iGCSE BIOLOGY NOTES – TRIPLE BIOLOGY

Note: sections in blue text are Paper 2 material

1 - THE NATURE AND VARIETY OF ORGANISMS

1 - Characteristics of Living Organisms
LO - (1.1)
All living organisms have the following 8 characteristics in common:
No Characteristic Comments
1 Move Move towards, for e.g. water and food
Move away from, for e.g. predators and poison
2 Respire Release energy from their food in the process of respiration
3 Sense/respond React to changes in their surroundings
4 Nutrition Take in food to obtain energy and materials for repair and growth
Nutrients include carbohydrates, fats, proteins, vitamins and materials
5 Excrete Waste such as CO2 and urine is removed
6 Reproduce Produce offspring so that the species survives
7 Grow Grow and develop into an adult
8 Homeostasis Internal conditions such as water content and temperature are kept stable

Cells

Eukaryotic - complex - e.g. animal and Prokaryotic - smaller and simpler e.g.
plant cells bacteria

2 - Plants, Animals, Fungi and Protoctists

LO - (1.2)
All eukaryotic organisms.
Organism Description Examples
Plants - Multicellular - Cereals
- Have chloroplasts to photosynthesise - Herbaceous legumes (e.g.
- Cell wall made of cellulose peas and beans)
- Store carbohydrates as sucrose or starch
Animals - Multicellular - Mammals
- No chloroplasts – no photosynthesis - Insects
- No cell walls
- Nervous coordination – respond to stimuli
- Move around
- Store carbohydrates as glycogen
Fungi - Single-celled OR multicellular – have body called mycelium - Yeast – single-celled
made up of hyphae (thread-like structures) (1). Hyphae contain - Mucor - multicellular
lots of nuclei (1).
- Can’t photosynthesise
- Cell walls made of chitin
- Most feed by saprotrophic nutrition – secrete enzymes out
onto food and then absorb all of it in
- Can store carbohydrates as glycogen
Protoctists - Single-celled and microscopic - Chlorella (plant – cell – like)
- Some have chloroplasts – similar to plant cells - Amoeba (animal – cell –
- Others are similar to animal cells like)

3 - Bacteria and Viruses

LO - (1.3), (1.4)
Bacteria are prokaryotic organisms:
Organism Description Examples
Bacteria - Single-celled and microscopic - Lactobacillus bulgaricus – is
- No nucleus rod shaped – used for making
- Have circular chromosome of DNA yoghurt
- Some can photosynthesise - Pneumococcus – is spherical
 - Most feed off other organisms – both living and dead

Viruses - Particles smaller than bacteria - Influenza virus (causes flu)

- Reproduce inside living cells – so is a parasite (depends on - Tobacco mosaic virus – stops
another organism to grow and reproduce) leaves of tobacco plants
- Infect all living things producing chloroplasts –
- Come in lots of different shapes and sizes leaves get discoloured
- Have a protein coat around genetic material (DNA or RNA) - HIV (causes AIDS)

Pathogens
Pathogens are organisms that cause disease. Egs are fungi, protoctists and bacteria. Viruses (although are not living
organisms) are also pathogens. Examples:
Organism Example Causes
Protoctist Plasmodium Malaria
Bacterium Pneumococcus Pneumonia
Virus Influenza virus Flu

2 – STRUCTURE AND FUNCTIONS IN LIVING ORGANISMS

4 - Levels of Organisation and Animal and Plant Cells
LO - (2.1), (2.2/2.3), (2.4)
Cells
Eukaryote – complex, e.g. animal and plant Prokaryote – smaller and simpler e.g. bacteria
cells

Note: organelles are tiny structures within cells – only seen through a microscope
Organelles both in animal and plant cells:
 Nucleus - contains genetic material (1) - controls cell. Surrounded
by its own membrane (1).
 Cytoplasm - jelly like - where chemical reactions take place -
contains enzymes which control the reactions.
 Cell membrane – forms the outer surface of the cell and cell
controls what substances go in and out.
 Mitochondria - where aerobic respiration takes place.
Respiration transfers energy that the cell needs to work.
 Ribosomes - where proteins are made.

Organelles only in plant cell:

 Cell wall - made of cellulose - is rigid and gives support and strength to the cell. Surrounds cell membrane.
 Chloroplasts - contains chlorophyll (green pigment) - absorbs light for photosynthesis - how food is made
 Vacuole - filled with cell sap (weak sugar/salt solution). Helps support the cell.

Cell Organisation
Tissue = a group of similar cells working towards a particular function.
E.g. xylem in plants – for transporting water and mineral salts
E.g. phloem in plants – for transporting sucrose and amino acids
A tissue can contain more than one cell type.

Organ = a group of different tissues working towards a particular function.

E.g. lungs in mammals
E.g. leaves in plants

Organ system – a group of organs working together

Each system does a different job.

E.g. in mammals – digestive system has organs: stomach, intestine, pancreas and liver.

Organism = a multicellular living thing, usually made up of many organ systems.

 5 - Specialised Cells and Stem Cells
LO - (2.5), (2.6)
Most cells don’t exactly look like the diagrams above, because they are specialised to carry out a particular function, so
their structures can vary.

Cell differentiation is when undifferentiated cells (called stem cells), change to become differentiated – specialised.

Stem cells are found:

(1) In adults – found in certain places only such as the bone marrow where they can only differentiate into blood
cells.
(2) Embryos – can differentiate into any types of cell depending upon what instructions are given to them.
Stem cells, both (1) and (2) type can be grown in a lab and ‘cloned’ and made to differentiate into specialised cells to use
in medicine and research.

Examples of uses of stem cells:

(1) Adult stem cells – Transferred from healthy bone marrow to patient’s bone marrow to make red blood cells and
replace faulty red blood cells.
(2) Embryonic stem cells – they have the potential to turn into any different cell type (1) so they can replace faulty
cells in sick people (1), produce insulin producing cells for diabetics or nerve cells for those with spinal injuries.

Risks of Using Stem Cells

Could get contaminated with a virus when grown in a lab (1), would be passed onto patient and make then more ill (1).

Against Stem Cell Research For Stem Cell Research

Because using human embryos Because saving existing people is
(potential life) is wrong more important than potential life
Compromise
- use unwanted babies from
abortion clinics which would have
gone in the bin anyway. BUT
campaigners want abortion
banned too.
They want other sources of stem
cells used so that there’s no use of
embryos

Note: stem cell research is not allowed everywhere – it is banned in many countries.

6 - Enzymes
LO - (2.10), (2.11/2.12), (2.13/2.14)
3 mark question: What is an enzyme?
An enzyme is a biological (1) catalyst which increases the speed of a reaction (1) without being changed or used up at
the end of the reaction. (1)

One way to increase speed of chemical reactions is to increase temperature. But this will speed up ALL reactions –
useful and non-useful. Also, temperature can only increase the speed up to a certain point.

So, living things produce enzymes that act as biological catalysts.

- Enzymes reduce the need for high temperatures to speed up reactions
- Enzymes speed up useful chemical reactions (metabolic reactions)

Enzymes are large proteins made up of chains

of amino acids folded up into unique shapes.
Enzymes are specific – chemical reactions
usually involve things either being split apart
or joined together. A substrate is a molecule
that is changed in a reaction. Every enzyme
molecule has an active site – the part where
the substrate joins onto the enzyme.
For an enzyme to work, the substrate needs to be the correct shape to fit into the active site – the ‘lock and key’ model

Temp and pH affect enzyme function –

Temp - Increase temperature = increase rate as enzymes and substrates gain energy and move around more and collide
more often. This is up to a certain temperature. After this optimum temperature, any more increase will denature the
enzyme (bonds inside it breaking, changing its shape and making the shape of the active site change), so that the
substrate doesn’t fit in anymore and so rate decreases.

pH – if pH is too high or too low, this will interfere with the bonds holding the enzyme together. This changes the shape
of the active site and denatures the enzyme.
All enzymes have an optimum pH at which they work best.

7 - Investigating Enzyme Activity

LO - (2.12)
Measuring how fast a product appears:
Hydrogen peroxide  water + oxygen (catalysed by catalase)
 Set up expt as shown
 Check how much oxygen is produced in the first minute at different
temperatures: 10oC, 20oC, 30oC, 40oC.
 Control all other variables such as pH, potato used, size of potato pieces, to
make it a fair test.
 Repeat the expt twice more

Measuring how fast a substrate disappears:

Starch  maltose (catalysed by amylase)
 Iodine solution changes from browny-orange to blue-black in the presence of starch.
 Add a drop of iodine solution in each well on the spotting tile.
 Every 10 sec drop a sample of the mixture into a well. When the iodine solution remains browny-orange record
the total time taken.
 Repeat with the water well at different temperatures to see how it affects the
time taken for starch to break down.
 Control all other variables such as conc of starch solution, conc of amylase,
volume of starch and amylase solution added to the iodine, volume of iodine
solution in the wells and the pH of the starch and amylase solution.

How pH affects enzyme activity – adapt the above experiments to make pH the changing variable by adding a buffer
solution with a different pH level to a series of different tubes containing the enzyme-substrate mixture.

8 - Diffusion, Osmosis and Active Transport

LO - (2.15)
Diffusion is the net movement of particles from an area of high concentration to an area of low
concentration.

The bigger the concentration gradient, the faster the rate of diffusion. Also, the larger the surface area over which
diffusion happens, the faster the rate of diffusion as more particles pass through at once.
Dissolved substances, e.g. O2, glucose, amino acids, H2O, go in and out of cell membranes by diffusion. Substances also
go in and out of cell membranes through osmosis and active transport as well as through diffusion.
Diffusion does not happen in solids, only in fluids (liquids and gases), because their substances are able to move around
randomly.
Osmosis is the net movement of water molecules across a partially permeable membrane, from a region of
high water concentration to a region of low water concentration.

 Partially permeable means that it has very small holes so that tiny molecules such as water could pass through.
A cell membrane is a partially permeable membrane.
 Osmosis is a type of diffusion that just looks at water molecules. Water molecules actually pass both ways as
they move about randomly, but they move more towards where there are less of them.
 The net movement of water molecules stops when there is an equal concentration of water molecules on either
side of the membrane. (1)
- Which way will osmosis take place?
- What will diffuse and what way will diffusion take place?
= water molecule = glucose molecule

Active Transport = movement of particles from low concentration to high concentration (1) (so against the
concentration gradient), using energy released in respiration (1).

Active transport uses energy from respiration.

Eg of active transport in humans – the gut
If there were no active transport, then nutrients would come out of the blood
and into the small intestine as there’s more nutrients inside the small intestine

Eg of active transport in plants –

root hair cell
If there were no active transport, then minerals would come out of the
root hair cell by diffusion as there’s more minerals inside the root hair
cell.

Diffusion/Osmosis Active Transport

High concentration to low concentration Low concentration to high concentration
Does not require energy – passive process Requires energy
Happens in liquids and gases (fluids) Happens in liquids and gases (fluids)
LO - (2.16)
Four Factors Affect the Movement of Substances
Organisms exchange substances with their environment - how easily depends upon 4 factors:
 their surface area to volume ratio (SA:V). The larger the SA, the faster the rate of diffusion, osmosis and active
transport. The larger the organism, the smaller its surface area is compared to its volume.

Small Organism

Large Organism
SA = 6cm2 SA = 96cm2
Vol = 1cm3 Vol = 64cm3
SA:V SA:V
6:1 = large SA: V 96:64 = 3:2 = small SA: V

Single celled organisms have a large surface area to volume ratio, so dissolved substances and gases diffuse
directly in and out of the cell membrane. Multicellular organisms have a small surface area to volume ratio and
so not enough substances can diffuse from outside in.
 Distance. The shorter the distance to travel, the faster the rate of diffusion, osmosis and active transport
 Temperature. The higher the temp, the faster the rate of diffusion, osmosis and active transport. Because
particles move faster when their temp increases.
 Conc. Gradient. The bigger the conc gradient, the faster the rate of diffusion, osmosis and active transport.
Because if there’s lots of particles on one side, there’ll be more to move across.

