A-Level Biology Formula Sheet – Key Equations, Processes & Must-Know Facts (Cambridge 9700)

This sheet follows the Cambridge International AS & A Level Biology syllabus (9700) for examinations in 2025, 2026 and 2027, topic by topic, from cell structure through to genetic technology. Biology has fewer plug-in formulas than physics or chemistry, so this sheet does what matters most for this subject: it puts the real equations and quantitative skills first, then sets out each process in order and the definitions that examiners expect to be stated precisely.

How to use this sheet: work through one topic at a time, cover the bullet points, and try to rebuild each process from memory before checking the box again. Use the equations actively — practise rearranging them and converting units — rather than just reading them. For the other boards in this series, see the GCSE Biology Formula Sheet, the IGCSE Biology Formula Sheet and the AP Biology Formula Sheet, or return to the Biology MCQs hub.

Draft note: this sheet is organised by the 2025–2027 syllabus. AS Level covers Topics 1–11; A Level covers those topics plus Topics 12–19.

AS Level Topics 1–11

Topic 1: Cell Structure

• Resolution is the smallest distance at which two separate points can still be seen as two points; magnification only makes an image larger, and a highly magnified image can still be blurred if resolution is poor.
• Electron microscopes give far higher resolution than light microscopes, so they reveal organelles and membranes in detail, while light microscopes are used for living material and larger cell structures.
• Eukaryotic cells contain a membrane-bound nucleus and membrane-bound organelles. Plant cells add a cell wall, chloroplasts and a large permanent vacuole; animal cells do not have these three features.
• Prokaryotic cells, such as bacteria, are generally 1–5 µm across, have circular DNA, 70S ribosomes and no membrane-bound organelles, and their cell walls are made of peptidoglycan.
• Viruses are not cells: each has a nucleic acid core of DNA or RNA inside a protein capsid, and some also carry an outer envelope made of phospholipids.
• Key organelle jobs to fix in memory: the nucleus holds genetic material; mitochondria release energy by aerobic respiration; chloroplasts carry out photosynthesis; ribosomes make proteins; the Golgi body modifies and packages proteins; lysosomes digest material; rough endoplasmic reticulum bears ribosomes, while smooth endoplasmic reticulum makes lipids.

Topic 2: Biological Molecules

• Tests to know: Benedict’s test for reducing sugars, iodine test for starch, emulsion test for lipids and biuret test for proteins. A non-reducing sugar is first hydrolysed with acid, then tested with Benedict’s solution.
• Glucose, fructose and maltose are reducing sugars; sucrose is a non-reducing sugar.
• Starch (amylose and amylopectin) is the plant storage polysaccharide and glycogen is the animal storage polysaccharide; both are compact and easily hydrolysed, which suits storage. Cellulose is a structural polysaccharide whose long, straight chains hydrogen-bond into strong fibres for plant cell walls.
• A triglyceride is one glycerol joined by ester bonds to three fatty acids; saturated fatty acids have no carbon-carbon double bonds, while unsaturated fatty acids have one or more.
• Phospholipids have hydrophilic phosphate heads and hydrophobic fatty acid tails, which is why they form bilayers in membranes.
• Proteins are built from amino acids joined by peptide bonds. Primary structure is the amino acid sequence; secondary structure is local folding into shapes such as helices; tertiary structure is the overall three-dimensional shape; quaternary structure is the assembly of more than one polypeptide chain.
• Haemoglobin is a globular protein with two alpha chains, two beta chains and a haem group containing iron; collagen is a fibrous protein whose molecules pack into strong fibres.
• Water is a polar solvent with hydrogen bonding between molecules, a high specific heat capacity and a high latent heat of vaporisation, all of which help organisms stay stable and transport dissolved substances.

Topic 3: Enzymes

• Enzymes lower the activation energy of a reaction without being used up. The substrate fits into the active site, forming an enzyme-substrate complex; the induced-fit model describes the active site changing shape slightly around the substrate.
• Raising temperature increases rate up to an optimum, then the enzyme denatures as bonds holding its shape break. Each enzyme also has an optimum pH, and extremes of pH denature it.
• More enzyme or more substrate raises rate only until another factor becomes limiting; at high substrate concentration the rate levels off because all active sites are occupied.
• A competitive inhibitor resembles the substrate, competes for the active site, and raises the apparent K_m without changing V_max. A non-competitive inhibitor binds elsewhere, changes the enzyme’s shape, and lowers V_max without changing K_m.
• Immobilised enzymes are fixed to a support such as alginate beads; they can be reused, are easy to separate from products, and stay stable over a wider range of conditions, though reaction rates may fall because substrates reach the active sites more slowly.

