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Revision checklist

All 395 objectives in the curriculum, taken straight from the lessons that teach them. Tap the dot beside one to rate how confident you are. Open the unit you are working on; the rest stay out of the way.

Jump to: Scientific method and quantitative biology · Cells, microscopy and biological organisation · Biological molecules, water and inorganic ions · Enzymes and metabolic control · Membranes and transport across cells · Nucleic acids, genomes and protein synthesis · Cell cycles, reproduction and development · Exchange surfaces and gas exchange · Plant transport and mineral nutrition · Animal transport and cardiovascular biology · Nutrition, digestion and health evidence · Pathogens, disease and immunity · Respiration and cellular energy · Photosynthesis and primary productivity · Nervous coordination, receptors, muscles and behaviour · Hormonal communication, plant responses and homeostasis · Inheritance and population genetics · Gene regulation, genomics and biotechnology · Classification, biodiversity and conservation · Evolution and speciation · Ecology, populations and environmental change

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Scientific method and quantitative biology

Variables and controls: what an experiment can show AQA Practical skills PS 1.1-1.2, 2.1-2.4, 3.1-3.3 · OCR A Module 1.1.1-1.1.3 · CAIE Paper 3 and Paper 5 (planning, analysis and evaluation) · Edexcel A Working as a biologist; core practical requirements

Name the independent, dependent and controlled variables in an investigation you have not seen before, and justify the levels chosen.
Distinguish a control variable from a control experiment, and say which of the two a question is asking about.
Explain what a negative control rules out and what a positive control rules out, and why those are different jobs.
Identify a confounding variable and explain why repeating the measurement does not deal with it.
Set out the evidence that would raise a correlation to a causal claim.
Use validity, accuracy, precision, repeatability and reproducibility to mean five different things.

Handling data: units, scales, rates and uncertainty AQA MS 0.1-0.5, 1.1, 1.3, 2.2, 3.1, 3.5, 3.6 · OCR A Module 1.1.3-1.1.4; mathematical requirements · CAIE Papers 3 and 5; mathematical requirements · Edexcel A Mathematical skills appendix; core practical analysis

Convert between units across the prefixes biology uses, and write very large and very small quantities in standard form.
Give an answer to a number of significant figures justified by the measurements it came from.
Calculate a percentage change and a percentage difference and say which one a question wants.
Find a rate as a gradient, including by drawing a tangent to a curve, and state its units.
Explain why a logarithmic scale is used for population size and for pH, and read a value off one.
Find the percentage uncertainty in a measurement and combine uncertainties through a calculation.

Statistics for biologists: spread, error bars and the three tests AQA MS 1.2, 1.3, 1.5-1.7, 1.9-1.11 · OCR A Module 1.1.4; mathematical requirements (statistics) · CAIE Paper 5 (analysis, conclusions and evaluation) · Edexcel A Mathematical skills appendix (statistics)

Choose between a mean, a median and a mode for a given set of biological data, and say why.
Calculate a standard deviation and explain what it shows that a range does not.
Interpret error bars, including what non-overlapping bars do and do not prove.
State a null hypothesis in the form a mark scheme accepts.
Choose between chi-squared, a t-test and Spearman's rank for a given question, and find the degrees of freedom.
Compare a calculated value with a critical value and write the conclusion in the wording examiners want.

Cells, microscopy and biological organisation

Cell structure: what each organelle is shaped for AQA 3.2.1.1 · OCR A 2.1.1 (d)-(f) · CAIE 1.2 · Edexcel A Topic 3.1-3.5

Describe the ultrastructure of an animal cell and of a plant cell, and say which structures belong to which.
Link the structure of the nucleus, mitochondrion, chloroplast, Golgi apparatus, lysosome and both kinds of endoplasmic reticulum to what each does.
Put the organelles of the secretory pathway in the order a protein meets them.
State where 80S and 70S ribosomes are found, and what a ribosome is made of.
Name the structures a plant cell has and an animal cell does not, and give a function for each.

Microscopy: magnification, resolution and what you can trust AQA 3.2.1.1 · OCR A 2.1.1 (a)-(c) · CAIE 1.1 · Edexcel A Topic 3.1

Define magnification and resolution and explain why they are not the same thing.
Explain why an electron microscope resolves finer detail than a light microscope.
Compare a light microscope, a TEM and an SEM by beam, resolution, specimen and the kind of image each produces.
Rearrange and use magnification = image size ÷ actual size, converting units correctly.
Describe how an eyepiece graticule is calibrated with a stage micrometer, and explain why artefacts appear in electron micrographs.

Prokaryotic cells and viruses: less machinery, same problems AQA 3.2.1.1 · OCR A 2.1.1 (g), 4.1.1 · CAIE 1.2 · Edexcel A Topic 6.5-6.7

Describe the structure of a prokaryotic cell and give a function for each part.
Compare prokaryotic and eukaryotic cells, including DNA, ribosomes and cell wall.
Explain what a plasmid is and why it is not part of the main chromosome.
Describe binary fission and calculate numbers of bacteria after a given time.
Describe the structure of a virus, using HIV, and justify the claim that viruses are not living.

Specialisation: how one genome becomes two hundred kinds of cell AQA 3.2.1.1, 3.8.2.1 · OCR A 2.1.6 (a)-(d) · CAIE 1.2, 5.1, 7.1 · Edexcel A Topic 3.13-3.17

Explain how cells with identical DNA come to differ, in terms of gene expression.
Define totipotent, pluripotent and multipotent, and give a source of each.
Describe the levels of organisation from cell to organ system, with examples.
Relate the structure of squamous epithelium, ciliated epithelium, xylem and phloem to their functions.
Explain why differentiated cells cannot usually be converted back into other cell types.

