Biology Revision Notes

Year 10 Topics

HideShow resource information

The Eye


Very Bright Light - Triggers a reflex that makes the pupil smaller, allowing less light in (light receptors detect the bright light, send a message along sensory neurone to the brain, where the message travels along a relay neurone to a motor neurone, which tells circular muscles in the iris to contract)

Dim Light - The opposite occurs. This time, the brain tells the radial muscles to contract, which makes the pupil bigger (dilate)


Distant Objects:

  • Ciliary muscles relax
  • Suspensory ligaments are tight
  • Lens goes thin (less curved)
1 of 42

The Eye

Near Objects:

  • Ciliary muscles contract
  • Suspensory ligaments relax
  • Lens becomes fat (more curved)


People are unable to focus on near objects, as:

  • The cornea/lens doesn't bend the light enough or the eyeball is too short, images of near objects are brought into focus behind retina.


People are unable to focus on distant objects, as:

  • The cornea/lens bends the light too much or the eyeball is too long, images brought into focus in front of the retina.
2 of 42

The Eye


  • Conjunctiva - Lubricates and protects the surface of eye
  • Cornea - Refracts light into the eye
  • Iris - Controls how much light enters the eye (diameter of pupil)
  • Lens - Focuses light onto the retina
  • Optic Nerve - Carries impulses from the receptors to the brain
3 of 42


Homeostasis is the maintenance of a constant internal environment. The inputs and outputs must be balanced:

  • Water content - balance between the water you gain and water you lose
  • Body temperature - you need to get rid of excess body heat when you're hot, but retain heat when the environment is cold. 

Water is taken into the body through food and drink.

How is water removed from the body? Body temp is kept at 37 degrees.

  • Through the skin as sweat The enzymes work best at this optimum temp.
  • Lungs in breath
  • Kidneys as urine

Hot day/Exercising: Cold day/Not Exercising:

  • Sweat a lot -  Don't sweat much
  • Produce less urine (more concentrated) -  Produce more urine (more diluted)
  • Lose more water through breath (breathe faster)
4 of 42

Homeostasis - Skin

The skin plays an important role in maintaining body temperature.

When you're too hot:

  • Lots of sweat is produced - when it evaporates it transfers heat from you to the environment, cooling you down.
  • Blood vessels close to the surface of skin widen = VASODILATION (allows more blood to flow near the surface, so it can radiate more heat into the surroundings)
  • Hairs lie flat

When you're too cold:

  • Very little sweat is produced
  • Blood vessels near the surface constrict = VASOCONSTRICTION (so that less heat can be transferred from the blood to the surroundings)
  • Shivering (movement generates heat in muscles)
  • Hairs stand erect (trap insulating layer of air, which helps keep you warm)
5 of 42

Coordination in Plants

Plants lack a nervous system but can respond to some stimuli.  These responses are fixed and known as TROPISMS (change their rate of growth). Plants respond mainly to light and gravity (directional stimuli).  Plants respond to the stimuli by growing towards it (positive tropism) or away from it (negative tropism)

  • PHOTOTROPISM - Plants respond to light by growing towards it.  This is called positive phototropsim, because the response is in the direction of the stimulus. 
  • GEOTROPISM - Plants responding to gravity, as roots grow downwards towards the pull of gravity(+G) and shoots grow upwards (-G) away from the pull of gravity.

AUXIN & LIGHT (The chemical that causes phototropism in plants is a plant hormone, auxin.)

  • It is made at the tip of the plant but moves away from the light as it diffuses downwards.
  • The greater the concentration of auxin on the shaded part of shoot causes cells to grow or elongate & this causes the shoot to bend towards the light.