Topic 4: Cell Membranes and Transport

• The fluid mosaic model describes a phospholipid bilayer in which proteins, cholesterol, glycolipids and glycoproteins are embedded and can move. Channel and carrier proteins allow facilitated diffusion; receptor proteins receive signals; glycoproteins act in cell recognition.
• Diffusion is passive movement down a concentration gradient. Facilitated diffusion uses channel or carrier proteins but still needs no energy. Active transport moves substances against a gradient using ATP and carrier proteins.
• Osmosis is the diffusion of water across a partially permeable membrane. Large quantities move by endocytosis (into the cell) and exocytosis (out of the cell).
• In a dilute solution, a plant cell takes in water, becomes turgid and is supported by the wall; in a concentrated solution it loses water and the protoplast pulls away from the wall (plasmolysis). An animal cell in a dilute solution swells and may burst, while in a concentrated solution it shrinks (crenation).
• A large surface area to volume ratio helps exchange, which is why small cells and folded surfaces exchange substances faster than large, smooth ones.

Topic 5: The Mitotic Cell Cycle

• The cell cycle runs: interphase (G₁, S and G₂ phases), then mitosis, then cytokinesis. DNA replicates in S phase; the cell grows and prepares for division in G₁ and G₂.
• Mitosis in order: prophase (chromosomes condense, nuclear envelope breaks down, spindle forms), metaphase (chromosomes line up on the equator, attached to spindle fibres), anaphase (sister chromatids are pulled apart to opposite poles) and telophase (nuclear envelopes reform around two identical sets of chromosomes).
• Mitosis produces two genetically identical daughter cells and is used for growth, replacement of cells, repair of tissues and asexual reproduction.
• Telomeres protect chromosome ends and shorten with repeated division; stem cells can divide and differentiate into specialised cell types. Uncontrolled mitosis can form a tumour, since cells divide without normal checks.

Topic 6: Nucleic Acids and Protein Synthesis

• A nucleotide is a pentose sugar, a phosphate group and a nitrogenous base. DNA is a double helix of two antiparallel strands joined by complementary base pairing and phosphodiester bonds along each backbone.
• DNA replication is semi-conservative: each new molecule keeps one original strand and one newly made strand. DNA polymerase builds the new strands and DNA ligase joins fragments on the lagging strand.
• ATP is itself a phosphorylated nucleotide and the immediate energy source for energy-requiring processes in the cell.
• Protein synthesis has two stages. In transcription, RNA polymerase copies the template strand of a gene into a primary RNA transcript, which is processed by removing introns and keeping exons to form mRNA. In translation, ribosomes read mRNA codons and tRNA molecules bring the matching amino acids, joined by peptide bonds into a polypeptide.
• The genetic code is a triplet code: each codon of three bases codes for one amino acid, with start and stop codons marking the beginning and end of coding. Gene mutations include substitution, insertion and deletion of bases; insertions and deletions shift the reading frame and usually change the protein more severely.

Topic 7: Transport in Plants

• Xylem vessels are dead, hollow, lignified tubes that carry water and mineral ions upwards; phloem sieve tubes, supported by companion cells, carry sucrose and amino acids from sources to sinks.
• The apoplast pathway runs through cell walls and spaces outside membranes; the symplast pathway runs through the cytoplasm connected by plasmodesmata. The Casparian strip, made of suberin in the endodermis, blocks the apoplast route and forces water into cells.
• Transpiration is water loss from leaves, mainly through stomata. The cohesion-tension mechanism explains upward movement: evaporation pulls a continuous column of water up the xylem.
• Xerophytic adaptations reduce water loss, for example sunken stomata, a thick cuticle, rolled leaves and reduced leaf surface area.
• Translocation is mass flow in the phloem: sucrose is actively loaded at a source, water follows by osmosis, pressure pushes sap towards a sink, and sucrose is unloaded and used or stored there.