9 - Diffusion and Osmosis Experiments

LO - (2.17)
Diffusion in a Non-Living System
 Cube with dilute sodium hydroxide and phenolphthalein (pink) added to dilute acid. After a while, the acid
diffuses in, neutralises the alkali (dilute sodium hydroxide), making the cube turn colourless.
  Can investigate size of cube against rate of diffusion. Cube with large SA/Vol ratio will lose its colour quicker.

Osmosis in Living System

 Have beakers with different sugar solutions. ((1) pure water, (2) a little concentrated sugar solution, (3) a little
more concentrated sugar solution, (4) very concentrated sugar solution).
 Place potato cylinders of known length in each beaker.
 Cylinders increase in length – have drawn in water by osmosis.
 Cylinders decrease in length – have lost water by osmosis.

Osmosis in Non-Living System

 Set up the apparatus as shown
 Through osmosis, the water will be drawn up the Visking tubing (which acts as a partially permeable membrane)
and this will force the solution up the glass tube.
 Other variables need to be kept constant such as volume of sucrose solution put into Visking
tubing, volume of sucrose solution put into the beaker, the temp of the beaker, the size of
the Visking tubing bag, etc.
 One way this experiment could be made more reliable is to repeat the experiment.

2 - HUMAN NUTRITION
10 - Biological Molecules
LO - (2.7), (2.8), (2.29)
Digestive enzymes break down big insoluble food molecules to small soluble food molecules.
Big insoluble food Enzyme used to Where enzyme is made Small soluble food molecule
molecule break down
Starch or glycogen Amylase - salivary glands Glucose/maltose (simple sugar)
(carbohydrate – (carbohydrase) - pancreas Maltose = 2 sugar units
contains C, H and O) - small intestine Glucose = 1 sugar unit
Maltose breaks down to glucose
Protein (contain C, Protease - stomach (called pepsin) Amino acids
N, H and O) - pancreas
- small intestine
Fat/lipids (contain C, Lipase - pancreas Fatty acids and glycerol
H and O) - small intestine

11 - Food Tests
LO - (2.9)
To prepare a sample of food for testing: grind food, add into beaker, add in distilled water – dissolve (stir), then filter
(using funnel and filter paper) off solid food bits.
Test for What is used What to do Results if testing substance is present
Reducing sugars (Note; Benedicts Heat 5 cm sample to
3 From blue to
there are reducing and solution (blue) 75oC and add 10 drops of - green or yellow (low conc glucose
non-reducing sugars) Benedicts solution and present) or
Biscuits/cereal/bread leave for 5 min - brick-red (high conc glucose present)
Starch Iodine solution Add few drops of iodine From orangey-brown to black or blue-
Pasta/rice/potatoes solution to 5 cm food
3 black
sample
Proteins Biuret Add 2 cm3 Biuret to 2 cm3 From blue to pink or purple
Meat/cheese food sample
Lipids (fats) Sudan III stain 5 cm3 unfiltered food Mixture separates into 2 layers – top
Olive oil/margarine/milk solution sample. Add 3 drops of layer = bright red
Sudan III solution

12 - A Balanced Diet
LO - (2.24), (2.25), (2.26)
We need different foods to get different nutrients. A balanced diet gives you the right proportions (1) of all the essential
nutrients: carbohydrates, proteins, lipids, vitamins, minerals, fibre and water (1).
Energy requirements vary in different people and for different factors:
More energy needed if:
 Activity – more active as need more energy for muscles working
 Age – teenager/child as need more to grow
  Pregnancy – as need more for baby to develop

Nutrient Found in… Function(s)

Carbohydrates Pasta, rice, sugar Provide energy
Lipids (fats and Butter, oily fish Provide energy, energy store and insulation
oils)
Proteins Meat, fish For growth and repair, and emergency energy source
Vitamin A Liver Improves vision and keeps skin and hair healthy
Vitamin C Fruit, e.g. oranges Prevents scurvy
Vitamin D Eggs, also made from sunlight For calcium absorption
Mineral – calcium Milk, cheese To make bones and teeth
Mineral – iron Red meat To make haemoglobin in blood
Water Food and drink Needed for everyday bodily functions – lost through urinating,
breathing, sweating
Dietary fibre Wholemeal bread, fruit Aid movement of food in gut

13 - Energy from Food

LO - (2.33)
Calorimetry – when food is burnt to see how much energy it contains.
1. Weigh some DRY food and add it to the end of a mounted needle
2. Add a set volume of water to a boiling tube (clamped)
3. Measure temp of water and record. Then set on fire the dry food with it being held under
the boiling tube
4. Continue with relighting the food every time the flame goes out, until the food does not
relight again
5. Measure the final temp of water and record
6. Then calculate the amount of energy in the food
Energy in food (J) = mass of water (g) x temp change of water (oC) x 4.2
Note: 1 cm water = 1 g water
3

4.2 = specific heat capacity of water (amount of energy (in J) needed to raise the temp of 1 g of water by 1oC)

Can calculate the energy in joules per gram:

Energy per gram of food (J/g) = energy in food (J)/mass of food (g)
Note: The expt can be improved by limiting the energy loss to the surroundings from the food as well as
insulating the boiling tube

14 - The Alimentary Canal

LO - (2.27), (2.28), (2.30), (2.31), (2.32)
The alimentary canal (gut) which runs through your body, has muscular tissue which makes circular muscular
contractions that squeeze balls of food (boluses) through (1) – this is called peristalsis. Peristalsis takes place so that the
canal doesn’t get clogged up with old bits of food (1).
1 – Mouth – teeth chew food and it is mixed with saliva, which contains amylase
(enzyme) which breaks down carbohydrates
2 – Oesophagus – food pipe – muscular tube that links the mouth to the stomach
3 – Stomach –
(1) Pummels the food with its muscular walls
(2) Food mixes with protease enzymes (pepsin) it produces, which digest proteins
(3) It produces hydrochloric acid (pH2) which kills bacteria and provides low pH
(optimum pH) for pepsin to work
4 – Liver – where bile is produced
5 – Pancreas – is a gland which makes protease, amylase and lipase (1) which are
released into the small intestine (1)
6 – Small intestine – (first part is called the duodenum and the last part is called the
ileum)
(1) Produces protease, amylase and lipase to complete digestion
(2) Food is absorbed through the gut wall into the blood and then taken to the rest of the body. (see Villi diagram)
7 – Large intestine (colon) – excess water from the food is absorbed here. If peristalsis happens too fast, then food
passes through the colon too quickly (1), which means that excess water is not absorbed from the food, resulting in
excess water in the faeces/diarrhoea (1).
8 – Rectum (the large part of the large intestine) – undigested food (faeces) is stored here
9 – Anus – undigested food leaves (is egested) from here as faeces
10 – Gall bladder – where bile is stored
Bile is made in the liver, is stored in the gall bladder and released into the small intestine. Bile does 2 things:
(1) It gives the small intestine an alkaline pH for the enzymes there to work well. Note: the hydrochloric acid in the
stomach makes the pH too acidic for the enzymes in the small intestine and so the bile is important to neutralise
the acid there and make the conditions alkaline.
(2) It emulsifies fats (breaks down into tiny droplets), so that lipase can work faster on them. Without this process,
fats may be digested more slowly.

Villus in Small intestine

The small intestine is adapted for absorption of food:
 It’s very long so there’s time to break down and absorb all the food
 There’s a large surface area for absorption because of the millions and millions of villi
 Each cell on the surface of a villi has its own microvilli – little projections that increase the
surface even more
 Villi have a single layer of cells so absorption happens over a small distance
 Villi have a good supply of blood for quick absorption

3 - PLANT NUTRITION AND TRANSPORT

15 - Photosynthesis
LO - (2.18), (2.19), (2.21)
Photosynthesis is where food (glucose) is made from the sunlight in the chloroplasts of the leaves of all green plants.
The chloroplasts contain chlorophyll (a green pigment) that absorbs the sunlight (energy) to do the following:
Carbon dioxide + water  glucose + oxygen
6CO2 + 6H2O  C6H12O6 + 6O2

Photosynthesis converts light energy to chemical energy (1), which is stored in the glucose (1). This chemical energy is
released when glucose is broken down during respiration.

Leaves are adapted for efficient photosynthesis (making food):

Leaf Cross Section

Leaves are also large to provide a large surface area to absorb lots of light.

16 - Rate of Photosynthesis
LO - (2.20)
Limiting factors affect the rate of photosynthesis. A limiting factor is something which stops
photosynthesis from happening any faster. They depend upon the environment.
(1) Light intensity – as light increases, the rate of photosynthesis increases up to a point.
After this, a different limiting factor affects the rate of photosynthesis.
Can change light intensity using a lamp in a lab and measuring it using a light meter
 (2) Concentration of CO2 – as CO2 increases, the rate of photosynthesis increases up to a point. After this, a different
limiting factor affects the rate of photosynthesis.
(3) Temperature – as the temperature increases, the rate of photosynthesis increases up to the optimum
temperature (usually 45oC) for the enzymes involved in photosynthesis to work. After
this optimum temperature, the enzymes start to denature (get damaged)

17 - Photosynthesis Experiments and More Photosynthesis Experiments

LO - (2.23)
Testing a leaf for starch:
(1) Place leaf in boiling water to stop any chemical reactions taking place inside
(2) Place leaf in boiling tube containing ethanol using electric water bath until leaf loses its chlorophyll and
becomes white-ish
(3) Rinse leaf and add a few drops of iodine solution – it will turn blue-black if starch is present

Using the above test, we can show that photosynthesis needs chlorophyll, CO2 and light.
Chlorophyll is needed: - Do the above test on a variegated leaf (has green and white parts). Only the green parts (those
that contain chlorophyll) will become blue-black.
CO2 is needed: - If you place a leaf near soda lime (which absorbs CO2), then the leaf will not become blue-black when
tested for starch.
Light is needed: - If you place a leaf in the dark for at least 48 hours, then the leaf will not become blue-black when
tested for starch.

In all of the above tests the other factors must be kept constant so that it is a fair test.

Oxygen production shows the rate of photosynthesis:

Canadian pondweed can be used to measure the effect of light intensity on
the rate of photosynthesis. The rate at which oxygen is produced increases
with increased rate of photosynthesis.
Set up the apparatus as shown:
The pondweed is left for a set amount of time to photosynthesise, and the
oxygen will collect in the capillary tube. Sodium hydrogen carbonate may be
added to make sure there’s enough CO2

 A source of white light is placed at a specific distance from the pondweed and left to photosynthesise for a set
amount of time.
 After the experiment is complete, the amount of oxygen produced is measured. The syringe is used to draw the
gas bubbles in the tube up alongside a ruler and the length of the gas bubble is measured. This is proportional to
the volume of oxygen produced.
 All other variables such as temperature, and time that the pondweed is left for must be controlled.
 Repeat the experiment twice with the light source at the same distance and the mean volume of oxygen
produced calculated.
 Then the whole experiment is repeated with the light source at different distances from the pondweed.

The experiment can be altered to measure the effect of temperature on photosynthesis (by putting the tube of
pondweed in a water bath at a set temperature) or measure the effect of CO2 on photosynthesis (by putting the tube of
pondweed in a measured amount of sodium hydrogen carbonate – which gives off CO2). The experiment can then be
repeated with different temperatures of water or different concentrations of sodium hydrogen carbonate.

An investigation to show that light is a requirement of photosynthesis:

Take 2 plants of same type (1), grow one in light and other in dark for a week (1), keeping all other factors (such as CO2
(1), H2O (1), temp), the same. Take a leaf from each plant and test it for starch (1) using iodine – it will go blue-black in
presence of starch (1). Repeat experiment (1). More starch would be produced in plant grown in light.