AUXIN & GRAVITY (Auxin also causes geotropism)

  • In shoot, auxin moves down to the lower side, more elongation of cells, bending shoot up.
  • In root, auxin moves down to lower side, reducing cell elongation, bending root down.
6 of 42

Animal Coordination

Animals respond to their environment, which helps the organisms survive. They increase their chance at survival by responding to changes in their external environment, and their internal environment to make sure that the conditions are always right for their metabolism (chemical reactions that go on inside them).  A change in the internal/external environment is called a stimulus

Receptors detect Stimuli and Effectors produce a response:

  • RECEPTORS - detect stimuli.  In the sense organs are groups of cells that detect external stimuli. 
  • EFFECTORS - are cells that bring about a response to stimuli. Include muscle cells and cells found in glands.  They respond in different ways - muscle cells contract, whereas glands secrete hormones.
  • Receptors communicate with effectors via the nervous system, the hormonal system or sometimes both.
7 of 42

Animal Coordination

Central Nervous System (CNS)

  • There are three main types of neurones; sensory, relay and motor neurones.
  • The CNS consists of the brain and spinal cord only.
  • When receptors in a sense organ detect a stimulus, they send electrical impluses along sensory neurones to the CNS.
  • The CNS then sends electrical impulses to an effector along a motor neurone.  The effector then responds accordingly.
  • The job of the CNS is to coordinate the response.  Coordinated responses always need a stimulus, receptor and an effector.
  • Because neurones transmit information using high speed electrical impulses, the nervous system is able to bring about very rapid responses

Reflexes help prevent injury

  • Reflexes are automatic responses to stimuli, can reduce chances of being injured, eg - bright light, pupils automatically get smaller so less light gets in eye, stops getting damaged. Eg - get a shock, body releases hormone adrenaline automatically.
  • The route taken by the information in a reflex (Receptor --> Effector) is called a reflex arc.
8 of 42

Animal Coordination


  • 1.  Finger gets burnt
  • 2.  Stimulation of the pain receptor
  • 3.  Impulses travel along the sensory neurone
  • 4.  Impulses are passed along a relay neurone, via a synapse.
  • 5.  Impulses travel along a motor neurone, via a synapse.
  • 6.  When impulses reach muscle, it contracts.


9 of 42

Levels of Organisation

Organelles ---> Cells ---> Tissues ---> Organs ---> Organ Systems

ORGANELLES in Animal and Plant Cells CELLS are specialised

  • Nucleus - Vacuole Cells are specialised to carry out a particular
  • Cell Membrane - Chloroplasts function. Eg - RBCs are specialised for 
  • Cytoplasm - Cell Wall carrying oxygen.

Similar Cells are organised into TISSUES

A tissue is a group of similar cells that work together to carry out a particular function.  Eg - plants have xylem tissue (transporting water & mineral salts) and phloem tissue (transporting sucrose and amino acids).  A tissue can contain more than one cell type.

Tissues are organised into ORGANS

  • An organ is a group of different tissues that work together, lungs in mammals and leaves on plants are examples of organs (made up of different tissue types)

ORGAN SYSTEMS - Organs work together to form OS. Each system does a different job. Eg - digestive system is made up of organs including stomach, intestines, pancreas and liver.

10 of 42

Organelle Functions

  • Nucleus - Contains the genetic material that controls the cell's activities.
  • Cell Membrane - Controls the substances that go in and out of the cell.
  • Cytoplasm - Where most of the cell's chemical reactions take place (contains enzymes which control these reactions)
  • Mitochondria - Breaks down glucose molecules to release energy.
  • Chloroplasts - Photosynthesis, which makes food for the plant, happens here. Contain a green substance called chlorophyll, used in photosynthesis.
  • Cell Wall - A rigid structure made of cellulose, surrounding the cell membrane. Supports and strengthens the cell.
  • Vacuole - Large organelle that contains cell sap (weak solution of sugars and salts) and it helps support the cell.
11 of 42

Variety of Living Organisms

  • PLANTS - Multicellular, chloroplasts, photosynthesis, cellulose cell walls, store carbohydrates as starch or sucrose
  • ANIMALS - Multicellular, no chloroplasts, take in food&digest it, no cell wall, store carbohydrates as glycogen
  • FUNGI - Some single-celled, no chloroplasts, external digestion (or saprotrophic nutrition), chitin cell wall, store carbohydrates as glycogen, body called mycelium (made up of hyphae),eg - yeast, pathogen: athletes' foot
  • BACTERIA - Single-celled, no chloroplasts, some can photosynthesise, no nucleus, circular chromosome of DNA, eg - lactobacillus bulgaricus, pathogen: pneumococcus
  • PROTOCTISTS - Single-celled, some have chloroplasts, photosynthesis or feed off dead or living organisms, some cellulose cell wall, eg - amoeba, pathogen: plasmodium
  • VIRUSES - Not cells, reproduce inside cells, eg - HIV, influenza, pathogen: HIV
12 of 42