Biological molecules, water and inorganic ions

Carbohydrates: from one sugar to a store of thousands AQA 3.1.1, 3.1.2 · OCR A 2.1.2 · CAIE 2.1, 2.2

Draw or recognise alpha and beta glucose, and say where the two differ.
Explain how a glycosidic bond forms, and say what is released when it does.
Name the two monosaccharides in maltose, sucrose and lactose.
Relate the structure of amylose, amylopectin, glycogen and cellulose to what each one does.
Carry out and interpret the Benedict's and iodine tests, including a quantitative Benedict's method.

Lipids: triglycerides, phospholipids and the ester bond AQA 3.1.3 · OCR A 2.1.2 · CAIE 2.2

Name the components of a triglyceride and the bond that joins them.
Explain how an ester bond forms, and count the water released.
Distinguish saturated from unsaturated fatty acids, and say what the double bond does.
Relate the structure of a triglyceride to its use as an energy store.
Explain why a phospholipid behaves differently in water from a triglyceride, and carry out the emulsion test.

Water and inorganic ions: the properties life depends on AQA 3.1.7, 3.1.8 · OCR A 2.1.2 · CAIE 2.4

Explain why a water molecule is polar, and how a hydrogen bond forms between two of them.
Derive each property of water from its hydrogen bonding rather than listing the properties.
Give a biological consequence of each property, naming an organism or a process.
Explain why ice floats, and what that means for life in a pond in winter.
State the role of hydrogen, iron, sodium, phosphate, calcium and nitrate ions.

Proteins: from one amino acid to a working shape AQA 3.1.4.1, 3.1.4.2 · OCR A 2.1.2 (e)-(h) · CAIE 2.3.1-2.3.6 · Edexcel A Topic 1.9-1.11

Draw the general structure of an amino acid and say what varies between the twenty.
Explain how a peptide bond forms, and what is released when it does.
Name the four levels of protein structure and the bond holding each one together.
Account for the difference between a globular and a fibrous protein using haemoglobin and collagen.
Explain denaturation in terms of bonds rather than in terms of the protein being 'killed'.

Enzymes and metabolic control

Enzymes: what a catalyst can and cannot do AQA 3.1.4.2 · OCR A 2.1.4 (a)-(d) · CAIE 3.1 · Edexcel A Topic 1.7-1.8

State what an enzyme does to the activation energy of a reaction, and what it leaves alone.
Describe the active site as a product of tertiary structure rather than of any one amino acid.
Set out the lock-and-key and induced fit models, and give the evidence that decided between them.
Use 'enzyme-substrate complex' and 'complementary' correctly in an explanation of specificity.
Explain why changing one amino acid far from the active site can still stop an enzyme working.

Factors affecting enzyme rate: temperature, pH and concentration AQA 3.1.4.2 · OCR A 2.1.4 (e)-(h) · CAIE 3.2 · Edexcel A Topic 1.8

Explain why the rate of an enzyme-catalysed reaction falls during a run, and why initial rate is the only fair comparison between conditions.
Account for the shape of the temperature curve as the sum of two opposing effects, and calculate a Q10.
Explain the effect of pH in terms of charge on R groups and the bonds that depend on it.
Interpret a substrate-concentration curve, naming what is limiting the rate in each part of it.
Draw all four curves with the right shape, including the asymmetry of the temperature curve.

Inhibition: how cells, poisons and medicines all turn enzymes down AQA 3.1.4.2 · OCR A 2.1.4 (i)-(k) · CAIE 3.2 · Edexcel A Topic 1.8

Distinguish competitive from non-competitive inhibition by where the inhibitor binds and what it does to the active site.
State the effect of each type on Vmax and on Km, and explain both effects in words rather than by quoting the graph.
Explain why raising the substrate concentration relieves one kind of inhibition and not the other.
Describe end-product inhibition and say why acting on the first enzyme of a pathway is the efficient choice.
Give the advantages of immobilising an enzyme for an industrial process, and one disadvantage.

Membranes and transport across cells

The fluid mosaic model: what a membrane is made of AQA 3.2.3 · OCR A 2.1.5 (a)-(c) · CAIE 4.1 · Edexcel A Topic 4.5

Explain why a phospholipid bilayer forms without anything assembling it.
Label a fluid mosaic membrane and give the job of every component on it.
Distinguish intrinsic from extrinsic proteins, and channel from carrier proteins.
Describe what cholesterol does at high temperature and at low temperature, and say why those two effects are not contradictory.
Explain how temperature and organic solvents change permeability, and describe the beetroot investigation that measures it.

Diffusion and osmosis: movement that costs nothing AQA 3.2.3 · OCR A 2.1.5 (d)-(f) · CAIE 4.2 · Edexcel A Topic 4.6

Define simple and facilitated diffusion and say what distinguishes them.
State how rate of diffusion depends on surface area, concentration difference and thickness, and apply that to a named exchange surface.
Define osmosis using water potential, and use the relationship between water potential, solute potential and pressure potential.
Explain what happens to a plant cell and to an animal cell placed in a solution of lower water potential than their contents.
Describe how a serial dilution of sucrose is used to find the water potential of potato tissue.

Active transport, co-transport and moving things in bulk AQA 3.2.3, 3.3.3 · OCR A 2.1.5 (g)-(h) · CAIE 4.2 · Edexcel A Topic 4.7

Explain how a carrier protein moves a substance against its concentration gradient, and where the energy comes from.
Describe the sodium-potassium pump, quoting what moves in each direction for each ATP hydrolysed.
Work through co-transport of glucose in the ileum as an ordered sequence, and say which step uses ATP.
Distinguish endocytosis from exocytosis and give a named example of each.
Compare all the transport mechanisms by direction, proteins used and energy required.