Topic 8: Transport in Mammals

• Mammals have a closed, double circulation: blood passes through the heart twice per circuit, once for the pulmonary circulation to the lungs and once for the systemic circulation to the body.
• Arteries have thick muscular and elastic walls for high pressure; veins have thin walls and valves to prevent backflow; capillaries have walls one cell thick for fast exchange.
• The cardiac cycle runs through atrial systole, ventricular systole and diastole, with valves preventing backflow. The left ventricle wall is thicker than the right because it pumps blood around the whole body.
• Heart rhythm is set by the sinoatrial node, which initiates impulses; the atrioventricular node delays them briefly, then the bundle of His and Purkyne tissue spread excitation through the ventricles so they contract from the base upwards.
• Haemoglobin carries oxygen: loading happens where oxygen partial pressure is high and unloading where it is low and carbon dioxide concentration is high. The Bohr shift describes how higher carbon dioxide concentration lowers haemoglobin’s affinity for oxygen, aiding release in respiring tissues.
• Carbon dioxide is carried mainly as hydrogencarbonate ions in plasma, with the chloride shift maintaining electrical balance as ions move across the red blood cell membrane. Some carbon dioxide also binds directly to haemoglobin as carbaminohaemoglobin.

Topic 9: Gas Exchange

• Air reaches the lungs through the trachea, bronchi and bronchioles to the alveoli. Cartilage keeps larger airways open; ciliated epithelium and goblet cells trap and move mucus; smooth muscle adjusts airway diameter.
• Alveoli are tiny air sacs with walls one cell thick, a rich capillary network and a moist surface, giving a huge total surface area and a very short diffusion distance for gas exchange.
• Ventilation moves air in and out: inspiration uses contraction of the diaphragm and external intercostal muscles to increase lung volume and lower pressure, while expiration is largely passive as muscles relax.
• Oxygen diffuses from alveolar air into capillary blood down its partial pressure gradient, and carbon dioxide diffuses the opposite way; breathing rate and depth adjust to keep blood gases within a narrow range.

Topic 10: Infectious Diseases

• Transmissible diseases spread by direct contact, contaminated water or food, vectors such as mosquitoes, and airborne droplets, among other routes. Control depends on the route: clean water and sanitation for cholera, vector control and drug treatment for malaria, and case-finding plus drug treatment for tuberculosis.
• Social and economic factors affect disease spread, including crowding, access to clean water, health services, education and the cost of treatment.
• Penicillin acts on bacteria by interfering with cell wall formation, weakening the wall so the bacterium bursts. Antibiotics do not work against viruses because viruses have no bacterial cell wall or bacterial metabolism to target.
• Antibiotic resistance spreads when resistant bacteria survive treatment and pass resistance genes on. Its impact is reduced by completing prescribed courses, avoiding antibiotics for viral infections, and restricting antibiotic use in farming and medicine to cases where they are needed.

Topic 11: Immunity

• Phagocytes such as neutrophils and macrophages engulf pathogens by phagocytosis and present their antigens. The immune system distinguishes self antigens on body cells from non-self antigens on pathogens.
• B-lymphocytes produce antibodies; plasma cells secrete large quantities of a specific antibody. T-helper cells stimulate B-lymphocytes and other immune cells, while T-killer cells destroy infected body cells.
• Antibodies are Y-shaped proteins with a variable region that binds a specific antigen and a constant region that links to immune cells; binding marks the pathogen for destruction and can neutralise toxins or clump pathogens together.
• Memory cells formed in the first response give long-term immunity, so a second exposure to the same pathogen triggers a faster and stronger response.
• Active immunity comes from making your own antibodies after infection or vaccination and lasts a long time; passive immunity comes from receiving ready-made antibodies, for example across the placenta or in breast milk, and is short-lived. Vaccination programmes reduce disease by building herd immunity in a population.
• Monoclonal antibodies are made by the hybridoma method, fusing an antibody-producing B-lymphocyte with a tumour cell so the line keeps dividing and secreting one identical antibody. They are used in diagnosis, for example pregnancy tests, and in treatment, for example targeting cancer cells.