Enzymes are catalysts produced by living things.  All living things have thousands of chemical reactions going on inside them all the time, which must be carefully controlled to get the right amounts of substances in the cells. The reactions occur faster if the temperature is raised, however there is a limit to how far you can raise the temperature before the cells are denatured.  

A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction.

  • Enzymes reduce the need for high temperatures and we only have enzymes to spped up the useful chemical reactions in the body - metabolic reactions.
  • Enzymes are all proteins and all proteins are made up of chains of amino acids.

Enzymes are specific

  • Chemical reactions involve things either being split apart or joined together
  • Substrate = molecule that is changed in a reaction
  • Every enzyme molecule has an active site - where a substrate joins on to the enzyme
  • Enzymes usually only speed up one reaction, as for an enzyme to work, a substrate has to be the correct shape to fit into the active site.
  • DENATURE - if it's too hot, some of the bonds holding enzyme break,& enzyme loses its shape, and so its active site doesn't fit the shape of the substrate anymore, so it can't catalyse the reaction and it stops, so enzyme can't function = denatured (irreversible)
13 of 42


Diffusion is the net movement of particles from an area of higher concentration to an area of low concentration across a partially permeable membrane. Diffusion occurs in both liquids and gases, as the particles in these substances are free to move about the body. The bigger the difference in concentration, the faster the diffusion rate.

Cell Membrane - Hold together the cell and let stuff in and out.  Substances can move in and out of cells by diffusion, osmosis and active transport.  Only very small molecules can diffuse through cell membranes, such as glucose, amino acids, water and oxygen.  Big molecules like starch and proteins can't fit through the membrane holes.

14 of 42


Osmosis is the net movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration. The holes in the partially permeable membrane are so small, that only tiny molecules (like water) can pass through, unlike bigger molecules (eg sucrose).

  • The water molecules pass both ways through the membrane during osmosis as they move about randomly all the time.
  • Because there are more water molecules on one side than the other, there's a steady net flow of water into the region with fewer water molecules (eg into sucrose solution)
  • This means that the sucrose solution gets more dilute and the water acts like it's trying to even up the concentration either side of the membrane.
15 of 42

Cells during Osmosis


16 of 42

Cells during Osmosis

PLANT CELL IN WATER - Plant cell goes turgid, It is more concentrated inside the cell than out.

PLANT CELL IN CONCENTRATED SOLUTION - Cytoplasm shrinks away from cell wall, flaccid, It is less concentrated inside the cell so the molecules leave the cell my osmosis

ANIMAL CELL IN WATER -Haemolysis, too much pressure,become so large cell membrane bursts, it is more concentrated inside the cell so the molecules enter by osmosis

ANIMAL CELL IN CONCENTRATED SOLUTION - Cells become shriveled, crinkly and crenated, it is less concentrated inside the cell so the molecules leave by osmosis

17 of 42

Diffusion and Osmosis Experiments


  • Fill a beaker with dilute hydrochloric acid, and using a scalpel, cut out a few cubes of agar jelly and put them in the beaker of acid.
  • If you leave the cubes for a while they'll eventually turn colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide.

