids, and lacteals which
transport the products of fat digestion.
Structure of a villus
Effect of lifestyle choices on the transport system
There are three aspects to health which can be called the health triangle.
Physical health – taking exercise and eating healthy
Social – spending time with friends
Mental – taking time to relax
Making healthy life choices can improve an individual’s health. Such choices can include
o
regular exercise
o
a balanced diet
o
socialising with friends
o
relaxation activities
Poor Lifestyle Choices
Making poor lifestyle choices can include the following
 high fat diet

high salt diet

lack of exercise

smoking tobacco

excess alcohol intake
High Fat diet
A high fat diet can lead to obesity, atherosclerosis, increased risk of stroke and heart attack. Atherosclerosis is a
narrowing of the arteries due to high fat and cholesterol in the diet. This reduces blood flow to certain organs and
increases the risk of strokes and heart attacks.
Salt
A diet high in salt also causes problems for the circulatory system as salt increases blood pressure. High
blood pressure (hypertension) adds extra strain on the arteries and heart which increases the risk of
heart attack and stroke.
Iron
A diet lacking in iron can lead to anaemia. Iron is required for the formation of haemoglobin which transports
oxygen in the blood. Lack or iron leads to anaemia.
Lack of exercise
Exercise plays a key role in keeping our bodies healthy. Exercise improves circulation and
strengthens the heart. Lack of exercise is a major contributory factor to obesity. People who
are obese are much more likely to develop type 2 diabetes, heart disease and colon cancer. By
exercising regularly and maintaining a healthy body weight the risks of developing these
diseases is greatly reduced.
Smoking
Cigarette smoke contains a substance called tar which builds up inside the lungs causing lung cancer and other
diseases of the lungs. Tar also damages the cilia that line the trachea which reduces the person’s ability to protect
the lungs from damage and infection.
Alcohol
Drinking alcohol in excess can cause;
Short term effects of drinking alcohol include blurred vision, impaired judgement, balance problems and slower
reaction times.
Long term effects include cirrhosis of the liver, stroke, high blood pressure; type 2 diabetes, atherosclerosis, and
mental health problems.
Environmental
Environmental factors such as heavy metal, radiation and pollution can also affect the circulatory system and cause
cancer.
Measuring Health
Pulse rate can be measured simply using your fingers and a stop watch or with a pulsometer. Exercise increases the
heart rate to meet the demanding need for oxygen and glucose of the muscles.
Lungs
The peak flow meter is used to measure the rate at which air can be forced from the lungs. It is used to detect
asthma.
Blood pressure
Blood pressure can be measured using a sphygmomanometer or with a stethoscope and cuff.
Hereditary factors also play a role in some medical conditions.
Control and Communication
Synapses
Where two neurones meet, there is a tiny gap called a synapse.
Signals cross this gap using chemicals. One neurone releases the
chemical into the gap. The chemical diffuses across the gap and
makes the next neurone transmit an electrical signal.
Endocrine glands such as the pituitary gland, thyroid gland and the pancreas release hormones into the
bloodstream.
Hormones are chemical messengers which bind to the cells with receptors at the target tissue. Therefore
only some tissues are affected by a specific hormone.
The pancreas is an endocrine gland which contains receptor cells to monitor blood glucose level. These
receptor cells produce the hormones insulin and glucagon to regulate these blood glucose levels.
Increase in blood glucose level
 Following a meal, a rise in blood glucose concentration is detected by recepotrs in the pancreas.
 The receptor cells release insulin into the bloodstream which carries the insulin to the liver.
 The insulin increases the permeability of the liver cells and uptake of glucose from the blood is
increased.
 In the liver cells, an enzyme converts the glucose to glucogen for storage.
 This reduces the blood glucose concentration, returning it to normal.
Decrease in blood glucose level