Nucleic acids, genomes and protein synthesis

DNA and RNA: four letters and a rule about pairing AQA 3.4.1 · OCR A 2.1.3 · CAIE 6.1 · Edexcel A Topic 2.4-2.6

Draw a nucleotide and name its three components.
Explain how the sugar-phosphate backbone is built and what is released as it forms.
State which bases pair, how many hydrogen bonds hold each pair, and why the pairing cannot be swapped around.
Say what 5′ and 3′ mean, and why the two strands are called antiparallel.
Account for four features of DNA structure in terms of the job the molecule does.
Compare DNA with mRNA, tRNA and rRNA, and give each kind of RNA its role.

DNA replication: one old strand in every new molecule AQA 3.4.1 · OCR A 2.1.3, 2.1.6 · CAIE 6.1 · Edexcel A Topic 2.7

Explain what semi-conservative replication means, in terms of what happens to the original strands.
Describe the roles of helicase and DNA polymerase, naming the bonds each one deals with.
Explain why one new strand is made continuously and the other in fragments.
Describe the Meselson-Stahl experiment and explain how its results eliminated two competing models.
Explain how a replication error becomes a mutation, and why most cause no harm.

The genetic code and transcription AQA 3.4.2 · OCR A 2.1.3, 6.1.1 · CAIE 6.2 · Edexcel A Topic 2.8

State the four properties of the genetic code and explain a consequence of each.
Explain, with numbers, why the code has to be read in threes rather than ones or twos.
Distinguish exons from introns, and a gene from the genome.
Describe transcription in sequence, naming the enzyme, the strand used and the bonds involved.
Explain what splicing does and why one gene can give rise to more than one polypeptide.
Explain why many base substitutions change nothing about the protein.

Translation: turning a message into a working protein AQA 3.4.2 · OCR A 2.1.3, 6.1.1 · CAIE 6.2 · Edexcel A Topic 2.9

Describe the structure of a ribosome and say what its two binding sites hold.
Explain the relationship between a codon and an anticodon, and say which molecule carries which.
Describe initiation, elongation and termination in order.
Explain where the energy for protein synthesis comes from and roughly how much is needed.
Describe what happens to a polypeptide after it leaves the ribosome.
Work from a given DNA sequence to the amino acid sequence it specifies.

Cell cycles, reproduction and development

The cell cycle: growth, copying, and one division that changes nothing AQA 3.2.2 · OCR A 2.1.6 · CAIE 5.1, 5.2 · Edexcel A Topic 3.7-3.9

Describe what happens in each phase of the cell cycle, and say which phase takes longest.
State what each of the three checkpoints checks, and what becomes of a cell that fails one.
Explain why a chromosome has two chromatids before mitosis and one after it.
Put the four stages of mitosis in order and say what defines each one, including what the spindle does.
Calculate a mitotic index from a count of cells and interpret what it means.
Describe binary fission in a prokaryote and set it against mitosis in a eukaryote.
Explain how uncontrolled cell division leads to a tumour, using the cycle's checkpoints.

Stem cells: what a cell can still become, and what fixes it AQA 3.8.2.1 · OCR A 2.1.6 · Edexcel A Topic 3

Define a stem cell, and say what self-renewal adds to being unspecialised.
Place a named cell at the right level of potency and justify the placement.
Give a real example of a totipotent, a pluripotent, a multipotent and a unipotent cell.
State where stem cells are obtained from, and what potency each source gives.
Explain why a specialised cell still carries every gene it will never use.
Set out the positions people hold on using embryos as a source, and the reasoning behind each.

Gametes and fertilisation: from two cells to a blastocyst Edexcel A Topic 3

Describe spermatogenesis and oogenesis, and give three ways in which they differ.
Relate each structure of a sperm and of an egg to the job that structure does.
Describe the acrosome reaction in the order the events happen.
Explain how the cortical reaction prevents polyspermy, and why polyspermy has to be prevented.
Describe what happens between fertilisation and implantation, and state where each takes place.

Exchange surfaces and gas exchange

Surface area to volume ratio: why size limits diffusion AQA 3.3.1 · OCR A 3.1.1 · CAIE 8.1, 9.1

Calculate a surface area to volume ratio for a cube, a sphere and a flattened body, and say what happens to it as the body gets bigger.
Explain why shape changes the ratio even when the volume is fixed.
State Fick's law as a proportionality and use it to predict how a change in area, gradient or thickness changes the rate.
Explain why diffusion works over micrometres and fails over millimetres.
List the features shared by specialised exchange surfaces and account for each one in terms of Fick's law.

Lungs: seventy square metres, folded into a chest AQA 3.3.2 · OCR A 3.1.1 · CAIE 9.1

Trace air from the trachea to an alveolus and name the tissues in the wall at each level.
Recognise trachea, bronchus, bronchiole and alveolus in a section, and justify the identification from what is in the wall.
Describe inspiration and expiration in the correct causal order: muscles, then volume, then pressure, then air.
Explain why quiet expiration costs almost nothing while inspiration always costs energy.
Calculate pulmonary ventilation rate, and read tidal volume, vital capacity and breathing rate off a spirometer trace.

Three other answers: tracheae, gills and stomata AQA 3.3.2 · OCR A 3.1.1, 3.1.3 · CAIE 7.2

Trace the path of oxygen from a spiracle to an insect's muscle cell and say why its blood plays no part.
Explain how tracheal fluid moves during activity and why that speeds up gas exchange.
Describe the structure of a bony fish gill from arch to lamella, and the buccal pump that drives water over it.
Explain why counter-current flow extracts far more oxygen than parallel flow would, using the gradient along the lamella.
Describe how a leaf exchanges gases and explain the trade-off that forces xerophyte adaptations.

