MATSEC IM Biology cheat sheet

Prokaryotic cells lack membrane-bound organelles and a nucleus; their DNA is a single circular chromosome plus plasmids, and ribosomes are 70S.

Eukaryotic ribosomes are 80S (60S + 40S subunits); the mitochondrion and chloroplast contain 70S ribosomes, evidence for endosymbiotic origin.

Magnification = image size ÷ actual size; use the same units on both sides before dividing.

Surface area to volume ratio falls as a cell enlarges, limiting diffusion-based exchange, which is why large cells divide or fold their membranes.

Enzyme activity peaks at optimum pH and temperature; above optimum temperature denaturation of the active site removes complementary shape and activity is not restored on cooling.

Competitive inhibitors raise the substrate concentration needed for a given rate; non-competitive inhibitors bind elsewhere and lower the maximum rate.

Water potential ψ = ψs (solute) + ψp (pressure); pure water at atmospheric pressure has ψ = 0, and water moves from higher to lower ψ.

ATP hydrolysis releases about 30 kJ per mole under cellular conditions; ATP is resynthesised by condensation with inorganic phosphate during respiration.

Test results: reducing sugar gives a brick-red precipitate with Benedict's after heating; starch gives blue-black with iodine; protein gives violet with Biuret; lipid gives a translucent emulsion in the emulsion test.

DNA replication is semi-conservative: helicase unwinds, DNA polymerase adds nucleotides 5' to 3', and each daughter duplex keeps one parental strand.

Transcription makes mRNA from the template strand; translation reads mRNA codons 5' to 3' against tRNA anticodons at the ribosome.

A monohybrid cross of two heterozygotes (Aa × Aa) gives a 3:1 phenotype ratio and 1:2:1 genotype ratio for complete dominance.

A test cross with a homozygous recessive reveals the genotype of a dominant-phenotype individual; a 1:1 offspring ratio indicates a heterozygote.

Dihybrid heterozygote cross (AaBb × AaBb) with independent assortment gives 9:3:3:1; deviation from this suggests linkage.

Sex-linked recessive traits appear more often in males because they carry one X chromosome, so one recessive allele is expressed.

Hardy-Weinberg: p + q = 1 and p² + 2pq + q² = 1, where p and q are allele frequencies and q² is the frequency of homozygous recessives.

Natural selection requires heritable variation, differential survival or reproduction, and change in allele frequency across generations.

Mutation, gene flow, genetic drift and non-random mating are the main agents that disturb Hardy-Weinberg equilibrium.

Transpiration pull depends on cohesion between water molecules, adhesion to xylem walls and tension from evaporation at the leaf; the transpiration stream is driven by water potential gradients.

Stomata open when guard cells take up K+ and water, becoming turgid; they close when guard cells lose water and become flaccid, often in response to ABA.

Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2; light-dependent reactions in thylakoids make ATP and NADPH, the Calvin cycle in the stroma fixes CO2.

Aerobic respiration yields about 30-32 ATP per glucose in eukaryotes; anaerobic respiration in muscle yields lactate and about 2 ATP per glucose.

Mammalian heart: the SA node sets the rhythm, the AV node delays the impulse, and the bundle of His and Purkinje fibres conduct it to the ventricles.

Cardiac output = heart rate × stroke volume; stroke volume rises with venous return and with sympathetic stimulation.

Nephron: ultrafiltration in the glomerulus, selective reabsorption of glucose and most water in the proximal tubule, and osmoregulation via ADH acting on the collecting duct.

Neurone impulse: depolarisation opens Na+ channels, repolarisation opens K+ channels; the refractory period enforces one-way conduction and limits impulse frequency.

Homeostasis uses negative feedback: a receptor detects deviation, a coordination centre compares to a set point, and an effector reverses the change.

A population's growth is exponential when resources are unlimited (dN/dt = rN) and logistic when a carrying capacity K applies (dN/dt = rN(K − N)/K).

Energy transfer between trophic levels is about 10% efficient, so food chains rarely exceed four or five levels.

Gross primary productivity minus respiratory losses equals net primary productivity; NPP is the energy available to consumers.

The carbon cycle moves carbon by photosynthesis, respiration, combustion, decomposition and dissolution in oceans; nitrogen fixation, nitrification, denitrification and decomposition move nitrogen.

Eutrophication sequence: nutrient enrichment, algal bloom, death and decomposition, oxygen depletion, death of aerobic animals.

Biodiversity indices: species richness counts species present; Simpson's index D = 1 − Σ(n/N)² rises with diversity, and a value near 1 indicates high diversity.