18 - Minerals for Healthy Growth

LO - (2.22)
Plants need the following main minerals for growth:
Mineral Used for Deficiency in causes Pic
Nitrogen (N) (needed in Making amino acids and proteins – Stunted growth and
 large amounts) needed for cell growth older leaves turn yellow

Phosphates (P) (needed The phosphorus is used to make Poor root growth and
in large amounts) DNA and cell membranes which are older leaves turn purple
needed for respiration and growth
Potassium (K) (needed in Helping enzymes needed for Poor flower and fruit
large amounts) photosynthesis and respiration growth and discoloured
leaves
Magnesium (Mg) (needed Making chlorophyll needed for Yellow leaves
in small amounts) photosynthesis

19 - Transport in Plants
LO - (2.51), (2.52), (2.53), (2.54), (2.55)
Cells need substances to live. Substances such as water, minerals and sugars need to come in and waste substances
such as CO2 need to leave. Unicellular organisms can have substances diffuse in and out easily, because the diffusion
distance is short. For multicellular organisms (animals and plants) however, direct diffusion from outside would be too
slow as the distance travelled would be too large so multicellular organisms need transport systems to move substances
in and out of cells quickly.
Plants have 2 transporting systems: xylem and phloem. Both are in every part of the plant but they’re separate.

Xylem Phloem
- Made of dead cells joined end to end with no end - Columns of elongated living cells with
walls between them and a hole down the middle small pores in the end to allow cell sap
- Strengthened by lignin to flow through
- Carry water and mineral salts through - Transport food substances (sugars) by
transpiration stream from roots to stem and leaves translocation from leaves to the rest of
- Transport in one direction the plant for use or for storage
- Transport in both directions

Root hair cells take in water:

Plant roots have root hair cells which give them a large surface area to absorb
water from the soil. Water is taken in by osmosis:

20 - Transpiration
LO - (2.56), (2.57)
Transpiration is the evaporation and diffusion of water from a plant’s surface.
Most transpiration happens at the leaves. So when water is lost through the stomata at the leaves, more is pulled up
from the roots and so there’s a constant transpiration stream of water through the plant.

Rate of Transpiration is Affected by 4 Factors:

- Light intensity increases and so rate of transpiration increases (1) because stomata open in light (1) and close in
the dark. More stomata open so more water escapes (1).
- Temperature increases and so rate of transpiration increases because water molecules have more energy with
high temperature so more evaporate and diffuse out of the stomata.
- Wind speed increases and so rate of transpiration increases because low water concentration outside leaf as the
wind blows water molecules away. So more water moves out due to diffusion = high diffusion gradient.
- Humidity increases and so rate of transpiration decreases because high water concentration outside leaf so low
diffusion gradient.

21 - Measuring Transpiration
LO - (2.58)
A potometer is used. Measure how far bubble moves after giving different conditions to the
plant:
 Light intensity – use a lamp to increase it. Place in a cupboard to decrease it
 Temperature – use warm room to increase temp and cold room to decrease it
 Wind speed – use a fan to increase it
 Humidity – use a carrier bag, spray water in it and cover plant with it

Method of setting up the control:

(1) Cut shoot (at a slant to increase SA) under water to prevent air from entering the xylem
(2) Assemble potometer under water and insert shoot under water so no air enters xylem
(3) Remove apparatus from the water keeping the capillary tube submerged in beaker of water
(4) Check apparatus is airtight/watertight
(5) Dry leaves allowing shoot to acclimatise and then shut tap
(6) Remove end of capillary tube from the beaker of water until one air bubble has formed, then put the end of the
tube back into the water
(7) Record the starting position of the air bubble
(8) Start a stop watch and record the distance the air bubble moves in a chosen amount of time, eg in an hour
(9) Keep variable conditions constant throughout the experiment, eg temp, air, humidity, etc.
(10)Set up another experiment, but this time changing either light intensity, temperature, wind speed or humidity.
(Remember: the plant size in the control should be the same size as the other experiments)

4 - RESPIRATION AND GAS EXCHANGE

22 - Respiration
LO - (2.34), (2.35), (2.36), (2.37), (2.38)
Respiration is the process of transferring energy from glucose, which happens constantly in every living cell

Some of the energy from glucose is transferred by heat. The energy transferred by respiration can’t be used directly by
cells – so its used to make a substance called ATP which stores energy needed for many cell processes. When a cell
needs energy, ATP molecules are broken down and energy is released.

2 types of respiration:
Aerobic Anaerobic
 Takes place in plenty of  Take place in lack of oxygen (‘without oxygen’)
oxygen (‘with oxygen’)  Produces 2 ATP molecules (less energy)
 Produces 32 ATP molecules  In animals: Glucose  lactic acid + less energy
(lots of energy)  Takes place when doing vigorous exercise – when body can’t supply
 Glucose (C6H12O6) + oxygen enough O2 to the muscles for aerobic respiration – even though your
(O2)  carbon dioxide (CO2) heart rate and breathing rate increase. So the body automatically
+ water (H2O) + lots of starts doing anaerobic respiration
energy  Glucose only partially breaks down and lactic acid is produced which
 Takes place most of the time builds up in the muscles and is very painful leading to a cramp
 In plants and yeast: Glucose  ethanol + carbon dioxide + energy

23 - Investigating Respiration
LO - (2.39)
Hydrogen carbonate indicator turns from orange to yellow in the presence of CO2 (and from orange to purple in a lack of
CO2)
Expt to demonstrate CO2 production by beans:
(1) Soak dried beans in water (1-2 days) so that they start to germinate (sprout) and respire
(2) For the control – boil the same amount of beans to kill them so that they can’t respire
(3) Place the same amount of hydrogen carbonate indicator in both test tubes with a gauze on
top and the beans on top of the gauze and seal with a rubber bung
(4) Leave apparatus for about an hour. The hydrogen-carbonate indicator in the test tube with
the germinating beans would turn yellow because of the presence of CO2 due to respiration,
whereas it would remain orange in the test tube with dead beans that cannot respire.
Note: you can carry out the above expt using other small living organisms such as woodlice or maggots with the control
being glass beads.

Measuring Temp Change Produced by Respiration

 (1) Prepare beans same as steps 1 and 2 in the above expt.
(2) Add each set of beans to a vacuum flask making sure there’s some room left inside for respiration to take place.
(3) Place a thermometer in each flask and seal top with cotton wool.
(4) Record the temperature of each flask daily for a week.
(5) Repeat expts.
Conclusion – the test flask’s temperature will increase because respiration is taking place in it.

24 - Gas Exchange – Flowering Plants

LO - (2.40), (2.41), (2.42), (2.43), (2.44), (2.45), (2.70)
Leaves photosynthesise:
6CO2 + 6H2O  C6H12O6 + 6O2
 CO2 diffuses from atmosphere into leaf through stomata as there’s lots of it outside leaf (high conc to low conc)
 O2 diffuses from leaf through stomata into atmosphere as there’s lots of it inside leaf (high conc to low conc)

Photosynthesis needs light.

DAY – plants respire and photosynthesise, but they photosynthesise more, so more O2 is released into the atmosphere.
NIGHT – no photosynthesis so only respiration taking place and CO2 released into the atmosphere.
The movement of CO2 between the inside and outside of a leaf at night-time:
Light intensity is low at night time (1), respiration takes place and plant produces CO2 (1), but not photosynthesis (1). So
there’s higher conc of CO2 inside leaf than outside (1) and so CO2 diffuses out of leaf (1)

Leaves are adapted for photosynthesis

No Adaptation How this adaptation helps
1 Broad Large surface area (SA) for diffusion
2 Thin Gases travel shorter distance to reach cells where they’re needed
3 Air spaces inside (spongy mesophyll Allows gases to easily move between cells. Also increases SA for
layer) gas exchange
4 Lower epidermis full of stomata Holes which allow gases (O2, CO2 and H2O) to diffuse in and out
5 Stomata close in the dark No photosynthesis taking place, so no need to open and so no
water can escape either so leaf doesn’t dry out.
6 Stomata close when there’s not enough Although this also stops photosynthesis taking place, it stops the
water coming in from the roots plant from drying out – which is worse
7 Guard cells control the opening and Guard cells surrounding stomata increase in volume to open
closing of the stomata stomata and decrease in volume to close them

Expt to show how light affects gas exchange in plants:

(1) Add same volume of hydrogen-carbonate indicator into 4 boiling tubes.
(2) Keep one boiling tube empty and place a bung in it
(3) Place similar sized healthy looking leaves in the other 3 boiling tubes and rubber bung from the top – trap the
leaf stem in the bung to stop it falling into the solution
(4) Wrap one tube in aluminium foil and a second in gauze
(5) Place all tubes in bright light for 1 hour
Results
Control tube Colour of hydrogen- Why
carbonate indicator
Aluminium covered Yellow No photosynthesis but respiration still taking place – CO2 present
tube
Gauze covered tube Orange Little photosynthesis and some respiration taking place – keeping
CO2 constant
Uncovered tube Purple Some respiration but lots of photosynthesis, so less CO2
 25 - The Respiratory System and Ventilation
LO - (2.46), (2.47)
The thorax is the top part of the body and is separated from the
lower part of the body by the diaphragm. The lungs are surrounded
by pleural membranes and are protected by the ribcage. The
intercostal muscles run between the ribs. The air we breathe in,
splits to 2 tubes (bronchi), then into the bronchioles and then
alveoli (air sacs) where gas exchange takes place.

Breathing In and Out

Breathing In Breathing Out
 Intercostal muscles contract pulling  Intercostal muscles relax allowing ribcage and
ribcage and sternum up and out sternum to drop in and down
 Diaphragm contracts flattening out  Diaphragm relaxes moving up
 Thorax volume increases  Thorax volume decreases
 Pressure inside decreases, drawing air in  Pressure inside increases, forcing air out

26 - Investigating Breathing
LO - (2.50)
 Investigating the effect of exercise on breathing:
(1) Sit for 5 min
(2) Count no. of breaths for 1 min
(3) Do 4 min of exercise (eg running) and count breaths for 1 min as soon as you stop
(4) Repeat steps 1-3 and work out mean for resting and after exercise
Note: control all variables eg use a stopwatch to time, maintain temp of the room by using a thermostat or air
conditioning.
Results:
Exercise increases breathing rate
Why: Muscles respire more during exercise and hence need more O2 quickly and need to get rid of CO2 quickly

 Investigate the release of CO2 in your breath:

(1) Set up the expt as shown and place same amount of limewater in each boiling tube
(2) Breathe into and out of the mouthpiece several times (air is drawn in from tube A
when breathing in and placed into tube B when breathing out)
Results:
- The limewater in tube A remains clear which means that there’s little CO2 in the
inhaled air (air breathed in).
- The limewater in tube B turns cloudy which means that there’s lots of CO2 in the
exhaled air (air breathed out).

27 - Gas Exchange – Humans

LO - (2.48), (2.40), (2.41), (2.49), (2.71)
At alveoli:
O2 diffuses from high conc in alveolus (1) to low conc (1) in blood
capillary (1)
CO2 diffuses from high conc in blood capillary to low conc in alveolus
At body cells:
O2 diffuses from high conc in blood capillary to low conc in cell.
CO2 diffuses from high conc in cell to low conc in blood capillary

The alveoli are specialised for gas exchange by:

 Being moist for gases to easily dissolve in
 Having thin walls (1 cell thick) so that gases don’t diffuse very far
 Having a good blood supply to maintain a high conc gradient
 Having a big surface area (because there’s millions of microscopic alveoli) for gas exchange
 Walls are permeable so that gases can easily diffuse across
Smoking causes a number of diseases:
Disease How
Emphysema Smoking damages the alveoli, reducing the surface area for gas exchange
Chest infections Tar in smoke damages the cilia (tiny hairs) in lungs and trachea. Cilia – help to keep the
trachea clear by sweeping mucus back towards the mouth. Cilia also work with mucus to
catch dust and bacteria before they reach the lungs
Smoker’s cough and Tar irritates the bronchi and bronchioles which causes extra mucus to be produced which
chronic bronchitis can’t be cleared away because of the damage to the cilia
Increased risk of CO (carbon monoxide) in smoke reduces the amount of O2 the blood can carry. To
coronary heart compensate, the heart rate increases leading to increased blood pressure, leading to
disease (e.g. heart) damaged arteries also leading to increased formation of blood clots.
Lung cancer Tobacco contains carcinogens which cause cancer

5 - BLOOD AND ORGANS

28 - Function of the Blood
LO - (2.59), (2.60), (2.61), (2.64)
Blood is made up of: red blood cells, white blood cells, platelets and plasma.
Component Function Adaptations to help it function
Red blood cells (RBC) Carry oxygen from - small biconcave disc – giving it large surface area to absorb (1)
lungs to rest of body - contain haemoglobin which combines with oxygen in the lungs
and releases it to cells (1)
- don’t have a nucleus so can carry more oxygen (1)

White blood cells Defend against - some change shape to digest micro-organisms - phagocytosis
(WBC) disease - some produce antibodies to fight micro-organisms
- some produce antitoxins to neutralise any toxins produced by
micro-organisms

Platelets Help clot blood - small fragments of cells

- help clot blood (plug the damaged area) so no blood flows out
of a wound and no microorganisms get in
- held together in a clot by a mesh of a protein called fibrin as
well as other clotting factors
Plasma – liquid bit of Carries everything in - carries RBC, WBC, platelets, glucose and amino acids (from gut),
blood the blood CO2 (from body cells to lungs), urea (from liver to kidneys to be
removed in the urine), hormones (which act as chemical
messengers) and heat energy

29 - White Blood Cells and Immunity

LO - (2.62), (2.63)
Pathogens are microorganisms that cause disease. They enter the body and reproduce rapidly. Our white blood cells
(part of our immune system) defend us against pathogens.