OSMOSIS - Potato Cylinders (living system) & Visking Tubing (non-living system)

  • Cut up a potato into identical cylinders
  • Get beakers with different sugar solutions in them; one pure water, other very concentrated sol.If the cylinders are longer than before then they will have drawn in water by osmosis, if they have shrunk a bit, then water will have been drawn out.
  • Tie a piece of wire around one end of some visking tubing and put a glass tube in the other end, fix the tubing around it with wire, then pour some sugar solution down the glass tube into the visking tubing. Put the visking tubing in a beaker of pure water - measure where the sugar sol. comes up to on the glass tube. 
  • Leave the tubing overnight, then measure where the liquid is in the glass tube, water should be drawn into the VT by osmosis and this will force the liquid up the glass tube.
18 of 42

Active Transport

Active Transport is the movement of particles against a concentration gradient (i.e. from an area of lower concentration to an area of higher concentration) using energy released during respiration It is used in the digestive system, when there is a low concentration of nutrients in the gut, but a high concentration of nutrients in the blood.


  • Surface Area to Volume Ratio (rate of D, O and AT is higher in cells with a larger SA:Vol ratio as the smaller cells have a larger SA:Vol ratio, this means substances would move into & out of this cell faster.
  • Temperature - the particles gain more energy when heated, so they move faster
  • Concentration Gradient - If there is a big difference in concentration between the inside and outside of the cell, substances move in and out of the cell faster.
19 of 42

Biological Molecules - Structure of Carbohydrates,

  • Carbohydrates - Made up of Simple Sugars, contain the elements carbon, hydrogen and oxygen. Starch and glycogen are large, complex carbohydrates, which are made up of many smaller units (eg glucose or maltose molecules) jointed together in a long chain. 
  • Proteins - Made up of long chains of Amino Acids, they contain carbon, nitrogen, hydrogen, oxygen and sometimes sulphur atoms.
  • Lipids - Made up of Glycerol and Fatty Acids, lipids contain carbon, hydrogen and oxygen atoms.
20 of 42

Test for Starch and Glucose & Balanced Diet


  • Add food and water to a test tube, add iodine solution.
  • If starch is present, the sampe changes from browny-orange to a blue-black colour.
  • If theres NO starch, it stays browny-orange.


  • Add food and water to a test tube, add Benedict's Solution and heat it.  If the test's positive, it will form a coloured precipitate, changing from Blue->Green->Yellow->Orange->Brick red
  • The higher the concentration of glucose, the further the colour change goes, so it is easy to compare the amount of glucose in different solutions.


  • Carbohydrates - Water
  • Proteins - Dietary Fibre
  • Lipids
  • Vitamins
  • Mineral Ions
21 of 42

A Balanced Diet


  • Carbohydrate          Pasta, rice  Provide energy
  • Lipids    Oily Fish Long term energy store
  • Proteins     Meat, fish Growth & repair of tissue, emergency energy
  • Vitamin -    A        Liver Improve vision, keep skin & hair healthy
  • "   "   "  -   C         Oranges Prevent scurvy 
  • "   "   "  -   D           Eggs Calcium absorption
  • Mineral Ions-Ca           Milk Make bones and teeth
  • "    "   "   - Iron   Red meat Make haemoglobin for healthy blood
  • Water   Food and Drink Replace water loss & every bodily function
  • Dietary Fibre   Wholemeal Bread Aids movement of food through the gut


  • Activity Level -  Need more energy than others as it is used up during exercise
  • Age - Children and teenagers need more energy than older people, for growth & generally they're more active.
  • Pregnancy -  Pregnant women need more energy that other women, got to provide the energy their babies need to provide.
22 of 42

Energy from Food Experiment

  • Skewer a wotsit onto a mounted needle.
  • Add 25cm3 of water to a boiling tube (held with a clamp), this will be used to measure the amount of heat energy released when the food is burnt.
  • Measure the temp of the water, then set fire to the wotsit using a bunsen burner. 
  • Hold the burning food under the boiling tube until it goes out, then relight the food and hold it under the tube, keep doing this until the food won't catch fire again.
  • Measure the temp of the water again, now work out:

Energy in food (J) = Mass of Water (g) X Temperature change of water( C) X  4.2

Energy per gram of food (J/g) = Energy in food (J)

  Mass of food (g)

23 of 42

Digestive Enzymes

These digestive enzymes break down big molecules (eg starch, proteins, fats) into smaller molecules (eg sugars, amino acids, glycerol and fatty acids):

  • AMYLASE converts STARCH into MALTOSE 

BILE - Made in the liver, stored in the gall bladder, then released into the small intestine. Its function is to neutralise stomach acid and emulsify fats.  The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the SI to work properly, bile is an alkaline, so it neutralises the acid and the enzymes work best in these alkaline conditions.  Emulsifies - breaks the fat into tiny droplets, much bigger surface area of fat for lipase to work on - faster digestion.