A Level Topics 12–19

Topic 12: Energy and Respiration

• ATP is the universal energy currency: it is made in small, usable amounts, releases energy quickly when hydrolysed, and is used for active transport, movement and anabolic reactions such as DNA replication and protein synthesis.
• ATP is synthesised by transfer of phosphate in substrate-linked reactions and by chemiosmosis in the membranes of mitochondria and chloroplasts.
• The four stages of aerobic respiration and where they happen: glycolysis in the cytoplasm, link reaction in the mitochondrial matrix, Krebs cycle in the mitochondrial matrix, and oxidative phosphorylation on the inner mitochondrial membrane.
• Glycolysis phosphorylates glucose, splits fructose 1,6-bisphosphate (6C) into two triose phosphate molecules (3C), which are oxidised to pyruvate (3C), producing ATP and reduced NAD. The net gain from glycolysis alone is 2 ATP.
• In the link reaction, pyruvate is converted to acetyl coenzyme A (2C) with coenzyme A carrying the acetyl group. In the Krebs cycle, oxaloacetate (4C) accepts the 2C fragment to form citrate (6C), which is converted back to oxaloacetate through decarboxylation and dehydrogenation, reducing NAD and FAD.
• In oxidative phosphorylation, electrons from reduced carriers pass along the electron transport chain, releasing energy that pumps protons across the inner membrane; protons flow back through ATP synthase to make ATP, and oxygen acts as the final electron acceptor, forming water.
• Aerobic respiration gives a much greater energy yield than anaerobic respiration, which is why the syllabus does not require a detailed total ATP count for aerobic respiration of one glucose molecule — learn the comparison, not a single disputed total.
• Anaerobic respiration: mammals carry out lactate fermentation and yeast carry out ethanol fermentation. Both regenerate NAD so glycolysis can continue, but yield far less energy than aerobic respiration.
• RQ values follow from the respiration equation: carbohydrate gives RQ = 1, because equal numbers of carbon dioxide and oxygen molecules are involved, while lipids give a lower RQ because they need proportionally more oxygen. Respirometers can measure RQ in germinating seeds or small invertebrates.
• Rice copes with waterlogged roots through aerenchyma (air spaces), ethanol fermentation in roots and faster stem growth.

Topic 13: Photosynthesis

• Photosynthesis transfers light energy into chemical energy in chloroplasts. The light-dependent stage happens on thylakoid membranes in the grana; the light-independent stage (Calvin cycle) happens in the stroma.
• In non-cyclic photophosphorylation, light excites electrons in photosystem II, then photosystem I; photolysis of water replaces lost electrons and releases oxygen, and the electron flow drives ATP synthesis by chemiosmosis and reduces NADP to reduced NADP.
• Cyclic photophosphorylation uses only photosystem I and makes ATP but no reduced NADP and no oxygen, which is useful when the Calvin cycle needs extra ATP.
• Chlorophyll a, chlorophyll b, carotene and xanthophyll absorb different wavelengths; absorption spectra and action spectra show which wavelengths drive photosynthesis most strongly. Pigments are separated by chromatography and identified by their R_f values.
• Calvin cycle in order: carbon dioxide combines with ribulose bisphosphate (RuBP, 5C) to give two molecules of glycerate 3-phosphate (GP, 3C); GP is reduced to triose phosphate (TP) using ATP and reduced NADP; most TP regenerates RuBP using ATP, while the rest leaves the cycle to make carbohydrates and other organic molecules.
• Limiting factors: light intensity, carbon dioxide concentration and temperature each cap the rate when in shortest supply. Raising a factor that is not limiting has no effect until it becomes the limiting factor.

Topic 14: Homeostasis

• Homeostasis keeps internal conditions, such as blood glucose and water potential, within narrow limits so enzymes and cells work efficiently. Control uses nervous coordination, endocrine coordination or both, with receptors detecting change and effectors carrying out the response.
• Negative feedback reverses a change: a rise triggers responses that lower the value, and a fall triggers responses that raise it, keeping the condition near its set point.
• The kidney filters blood by ultrafiltration: high pressure forces water, ions, glucose, urea and small solutes out of the glomerulus into Bowman’s capsule, while cells and large proteins stay in the blood. Useful substances are then selectively reabsorbed, mainly in the proximal convoluted tubule, and urine is concentrated in the loop of Henle, distal convoluted tubule and collecting duct.
• Osmoregulation uses antidiuretic hormone (ADH): when blood water potential falls, ADH release increases, aquaporins are inserted into collecting duct walls, more water is reabsorbed, and urine volume falls. When blood water potential rises, ADH falls and more water is lost in urine.
• Blood glucose control: a rise after eating triggers insulin release, increasing glucose uptake and conversion to glycogen; a fall triggers glucagon release, increasing glycogen breakdown and glucose release into the blood. Cell signalling in this control involves G-proteins, adenylyl cyclase, cyclic AMP and enzyme cascades that amplify a small hormonal signal.
• In plants, stomata open and close through guard cell turgor changes. Abscisic acid promotes stomatal closure under water stress, reducing water loss while also limiting carbon dioxide uptake.