Human health risk factors include smoking (lung cancer, CHD), high salt intake (hypertension), obesity and lack of exercise (type 2 diabetes), and UV exposure (skin cancer).

Antibiotic resistance spreads by natural selection under antibiotic pressure plus horizontal gene transfer of resistance plasmids between bacteria.

Conservation strategies: in-situ protection of habitats and corridors, ex-situ seed banks and captive breeding, and sustainable management of exploited populations.

Mitosis stages in order: prophase, metaphase, anaphase, telophase; in metaphase chromosomes align at the equator, and in anaphase centromeres separate.

Mitosis produces two genetically identical diploid cells; meiosis has two divisions and produces four haploid cells that are genetically varied.

Meiosis I crossing over in prophase I and independent assortment in metaphase I are the main sources of genetic variation in gametes.

Diffusion rate increases with steeper concentration gradient, higher temperature, larger surface area and shorter diffusion distance, and is faster for smaller molecules.

Osmosis is the net movement of water across a partially permeable membrane from higher to lower water potential.

Active transport uses ATP and carrier proteins, can move substances against a concentration gradient, and is saturable.

Plasmolysis occurs when a plant cell loses water to a solution of lower water potential; the protoplast shrinks away from the cell wall.

Mitotic index = number of cells with visible chromosomes ÷ total cells counted, used to compare growth or tumour tissue.

Osmolarity comparisons: an animal cell in a hypotonic solution swells and may lyse; in a hypertonic solution it shrinks (crenation).

Blood glucose control: rising glucose triggers insulin release, which increases uptake and glycogen formation; falling glucose triggers glucagon, which promotes glycogen breakdown.

Type 1 diabetes is insulin deficiency requiring injection; type 2 diabetes is insulin resistance linked to obesity and managed with diet, exercise and medication.

Gas exchange in alveoli is efficient because of a large surface area, thin walls, moist surface and a maintained concentration gradient by blood flow.

Lung volumes: tidal volume is the air moved in one normal breath, vital capacity is the maximum voluntary breath, and residual volume cannot be exhaled.

Vaccination produces memory B and T cells, giving a faster, larger secondary response on later exposure to the same antigen.

Antibodies are proteins with specific binding sites that bind antigens, agglutinating pathogens and marking them for phagocytosis.

Surface area to volume ratio, ventilation and blood supply determine the rate of heat loss; sweating and vasodilation increase heat loss, shivering and vasoconstriction reduce it.

Ecological sampling: quadrats estimate population size by mean density × area, and mark-recapture estimates N = (M × C) ÷ R, where R is marked recaptures.

Indicator species signal pollution: lichens indicate SO2 levels, and mayfly larvae indicate clean, well-oxygenated water.

Carbohydrates: monosaccharides are reducing sugars, disaccharides form by condensation with a glycosidic bond, and polysaccharides such as starch and glycogen are storage polymers.

Proteins are polymers of amino acids joined by peptide bonds; primary structure is the sequence, secondary is alpha helix or beta sheet, tertiary is 3D folding, quaternary is multiple polypeptides.

Lipids are non-polar and dissolve in organic solvents; triglycerides are glycerol plus three fatty acids joined by ester bonds.

A colorimeter measures absorbance to quantify a colour change; a calibration curve of known concentrations converts absorbance to concentration.

Chromatography separates pigments by differing solubility in the solvent and affinity for the stationary phase; Rf = distance moved by spot ÷ distance moved by solvent front.

Serial dilution: each step multiplies concentration by the same factor, so a 1:10 series gives 10⁻¹, 10⁻², 10⁻³ and so on.

Benedict's quantitative test uses a calibration series because the precipitate colour intensity relates to reducing sugar concentration.

Enzyme rate is measured as product formed or substrate used per unit time; initial rate is taken from the steepest linear part of the curve.

A quadrat is placed randomly to avoid bias; a transect is used when a gradient such as a shore or woodland edge is being studied.

Mark-recapture assumptions: marked individuals mix randomly, marks are not lost, and marking does not affect survival or catchability.

Pyramids of numbers can invert (one tree supporting many insects); pyramids of energy never invert because energy is lost at each transfer.

Succession: pioneer species colonise bare substrate, modify conditions, and are replaced until a stable climax community forms.

The greenhouse effect is enhanced by CO2 and methane from combustion, deforestation and agriculture, raising mean global temperature.

Acid deposition forms when SO2 and NOx react with water vapour to give sulfuric and nitric acids, damaging leaves and mobilising aluminium in soils.