24 of 42

Functions of Organs & Peristalsis

  • MOUTH -  Food is broken down by the teeth, and saliva is produced, containing amylast which begins the breakdown of starch. 
  • OESOPHAGUS -  Connects the mouth and stomach
  • STOMACH -  Pummels food with its muscular walls, produces the protease enzymes, pepsin. Produces hydrochloric acid for 2 reasons: kill bacteria, give right pH for the protease enzyme to work.
  • LIVER - Where bile is produced
  • PANCREAS -  Produces protease, amylase and lipase enzymes, releases into SI
  • GALL BLADDER - Where bile is stored
  • LARGE INTESTINE - Where excess water is absorbed from the food
  • SMALL INTESTINE - Produces protease, amylase & lipase enzymes to complete digestion. This is also where the nutrients are absorbed out of the alimentary canal into the body.
  • ANUS - Where faeces are removed from your body

Food is moved through the gut by peristalsis.  There's muscular tissue all the way down the alimentary canal, its job is to squeeze balls of food through your gut.  This squeezing action, which is waves of circular muscle contractions, this is called peristalsis. 

25 of 42

Digestive Process

  • Ingestion - Putting food/drink into your mouth and chewing it.
  • Digestion - The break-down of large, insoluble molecules into small, soluble molecules.  Your body has mechanical (teeth & stomach muscles) and chemical (enzymes and bile) ways to digest your food.
  • Absorption - Process of moving molecules through the walls of the intestines into the blood. Digested food molecules are absorbed into the SI, water is mainly absorbed by the LI.
  • Assimilation - When digested molecules have been absorbed, they're moved into body cells. Digested molecules become part of the cells, this is assimilation. 
  • Egestion - Undigested stuff forms faeces, which are no use to your body, so are removed through the ****.


  • Single Permeable Layer = good blood supply for quick absorbtion (SADLY)
  • Big Surface area = lots of room for absorption (BLAIR)
  • Microvilli = aids food into the blood/extends surface area (MARRIES)
  • Long = time to break down & absorb all food until it reaches the end (LOUIS)
26 of 42


Photosynthesis produces glucose using sunlight. It occurs inside the chloroplasts of a leaf and other green parts of a plant.  They contain a pigment called chlorophyll, which absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose. Oxygen is also produced. It converts light energy to chemical energy, which is stored in the glucose.  This chemical energy is released when glucose is broken down during respiration.

carbon dioxide  +  water ---------->    glucose  +  oxygen

6CO2   +   6H2O      ----------->   C6H12O6  +   6O2


  • Broad - Large Surface Area exposed to light (BLAIR)
  • Chloroplasts - In the palisade layer, near to top where there's most light (CAN'T)
  • Transparent - Upper epidermis is transparent so light can pass through palisade layer (TAKE)
  • Vascular Bundles - Deliver water to leaf, take glucose from photosynthesis (VANESSAS)
  • Waxy Cuticle - Reduce water loss by evaporation (WHINING)
27 of 42

Rate of Photosynthesis

There are 3 limiting factors of photosynthesis:

1.  Not enough light slows down the Rate of Photosynthesis

Chlorophyll uses light energy to perform photosynthesis, so it is slow when the light is dim. If the light intensity if increased, the P. rate will increase steadily, but only up to a certain point, as temp and CO2 are now the limiting factors.

2.  Too little Carbon Dioxide also slows it down

CO2 is needed for photosynthesis.  Increasing the concentration of CO2 will only increase the rate of P. up to a point, after the graph flattens out, CO2 is no longer the limiting factor. 

3.  Temperature must be just right

Temperature affects the rate of P. as it affects the enzymes involved. As the temp increases, so does the rate of P. up to a point. If the temp is over 45 degrees, the plants enzymes will be denatured, so the rate of P. rapidly increases. Usually, if the temp is the limiting factor, it's usually because it's too low. 