2 different types of white blood cells: phagocytes and lymphocytes

Phagocytes Lymphocytes
- detect foreign - all pathogens have specific antigens on their surface. Lymphocytes start producing antibodies
things in the (1) when they come across foreign antigens. The antibodies specifically lock onto the antigens
body and engulf (1) and mark them out for destruction by other white blood cells (1). That specific antibody is
and digest them then reproduced rapidly to mark all the pathogens and attack them.
- non-specific – Memory cells are also produced which remember the specific antigen belonging to that
attach to pathogen, so that if that pathogen invades again, the specific antibodies can be produced (from
anything memory) quickly and kill the pathogen before it makes us ill. This is the reason why we are
foreign immune to most diseases after having it once.

Vaccination
When infected with a new pathogen, we could get very ill or even die by the time the lymphocytes produce the right
antibodies. To avoid this, some diseases are vaccinated against. This is when dead or inactive pathogens are injected in
the body (1) that trigger an immune response due to the antigens on their surface (1). The lymphocytes produce
antibodies to attack them and more importantly, memory cells are produced and remain in the blood (1) which are able
to produce the antibodies to kill the same pathogen more quickly before they became ill (1) should the person get
infected with the real pathogen.

30 - Blood Vessels
LO - (2.68)
Arteries Carry blood away Carries blood at high pressure so walls are strong and elastic (so can
from the heart stretch back) and thick compared to the size of the lumen. Their elastic
fibres allow arteries to expand. Largest artery = aorta

Capillaries Involved in gas Tiny – microscopic (1). Carry blood really close to every cell of the body (1),
exchange at cells to exchange substances between them (1). So their walls are permeable
(1) and 1 cell thick (1) so diffusion takes place over small distance (rate of
diffusion is increased) (1)
Veins Carry blood to Carry blood at low pressure so they’re not that thick - lumen is big. Have
the heart valves to keep blood flowing in right/one direction. Largest = vena cava

31 - The Heart
LO - (2.65), (2.66)
Path of blood:
Right atrium receives (1) deoxygenated blood from the
body (from vena cava) (1) Deoxygenated blood moves
through right ventricle (1) which pumps it to the lungs (via
pulmonary artery) (1) Left atrium receives oxygenated
blood from the lungs (through pulmonary vein)
The oxygenated blood then moves through the left
ventricle, which is pumped out round the whole body (via
the aorta)

Ventricles pump blood out of the heart (1).

Left ventricle has a thicker muscular wall than the right
ventricle. This is because it needs to pump blood around
the whole body (1) under high pressure so has thick
muscular walls (1), whereas the right ventricle pumps it
just to the lungs (1) at lower pressure and so the walls are less muscular and thinner (1). The blood is also under higher
pressure in the left ventricle than that in the right ventricle. Valves in the heart prevent backflow of blood (1).

Exercise Increases Heart Rate

Exercise needs more energy for muscles which means more respiration because more O2 needed into cells and more
CO2 removed from blood in the process of more respiration. So blood needs to flow faster and so heart rate increases.
This is how the body sorts this out:
 Exercise increases CO2 in the blood
 The receptors in the aorta and carotid artery detect high CO2
 The receptors send signals to brain which in turn sends signals to the heart causing it to contract more
frequently and with more force.

Hormones also cause heart rate to increase:

When an organism is threatened, the adrenal glands release adrenaline (1) which binds to specific receptors in the heart
(1) causing the heart muscle to contract more frequently with more force (1). This increases the O2 supply to the cells,
getting the body ready for action (where more energy will be needed).

32 - Circulation and Coronary Heart Disease

LO - (2.69), (2.67)
Pulmonary means to the lungs
Hepatic means to the liver
Renal means to the kidneys
 To Organ From
Pulmonary ARTERY Lungs Pulmonary VEIN
Vena cava Heart Aorta
Hepatic ARTERY Liver Hepatic VEIN
Renal ARTERY Kidney Renal VEIN

Coronary Heart Disease

CHD is when coronary arteries (those that supply blood to the heart muscle) get
blocked by layers of fatty material building up. Causing arteries to become narrow, so
blood flow is restricted and there’s a lack of O2 to the heart muscle leading to a heart
attack.

Risk factors that increase chances of getting CHD:

 Having lots of saturated fats (which deposit inside the arteries)
 Smoking which increases blood pressure which can cause damage to the
inside of arteries. Chemicals from cigarette smoke can also cause damage
making it more likely that fatty deposits can form narrowing the arteries.
 Inactivity leading to high blood pressure which damage the inside of arteries
causing fatty deposits to form there.

33 - Excretion – The Kidneys

LO - (2.71), (2.72), (2.73), (2.74), (2.75), (2.76), (2.77), (2.79)
Excretion is the removal of waste products.
Organ Waste product
Lungs CO2
Skin Sweat
Kidneys Urine

The kidneys are part of the urinary system. Their roles are:
 Removal of urea (which is produced in the liver from excess amino acids) from
the blood
 Adjustment of ion (salt) levels in the blood
 Adjustment of water content in the blood

Each kidney contains thousand of nephrons. What takes

place in each nephron:
(1) Ultrafiltration – blood from the kidneys from the
renal artery flows through the glomerulus (1) (a
bundle of capillaries at the start of the nephron). A
high pressure builds up (1)which filters small
molecules out of the blood into the Bowman’s
capsule as glomerular filtrate (1). Big molecules
such as proteins and blood cells are left in the
blood and all smaller molecules such as water,
urea, ions and glucose come out as the glomerular
filtrate into the Bowman’s capsule.
(2) Reabsorption – as the glomerular filtrate flows
along the nephron, useful substances are
selectively absorbed back into the blood:
- all glucose is absorbed back from the proximal
convulated tubule by active transport, as it’s needed for respiration
- some ions are reabsorbed
- some water is reabsorbed from the collecting duct through osmosis
(3) Release of wastes – urine is formed from the remaining substances such as urea, ion and water. This flows out
of the nephron, through the ureter and down the bladder where it is stored before being released via the
urethra.
 34 - Osmoregulation – The Kidneys
LO - (2.72), (2.78)
Osmoregulation is when the body constantly balances the water coming in through food and drink against water going
out through sweating, breathing and urinating. This is done by adjusting how much water is reabsorbed by the kidneys.
If it’s a lot, then the urine is more concentrated with a smaller volume.
Brain detects too little water in blood Brain detects too much water in blood

Instructs pituitary gland to release more Instructs pituitary gland to release less ADH
ADH

ADH makes the collecting ducts of the Collecting ducts of the nephrons are less
nephrons more permeable so more water is permeable so less water is reabsorbed back
absorbed back into the blood into the blood

Note: ADH = anti-diuretic hormone

Osmoregulation is controlled by negative feedback mechanism – meaning that if the water content gets too high or too
low, a mechanism will be triggered that brings it back to normal.

For eg, on a hot day whilst running, the urine you produce would be darker in colour because sweating causes water to
be lost from the skin and not much water left in the blood (1). The brain detects the decreased water content in the
blood (1) and instructed the pituitary gland to release ADH into the blood (1). ADH makes the collecting ducts of the
nephron more permeable (1) so water is reabsorbed back into the blood (1) resulting in less water being released into
the urine and so the urine is more concentrated and darker in colour (1).

6 – COORDINATION AND RESPONSE

35 - The Nervous System and Responding to Stimuli
LO - (2.80), (2.82), (2.87), (2.88), (2.89)
Animals increase their chances of survival by responding to changes in their external environment and changes in their
internal environment (so that the conditions for their metabolism are always right). Any change in the internal or
external environment is called a stimulus.
 Receptors = cells that detect stimuli. There are many types of receptors, including taste receptors, smell
receptors, sound receptors, light receptors in the eyes, pain receptors in the skin.
 Effectors = either a muscle (which contracts) or a gland (which secretes hormones), which responds to a stimuli.
Receptors communicate with effectors via the nervous system or the hormonal system or both.

The Central Nervous System (CNS) Coordinates Information

The nervous system detects and reacts to stimuli in the environment. The hormonal/endocrine system also coordinates
a response to stimuli).
Central Nervous System (CNS) = brain and spinal cord only
The job of the CNS is to coordinate a response. Coordinated responses always need a stimulus, a receptor (the cells in
the sense organs that detect stimuli) and an effector (a muscle or a gland).
The nervous system is made up of neurones (nerve cells)
(1) Sensory neurones – carry information (electrical impulses) from receptors (sense organ) to CNS
(2) Relay neurones – connect sensory neurones and motor neurones
(3) Motor neurones – carry information (electrical impulses) from the CNS to the effectors.
The CNS gives very rapid responses because neurones transmit information using high speed electrical impulses.

Synapses connect Neurones

The connection (gap) between 2 neurones is called a synapse. The
nerve signal is transferred by chemicals called neurotransmitters
which diffuse across the gap from one neurone to the next. These
chemicals then set off a new electrical signal in the next neuron.
 36 - Reflexes
LO - (2.90)
Reflexes are rapid and automatic responses to certain stimuli that reduce
chances of injury. Eg bright light in eyes, pupils getting smaller to reduce
the amount of light getting in so as to limit damage.
The route taken by the information in a reflex (from receptor to effector)
is called a reflex arc.
In this reflex arc:
- the pain receptors in the hand detect pain
- an impulse travels along a sensory neurone to the CNS (spine)
- then the impulse passes along to a relay neurone
- then the impulse passes along to the motor neurone to the effector
(muscle in this example which pulls the hand away)
- this all happens extremely fast that it misses the brain in the response

Stimulus (e.g. seeing a cat)  receptor (e.g. eyes)  sensory neurone  CNS 
motor neurone  effector (e.g. muscle)  response (e.g. move)

37 - The Eye
LO - (2.91), (2.92)
Part of the Eye What it does
Conjunctiva Lubricate and protects the surface of the eye
Sclera The tough outer layer protecting the eye
Cornea The transparent outer layer at the front. It refracts (bends) light into the eye. It has no blood
vessels to supply it with oxygen and so oxygen diffuses in from the outside
Iris Controls the diameter of the pupil which controls how much light comes into the eye
Lens Focuses the light onto the retina (light sensitive part, covered with rods and cones). Rods
sensitive in dim light but can’t see colour. Cones are sensitive to colour but not good in dim light
Optic nerve Carries impulse from the receptors on the retina to the brain
Very bright light can damage the retina and so the eye has a reflex to protect it:
- BRIGHT LIGHT – Light receptors in retina detect bright light  send message along sensory
neurone to the brain. The message then travels along a relay neurone to a motor neurone
telling the circular muscles in the iris to contract  making the pupil smaller  less light
enters the eye.
- DIM LIGHT – This time the brain tells the radial muscles in the iris to contract  making the
pupils bigger  more light enters the eye

Focusing on Near and Distant Objects

Ciliary Muscles Suspensory Ligaments Lens Amount Lens Refracts Light
Near Contract Slacken Fat Increase
Far Relax Contract Thin Decreases
If the lens cannot refract the light by the right amount (so that it focuses on the retina), the person will be either short-
or long-sighted.
Long-Sighted (hyperopia) Short-Sighted (myopia)