Deforestation reduces carbon storage, increases soil erosion and reduces transpiration, which can lower local rainfall.

Conservation of endangered species requires large effective population size, genetic diversity, habitat area and control of hunting and invasive species.

Human population growth is driven by falling death rates while birth rates remain high, producing a rapid expansion phase before demographic transition.

Chi-squared test: χ² = Σ((O − E)² ÷ E), with degrees of freedom = number of classes − 1, used to test whether observed ratios fit expected ratios.

Probability of two independent events both occurring is the product of their separate probabilities.

A pedigree showing affected males only, with no affected females, suggests X-linked recessive inheritance.

Restriction enzymes cut DNA at specific recognition sequences, producing sticky ends used in gene cloning.

Gel electrophoresis separates DNA fragments by size; smaller fragments move further through the gel towards the positive electrode because DNA is negatively charged.

PCR uses denaturation, primer annealing and extension by a heat-stable DNA polymerase to amplify DNA exponentially.

Genetic modification steps: identify the gene, cut with restriction enzymes, insert into a vector such as a plasmid, transfer to host cells, and select transformed cells.

Codominance gives both phenotypes expressed in heterozygotes (AB blood group); incomplete dominance gives an intermediate phenotype.

Xylem transports water and mineral ions upward and is dead, lignified tissue; phloem transports sucrose and amino acids in both directions and is living tissue with sieve plates.

Translocation is driven by pressure flow: sucrose loaded at the source lowers water potential, water enters, and the resulting pressure pushes sap to the sink.

Root hair cells increase surface area for absorption of water and mineral ions; nitrate is needed for amino acid and protein synthesis.

Photosynthesis limiting factors: light intensity, CO2 concentration and temperature; the factor in shortest supply limits the rate.

Insect-pollinated flowers have large, scented, coloured petals and sticky pollen; wind-pollinated flowers have small petals, exposed anthers and feathery stigmas.

Seed germination requires water, oxygen and a suitable temperature; water activates enzymes that break down stored food reserves.

Plant growth substances: auxins promote cell elongation and phototropism; gibberellins promote stem elongation and seed germination.

Fertilisation in flowering plants: pollen tube grows down the style, and the male gamete fuses with the egg in the ovule to form a zygote.

The menstrual cycle: FSH stimulates follicle development, oestrogen thickens the uterus lining, LH triggers ovulation, and progesterone maintains the lining.

Fertilisation occurs in the oviduct; the zygote divides by mitosis to form a blastocyst that implants in the uterus lining.

Contraceptive pills containing oestrogen and progesterone inhibit FSH and LH release, preventing follicle development and ovulation.

Innate defences include skin, mucus, stomach acid and phagocytes; adaptive immunity involves B lymphocytes producing antibodies and T lymphocytes killing infected cells.

Antibiotic resistance arises because mutations conferring resistance are selected when antibiotics kill susceptible bacteria; the resistant bacteria then multiply.

Pathogen transmission routes: airborne droplets, contaminated water and food, direct contact, vectors and body fluids.

Cholera is caused by Vibrio cholerae and causes watery diarrhoea and dehydration; oral rehydration therapy replaces water and salts.

Malaria is caused by Plasmodium transmitted by female Anopheles mosquitoes; control targets mosquito larvae and uses bed nets.

Herd immunity protects unvaccinated individuals when a high proportion of the population is immune, reducing transmission.

A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring.

Binomial naming uses genus (capitalised) then species (lower case), both italicised, for example Homo sapiens.

The five-kingdom model uses Prokaryotae, Protoctista, Fungi, Plantae and Animalia; the three-domain model separates Bacteria, Archaea and Eukarya.

Fossils provide evidence of evolution through changes in structure over time and can be dated to show succession of forms.

Homologous structures share a common origin but may differ in function; analogous structures have similar function but different origins.

Antibiotic and pesticide resistance are observable examples of natural selection occurring in short timescales.

Speciation occurs when populations become reproductively isolated, for example by geographical separation, and diverge by mutation and selection.

Classification uses observable features and biochemical evidence such as DNA and protein sequences to infer evolutionary relationships.

Biodiversity loss is driven by habitat destruction, overexploitation, pollution, invasive species and climate change.

Glycolysis occurs in the cytoplasm, converts glucose to pyruvate and yields a net 2 ATP and 2 NADH per glucose.

The Krebs cycle occurs in the mitochondrial matrix and yields reduced coenzymes NADH and FADH2 that feed the electron transport chain.

Oxidative phosphorylation occurs on the inner mitochondrial membrane; the electron transport chain creates a proton gradient that drives ATP synthase.