28 of 42

Testing Leaves for Starch

  • Dunk the leaf in boiling water to kill it (with forceps), which stops any chemical reactions.
  • Put the leaf in a boiling tube with some ethanol and heat the tube in a water bath.  This gets rid of any chlorophyll that's inside the leaf.
  • Finally rinse the leaf in cold water & add drops of iodine to it. If starch is present, it will turn blue-black, and if not, it turns brick-red.

Starch Test shows whether photosynthesis is taking place

CHLOROPHYLL - you can show that chlorophyll is needed for P. using variegated leaves, in which only the green parts of the leaf contain chlorophyll.  Take a leaf from a plant that has been exposed to light, record which bits are green/aren't green. Test the leaf for starch (above) and only the green bits turn blue-black.  This suggests that only the parts that contained chlorophyll are able to photosynthesise and produce starch. 

CO2 -  You can show that CO2 is needed for photosynthesis with this apparatus.

  • The soda lime will absorb CO2 out of the air in the jar.
  • Leave the plant in the jar for a while then test for S, it won't turn blue-black.
  • This shows that no starch has been made in the leaf, so CO2 is needed for P.

29 of 42

More Photosynthesis Experiments

STARCH TEST - shows whether photosynthesis is taking place

  • To show that light is needed for photosynthesis you need a plant that's been grown without any light (eg cupboard)
  • Cut a leaf from the plant & test for starch, the leaf won't turn blue-black.
  • This shows that light is needed for photosynthesis as no starch has been made.

Oxygen production shows the rate of Photosynthesis

  • Canadian pondweed can be used to measure the effect of light intensity on the rate of P.  The rate at which pondweed produces oxygen corresponds to the rate at which its photosynthesi-sing, faster rate of O2 production, the faster the rate of P.
  • A source of white light is placed as specific distance from pondweed.
  • Pondweed left to P. for set amount of time. 
  • When it P's, the O2 will collect in the capillary tube.
  • At the end of experiment, the syringe is used to draw the gas bubble 
  • in the tube up alongside a ruler & length of gas bubble measured, this is 
  • proportional to the volume of O2 produced. Any other variables need controlling.
  • Experiment is then repeated with light source placed at different distances from pondweed.
30 of 42

Mineral Ions for Plants

NITRATES - Contain nitrogen for making amino acids and proteins. These are needed for cell growth. If a plant can't get enough nitrates it will be stunted and will have yellow, older leaves.

MAGNESIUM - Magnesium is one of the most significant as it's required for making chlorophyll (needed for photosynthesis).  Plants without magnesium have yellow leaves.

31 of 42

Transport in Plants

Multicellular organisms need Transport Vessels

In multicellular organisms, direct diffusion from the outer surface would be too slow - that's because substances (eg water, minerals and sugars) would have to travel large distances to reach every single cell.  So multicellular organisms need transport systems to move substances to and from individual cells quickly.


Xylem tubes transport water and minerals: Phloem tubes transport food:

  • The xylem carry water & mineral salts from  -  They transport sugars, like sucrose, &   the roots up the shoot to the leaves in the    amino acids from where they're made in  transpiration stream. leaf to other parts of the plant. -  Movement of food substances around the ROOT HAIR CELLS - take in water plant is known as translocation.
  • Cells on the plant roots grow into long 'hairs' which stick out into the soil.  Each branch of a root will be covered in millions of these microscopic hairs. This gives the plant a big SA for absorbing water from the soil. Water is taken in by osmosis. There's usually a higher concentration of H2) in the soil than there is inside the plant so water is drawn into cell by O.
32 of 42


Transpiration is the loss of water from a plant through the stomata through diffusion and evaporation, in the leaves.

  • It is caused by the evaporation & diffusion of water from a plant's surface. Most transpiration happens at the leaves.  This evaporation creates a slight shortage of water in the leaf, & so more water is drawn up from the rest of the plant through the xylem vessels to replace it.
  • This in turn means more water is drawn up from the roots, & so there's a constant transpiration stream of water through the plant.
  • The rate of transpiration is low at night, as there is no light so the plant cannot photosynthesise and doesn't need CO2, so the stomata closes, preventing water loss.