Plant transport and mineral nutrition

Xylem and the transpiration stream: the pull comes from the top AQA 3.3.4.2 · OCR A 3.1.3 · CAIE 7.1, 7.2 · Edexcel A Topic 4.1-4.4

Describe how a root hair cell is built for absorbing water and mineral ions.
Trace water across the root cortex by the apoplast and symplast routes, and say where each one has to cross a membrane.
Explain what the Casparian strip does and why it hands the plant control over what reaches the xylem.
Account for every feature of a xylem vessel in terms of the job the tissue does.
State the cohesion-tension theory and name the property of water each step depends on.
Set up a potometer, and say exactly which quantity the reading is.
Name the ions a plant takes up and what a shortage of each one looks like.

Transpiration: the price of keeping the stomata open AQA 3.3.2, 3.3.4.2 · OCR A 3.1.3 · CAIE 7.2 · Edexcel A Topic 4.1-4.4

Define transpiration and explain why a photosynthesising plant cannot avoid it.
Predict and explain the effect of light, temperature, humidity and air movement on the rate, in every case by naming what happens to the gradient.
Describe how a guard cell opens a stoma, from the proton pump to the turgor.
Explain why the shape and wall thickness of a guard cell turn turgor into an open pore rather than a fatter cell.
Account for xerophyte and hydrophyte adaptations by saying what each does to the water potential gradient.
Process potometer data: calculate rates, compare conditions and state what was controlled.

Phloem and translocation: pumped at the ends, flowing in the middle AQA 3.3.4.2 · OCR A 3.1.3 · CAIE 7.2 · Edexcel A Topic 4.1-4.4

Describe a sieve tube element and a companion cell, and relate each feature to the job it does.
Explain how sucrose is loaded into a sieve tube at a source, naming the pump and the co-transporter.
Explain how loading and unloading create the pressure gradient that mass flow depends on.
Identify sources and sinks, including an organ that is both at different times of year.
Describe ringing, aphid stylet and tracer experiments and say what each one does and does not establish.
Evaluate the mass flow hypothesis, giving evidence on both sides.

Animal transport and cardiovascular biology

The heart and the cardiac cycle: pressure decides everything AQA 3.3.4.2 · OCR A 3.1.2 (h)-(k) · CAIE 8.3 · Edexcel A Topic 1.1-1.6

Explain why a large, active animal needs a mass transport system when a flatworm does not.
Say what double circulation gives a mammal that single circulation cannot.
Label the mammalian heart and account for the thickness of the left ventricle wall in terms of the pressure it generates.
Describe the three stages of the cardiac cycle, giving the pressure change responsible for every valve movement.
Read a pressure-against-time graph: identify each curve and mark where each valve opens and shuts.
Calculate cardiac output, stroke volume or heart rate from the other two.
Trace an impulse from the SAN to the ventricle walls and explain why the delay at the AVN matters.

Blood vessels and tissue fluid: what leaks out and what comes back AQA 3.3.4.2 · OCR A 3.1.2 (c)-(g) · CAIE 8.1 · Edexcel A Topic 1.3-1.5

Relate the structure of an artery, arteriole, capillary, venule and vein to its function and to the pressure it carries.
Explain why a capillary wall is one cell thick and why the blood moves through it slowly.
Account for the formation of tissue fluid at the arteriole end of a capillary bed using hydrostatic and oncotic pressure.
Account for the return of most of that fluid at the venule end using the same two pressures.
Describe what the lymphatic system does with the fluid that is not returned.
Explain three different causes of oedema using nothing but hydrostatic and oncotic pressure.

Haemoglobin: an S-shaped curve and everything it explains AQA 3.3.4.1 · OCR A 3.1.2 (l)-(o) · CAIE 8.2 · Edexcel A Topic 1.6, 7.10

Describe haemoglobin as a conjugated globular protein and say how many oxygen molecules one molecule carries.
Explain cooperative binding and use it to account for the sigmoid shape of the dissociation curve.
Read percentage saturation off a dissociation curve and calculate how much oxygen is unloaded between two partial pressures.
Explain the Bohr shift and why it is useful in exercising muscle.
Interpret a curve that lies to the left or to the right of the human adult curve, including foetal, high-altitude and small-mammal haemoglobins.
Describe how carbon dioxide is carried, including the role of carbonic anhydrase and the chloride shift.

Nutrition, digestion and health evidence

Digestion and absorption: one tube, four chemistries AQA 3.3.3 · OCR A 2.1.4, 2.1.5 (the enzymes and the transport, not digestion as a topic) · CAIE 4.2 (membrane transport only) · Edexcel A Topic 1.5-1.6

Describe digestion as hydrolysis, and say what physical digestion contributes to it.
Name the enzymes acting on carbohydrate, protein and lipid, and state where each works.
Explain why endopeptidases are needed before exopeptidases can work quickly.
Explain emulsification as an argument about surface area, and calculate the change.
Describe the role of micelles in lipid absorption, and say what is and is not absorbed.
Explain the co-transport of glucose and amino acids with sodium ions, and say where the ATP is spent.

Diet, energy and how to read a health claim AQA 3.3.4.2 (evaluating risk-factor data) · OCR A 2.1.2 (the molecules a diet supplies) · CAIE not examined as a topic · Edexcel A Topic 1.7-1.10

Define basal metabolic rate and state what a person's BMR mostly depends on.
Calculate an energy balance and explain why a small daily surplus does not extrapolate.
State what a diet must supply beyond energy, and give a named consequence of each shortfall.
Distinguish a cohort study, a case-control study and a randomised controlled trial by what each starts with.
Name the confounder, the reverse causation or the measurement problem in a given dietary study.
Convert a relative risk into an absolute risk, and say which one a reader needs.