Unable to focus on near objects Unable to focus on distant objects

Cornea or lens doesn’t refract light enough or eyeball Cornea or lens refracts light too much or eyeball is too
is too short long
Image brought into focus behind retina Image brought into focus in front of retina
Corrected using glasses with a convex lens: Corrected using glasses with a concave lens:
 38 - Hormones
LO - (2.86), (2.94), (2.95)
Hormones are chemicals which are produced in glands and that are directly released into the blood and carried in the
blood plasma to affect target cells. They control things in organs and cells that need constant adjustment.
Hormone Source Role Effects
Adrenaline Adrenal glands (on Prepares the body for a Increase heat rate, blood flow to muscles and
top of kidneys) ‘fight or flight’ response blood sugar level
Insulin Pancreas Helps control blood Stimulates the liver to turn glucose to
sugar level glycogen for storage
Testosterone Testes Main male sex hormone Promotes male secondary sexual
characteristics
Progesterone Ovaries Supports pregnancy Maintains the lining of the uterus
Oestrogen Ovaries Main female sex Controls the menstrual cycles and promotes
hormone the female secondary sexual characteristics
ADH (anti- Pituitary gland (in Controls water content Increases the permeability of the kidney
diuretic brain) tubules to water
hormone)
FSH Pituitary gland Female sex hormone - Causes an egg to mature in an ovary.
- Stimulates the ovaries to produce oestrogen
LH Pituitary gland Female sex hormone Stimulates the release of an egg from an ovary
Both nerves and hormones produce change, however there are differences:
Nerves Hormones
Electrical impulses/signals Chemical signals
Fast action Slow action
Act over a short time Act over a long time
Act over a specific area Act over a more general area
39 - Homeostasis and More on Homeostasis
LO - (2.71), (2.81), (2.93)
Homeostasis = the maintenance of a constant internal environment.
Homeostasis is regulated by nervous and hormonal communication. Homeostasis is important because the body cells
need the right conditions in order to function properly.

Water content kept constant:

Water is taken in as food and drink and is lost through sweat, breath and urine.
Hot day or lots of exercise causes: Cold day or when no exercise:
- less urine produced - more urine produced
- concentrated urine (less water in it – deep colour) because more - dilute urine (more water in it – pale
water is lost through breath colour)
Body temperature kept constant:
Enzymes work best at 37oC. The brain is sensitive to the blood temperature in the brain (1). The brain also receives
messages from the temperature receptors in the skin (1) that let it know skin temperature. The brain then activates the
necessary effectors to make sure the body temperature is just right (1):

When Too Hot When Too Cold

 sweat is produced (1)  very little sweat is produced (1)
which evaporates (1) so sweat doesn’t transfer heat
taking heat energy from the body to the environment
away from the body when it evaporates (1)
with it – so cooling the  vasoconstriction takes place –
body down (1) the blood vessels supplying the skin
 Vasodilation takes place (1) – the blood vessels constrict more so that less blood
supplying the skin dilate more so that more blood travels near the surface (1) so that less heat energy is lost to
travels near the surface of the skin (1) so that more the surroundings, which helps to keep the body warm (1)
heat energy from the blood can be lost to the  hair stands on end to trap an insulating layer of air to keep
surroundings, cooling the body (1) the body warm
 hair lies flat (1), to avoid trapping an insulating  shiver, which increases rate of the respiration, which
layer of air (1) which would keep the body warm (1) transfers more energy to warm the body.
Small organisms have bigger surface area to volume ratio and so heat up or cool down quicker because there’s more
area for the heat to transfer across. This is why animals living in cold conditions, with a smaller surface area are round
and compact to reduce heat loss.

40 - Responses in Plants
LO - (2.83), (2.84), (2.85)
Plants are more likely to survive if they respond to:
 Changes in the environment
- They sense direction of light and their shoots grow towards it to maximise photosynthesis
- They sense direction of gravity and their roots grow towards it
- Climbing plants sense touch so that they can climb towards light
 Predators
- Cattle eat a lot of white clover when there’s not enough grass. White clover responds by producing
substances that are toxic to cattle
 Abiotic stress
- Carrots produce anti-freeze proteins at low temperature – the proteins bind to ice crystals and lower the
temperature that water freezes at, stopping more ice crystals from growing

Auxin is a plant hormone which controls growth at the tips of shoots and roots. It moves through the plant in solution. It
is produced in the tips. If the tip of a shoot or root is removed, no auxin is available and so it may stop growing. Auxins
are involved in the growth responses of plants to light (phototropism) and gravity (geotropism).

Shoots Positively phototropic – Negatively geotropic –

grow towards light. grow away from gravity.
Auxin goes onto shaded Auxin goes into gravity
side (1) and makes the side and makes the cells
cells elongate there (1) so elongate there so the shoot grows away from
the shoot grows towards the light (1) gravity
Roots Negatively Positively geotropic –
phototropic – grow grows towards gravity.
away from light. Auxin goes onto gravity
Auxin goes onto side and inhibits cells
shaded side and growing here so that other cells can elongate so the
inhibits cells growing here so that other cells can root grows towards gravity and down into the soil so
elongate so that the root grows away from the light as to absorb more nutrients.

7 – REPRODUCTION AND INHERITANCE

41 - Asexual Reproduction and Mitosis
LO - (3.1), (3.28), (3.29)
Mitosis is when a cell divides in two. Both cells are genetically identical. Some organisms produce offspring (children) by
asexual reproduction – using mitosis. These organisms include bacteria and some plants.

Asexual reproduction involves only one parent. The offspring have identical genes to the parent – so there’s no
variation between parent and offspring

Mitosis is when a cell reproduces itself by splitting to form 2 cells with identical sets of chromosomes.

If the cell is not dividing, the DNA is spread out in long strings

When the cell gets the signal to divide, the cell doubles its DNA (1) so that there’s one copy for
each new cell (1). The DNA forms X shaped chromosomes.
The chromosomes line up at the centre of the cell and cell fibres pull them apart. The 2 arms of
each chromosome go to opposite ends of the cell
Membranes form around each of the sets of chromosomes, becoming the nuclei of the 2 new
cells. Then the cytoplasm divides, giving 2 new cells which are genetically identical
Mitosis is not just for asexual reproduction, but it is used in all plants and animals for growth and repair of damaged
tissue. Cloning also involves mitosis.

42 - Sexual Reproduction and Meiosis

LO - (3.1), (3.2), (3.30), (3.31), (3.32)
Sexual reproduction is where genetic information from two organisms (a mother and a father), is combined to produce
offspring which are genetically different to either parent.

The mother and father produce gametes (sperm – from father and egg – from mother). Gametes are haploid – have 23
chromosomes.

During fertilisation the male gamete (sperm) fuses with the female gamete (egg) to form a zygote which then has the
full 46 chromosomes. After this, the zygote undergoes cell division by mitosis and so develops into an embryo.

Sexual reproduction involves the fusion of male and female gametes. Because there are 2 parents, the offspring
contains a mixture of their parents’ genes.

Meiosis is a type of cell division which takes place in the reproductive organs (testes and ovaries)
Meiosis produces 4 haploid cells whose chromosomes are not identical.

The cell duplicates its DNA.

One arm of each x-shaped chromosome is an exact copy of the other arm
The chromosomes line up in pairs in the centre of the cell

The pairs are pulled apart so that each new cell only has one copy of each chromosome.
Each new cell will have a mixture of the mother’s and father’s chromosomes – causing
genetic variation
The chromosomes line up again in the centre of the cell and now the chromatids are pulled
apart. 4 haploid gametes are created. Each gamete has a single set of chromosomes which
are all genetically different.
Meiosis is necessary for sexual reproduction because it’s needed to produce gametes (1) so
that when 2 gametes fuse at fertilisation, the chromosomes from the mother and from the
father can pair up (1) and the zygote ends up with the full number of chromosomes (1).

So meiosis produces genetic variation by:

(1) producing gametes that are genetically different to each other (1)
(2) a male gamete and a female gamete then combine at random at fertilisation (1) so the offspring inherits a
random mixture of chromosomes from both parents (1). This mixing up of the chromosomes/genes creates
genetic variation.

43 - Sexual Reproduction in Plants

LO - (3.3)
Part of flower Function
Stamen – male Anther Contains pollen grains (male gametes)
reproductive part Filament The stalk that supports the anther
Carpel – female Stigma End bit that pollen grains attach to
reproductive part Style Rod like section that support the stigma
Ovary Contains female gametes (eggs) inside ovule
Pollination = transfer of the pollen from the anther (1) to a stigma (1)
so that male gametes can fertilise female gametes (1).
Self-pollination = sexual reproduction involving only one plant/ the
transfer of pollen from an anther to a stigma on the same plant.
Cross pollination = sexual reproduction where pollen from the anther
of one plant is transferred to the stigma of another.
Cross pollination relies of insects or wind:

Insect Pollination - Adaptations Wind Pollination - Adaptations

 Have brightly coloured petals to attract  Small, dull petals as don’t need to attract insects
insects  No nectaries or scent as don’t need to attract insects
 Have scented flowers and nectaries  Have lots of pollen grains – small and light so that they
(secrete nectar) to attract insects can be easily carried by the wind
 Have big, sticky pollen grains – so as to  Have long filaments that hang the anthers outside the
stick to insects that go from flower to flower so that lots of pollen can be blown by the wind
flower  Have a large and feathery stigma (often hanging
 Stigma is sticky so that pollen sticks to it outside the flower) to catch pollen as it’s carried past
the wind.

44 - Fertilisation and Germination in Plants

LO - (3.4), (3.6)
 When a pollen grain lands on a stigma, a pollen tube grows out of the pollen grain and down through the style
to the ovary and into the ovule (1).
 The nucleus from the male gamete (pollen grain) moves down the tube to join the female gamete in the ovule
(1).
 Fertilisation then occurs – when the 2 nuclei fuse together to make a zygote (1). This then divides by mitosis to
form an embryo (1).
 Each fertilised female gamete forms a seed (1) with the ovary around it forming the fruit.

Germination = when a seed starts to grow. Germination needs the right conditions:
 Water – to activate the enzymes that break down the food reserves in the seed
 Oxygen – for respiration needed for energy for growth
 A suitable temperature – for the enzymes in the seed to work

A developed seed contains an embryo and a store of food reserves in a hard seed coat. As the seed germinates, it gets
its glucose for respiration (energy) from its own food store. Once the plant has grown enough to produce green leaves,
it can create its own energy from photosynthesis.

45 - Investigating Seed Germination

LO - (3.5)
Investigating the conditions required for germination:
4 boiling tubes with cotton wool inside and 10 seeds in each in the following conditions:
Tube 1 – (control) – with water, oxygen and room temperature
Tube 2 – oxygen and room temperature BUT NO WATER
Tube 3 – water, oxygen AND LOW TEMPERATURE (place in fridge)
Tube 4 – water, room temperature BUT NO OXYGEN (in boiled water which has no oxygen, with oil at top so as to
stop oxygen from the air from entering

Leave the tubes for a number of days. Results = germination will take place in control tube 1 only as all the conditions
for germination are present here.

46 - Asexual Reproduction in Plants

LO - (3.7)
Plants can reproduce asexually by a number of methods:
 Naturally, for eg the strawberry plant where the plant sends out runners which are rapidly growing stems that
grow sideways from the plant above the ground (1). The runners takes root, producing new plants (which are
clones or the original plant) that begin to grow (1).
 Artificially, for eg, gardeners take cuttings from parent plants and keep them moist until they plant them in the
ground to grow. They are a clone of the parent plant grown quickly and cheaply.

47 - Human Reproductive Systems

LO - (3.8), (3.13)
Sperm are male gametes which, after
puberty, are made in the testes all the
time. Sperm mixes with a liquid to make
semen, which is ejaculated from the
penis into the vagina for the female
during sexual intercourse.