   Mass lost/gained    X        100

Initial mass

33 of 42

More Transpiration


  • Light intensity - The brighter the light, the greater the transpiration rate. Stomata begins to close as it gets darker.  Photosynthesis can't happen in the dark, so they don't need to be open to let CO2 in. When the stomata is closed, very little water can escape.
  • Temperature -  The warmer it is, the faster transpiration occurs as the particles have more energy to evaporate & diffuse out of the stomata.
  • Wind Speed - The higher the wind speed around the leaf, the greater the transpiration rate, as if the wind speed is high, the water vapour surrounding the leaf is swept away, keeping a low concentration of water in the air outside the leaf. Diffusion then happens quickly from hgih concentration to low concentration. If the wind speed is low, the water vapour just surrounds the leaf & doesn't move away, meaning there's a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn't happen as quickly.
  • Humidity - The drier the air around the leaf, the faster transpiration happens. If the air is humid there's a lot of water in it already, so there's not much of a difference between the inside and outside of the leaf.  Diffusion happens fastest if there's a really high concentration in one place, and a really low concentration in the other. 
  • Potometers can be used to estimate transpiration rate (can see how fast the air bubble moves)
34 of 42


Respiration is not 'Breathing in and out'.

  • It goes on it every cell in your body.  It is the process of releasing energy from glucose. The chemical energy is used to do things like create large molecules from smaller ones & help contract muscles. 
  • There are 2 types of respiration; aerobic and anaerobic.
  • Respiration is the process of releasing energ from glucose, which happens constantly in every living cell. 


Happens when there's plenty of oxygen availiable. Aerobic means 'with oxygen' at it's the most efficient way to release energy from glucose. This respiration is used most of the time.

Glucose  +  Oxygen  -------->  Carbon Dioxide  +  Water  (+Energy)

C6H12O6  +  6O2  -------->  6CO2  +  6H2O  (+Energy)

(reverse of photosynthesis equation)

35 of 42



  • When you do vigorous exercise your body can't supply enough oxygen to your muscles for aerobic respiration - your muscles have to start respiring as well.
  • Anaerobic means 'without oxygen'.  It is not the best way to convert glucose into energy becuase it releases much less energy than aerobic respiration. In anaerobic respiration, the glucose is only partially broken down, and lactic acid is produced.
  • The lactic acid builds up in the muscles and it gets painful and also leads to cramp.

Glucose  -------->  Lactic Acid (+Energy)

  • Anaerobic respiration in plants is slightly different, as they can respire without oxygen too, but they produce ethanol and CO2 instead of lactic acid.

Glucose  -------->  Ethanol  +  Carbon Dioxide  (+Energy)

36 of 42

Carbon Dioxide Experiments

CO2 production can be detected using an indicator.

  • You can use hydrogen-carbonate solution to show that living organisms produce CO2 as they respire. Normally this solution is orange, but it changes colour to a lovely yellow in the presence of CO2.
  • Soak some dried beans in water for a day or two, they will start to germinate, which will respire.
  • Boil a similar-sized, second bunch of dried beans, this will kill the beans and make sure they can't respire, the dead beans will act as your control.
  • Put some hydrogen-carbonate indicator into two test tubes.
  • Place a platform made of gauze into each test tube and place the beans on this.
  • Seal the test tubes with a rubber bung.
  • Leave the apparatus for a set period of time
  • During that time the CO2 produced by the germinating beans should have an effect on the hydrogen-carbonate indicator - it will have turned yellow.
37 of 42

Gas Exchange in Plants

Plants exchange gases by diffusion.