Cholesterol, atheroma and what a risk factor means AQA 3.3.4.2 (risk factors and cardiovascular disease) · OCR A 3.1.2 (transport in animals, as context) · CAIE not examined as a topic · Edexcel A Topic 1.11-1.15

Describe cholesterol as a sterol and state four things the body needs it for.
Explain what a lipoprotein is and distinguish LDL from HDL by composition and function.
Describe the formation of an atheroma in sequence, from endothelial damage to a fibrous plaque.
Explain how a plaque leads to angina, to a myocardial infarction and to an aneurysm.
State precisely what the term 'risk factor' licenses you to claim, and what it does not.
Account for why the evidence on LDL is regarded as causal while the evidence on HDL is not.

Pathogens, disease and immunity

Pathogens and non-specific defences AQA 3.2.4 · OCR A 4.1.1 · CAIE 11.1 · Edexcel A Topic 6.5

Name the four groups of pathogen and give a disease caused by each.
Explain how a pathogen damages its host, using toxins and cell lysis as the two standard exam routes.
Distinguish a physical barrier from a chemical one, with named examples of both.
Describe phagocytosis as an ordered sequence, ending with antigen presentation.
Explain why an antibiotic that cures tuberculosis does nothing whatever for influenza.

The specific response: selected, cloned, remembered AQA 3.2.4 · OCR A 4.1.1 · CAIE 11.1 · Edexcel A Topic 6.6

Explain what an antigen is and how a lymphocyte distinguishes self from non-self.
Describe clonal selection and clonal expansion, and say which cell does which.
Set out the roles of T-helper cells, T-killer cells, B cells, plasma cells and memory cells without confusing any two of them.
Put the events from infection to circulating antibody into the right order.
Account for the secondary response being faster, larger and longer-lasting than the primary one.

Antibodies, vaccination and the four kinds of immunity AQA 3.2.4 · OCR A 4.1.1 · CAIE 11.2 · Edexcel A Topic 6.7

Describe the structure of an antibody and relate each feature to what it does.
Explain agglutination, neutralisation and opsonisation without claiming that antibodies destroy pathogens.
Classify an example of immunity as active or passive and natural or artificial, and justify the classification.
Explain how vaccination protects an unvaccinated person, and why a threshold coverage exists.
Explain why the influenza vaccine changes annually and the measles vaccine does not.
Set out both sides of an ethical question about vaccine trials without asserting a conclusion.

Respiration and cellular energy

Spending ATP to make ATP: glycolysis and the link reaction AQA 3.5.2 · OCR A 5.2.2 · CAIE 12.1, 12.2 · Edexcel A Topic 7.3-7.4

Describe the structure of ATP and explain what its hydrolysis releases, with a figure.
Give three reasons ATP suits a cell better than releasing a glucose molecule's energy in one go.
State where each of the four stages of respiration happens, and why glycolysis needs no oxygen.
Describe glycolysis as phosphorylation, lysis and oxidation, with the net yield per glucose.
Describe the link reaction, naming the decarboxylation and the dehydrogenation.
Keep a running tally of ATP, reduced NAD and carbon dioxide per molecule of glucose.

The Krebs cycle and oxidative phosphorylation AQA 3.5.2 · OCR A 5.2.2 · CAIE 12.2 · Edexcel A Topic 7.4-7.5

Describe one turn of the Krebs cycle and account for all of the carbon that enters it.
State the products of the cycle per turn and per molecule of glucose.
Explain how electron transfer along the chain produces a proton gradient across the inner membrane.
Explain how the gradient is used to make ATP, naming the enzyme and the direction of proton movement.
State the role of oxygen precisely, and say what happens to the chain without it.
Explain why a measured ATP yield falls short of the theoretical 38.

Anaerobic respiration and the respiratory quotient AQA 3.5.2 · OCR A 5.2.2, 5.2.3 · CAIE 12.2, 12.3 · Edexcel A Topic 7.5-7.7

Explain why glycolysis can continue without oxygen and what must be regenerated for it to do so.
Describe lactate fermentation and explain what happens to the lactate afterwards.
Describe ethanol fermentation in yeast and compare it with the animal route.
Compare anaerobic and aerobic yields per molecule of glucose.
Explain how lipids and proteins enter respiration and why lipid yields more energy per gram.
Calculate a respiratory quotient and interpret values of 0.7, 1.0 and above 1.0.
Describe how a respirometer is used, including its controls.

Photosynthesis and primary productivity

Chloroplasts: catching light and turning it into ATP AQA 3.5.1 · OCR A 5.2.1 · CAIE 13.1 · Edexcel A Topic 5.4

Name the parts of a chloroplast and give each one a job it does in photosynthesis.
Explain why a leaf looks green, using the absorption spectrum of chlorophyll.
Say what an action spectrum measures and why it resembles an absorption spectrum.
Separate leaf pigments by chromatography and calculate an Rf value from your own chromatogram.
Describe the light-dependent reactions in order, from a photon to reduced NADP.
Distinguish non-cyclic from cyclic photophosphorylation by their products.

The Calvin cycle: three steps, and the arithmetic behind them AQA 3.5.1 · OCR A 5.2.1 · CAIE 13.1 · Edexcel A Topic 5.5

Describe the three stages of the Calvin cycle and say where each takes place.
State what rubisco does and how many molecules of GP one turn produces.
Explain what reduced NADP and ATP each contribute to the reduction of GP.
Work out how many turns, how many TP and how much ATP a molecule of glucose costs.
Predict and explain the changes in GP, TP and RuBP when light or carbon dioxide is withdrawn.