Topic 15: Control and Coordination

• Neurones carry impulses: sensory neurones carry impulses from receptors towards the central nervous system, intermediate neurones link neurones within it, and motor neurones carry impulses to effectors.
• At rest, a neurone membrane is polarised because sodium ions are pumped out and potassium ions diffuse out more readily, leaving the inside negative. A stimulus opens sodium channels, sodium ions flood in, and the membrane depolarises; potassium ions then leave to repolarise it, and the brief refractory period prevents impulses travelling backwards.
• Myelinated neurones conduct faster by saltatory conduction, where impulses jump between nodes of Ranvier instead of travelling along the whole membrane.
• At a cholinergic synapse, an impulse opens calcium channels in the presynaptic knob, vesicles release acetylcholine into the cleft, it binds receptors on the next membrane and triggers a new impulse, then it is broken down so the synapse can reset.
• At a neuromuscular junction, acetylcholine triggers an action potential in the muscle fibre membrane, which spreads through T-tubules and releases calcium ions from the sarcoplasmic reticulum. Calcium ions expose myosin-binding sites on actin by moving tropomyosin (controlled by troponin), myosin heads pull actin filaments past each other using ATP, and the sarcomere shortens.
• Plant coordination uses hormones: auxin promotes cell elongation in shoots by proton pumping and cell-wall acidification, and gibberellin promotes stem elongation and barley seed germination.

Topic 16: Inheritance

• Meiosis halves the chromosome number: homologous chromosomes separate in the first division and sister chromatids separate in the second, producing four haploid cells that are genetically different. Crossing over in prophase I, independent assortment and random orientation of chromosomes, and random fertilisation all create variation.
• A gene is a sequence of DNA coding for a polypeptide; its locus is its position on a chromosome; alleles are different versions of the same gene. Dominant alleles are expressed in heterozygotes, recessive alleles only in homozygotes, and codominant alleles are both expressed.
• Sex linkage places genes on sex chromosomes, so inheritance patterns differ between males and females. Autosomal linkage holds genes on the same chromosome together unless crossing over separates them, which changes expected ratios.
• Epistasis is interaction between genes at different loci, where one gene masks or modifies the effect of another. The syllabus does not require expected ratios for different types of epistasis, so learn the concept and recognise it from data rather than memorising ratio tables for it.
• The chi-squared test checks whether observed results differ significantly from expected results. Compare the calculated value with the critical value at the chosen probability level: if it exceeds the critical value, the difference is significant and the null hypothesis is rejected.
• Gene control in eukaryotes uses transcription factors and regulatory genes to switch structural genes on and off in different cells. In bacteria, the lac operon shows repressible and inducible control: genes for lactose metabolism switch on when lactose is present.
• Genes determine phenotype through proteins: examples in the syllabus include the TYR gene and albinism, the HBB gene and sickle cell anaemia, the F8 gene and haemophilia, and the HTT gene and Huntington’s disease.

Topic 17: Selection and Evolution

• Variation is continuous (for example height, showing a range with many intermediates) or discontinuous (for example blood group, with distinct categories). Continuous variation is strongly influenced by environment and many genes; discontinuous variation is usually controlled by one or a few genes.
• Natural selection works through variation, competition, differential survival and reproduction, and inheritance of advantageous alleles. Stabilising selection favours the average, directional selection favours one extreme, and disruptive selection favours both extremes.
• Genetic drift, the founder effect and the bottleneck effect change allele frequencies by chance, especially in small populations. Antibiotic resistance in bacteria is natural selection in action: resistant bacteria survive treatment and pass resistance on.
• The Hardy–Weinberg principle applies only when a population is large, mating is random, and there is no mutation, migration or selection. Start from the recessive phenotype frequency (q²), take its square root for q, then p = 1 − q.
• The t-test compares the means of two samples to judge whether a difference is significant; the syllabus provides its formula, so learn when to use it rather than memorising it.
• Evolution is change in allele frequencies in a gene pool over generations. Speciation needs reproductive isolation: allopatric speciation follows geographic separation, while sympatric speciation happens within one area, for example through ecological or behavioural isolation. DNA sequence evidence reveals evolutionary relationships.
• Artificial selection (selective breeding) is humans choosing parents with desired traits, for example disease resistance in wheat and rice, higher yield in maize and higher milk yield in dairy cattle.