  • When plants photosynthesise they use up CO2 from the atmosphere and produce O2 as a waste product. 
  • When they respire they use up O2 and produce CO2 as a waste product, so there's lots of gases moving to and fro in plants, and this movement happens by diffusion.
  • Photosynthesis only happens during the day (light) but plants must respire all the time, day and night, to get the energy they need to live. 
  • During the day (high light intensity) plants make more oxygen by photosynthesis than they use in respiration. So in daylight, they release oxygen. They also use up more CO2 than they produce, so they take in CO2.
  • At night (low light intensity) though plants only respire - there's not enough light for photosynthesis. This means they take in oxygen and release CO2, just like us.


  • Broad - Large surface area for diffusion of gases
  • Air Spaces - Increase SA for gas exchange and allow gases to move easily between cells
  • Thin - Gases only have to diffuse over a short distance
38 of 42

The Respiratory System & Ventilation

You need to get oxygen into your bloodstream to supply your cells for respiration, and need to get rid of CO2 from your blood. This all happens in the lungs when you breathe air in and out.

  • The lungs are in the thorax, which is separated from the lower part of the body by the diaphragm. The lungs are like sponges and are protected by the ribcage, and surrounded by the pleural membranes.
  • The air that you breathe in goes through the trachea, this splits into two tubes called bronchi, one going to each lung. The bronchi split into progressively smaller tubes called bronchioles.
  • The bronchioles finally end at small bags called alveoli where the gas exchange takes place.


  • Intercostal muscles contract -  Intercostal muscles relax
  • Diaphragm contracts -  Diaphragm relaxes
  • Thorax volume increases -  Thorax volume decreases
  • Decreases pressure, drawing air in -  Air is forced out

EXERCISE - Count breaths while sitting still. Do 4 mins exercise, count breaths per min after. Make 2 others do it too, reliable. Breathing rate increases, muscles respire more during exercise. They need to be supplied with more O2 & more CO2 removed.

39 of 42

Gas Exchange in Humans

Millions of tiny air sacs in the lungs called alveoli carry out Gas Exchange in the body. Blood passing to the next alveoli has just returned to the lungs from the rest of the body,so it contains lots of CO2 and very little O2. Oxygen diffuses OUT of the alveolus (high concentration) into the blood (low concentration). CO2 diffuses out of the blood (high concentration) into the alveolus (low concentration) to be breathed out.  When the blood reaches body cells, oxygen is released from the RBCs (high conc.) and diffuses into the body cells (low conc.). At the same time, CO2 diffuses out of the body cells (high conc.) into the blood (low conc.). It is then carried back to the lungs.


  • Moist Lining - for gases to dissolve in (MUNCH) the
  • Blood Supply - maintain a high concentration gradient (B)
  • Large Surface Area - lots of room for gases to diffuse into and out (L)
  • Thin, permeable walls - gases can diffuse across easily  (T)
40 of 42


4 main components:   Plasma, Platelets, Red Blood Cells & White Blood Cells


Basically blood minus the blood cells, it is the pale yellow liquid which carries just about everything that needs transporting around your body: RBCs, WBCs, platelets, CO2, Urea, hormones, heat energy, digested food products


When you damage a blood vessel/get a wound, platelets clump together to plug the damaged area, this is known as blood clotting, which stop you losing too much blood and prevent microorganisms from entering the wound. In a clot, platelets are held together by a mesh of protein called fibrin.

RED BLOOD CELLS - adapted for function:

  • Biconcave disc shape - Large SA for absorbing and releasing oxygen BLAIR
  • Haemoglobin - gives blood its colour, lungs react with O2 = oxyhaemoglobin HATES
  • No nucleus - frees up space for more haemoglobin, carry more oxygen NATE

41 of 42



The immune systen deals with pathogens. Pathogens are microorganisms that cause disease. Once they have entered your body they'll reproduce rapidly unless they're destroyed. White blood cells do this. There are 2 different types of white blood cell: phagocytes and lymphocytes.


  • Every pathogen has unique molecules (called antigens) on its surface.
  • When lymphocytes come across a foreign antigen, they will start to produce proteins called antibodies, which lock on to the invading pathogens and mark them out for destruction by other white blood cells. The antibodies produced are specific to that type of antigen, they won't lock onto any others.
  • Antibodies are then produced rapidly
42 of 42


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cells, tissues and organs resources »