Limiting factors and primary productivity AQA 3.5.1, 3.5.3 · OCR A 5.2.1, 6.3.1 · CAIE 13.2, 18.1 · Edexcel A Topic 5.6

Identify the limiting factor from any region of a rate graph and justify the choice.
Explain what changes the gradient of such a graph and what changes the height of the plateau.
Use the principle of limiting factors to explain what a commercial grower controls, and why.
Define the compensation point and explain what it means for a plant's carbon balance.
Distinguish gross from net primary productivity and quote productivity in the correct units.
Calculate the percentage of energy transferred between trophic levels and explain why it is small.

Nervous coordination, receptors, muscles and behaviour

Receptors: turning a stimulus into something a neurone can carry AQA 3.6.1.3 · OCR A 5.1.3, 5.1.5 · CAIE 15.1.1-15.1.2 · Edexcel A Topic 8.11-8.14

Put the stages from stimulus to response in order, and name the three neurones in a spinal reflex arc.
Explain what makes a reflex fast, and what it protects you from.
Describe how pressure on a Pacinian corpuscle produces a generator potential.
Distinguish a generator potential from an action potential, using the word graded correctly.
Compare rods and cones on sensitivity, acuity, pigment and distribution, and explain the first two using convergence.

The action potential: the same size, however hard you push AQA 3.6.2.1 · OCR A 5.1.3 · CAIE 15.1.3-15.1.5 · Edexcel A Topic 8.8-8.10

Explain how the sodium-potassium pump and the membrane's permeability produce a resting potential of about −70 mV.
Describe depolarisation, repolarisation and hyperpolarisation in terms of which gates are open.
State the all-or-nothing principle and say what does vary with stimulus strength.
Explain the refractory period and give its three consequences.
Account for conduction speed using myelination, axon diameter and temperature.

The synapse: transmission, and why it runs one way AQA 3.6.2.2 · OCR A 5.1.3 · CAIE 15.1.6-15.1.8 · Edexcel A Topic 8.10

Label a cholinergic synapse and say what each part does.
Describe transmission across it in the right order, from arriving impulse to enzyme clearing the cleft.
Explain why transmission is unidirectional, using the position of vesicles and receptors.
Distinguish spatial from temporal summation, and explain what an inhibitory synapse does.
Explain how a named drug produces its effect at a synapse.

Sliding filaments: shortening a muscle without shortening anything AQA 3.6.3 · OCR A 5.1.5 · CAIE 15.2 · Edexcel A Topic 7.13-7.16

Describe the structure of skeletal muscle from whole muscle down to the sarcomere.
Explain how an impulse at the neuromuscular junction leads to calcium release inside the fibre.
Describe the sliding filament mechanism, including the roles of calcium, tropomyosin, ATP and the myosin head.
State what happens to the A band, I band and H zone during contraction, and why.
Compare slow and fast twitch fibres, and explain how ATP is supplied to a working muscle.

Hormonal communication, plant responses and homeostasis

Hormones: a message broadcast in the blood that only some cells can read AQA 3.6.4.1 · OCR A 5.1.1, 5.1.4 · CAIE 14.1 · Edexcel A Topic 7 (homeostasis and feedback)

Distinguish an exocrine gland from an endocrine gland by where its secretion goes.
Describe the relationship between the hypothalamus and the two lobes of the pituitary.
Explain why a peptide hormone needs a second messenger and a steroid hormone does not.
Describe the adrenaline cascade in order, from binding to glucose leaving the liver cell.
Explain negative feedback using receptor, coordinator and effector, and say what positive feedback does instead.
Compare nervous and hormonal coordination on speed, route, duration and target.

Blood glucose: two hormones, one liver, and two different diabetes AQA 3.6.4.2 · OCR A 5.1.4 · CAIE 14.1 · Edexcel A Topic 7 (homeostasis)

State the normal blood glucose concentration and name the three places glucose in the blood comes from.
Describe the effects of insulin and of glucagon, naming the cells that secrete each.
Use glycogenesis, glycogenolysis and gluconeogenesis correctly.
Describe how a beta cell secretes insulin, from glucose entering to vesicles fusing.
Distinguish type 1 from type 2 diabetes by cause, and say how each is managed.
Read a glucose tolerance test curve and justify a diagnosis from it.

The kidney: filter everything, then take almost all of it back AQA 3.6.4.3 · OCR A 5.1.2 · CAIE 14.1

Label a nephron and name the parts in the order the filtrate meets them.
Explain ultrafiltration in terms of hydrostatic pressure and the three layers of the barrier.
Describe selective reabsorption at the proximal convoluted tubule, including co-transport.
Explain how the loop of Henle builds a concentration gradient in the medulla.
Describe the control of water potential by osmoreceptors, ADH and aquaporins.
State what a dialysis fluid must contain, and justify each component.

Plant responses: tropisms, auxins and the classic experiments AQA 3.6.1.1 · OCR A 5.1.5 · CAIE 15.3, 14.2

Define a tropism and name the common ones with their stimulus and direction.
State what Darwin's, Boysen-Jensen's and Went's experiments each establish, and what they do not.
Explain how auxin causes a cell to elongate, using the cell wall.
Explain why the same auxin distribution bends a shoot upwards and a root downwards.
Describe the effects of gibberellins and of abscisic acid.
Give a commercial use of a plant growth substance and explain how it works.