Between meals, or during the night, the blood glucose concentration decreases.
Different receptor cells in the pancreas detect this and increase the production of glucagon (lower
production of insulin).
The glucagon travels to the liver where it makes the cells less permeable to glucose.
An enzyme is activated and it converts glycogen to glucose.
This raises the blood glucose concentration, returning it to normal.
Diabetes Mellitus
This is a condition in which some or all of the Insulin secreting cells are non-functional. This causes a rise in
blood sugar level causing sugar to be excreted in the urine, as there is too much to be reabsorbed. This can
cause weight loss and wasting of tissues, however, it can be controlled by Insulin injections and controlled
diet.
Biological actions in response to internal and external changes to
maintain stable body systems
1. The Nervous System


Is made up of the brain, spinal cord, and nerves
The brain and the spinal cord make up the Central Nervous System (CNS)
2. Parts of our body we use to sense things are called SENSE ORGANS – eye, ear, mouth, skin, nose.
Each SENSE ORGAN has special cells called RECEPTOR CELLS that become stimulated by different
things
 Receptors in eye are sensitive to light
 Receptors in ear are sensitive to sound
 Receptors on the tongue are sensitive to chemicals
 Receptors in nose are sensitive to chemicals
 Receptors in the skin are sensitive to touch, pressure, pain, temperature
3. When receptor cells become stimulated, information is sent along nerve fibres to the CNS to be
processed.
4.The processed information is then sent from the CNS along nerve fibres to effectors (such as muscle) to
carry out a response.
Receptors
Effectors
nerves
(sense organs)
STIMULUS
CNS
nerves
(muscles)
RESPONSE
5. A reflex action is a rapid, protective response carried out when nerve impulses pass to the spinal cord
rather than the brain.
2. Nerve
3. Nerve
4. Nerve
1.
Receptors
Spinal
cord
5. Effector (muscle)
6. Examples of reflex actions include: pulling away from a hot object, blinking and sneezing.
7. A person's reaction time is a measure of how fast they can respond to a situation or stimulus.
 Alcohol, certain drugs and excitement can affect a person’s reaction time.
Reaction time can be a useful indicator of a person’s state of health. A long slow reaction time can indicate
that the person is suffering one or more of the following:
o
o
o
o
Diabetes
Brain disorder
Nerve disorder
Arterial disease
8. Some areas of the skin are more sensitive than others. They “feel” more.
The skin on a finger tip can detect smaller differences in the feel of an object than the skin on the back, so
is said to be more sensitive.
Sensitive areas of the skin are this way because they have many touch receptor cells (a large density)
connected to larger nerves.
For example…
Many skin touch receptors
at a fingertip
Fewer skin touch
receptors at the back
9. Homeostasis
Homeostasis is the maintenance of a constant environment in the body.
Homeostasis tries to make sure that our body has correct levels of water, glucose and is at the correct
temperature no matter what situation we place ourselves in.
10. Maintaining body temperature by homeostasis
It is important that the core body temperature remains as close to 37oC as possible. The normal range is
36-37.5oC
Above or below the normal range can prevent essential chemical reactions from taking place inside the
body’s cells and can ultimately lead to death.
o
43 C - DEATH
o
42 C - CONVULSIONS
o
C
o
41 C – HEAT STROKE
o
40 C - FEVER
o
39 C – FLUSHED SKIN
o
38 C – INCREASED SWEATING
36 -37.5oC - NORMAL
o
35 C – VIOLENT SHIVERING
o
33 C – STRONG URGE TO SLEEP
o
30 C - COMA
o
28 C - DEATH
11.
A part of the brain called the hypothalamus is the body’s temperature monitoring centre
Nerve impulses pass information regarding body temperature to this part of the brain to be processed
Nerve impulses are sent to parts of the body (effectors) which will work to return body temperature to its
normal level.
Hypothalamus
12. When body temperature is high
Parts of the skin act as effectors to reduce body temperature.
 Sweat glands increase the rate of sweating. Water liquid turns to vapour on the skins surface and
has a cooling effect.
 There is increased blood flow to the surface of the skin to allow heat to be lost by radiation. This is
why a person’s face may appear red when they become too hot!
13. When body temperature is low