Anaerobic respiration in yeast produces ethanol and CO2; in mammalian muscle it produces lactate, allowing glycolysis to continue by regenerating NAD.

Photosynthetic pigments absorb mainly red and blue light and reflect green; chlorophyll a and b absorb at slightly different wavelengths.

Light-dependent reactions split water (photolysis), releasing oxygen and providing electrons, and produce ATP and reduced NADP.

The Calvin cycle uses ATP and reduced NADP to fix CO2 onto ribulose bisphosphate via rubisco, forming triose phosphate.

Net primary productivity = gross primary productivity − respiration; it limits the biomass available to consumers.

Respiratory quotient = CO2 produced ÷ O2 consumed; about 1.0 for carbohydrate and about 0.7 for lipid.

Variables: independent variable is changed, dependent variable is measured, and controlled variables are kept constant to make the comparison valid.

A null hypothesis states there is no significant difference or correlation; it is tested statistically rather than proved.

Precision refers to repeatability of measurements; accuracy refers to closeness to the true value.

Percentage change = (final value − initial value) ÷ initial value × 100.

Aseptic technique: sterilise equipment, flame the neck of containers, and work near a flame to reduce contamination.

Rate calculations use the tangent to a curve at a given time when the graph is not linear.

A line of best fit and correlation do not establish causation; a controlled experiment is needed to show cause.

Ethical and safety considerations in biology practicals include consent for human data, humane treatment of animals, and disposal of cultures by autoclaving.

Units and significant figures should be consistent; magnification answers should be given in the same unit as the scale bar.

Negative feedback reverses a deviation from a set point; positive feedback amplifies it, as in oxytocin during childbirth.

Thermoregulation: the hypothalamus detects blood temperature; responses include sweating, vasodilation, shivering and vasoconstriction.

Blood glucose is monitored by the pancreas; insulin lowers glucose and glucagon raises it, acting on liver and muscle cells.

Osmoregulation: the hypothalamus detects plasma water potential, and ADH from the posterior pituitary increases collecting duct permeability to water.

The reflex arc order is receptor, sensory neurone, synapse, relay neurone, motor neurone, effector.

Synaptic transmission: an impulse releases neurotransmitter into the cleft, which binds receptors on the postsynaptic membrane and may excite or inhibit.

The endocrine system uses hormones carried in blood to target cells with complementary receptors; responses are slower but longer lasting than nervous responses.

Phototropism is caused by auxin redistribution to the shaded side, increasing cell elongation there and bending the shoot towards light.

Plant responses to touch and gravity (thigmotropism, geotropism) are also controlled by growth substances rather than nerves.

Bacteria reproduce by binary fission; in favourable conditions populations grow exponentially, with the rate depending on temperature and nutrients.

A culture growth curve has lag, log, stationary and decline phases; the log phase gives the fastest growth rate.

Sterilisation kills all microorganisms; disinfection reduces numbers on surfaces but may not kill spores.

Antibiotics such as penicillin target bacterial cell walls or ribosomes and are ineffective against viruses.

Fermenters control temperature, pH, oxygen supply and nutrient levels to maximise product yield from microorganisms.

Yogurt and cheese production rely on bacterial fermentation of lactose to lactic acid, lowering pH and curdling milk.

Bread making uses yeast anaerobic respiration, producing CO2 that raises the dough and ethanol that evaporates during baking.

Monoclonal antibodies are produced from a single clone of hybridoma cells and bind one specific antigen.

Gene therapy delivers a functional allele to cells with a defective allele, but delivery, immune response and long-term expression remain limiting problems.

Random sampling uses random coordinates in the area to avoid selection bias; systematic sampling uses a belt transect across a gradient.

Population density = number of individuals ÷ area sampled; the mean of several quadrats gives a better estimate than one.

Percentage cover and frequency are used for plants that are hard to count individually.

Abiotic factors measured in fieldwork include light intensity, soil pH, soil moisture, temperature and oxygen concentration in water.

A kite diagram shows the distribution of species along a transect and is used to display zonation.

Sustainable management of fisheries uses quotas, mesh size limits and protected areas to allow breeding stocks to recover.

Reforestation and reduced deforestation increase carbon sequestration and reduce soil erosion and flooding risk.

Recycling and reducing demand for finite resources reduce habitat destruction associated with extraction.

Environmental impact assessments predict effects of a project and propose mitigation before approval.

The enhanced greenhouse effect is linked to rising atmospheric CO2 from fossil fuel combustion, cement production and deforestation.