Inheritance and population genetics

Meiosis: two divisions, and why no two gametes come out the same AQA 3.2.2 · OCR A 2.1.6 · CAIE 16.1 · Edexcel A Topic 3.10-3.13

Say which chromosomes separate in the first division and which in the second, and why that order matters.
Describe how a bivalent forms and what crossing over does to the chromatids in it.
Work out how many chromosome combinations a gamete could carry, given the haploid number.
Track chromosome number and chromatid number through both divisions without losing count.
Set out the differences between mitosis and meiosis in terms an examiner can mark.

Monohybrid inheritance: genetic diagrams that score AQA 3.7.1 · OCR A 6.1.2 · CAIE 16.2 · Edexcel A Topic 2.10-2.13

Use the terms gene, allele, locus, genotype and phenotype in the sense a mark scheme uses them.
Set out a monohybrid genetic diagram with every line an examiner expects to see.
Predict and interpret ratios for complete dominance, codominance and multiple alleles.
Work out blood group possibilities from parental genotypes and the reverse.
Handle a sex-linked cross, including why sons and daughters are affected at different rates.

Two genes at once: 9 : 3 : 3 : 1, the ways it breaks, and the chi-squared test AQA 3.7.1 · OCR A 6.1.2 · CAIE 16.2 · Edexcel A Topic 3 (dihybrid crosses only)

Work out the gametes a dihybrid parent produces and use them to build a 16-cell Punnett square.
Predict the 9 : 3 : 3 : 1 and 1 : 1 : 1 : 1 ratios and say what each assumes.
Recognise autosomal linkage from a test cross result and calculate a recombination frequency.
Identify epistasis from a modified dihybrid ratio and explain it through a pathway.
Carry out a chi-squared test in full, from null hypothesis to a conclusion that names the probability.

Hardy-Weinberg: what alleles do in a population when nothing acts on them AQA 3.7.2 · OCR A 6.1.2 · CAIE 17.2 · Edexcel A not listed

Define a gene pool and calculate an allele frequency from genotype counts.
State the Hardy-Weinberg principle and the five conditions it assumes.
Use p + q = 1 and p² + 2pq + q² = 1 to move between allele and genotype frequencies.
Calculate carrier frequency from the frequency of a recessive phenotype, and turn frequencies into numbers of individuals.
Explain what a departure from Hardy-Weinberg proportions shows about a population.

Gene regulation, genomics and biotechnology

Control of gene expression: which genes a cell reads AQA 3.8.2.1, 3.8.2.2 · OCR A 6.1.1 · CAIE 16.2 · Edexcel A Topic 3

Explain what a transcription factor is and how one alters the rate of transcription of a particular gene.
Describe how the lac operon switches on when lactose arrives, naming the regulatory gene, the promoter, the operator and the structural genes.
Describe how oestrogen switches a gene on, and explain why a steroid hormone can take that route and a peptide hormone cannot.
Explain how DNA methylation and histone acetylation change the accessibility of a gene, and say which way each one pushes.
State precisely what epigenetic inheritance is known to involve, and where the evidence in humans runs out.
Explain how small interfering RNA stops a protein being made from a gene that has already been transcribed.

Mutation and cancer: what goes wrong, and where it goes wrong AQA 3.8.1, 3.8.2.1, 3.8.2.3 · OCR A 6.1.1, 6.1.2 · CAIE 6.2, 16.2 · Edexcel A Topic 3

Name the types of gene mutation and give the consequence of each at the level of the polypeptide.
Explain why many base substitutions change nothing about the protein, and why a deletion of one base usually changes everything.
Distinguish a mutation in a gene from one in a control sequence, and give an example of each.
Explain the difference between a proto-oncogene and a tumour suppressor gene, including how many alleles must be affected.
Explain how methylation of a promoter can silence a tumour suppressor gene without altering a single base.
Describe the therapeutic uses of stem cells and set out the ethical arguments on both sides of the embryonic case.

Recombinant DNA technology: isolating, inserting and expressing a gene AQA 3.8.4.1 · OCR A 6.1.3 · CAIE 19.1, 19.2 · Edexcel A Topic 2, Topic 6

Describe the three ways of obtaining a gene, and say which one suits which situation and why.
Explain what a sticky end is, why the same restriction enzyme must be used on gene and vector, and what ligase does afterwards.
Describe transformation and explain why marker genes are needed at all.
State the three temperatures of the polymerase chain reaction and explain what each step needs its own temperature for.
Calculate the number of copies produced by a given number of PCR cycles, and explain why a real reaction falls short of it.
Explain how gel electrophoresis separates DNA fragments, in terms of charge and of the gel itself.

Genomes, screening and gene therapy: what a sequence is good for AQA 3.8.3, 3.8.4.2, 3.8.4.3 · OCR A 6.1.3 · CAIE 19.2 · Edexcel A Topic 2, Topic 6

Say what a genome project produces, and what still has to be done before a sequence becomes useful.
Explain why a prokaryote's genome gives its proteome almost directly and a eukaryote's does not.
Explain how a DNA probe works and what a microarray adds to it, distinguishing genotyping from expression profiling.
Distinguish genetic screening from genetic counselling, and state what non-directive counselling involves.
Describe how a DNA profile is produced from variable number tandem repeats, and interpret a match probability correctly.
Compare somatic with germ line gene therapy, and set out why the second is the more contested.