Ova are female gametes. An ovum (egg)

is produced every 28 days from one of the two ovaries. It then
passes into the Fallopian tube where it may meet a sperm
that may have entered via sexual intercourse. If it doesn’t get
fertilised, it breaks up and passes out of the vagina during
menstruation. If it is fertilised, it started to divide and travel
down to the uterus (womb) where it attaches to the
endometrium (uterus lining).
Here it continues to develop into an embryo.

Hormones promote sexual characteristics at puberty

Girls/Women Boys/Men
Oestrogen causes: Testosterone causes:
- Extra hair under arms and on pubic area - Extra hair under arms and on pubic area
- Hips to widen - Extra hair on face and body
- Development of breasts - Penis and testicles to enlarge
- Ovum release and start of periods - Sperm production
- Deepening of voice

Starting at puberty, females undergo a monthly menstrual cycle – the body prepares the uterus (womb) in case it
receives a fertilised ovum (egg).

48 - The Menstrual Cycle and Pregnancy

LO - (3.9), (3.10), (3.11), (3.12)
4 stages:
Stage Day(s) What happens
1 1-4 Uterus lining breaks down - menses
2 4-14 Uterus lining builds up again ready to receive a fertilised egg
3 14 Ovulation - egg develops and is released
4 15 - 28 Uterus wall is maintained - if no fertilised egg, then menses start at day 28 (day 1)

4 hormones involved in the menstrual cycle.

Hormone Produced in What it does
1 FSH (Follicle- pituitary gland  Causes egg to mature in follicles (in ovaries)
Stimulating  Stimulates ovaries to produce oestrogen
Hormone)  Oestrogen inhibits the release of FSH
2 Oestrogen ovaries  Causes lining of uterus to grow
 Stimulates release of LH
3 LH (Luteinising pituitary gland  Stimulates release of an egg (ovulation) at day 14
Hormone)
4 Progesterone Follicle remains after  Maintains lining of uterus after ovulation (1) (because
ovulation (in ovaries) uterus is preparing to receive a fertilised egg/zygote) (1)
 Inhibits release of LH and FSH

So progesterone stops more eggs from maturing and being released whilst one egg is already in the uterus.
Embryo Development
The fertilised ovum develops into an embryo and implants in the uterus. The
placenta then develops which lets the blood of the embryo and mother get
very close to allow the exchange of food, oxygen and waste. The amnion
membrane forms around the embryo containing amniotic fluid which protects
the embryo against knocks and bumps. The embryo becomes a foetus when it
starts to look human.

49 - DNA, Genes and Chromosomes

LO - (3.14), (3.14), (3.15), (3.16)

The nucleus contains genetic material as chromosomes.

Chromosomes are made up of DNA.
Body cells are diploid – have two pairs of each
chromosome – one from the mother and one from the
father. So they have 46 chromosomes altogether (23
pairs).

DNA is a long list of instructions on how to put an organism together and make it work. An organism’s genome is all the
DNA it has. Each gene is a length of DNA which codes for a particular protein (1). Proteins determine inherited
characteristics (1), and most processes in the body as both of these are due to proteins. There can be different versions
of the same gene (alleles) (1), that give different versions of a characteristic (1).

DNA is a molecule which has 2 strands coiled together in a double helix (2 spirals). The 2 strands are held together by
chemical bases (adenine (A), thymine (T), cytosine (C) and guanine (G). The bases are paired by complementary base
pairing – C is always with G and A is always with T.

50 - Protein Synthesis More on Protein Synthesis

LO - (3.17), (3.18)
Each gene is a length of DNA which codes for a particular protein. The order of bases in a gene is what decides the order
of the amino acids in a protein. Each amino acid is coded for by a sequence of 3 bases in the gene – called a codon.
DNA contains 4 different bases and each codon in a gene contains 3 bases. So there’s 43 = 64 possible combinations.
Since there are only 20 amino acids, some codons code for the same amino acid.
The amino acids are joined together (following the order of the bases in the gene) in a chain and then folds up to make
proteins with a different, specific shape, which means each protein has a specific function.

Many regions of DNA are non-coding and don’t code for amino acids. They switch genes on and off and control whether
or not a gene is expressed (used to make a protein). Despite this, some of these regions are still involved in protein
synthesis.

Proteins are made in the cell cytoplasm on ribosomes. Because DNA is too big, it can’t move out of the nucleus. But the
cell needs to get the information from the DNA in the nucleus to the ribosome in the cytoplasm. Messenger RNA
(mRNA) does this. mRNA is made in the nucleus and is made of bases just like DNA, however it is shorter, has a single
strand and has uracil (U) instead of thymine (T) as a base. So the purpose of mRNA is to carry the coding information
from DNA in the nucleus (1), to the ribosomes in the cytoplasm – where protein synthesis takes place (1).
Proteins are made in 2 stages:

(1) Transcription (Making mRNA)

RNA polymerase (an enzyme) binds to a region of non-coding DNA in front of a gene (1). The 2 DNA strands unzip
and the RNA polymerase moves along one of the strands of DNA (the coding DNA) (1). Base pairing ensures that the
mRNA is complementary to the gene (1), (C with G and A with U) to the base sequence of the coding DNA (1). Once
the mRNA is made, it moves out of the nucleus and joins to a ribosome in the cytoplasm (1).

(2) Translation
The mRNA bonds to a ribosome.
 Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA). The role of tRNA is
to ensure amino acids come to the ribosome in the correct order. The order in which the amino acids are brought to
the ribosome matches the order of codons in the mRNA (which is the complementary order of bases from the gene
from DNA). Part of the tRNA’s structure is called an anticodon – which is complementary to the codon for the amino
acid. The pairing of the codon and anticodon makes sure that the amino acids are brought to the ribosome in the
correct order (1). The amino acids are joined together by the ribosome, then folds into a unique shape making a
protein (1).

2 proteins have different functions because: each protein is coded for by a different gene (1). Each gene has a different
sequence of bases (1) that codes for a different number and order of amino acids (1), which produce different proteins
with different functions. (1)

51 - Genetic Diagrams and More on Genetic Diagrams

LO - (3.19), (3.20), (3.21), (3.22), (3.23), (3.25)
The genes you inherit control what characteristics you develop. Some characteristics are controlled by one gene, for eg
red-green colour blindness, however, most characteristics are controlled by different versions of the same gene called
alleles. Alleles are represented by letters in a genetic diagram. We have two versions (alleles) of every gene in our body -
one on each chromosome in a pair.
 Recessive alleles (shown as a small letter) = those that are expressed only if there are no dominant ones present.
Both alleles must be recessive to be expressed.
 Dominant alleles (shown as a capital letter) - those that are expressed. Either or both alleles could be dominant for
it to be expressed.
 Heterozygous = having one recessive and one dominant allele
 Homozygous recessive = having both same alleles - recessive
 Homozygous dominant = having both same alleles - dominant
 Genotype = the combination of alleles
 Phenotype = the characteristic
 Some characteristics are caused by codominant alleles. Neither allele is recessive so both characteristics of both
alleles are shown, eg blood group AB for allele A and allele B

A genetic diagram suggests the probability of the outcome of the offspring , so the number of offspring will not always
be exactly in the proportions shown by the genetic diagram as fertilisation is random.
(1) Show the punnet square for brown eyed parents producing a 3:1 ratio of brown eyes to blue eyes.
(2) Show a punnet square for a brown eyed parent and a blue eyed parent producing all brown eyed offspring.
(3) Predict the ratio of brown eyes to blue eyes of the offspring for a cross between a heterozygous parent and a
homozygous recessive parent. Give the ratio of genotypes as well.

You might need to work out the outcome of a monohybrid cross involving codominant alleles.
Blood type is determined by 2 codominant alleles (A and B) and one recessive one (O).
Blood type A = AA and AO
Blood type B = BB and BO
Blood type AB = AB
Blood type O = OO
Here there is a 50% chance that the offspring will have blood type AB, 25% they’ll have
blood type A and 25% chance they’ll have blood type B.

52 - Family Pedigrees and Sex Determination

LO - (3.24), (3.26), (3.27)
From the family tree, answer the following questions:
(1) Is the allele for cystic fibrosis dominant or recessive?
(2) If both parents are carriers of the disease, what percentage chance is there that the offspring would be a carrier?
(3) If both parents are carriers of the disease, what percentage chance is there that the offspring would have the
disease?
(4) If both parents are carriers of the disease, what percentage chance is there that the offspring would neither be a
carrier nor have the disease?
(5) If one parent was a carrier and the other not a carrier or have the disease, what percentage chance is there that the
offspring would be a carrier?
(6) If one parent was a carrier and the other not a carrier or have the disease, what percentage chance is there that the
offspring would have the disease?
(7) If one parent was a carrier and the other not a carrier or have the disease, what percentage chance is there that the
offspring would neither be a carrier nor have the disease?

Your chromosomes control whether you’re male or female

There are 23 pairs of chromosomes in the human cell. The 23rd pair are the sex chromosomes.
Males = XY (there can be sperm with an X chromosome or sperm with a Y chromosome)
Females = XX (all eggs have one X chromosome)
When making sperm, the X and Y chromosomes are divided by meiosis, each into a sperm. There is a 50% chance of
getting a Y chromosome and 50% chance of getting an X chromosome for each sperm.
A genetic diagram can show the probability of outcomes of how different genes or chromosomes combine.
For the sex gametes, (sperm and egg) a genetic diagram (punnet square) looks like this:

Punnet Square The other genetic diagram

There is a 1:1 ratio of having a girl:boy. So a 50% chance of having a girl and a 50% chance of having a boy.
Sex is determined by whether the sperm that fertilises an egg carries an X or a Y chromosome.

53 - Variation
LO - (3.33)
Variation is caused by a mixture of genetic and environmental factors. Factors which are affected by genes are: eye
colour, hair colour, inherited disorders and blood group
Environmental factors in plants is much greater. They include: sunlight, moisture level, temperature and mineral
content of the soil.

For some characteristics it is hard to say whether they are due to genetic variation or environmental variation. These
include: health, intelligence and sporting ability.

54 - Evolution and Natural Selection

LO - (3.38)
Theory of evolution: Life began as simple organisms from which more complex
organisms evolved (rather than just popping into existence).

Evolution takes place over millions of years and is still happening today – eg in bacteria which are becoming resistant to
antibiotics.

Survival of the Fittest

 Through observations and experiments, Darwin concluded that organisms with the most useful characteristics for
the environment would be more successful competitors (fittest) and are more likely to survive. These successful
organisms would reproduce and pass on the alleles (genes) for their characteristics to their offspring.
 The organisms with the characteristics that are not useful would die and so not have any offspring to pass their
alleles (genes) onto.
 And so, over time, all the species would have the useful characteristics. So the best features are naturally selected
and the species becomes more and more adapted to its environment.
For eg: Rabbits showed variation; some with big ears and some with short ears (1). Big ears one hears predators and
dives for cover quickly, short eared one doesn’t (1). Big eared one survives (1), breeds and passes on its alleles (genes)
to its offspring (1). Now its offspring all have big ears (1). Short eared ones die out (1).

Variations that are caused by the environment are not involved in natural selection. Only those that are genetic are
passed on to the next generation and influence the evolution of the species.

55 - Mutations and Antibiotic Resistance

LO - (3.34), (3.35), (3.36), (3.37), (3.39)
A mutation is a rare random change in an organism’s DNA (1) that can be inherited (1).
Mutations change the sequence of DNA bases in a gene (1), which can change the protein produced by a gene (1) and
lead to a different phenotype, increasing variation (1). As the sequence of DNA bases codes for the sequence of amino
acids that makes up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for.