Parts of the skin and the body’s skeletal muscles act as effectors to increase body temperature.
Sweat glands decrease the rate of sweating to reduce cooling down.
There is decreased blood flow to the surface of the skin to reduce heat loss by radiation
Hairs on the surface of the skin become raised to trap a layer of air between the hair and the
skin. The layer of air acts as insulation to reduce heat loss from the body
Skeletal muscles rapidly contact for brief periods to generate heat. This process is called shivering.
14. Maintaining blood glucose level by homeostasis






Glucose is a sugar needed to provide energy for living cells
It is important that the concentration of glucose in the blood is kept at a constant level.
Having too much glucose in the blood for long periods of time can cause serious health problems.
The vessels that supply blood to vital organs can become damaged, which can increase the risk of
heart disease and stroke, kidney disease, vision problems, and nerve problems.
Having too little glucose in the blood is also dangerous. Effects can range from moodiness to
more serious issues such as seizures, unconsciousness, and (rarely) permanent brain
damage or death.
Blood glucose levels rise after eating a meal.
Blood glucose levels fall after exercise because the glucose has been used to provide energy for
activity.
15. The action of insulin
 The pancreas monitors the level of blood glucose
 Excess blood glucose causes the pancreas to produce the hormone insulin.
 Insulin will allow excess glucose to become glycogen – a molecule that can be stored by the liver
16. Diabetes




A person is said to have diabetes when the body can’t control excess glucose with insulin.
Blood glucose levels can become dangerously high
There are two types of diabetes- type 1 and type 2.
In Type 1 diabetes, the pancreas is unable to make enough insulin.
The cause of type 1 diabetes is believed to be:
Genetics– The genes that come from a person’s Mum and Dad
Self-allergy-When the body attacks a part of itself
The environment in which we live– Coming into contact with a virus or chemical
 In Type 2 diabetes, the pancreas still makes insulin but the insulin doesn’t work very well.
 In type 2 diabetes, our genes and our culture can play an important role but it is also linked with
being overweight and not getting enough exercise
 As a result of the high blood sugar, the person might feel thirsty, tired, and hungry, pass urine
frequently and have blurry vision.
 The good news about diabetes is that it can be treated. Having a healthy eating plan and doing
regular exercise are keys to staying well with diabetes.
 In type 1 diabetes, insulin injections are needed to control the blood sugar levels.
 In type 2 diabetes, it may be tablets and / or insulin injections that may be required.
 In both types of diabetes, daily blood sugar checks using a meter helps a person to know whether
the treatment plan is working or needs adjusting.
17. Maintaining internal body conditions through behaviour



Behaviour also plays a part in maintaining internal body conditions. Unlike homeostasis, actions that
are carried out are thought about (conscious)
Body temperature can be raised by wearing warm clothes, exercising, moving to a warm area or
having a warm drink. Body temperature can be lowered by removing clothes, moving to a cooler
area or having a cool drink.
Blood glucose levels can be regulated by a person’s diet.
A behavioural response is carried out due to the following sequence of events:
Environmental
stimulus
Nerve impulse
Receptor stimulated
transmitted
Nerve impulse
Effector stimulated
Passed through nervous
system
Behavioural
response
Close examination of different species allows a scientist to see that the behaviour increases their chance
of survival.
Animal
Environmental
stimulus
Behavioural
response
How this
increases chance
of survival
Maggot
Range of
humidity
Maggots gather in
a damp area
Skin is prevented
from drying out.
Swallow
Decreasing day
length
Swallows migrate
to a warmer
climate
Avoids cold
temperatures and
shortage of food
in winter
Kangaroo rat
Range of
temperature
Is nocturnal
Avoids extreme
desert daytime
heat
Scientists can use pieces of equipment called choice chambers to observe behaviour patterns in animals.
Different conditions can be set up in each section of the choice chamber to observe which is most
favourable for the animals’ survival. The most favourable condition will be where the animals gather
most
Animals placed in
here
Moist/
warm/light
Dry / cool/dark
Many animals should be placed in the choice chamber to account for variation in behaviour.
Animals should be left for a suitable period of time before results are noted to allow for a response to be
made.