Topic 18: Classification, Biodiversity and Conservation

• Taxonomic hierarchy in order: domain, kingdom, phylum, class, order, family, genus, species. The three-domain system is Archaea, Bacteria and Eukarya; within the Eukarya domain the syllabus covers the four kingdoms Protoctista, Fungi, Plantae and Animalia.
• Species concepts differ: the biological concept defines species by interbreeding to give fertile offspring, the morphological concept by observable structure, and the ecological concept by niche. Viruses are classified separately, by nucleic acid type and whether the genome is single- or double-stranded DNA or RNA.
• Biodiversity covers genetic diversity within a species, species diversity within a habitat, and ecosystem diversity across habitats. Sampling methods include frame quadrats, line transects, belt transects and mark-release-recapture.
• Spearman’s rank correlation and Pearson’s linear correlation test relationships between two variables, for example how a biotic or abiotic factor affects species distribution. Their formulae are provided in the exam, so learn which test fits the data type.
• Conservation threats include habitat loss and degradation, hunting, competition from invasive species and climate change. Conservation methods include zoos, botanic gardens, national and marine parks, frozen zoos, seed banks, IVF, embryo transfer and surrogacy, alongside international agreements such as CITES and the IUCN Red List framework.

Topic 19: Genetic Technology

• Genes are obtained by cutting donor DNA with restriction endonucleases, making genes from mRNA using reverse transcriptase, or synthesising them chemically. Sticky ends are joined by DNA ligase into plasmids carrying a promoter and a marker gene, then transferred into host cells.
• PCR amplifies a chosen DNA sequence using primers, DNA polymerase (Taq polymerase, which survives high temperatures) and repeated heating and cooling cycles. Gel electrophoresis then separates the fragments for analysis.
• Microarrays compare gene expression by testing many genes at once, and genome sequence databases let researchers compare genes and proteins across species.
• Medical uses include recombinant human insulin, factor VIII for haemophilia treatment, and adenosine deaminase for severe combined immunodeficiency (SCID). Genetic screening tests for alleles such as BRCA1 and BRCA2, Huntington’s disease and cystic fibrosis, and gene therapy aims to add a working gene copy to treat inherited disease.
• Agricultural uses include GM salmon, herbicide-resistant soybean and insect-resistant cotton, which can improve yield and food quality but raise social and ethical questions about safety, labelling, effects on wild species and control of seed supply.
• Gene editing can insert, delete or replace DNA sequences, which differs from older genetic modification because it targets a precise location in the genome.

Keep Revising

Biology at this level rewards processes learned in order, not isolated facts. For each topic, practise writing the sequence from a blank page: the stages of respiration and photosynthesis, the cardiac cycle, the nephron, the action potential, meiosis, and the Calvin cycle. Then practise the numbers: magnification conversions, RQ from a respiration equation, a chi-squared test from a cross, Hardy–Weinberg frequencies from a phenotype count, a Lincoln index estimate and a Simpson’s index calculation. When an answer needs a definition, state it in full and use the syllabus term — vague wording loses marks even when the idea is right. Finally, revisit the topics that link together, such as enzymes with respiration, membranes with transport, and inheritance with selection, because exam questions often cross topic boundaries. For the other boards, see the GCSE Biology Formula Sheet, the IGCSE Biology Formula Sheet and the AP Biology Formula Sheet, or return to the Biology MCQs hub.

A-Level Biology Section MCQs

Topic-wise practice questions for Cambridge International AS & A Level Biology 9700 — 30 MCQs per topic with answers and explanations.

• Cell structure
• Biological molecules
• Enzymes
• Cell membranes and transport
• The mitotic cell cycle
• Nucleic acids and protein synthesis
• Transport in plants
• Transport in mammals
• Gas exchange
• Infectious diseases
• Immunity
• Energy and respiration
• Photosynthesis
• Homeostasis
• Control and coordination
• Inheritance
• Selection and evolution
• Classification, biodiversity and conservation
• Genetic technology