A mutation in the gene that codes for an enzyme

- could lead to a change in the shape of the enzyme’s active site – altering its function
- could cause the stop of the production of the enzyme altogether
Mutations can lead to a different phenotype, increasing variation. Mutations can:
- have no effect on the phenotype, especially if they happen in the unimportant region of the DNA, or if the
mutated codon still codes for the same amino acid, or if the mutation happens in a recessive allele
- have some effect on the phenotype
- have a significant effect on the phenotype. These mutations are very rare and can be harmful (eg lead to cancer)
or beneficial (eg giving bacteria a survival advantage – in becoming antibiotic resistant).
Mutations can happen spontaneously, however the chances of mutation is increased by exposure to:
- ionising radiation (eg X-rays and ultraviolet rays)
- chemicals called mutagens (eg chemicals in tobacco)

Bacteria can Evolve and Become Antibiotic- Resistant

Bacteria sometimes develop random mutations in their DNA leading to changes in the bacterium’s characteristics. This
can sometimes mean that the bacterium is less affected by a particular antibiotic. The allele for antibiotic resistance
survives and is passed on to lots of offspring, whilst the non-resistant bacteria die. Soon, all the bacteria would become
antibiotic resistant. This is an example of natural selection. Bacteria that can’t be killed by antibiotics are problematic.
MRSA are examples of bacteria that are resistant to most antibiotics and MRSA are becoming more common.

SECTION 8 – ECOLOGY AND THE ENVIRONMENT

56 - Ecosystems and Biodiversity
LO - (4.1), (4.3), (4.5)
- Habitat - place where organism lives
- Population - ALL organisms of ONE species in a habitat
- Community - the populations of different species in a habitat
- Ecosystem – all the living organisms (biotic) living in a particular area and all the non-living (abiotic) conditions.

Biodiversity is the variety of different species of organisms on Earth, or within an ecosystem.

 High diversity is important as it helps make ecosystems remain stable because different species depend upon
each other for shelter and food.
 Human activities, including deforestation, pollution and global warming are reducing biodiversity.

The environment is changing all the time because of abiotic (non-living) factors and biotic (living) factors. Both abiotic
and biotic factors affect population size as well as distribution of a population i.e. where they live.

Abiotic Factors Biotic Factors

 Temperature  Availability of food* - increases
 Light intensity (plants only) biodiversity because more food equals
 Moisture level more organisms
 Soil pH  Competition* - decreases biodiversity as
 Pesticides* - decrease biodiversity as they build up organisms compete with resources
in the food chain (bioaccumulation – when (animals compete for space/territory,
concentration of pesticide increases at each level of food, water, shelter and mates) (plants
the food chain, so that the top level organisms compete for light, space, minerals and
receive a toxic dose) water)
 Fertilisers* - decreases biodiversity as excess  Predation* - decrease biodiversity as
fertiliser is leaked into lakes causing eutrophication increase in predators decreases prey as
leading to death of organisms more are eaten

57 - Using Quadrats
LO - (4.2), (4.4)
A quadrat is a square frame of a known size, eg 1m2
 Place a quadrat on the ground at a random point in a sample area and count the number of organisms within it.
Note: the quadrats are placed at random to make sure the results are representative of the whole sample area. To
 randomly place quadrats – we can divide the area into a grid and place the quadrats at coordinates selected using a
random number generator.
 Repeat a number of times and take a mean average to work out how many per quadrat. Mean = total number of
organisms/number of quadrats
 Repeat the above in a second sample area.
 Compare the 2 means.
Note: accuracy can be improved by using a larger sample size or by using data from more quadrats.

Estimating the population size

 Work out the mean number of organisms per m2 (like as in the above first 2 points)
 Multiply the mean per m2 by the total area (in m2) of the habitat

Using Belt Transects to Study Distribution Across a Habitat

Sometimes abiotic factors will change across a habitat. We can use quadrats to see how organisms are distributed
across a habitat. The quadrats are laid out along a line, forming a belt transect:
 Make a line in the area of study (1)
 Place quadrats next to each other along the line at regular intervals (eg every 2 metres) (1)
 Count the organisms you’re interested in within each quadrat (1) (or estimate percentage cover by a particular
type of organism)
 Other data can also be recorded such as an abiotic factor you’re interested in (for eg light intensity measured
using a light meter)
 Repeat the above steps several times
 Work out the mean number of organisms for each quadrat along the transect
 Plot a graph of your results. This will help you to see if the changing abiotic factor is correlated with a change in
the distribution of the species you’re studying.

58 - Pyramids of Number, Biomass and Energy

LO - (4.6), (4.7)
Food chains show what’s eaten by what in an ecosystem. They start with a producer (a green plant which makes its own
food by photosynthesis from energy from the Sun). The producers are eaten by a primary consumer, which is eaten by
secondary and tertiary consumers. All these organisms eventually die and are eaten by decomposers, eg bacteria.
Decomposers break down dead material and waste. Each stage (eg producers, primary consumer, etc.) is called a
trophic level.

Pyramids of Numbers and Pyramids of Biomass

In the following table, the pyramids contain dandelions (producers) which are on trophic level 1, rabbits (primary
consumer) which are on trophic level 2, foxes (secondary consumer) which are on trophic level 3 and fleas (tertiary
consumer) which are on trophic level 4.
Pyramid of Biomass Pyramid of Number
A pyramid shape. Not necessarily a pyramid shape.
Show the relative mass of living material at each trophic level. Show the number of organisms at each trophic level
An example: An example:

Note: If asked to draw, both pyramids of biomass and pyramids of numbers must be drawn to scale as well as each
trophic level labelled.

Pyramids of energy show the energy transferred to each trophic level in a food chain. They are also always a pyramid
shape.

59 - Energy Transfer and Food Webs

LO - (4.8), (4.9)
All energy comes from the Sun. But only about 1% is delivered to producers as most is transferred to surroundings.
So producers use the Sun’s energy (light) to make food. Some of this energy is stored as biomass which gets transferred
to the next trophic level (around 10%). In fact, between trophic levels, only a small percentage of biomass (energy) is
transferred to the next trophic level. This is because:
 Organisms don’t always eat ALL of the organisms they are consuming. For example, bones are not eaten.
 Organisms get rid of some biomass through excretion, respiration, energy created to keep warm, etc.
Food chains cannot support more than 4 or 5 trophic levels because energy is lost at each trophic level (1), so there’s
not enough energy to support more levels (1)

Food webs show how food chains are linked. All the species in a food web are interdependent, which means that if one
species changes, it affects all the other species. YOU NEED TO BE ABLE TO STATE HOW ONE SPECIES AFFECTS ANOTHER
IN A GIVEN FOOD WEB.

60 - The Carbon Cycle

LO - (4.10)
Living things need carbon, water, nitrogen, etc. to survive. These materials are recycled through biotic (living) parts of
the ecosystem (animals, plants and microorganisms) and abiotic (non-living) parts of the ecosystem (air and soil).

The carbon cycle shows how carbon is

recycled:

The only way carbon comes out of the

atmosphere is through photosynthesis
by green plants. CO2 comes out of the
atmosphere like this. Green plants use
the carbon to make carbohydrates, lipids
and proteins.

Ways in which carbon goes into the

atmosphere are:
 Burning of fossil fuels and animal
and plant products - gives off CO2. Fossil fuels are formed from dead animals and/or plants which contain carbon.
 Respiration by plants, animals, micro-organisms and detritus feeders (animals that feed off other dead animals).
Microorganisms break down material from dead materials (1) and return carbon to the air as carbon dioxide
through respiration (1).

Ways in which carbon goes into the ground:

 Animals and plants dying and decomposing. (The decomposers releasing CO2 into the atmosphere through
respiration).
 Animals producing waste and decomposing. (The decomposers releasing CO2 into the atmosphere through
respiration).
Eventually becoming fossil fuels: plants become coal and animals become oil and gas.

Ways in which carbon travels along to other organisms:

 Animals eating plants and other animals along the food chain.
 Plants and animals used for clothing, furniture, etc.

Decomposition means that habitats can be maintained for organisms that live there, eg nutrients are returned to the
soil and waste material doesn’t just get piled up.

61 - The Nitrogen Cycle

LO - (4.11)
The nitrogen cycle shows how nitrogen is recycled:
For living organisms to be
able to use nitrogen (to make
proteins, etc.), the nitrogen
(78%) from the air must be
fixed into nitrogen
compounds in the soil which
plants can use. There are 2
ways this happens:
 Lightning changes N2
in the air to nitrates
in the soil
 Nitrogen fixing
bacteria in the roots
of some plants

There are 4 types of bacteria

involved in the nitrogen cycle:
 Nitrogen-fixing bacteria – Turn nitrogen gas (from air) into nitrogen compounds that plants can use
 Nitrifying bacteria – turn ammonium ions in decaying matter into nitrates (nitrification)
 Denitrifying bacteria – turn nitrates back into nitrogen gas
 Decomposers – break down proteins in rotting plants and animals and urea (in animal waste) and turn them
into ammonia (a nitrogen compound). This forms ammonium ions in the soil.
Nitrates are taken up by plants. Plants then use the nitrogen in the nitrates to make proteins. The nitrogen is passed
onto animals when animals eat plants.

62 - Air Pollution
LO - (4.12)
 Carbon monoxide: mostly released by car emissions when the fuel burns without enough oxygen. Carbon
monoxide is poisonous as it combines with haemoglobin and stops red blood cells from carrying oxygen.
Most modern cars are now fitted with catalytic converters that turn the carbon monoxide to carbon dioxide
decreasing the amount of carbon monoxide released into the air.
 Acid rain: caused by sulphur dioxide which is released when fossil fuels are burned in cars and power stations.
The sulphur impurities in fossil fuels burns and becomes sulphur dioxide. The sulphur dioxide mixes with rain
clouds and forms dilute sulphuric acid. This falls in the rain (acid rain). (1)
Acid rain causes lakes to become acidic which causes many plants and animals within it to die as they are
sensitive to a pH change. (1)
Acid rain kills trees and leaves and releases toxic substances in the soil which makes it harder for trees to take
up nutrients. (1)

63 - The Greenhouse Effect

LO - (4.13), (4.14), (4.15)
‘Greenhouse gases’ such as CO2, methane, water vapour, CFCs and nitrous oxide absorb energy that is radiated away
from the Earth (1) and re-radiate it in all directions, including back to Earth (1). In this way, the Earth remains warm
because the heat energy of the Sun is trapped in. If this were not happening, the Earth would be very cold and not able
to sustain life.
However, the level of greenhouse gases is rising too much (1), which has enhanced the greenhouse effect (1), which
means that the Earth is heating up more and more - global warming (1). Global warming is causing climate change such
as changing rainfall patterns.

The Consequences of Global Warming

High temp causes sea water to expand and ice at the polar ice caps to
melt (1) causing sea water to rise which leads to flooding and loss of
habitats (1), and could affect food webs and crop growth.
Changing rainfall patterns (1) could lead to changing crop growth
patterns/ less food being grown (1).

Human Activity Produces Lots of Greenhouse Gases

  Carbon dioxide is released through car exhausts and burning fossil fuels. Large areas of forest are also being cut
down (deforestation) for timber and to clear land for farming. All of this contributes to more carbon dioxide in
the atmosphere.
 Methane gas is produced by rotting plants in marshland, rice growing and cattle rearing. Rice growing and cattle
rearing has increased due to more food needed and so this has increased the methane gas in the atmosphere.
 Nitrous oxide is released by bacteria in soils and oceans, and from vehicle engines and industry. More use of
fertilisers and vehicles and industry has increased nitrous oxide in the atmosphere.
 CFCs used to be used in aerosol sprays (eg deodorants) and fridges. Most countries do not produce them
anymore as CFCs also contribute to ozone depletion, however some CFCs still get released from for eg old
fridges.

64 - Water Pollution and Deforestation

LO - (4.16), (4.17), (4.18)
Eutrophication – when too much fertiliser (nitrates and phosphates) is put on fields and is washed away with rain water
through the soil (leached) into the rivers and lakes. The extra nutrients cause algae to grow fast and block out the light
(1). Plants in the water do not get enough light for photosynthesis (1) and so die and decompose (break down).
Microorganisms that feed on decomposing plants now have more food (1) and so increase in number and deplete (use
up) all the oxygen in the water when respiring (1). Other organisms (eg fish) that need oxygen for aerobic respiration die
(1).
Eutrophication can also be caused by sewage pollution entering the lakes and rivers. Sewage contains lots of phosphates
(from detergents) and nitrates from urine and faeces.