Classification, biodiversity and conservation

Classification and phylogeny: sorting by ancestry, not by looks AQA 3.4.5 · OCR A 4.2.2 · CAIE 18.1 · Edexcel A Topic 4 (biodiversity and natural resources)

Write the eight taxonomic ranks in order and name a group at each rank for a named organism.
Write a binomial correctly and say what each part of it means.
State the biological species concept and give two situations it cannot handle.
Distinguish a phenetic from a phylogenetic classification, and explain why convergent evolution defeats the first.
Describe the evidence from ribosomal RNA that split the prokaryotes into two domains.
Explain how DNA sequences, amino acid sequences and immunological comparisons are used to estimate how closely two species are related.
Read a cladogram: say what it asserts, and say what it does not.

Measuring biodiversity: richness, evenness and the index that catches both AQA 3.4.6, 3.4.7 · OCR A 4.2.1 · CAIE 18.2 · Edexcel A Topic 4 (biodiversity and natural resources)

Distinguish species richness from species diversity, and say what evenness adds.
Calculate an index of diversity using the form your board specifies, and state which form you have used.
Explain why one Simpson form rises with diversity and the other falls, and interpret a value correctly either way.
Describe how genetic diversity within a species is measured, and why observable characteristics are a poor measure of it.
Explain how agriculture and monoculture reduce diversity at the habitat, species and genetic levels, and describe measures that offset this.

Conservation: keeping a species where it lives, or somewhere else AQA 3.7.4 · OCR A 4.2.1 · CAIE 18.3 · Edexcel A Topic 4 (biodiversity and natural resources)

Define in situ and ex situ conservation and give examples of each.
Explain the advantages and the limitations of each approach, and why most programmes use both.
Describe how a seed bank collects, dries, stores and tests seed, and explain which species it cannot store.
Outline what CITES and the Convention on Biological Diversity each do.
Set out the economic, ecological, ethical and aesthetic cases for conservation, and the objection each one meets.
Discuss a case where conservation succeeded and one where the outcome is genuinely disputed.

Evolution and speciation

Natural selection: variation, selection and allele frequency AQA 3.4.3, 3.4.4 · OCR A 4.2.2, 6.1.2 · CAIE 17.1, 17.2 · Edexcel A Topic 4

Name the sources of genetic variation and say which one produces an allele that did not exist before.
Distinguish variation that can be selected on from variation that cannot be inherited.
Define fitness and selection pressure in terms an examiner can credit.
Recognise stabilising, directional and disruptive selection from a distribution and from a description.
Explain why selection acts on phenotype while evolution is measured as a change in allele frequency.
Write about selection without using language that implies organisms change on purpose.

Resistance, drift and the evidence: selection where you can watch it happen AQA 3.4.4, 3.7.3 · OCR A 4.2.2, 6.1.2 · CAIE 17.2, 17.3 · Edexcel A Topic 4, Topic 6

Explain the origin of antibiotic resistance in a bacterial population without implying the antibiotic caused it.
Distinguish vertical from horizontal transfer of a resistance gene, and say why the second is faster.
Give the biological reason a prescribed course of antibiotics is finished.
Describe pesticide resistance and explain why a refuge of untreated crop slows it.
Set out the fossil, anatomical, biochemical and biogeographical evidence for common ancestry.
Distinguish genetic drift and the founder effect from natural selection, and say when each matters most.

Speciation: how one gene pool becomes two, and why the line is genuinely fuzzy AQA 3.4.5, 3.7.3 · OCR A 4.2.2, 6.1.2 · CAIE 17.3, 18.1 · Edexcel A Topic 4, Topic 5

State the biological species concept and identify situations in which it cannot be applied.
Explain what reproductive isolation means and why it is the event that creates a species.
Describe allopatric speciation as a sequence, from one gene pool to two.
Describe sympatric speciation and explain why it is harder, with polyploidy as the clearest route.
Classify isolating mechanisms as prezygotic or postzygotic and give an example of each.
Discuss the timescale of speciation and why the boundary between two species is often not sharp.

Ecology, populations and environmental change

Populations and their limits: what stops the numbers rising AQA 3.7.4 · OCR A 6.3.2 · CAIE 18.1, 18.2 · Edexcel A Topic 5

Use population, community, habitat and ecosystem as four different words with four different meanings.
Describe each phase of a sigmoid growth curve in terms of birth rate and death rate.
Sort a limiting factor into density-dependent or density-independent, and justify the choice.
Distinguish intraspecific from interspecific competition and predict what each does to a population.
State the competitive exclusion principle and use the ecological niche to explain it.
Explain why the predator peak lags the prey peak, and why that undermines the usual story about predators.
Estimate a population by mark, release and recapture, and say which assumption a given problem breaks.

Nutrient cycles: nitrogen, phosphorus and eutrophication AQA 3.5.4 · OCR A 6.3.1 · CAIE 18.1 · Edexcel A Topic 5

Explain why plants cannot use nitrogen gas and must take up nitrate, or some ammonium, instead.
Name the four bacterial processes of the nitrogen cycle and state what each converts into what.
Say which of the four need oxygen and which needs its absence, and use that to explain a farming practice.
Describe the phosphorus cycle and explain why it has no gaseous stage.
Set out eutrophication as a sequence of consequences and identify the step that actually removes the oxygen.
Calculate the nitrogen applied to a field from the mass of fertiliser, and estimate what leaches from it.

Succession: how bare rock becomes woodland, and why we stop it AQA 3.7.4 · OCR A 6.3.2 · CAIE 18.1 · Edexcel A Topic 5

Describe primary succession from a pioneer species to a climax community, naming what changes at each stage.
Explain how a pioneer species alters the abiotic environment and why that leads to its own replacement.
Distinguish primary from secondary succession and explain why secondary succession is faster.
Explain what a plagioclimax is and why conservation management often maintains one.
Describe how succession is investigated in the field, including the use of a chronosequence.
State what a long-term ecological dataset can establish and what it cannot.

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