Deforestation Affects the Soil, Evapotranspiration and Carbon Cycle

Deforestation (chopping down trees) causes:
 Leaching – trees use up nutrients from the soil before they’re leached away but they return these nutrients back
to the soil when their leaves die (1). When trees are removed, the nutrients get leached away and don’t get
replaced, giving infertile soil (1).
 Soil erosion – tree roots hold soil together (1), but when they’re removed then soil can be washed away by rain
(eroded) leaving infertile ground (1)
 More carbon dioxide in the atmosphere because trees take out carbon dioxide from the atmosphere in
photosynthesis – but if there’s less trees then there will be more carbon dioxide (1). Also, trees store carbon and
when they’re cut down and burnt carbon dioxide is released into the air – if there are more trees cut and burnt
then there will be more carbon dioxide (1). Any trees that aren’t burnt are decomposed by microorganisms,
which release CO2 by respiration (1).
 Trees contribute to evapotranspiration (water evaporating from the Earth’s surface and from plant
transpiration). When trees are cut down, evapotranspiration is reduced (1) which results in a reduction in
precipitation/rainfall, which leads to the local climate being drier (1).

SECTION 9 - USE OF BIOLOGICAL RESOURCES

65 - Increasing Crop Yields
LO - (5.1), (5.2), (5.3), (5.4)
Plants need light, carbon dioxide and temperature to photosynthesise and grow well. There are ways in which we can
maximise the growth of plants:
 Greenhouses (glasshouses) or polytunnels (big tube-like structures made from polythene) – these create
artificial conditions for plant growth by:
o Keeping free from pests and disease
o Trapping Sun’s heat in (or using heaters in the winter)
o Lights on even after the Sun goes down
o Increase carbon dioxide by using paraffin heaters (gives out CO2)
o Control the amount of water supplied
 Add fertilisers – Fertilisers contain nitrogen, potassium and phosphorus, which are needed by plants in order to
carry out life processes (1). These elements may be missing from the soil, so fertilisers are used to replace them
(1), or to add more to the soil (1).
 Pest control – microorganisms, insects and mammals can feed on crops decreasing crop yield. Farmers kill them
through certain methods:
o Pesticides – kill pests. Are poisonous to other wildlife and humans also, so must be used carefully
o Biological control – using other organisms to reduce the number of pests. The organism used for
biological control could be: predators (eg ladybirds eat aphids), parasites (eg some fleas lay their eggs
on slugs, eventually killing them) or disease causing (eg bacteria that affect caterpillars). Biological
 control could be long lasting and less harmful to wildlife. But introducing new organisms can cause
problems, eg cane toads were introduced in Australia to eat beetles, but they are now a major pest
themselves because they poison the native species that eat them.

66 - Bacteria and Making Yoghurt

LO - (5.7), (5.8)
Fermentation is when microorganisms break sugars down by anaerobic respiration to release energy. Yoghurt is made
this way:
 The equipment is sterilised to kill off any unwanted microorganisms.
 Milk is pasteurised (heated up to 72oC for 15 seconds) – to kill off unwanted microorganisms.
 It is then cooled
 Lactobacillus bacteria are added and the mixture incubated (heated to approx. 40oC) in a fermenter
 The bacteria ferment the lactose sugar in the milk to form lactic acid which causes the milk to clot and solidify
into yoghurt
 Flavours and colours are then added and the yoghurt packaged

Microorganisms Are Grown in Fermenters

Microorganisms like bacteria can be grown to make useful stuff like penicillin or insulin. They are grown in large
containers called fermenters with the conditions inside kept at optimum level so that a high yield of products is made:
 Temp kept at optimum – water-cooled jacket makes sure it doesn’t get too hot so that the enzymes in the
microorganisms denature
 pH is kept at optimum
 nutrients needed by the microorganisms for growth provided in the liquid
culture medium
 microorganisms are always kept in contact with fresh medium by paddles
that stir the medium
 sterile air is pumped in to provide oxygen (if needed for them to respire and provide energy for growth)
 vessels are sterilised between uses with superheated steam. The aseptic conditions ensure that unwanted
microbes are removed (1), so that product yield is increased as the microorganisms aren’t competing with other
organisms (1). It also means that the product doesn’t get contaminated from other microbes (1).

67 - Yeast and Making Bread

LO - (5.5), (5.6)
Making bread:
 Yeast, flour, water and some sugar are mixed together into a dough and then left in a warm place to rise.
 The yeast makes the bread rise by breaking down the carbohydrates in the flour to sugars (1).
 It then uses these sugars in aerobic respiration, producing CO2 (1).
 When the oxygen runs out, the yeast switches to anaerobic respiration (fermentation) which produces CO2 (1)
and alcohol (ethanol). The CO2 produced is trapped in bubbles in the dough (1). These bubbles of gas expand
causing the dough rise (1).
 The dough is then baked in an oven, where the yeast continues to ferment until the temperature of the dough
rises enough to kill the yeast and the alcohol produced boils away.
 With the yeast dying, there is no more fermentation and so the bread stops rising but pockets of air remain
where the CO2 was trapped.

Experiment to investigate how the rate of CO2 production by yeast during anaerobic respiration changes under different
conditions:
 Mix together some sugar, yeast and distilled water in a test tube
 Add a layer of oil on top (for anaerobic conditions – to prevent oxygen
from entering)
 Add a bung and attach to a second test tube containing water.
 Place the yeast tube in a water bath at a certain temp
 Leave tube to warm up a little, then count how many bubbles are
produced in a given time (eg 1 min)
 Calculate the rate of CO2 production by dividing the number of bubbles
produced by the time taken. This gives an indication of respiration rate.
 Repeat the experiment with the water bath set at different temps
Results: as the temp increases, the rate of CO2 increases up to the optimum temperature because the enzymes involved
work best at optimum temp. Any increase in temp beyond optimum could result in the rate decreasing because the
enzymes would start to denature.
Note: you could test different conditions for eg vary the sugar concentration and keep the temp the same, or you could
make the experiment more accurate by collecting the gas produced in a syringe.

68 - Selective Breeding
LO - (5.10), (5.11)
Selective breeding (or artificial selection) is when we artificially select plants or animals with useful characteristics to
breed so that their genes are passed on to their offspring. The offspring then has the combined useful characteristics of
the parents, for eg:
 Animals that produce more meat or milk, have speed, fertility, good mothering skills etc.
 Plants with disease resistance, attractive flowers, nice smell, etc.

How to Selectively Breed

 Select the characteristics you’re after in a male and a female and breed them with each other (1).
 Select the best male and female offspring and breed them together (1).
 Continue this process over several generations (1) until the desired characteristics get stronger and stronger.
Eventually all the offspring will have the characteristic.

Examples of selective breeding:

 Cows are selectively bred to give high meat yield – the largest cows and bulls are bred together. Then their
offspring which have the largest meat yields are bred together. This continues for several generations and so
eventually cows with very large meat yields are produced.
Mating cows and bulls naturally can be difficult, so often artificial insemination is used where semen is inserted
into cows. It’s quicker and cheaper to transport semen than the bull itself. The semen can also be used to
impregnate multiple cows and can be stored even after the bull has died.
 Selectively breeding an increase in the number of sheep. Female sheep (ewes) who produce large numbers of
offspring are bred together with rams whose mothers have large numbers of offspring. The characteristic of
having large numbers of offspring is passed on to the next generation.
 Selectively breeding an increase in crop yield – tall wheat plants which have good grain but can be damaged by
the wind and rain are cross-bred with dwarf wheat plants that have a lower grain yield but can resist the wind
and rain. The result is a variety of wheat that gives high grain yield but also resists bad weather.

69 - Fish Farming
LO - (5.9)
We are catching so many fish that we must be careful that we don’t overfish and have none left. Solutions to this
problem are:
 Fish farms – fish are kept in cages in the sea so that they don’t use too much energy swimming out. The cages
also protect them from interspecific predation (being eaten by other animals such as birds and seals). They are
fed a diet of food pellets that’s carefully controlled, so they maximise energy and grow big. Young fish are
reared in special tanks to ensure many survive as possible. The younger and bigger fish are also kept separate to
stop intraspecific predation (organisms eating species of the same species - fish eating fish). Fish kept in cages
are more prone to disease and parasites so pesticides can be used. Or to reduce pollution from chemical
pesticides, biological control could be used.
 Fish tanks – freshwater fish can be farmed in ponds or indoor tanks where the conditions can be controlled,
such as water temp, pH and oxygen level, amount of food given and levels of pollution by cleaning away waste
food and fish poo.

70 - Genetic Engineering
LO - (5.12), (5.13), (5.14), (5.15), (5.16)
Genetic engineering is when a desired gene from one organism is
transferred to another organism so that it also has the desired
characteristic.
Vectors can be used to transfer DNA into a cell. There are 2 types:
(1) Plasmids – these are small, circular molecules of DNA found in
bacteria that can be transferred between bacteria
(2) Viruses which insert DNA into the organisms they infect

How genetic engineering works:

  The DNA you want to insert (for eg the gene for human insulin) is cut out of a cell using a restriction enzyme.
(Note: restriction enzymes recognise specific sequences of DNA and cut the DNA at these points)
 The vector DNA is then cut open using the same restriction enzyme.
 The vector DNA and the desired gene are mixed together with ligase enzyme. Note: ligase enzymes are used to
join two pieces of DNA together.
 The ligase joins the two pieces of DNA together to produce recombinant DNA. Note: recombinant DNA is two or
more different bits of DNA stuck together.
 The recombinant DNA is inserted into other cells, for eg bacteria (1), which can now use the desired gene to
make the protein (human insulin) you want (1). Eg bacteria containing the gene for human insulin can be grown
in huge numbers in a fermenter (1) to produce insulin for people with diabetes.

Organisms that contain genes transferred from another species are called transgenic.

GM Crops pros: GM Crops cons:

 Can make more food where needed  Concerns that changing an organism’s genes might create
by making plants insect-resistant so unforeseen problems which could then be passed on to future
farmers don’t need to spray pesticides generations.
which can also harm other organisms.  Concerns that they may affect food chains and human health
Also by making them resistant to  Transplanted genes may get into the environment and give
herbicides so that farmers can spray advantages to organisms that we don’t want taking advantage,
herbicides to kill weeds without for eg weeds could be affected by the herbicide resistant gene
affecting them and become ‘superweeds’.

71 - Cloning
LO - (5.17), (5.18), (5.19), (5.20)
Cloning plants:
Micropropagation (tissue culture) is a technique used to clone plants:
 Small pieces (explants) from the tips or stems and the side shoots of a plant with the desired characteristics (for
eg large fruit) are taken (1)
 The explants are sterilised to kill any microorganisms
 They are then grown in vitro (1) – placed in a petri dish containing a nutrient medium (1) containing nutrients as
well as growth hormones
 The cells in the explant divide and grow into a small plant (1). Note: Further explants can be taken if large
quantities of the desired plant are needed
 The small plants are taken out of the medium, planted in soil and put into greenhouses – they will be genetically
identical to the original plant.

Micropropagation is beneficial for commercial farmers because lots of plants with desirable characteristics can be
grown.

Cloning animals:
The method used to clone the first mammal – Dolly the sheep in 1996:
 The nucleus of a sheep’s egg cell was removed creating an enucleated cell (one without a nucleus)
 A diploid nucleus (46 chromosomes) – a cell from the udder of another sheep, was inserted into the enucleated
cell.
 The cell was stimulated by electric shock so that it started dividing by mitosis, as if it was a normal fertilised egg
 The dividing cell was implanted into the uterus of another sheep to develop until it was born.
Note: other animals can also be cloned using this method.

Cloning is preferred to naturally reproducing animals because:

 Cloning means the useful genetic characteristics are always passed on
 Farmers don’t have to wait for breeding season
 Infertile animals can be cloned.

Risks involved in cloning animals:

 Cloned animals might not be as healthy as normal ones
 Cloning is a new science which may have unknown consequences
 At present, cloning is difficult, time consuming and expensive

Cloned transgenic animals can be used to produce human proteins:

  Transgenic cows and sheep can have human genes transferred into their cells so that they produce human
proteins such as human antibodies for arthritis, cancer and multiple sclerosis in their milk
 Transgenic chickens can produce human proteins in their egg white
These transgenic animals can then be cloned so that the useful genetic characteristic is passed on.