Methane is a more potent greenhouse gas per molecule than CO2 but has a shorter atmospheric residence time.

Climate change effects include rising sea levels from thermal expansion and ice melt, changed species distributions and more extreme weather.

Air pollutants: particulates from combustion damage lung tissue; carbon monoxide binds haemoglobin and reduces oxygen transport.

Water pollution indicators include biochemical oxygen demand, which rises with organic pollution, and indicator species such as lichens.

Deforestation and intensive agriculture reduce soil fertility and increase erosion and runoff.

Conservation of biodiversity requires habitat protection, legal protection of species and international agreements on trade and emissions.

Reducing, reusing and recycling materials lowers energy demand and associated emissions.

Sustainable development meets present needs without compromising the ability of future generations to meet theirs.

DNA is a double helix with complementary base pairing: adenine pairs with thymine (two hydrogen bonds), guanine with cytosine (three hydrogen bonds).

RNA contains ribose and uracil instead of thymine and is usually single-stranded; mRNA carries the code, tRNA carries amino acids, rRNA forms ribosomes.

The genetic code is degenerate, meaning most amino acids are coded by more than one triplet, and it is non-overlapping and universal.

A gene mutation is a change in base sequence; substitution may alter one codon, while insertion or deletion causes a frameshift.

Sickle cell anaemia results from a substitution in the beta-globin gene, changing glutamic acid to valine and altering haemoglobin shape.

Protein synthesis: mRNA is transcribed in the nucleus, spliced, exported, and translated by ribosomes into a polypeptide chain.

The lac operon is an example of gene regulation in bacteria, induced when lactose is present and glucose is absent.

DNA profiling uses repeated sequences to compare individuals and is used in forensics and paternity testing.

Mammalian circulation is a double system: the pulmonary circuit carries blood to the lungs and the systemic circuit to the body.

Arteries carry blood away from the heart under high pressure with thick elastic walls; veins carry blood back to the heart with valves preventing backflow.

Capillaries have walls one cell thick to allow rapid exchange by diffusion between blood and tissue fluid.

The left ventricle has a thicker wall than the right because it pumps blood around the whole body.

Haemoglobin binds oxygen cooperatively, giving an S-shaped dissociation curve; the curve shifts right with higher CO2 (Bohr shift), releasing more oxygen to active tissues.

The heart's cardiac cycle: atrial systole, ventricular systole, diastole; valves open and close due to pressure differences.

Transpiration rate increases with higher temperature, wind speed and light intensity, and with lower humidity.

Xylem vessels are lignified and dead, providing support and a continuous column for water movement.

Phloem sieve tubes have companion cells that supply ATP for active loading of sucrose.

Asexual reproduction produces genetically identical offspring by mitosis; sexual reproduction produces genetically varied offspring by meiosis and fertilisation.

In mammals, the placenta allows exchange of nutrients, oxygen and waste between maternal and fetal blood without mixing them.

Human gestation is about 38-40 weeks; organogenesis occurs mainly in the first trimester.

Growth can be measured by increase in mass or length; a growth curve plots size against time and may show sigmoid shape.

Plant growth occurs at meristems: apical meristems lengthen shoots and roots, and lateral meristems increase girth.

Cell differentiation produces specialised cells with specific structures and functions, controlled by gene expression.

Cloning produces genetically identical organisms; cuttings and tissue culture are plant cloning methods.

Selective breeding chooses parents with desired traits, reducing genetic diversity over generations.

Adaptations are structural, behavioural or physiological features that increase survival and reproductive success in a habitat.

Xerophytes reduce water loss with thick cuticles, sunken stomata, rolled leaves and reduced leaf area.

Hydrophytes have large air spaces for buoyancy and thin cuticles because water loss is not limiting.

Behavioural adaptations include migration, hibernation and courtship displays that increase survival or reproductive success.

Courtship behaviour allows species recognition and synchronises mating, reducing wasted reproductive effort.

Innate behaviour is inherited and stereotyped; learned behaviour is modified by experience.

Taxonomy groups organisms by shared characteristics into kingdom, phylum, class, order, family, genus and species.

A dichotomous key uses paired contrasting statements to identify an organism step by step.

Enzymes are biological catalysts that lower activation energy by providing an alternative reaction pathway; they are not consumed.

The lock-and-key and induced-fit models describe substrate binding to the active site; induced fit involves a change in active site shape on binding.

Enzyme activity is affected by substrate concentration, enzyme concentration, temperature, pH and inhibitors.

At low substrate concentration the rate is proportional to substrate concentration; at high concentration the enzyme is saturated and the rate plateaus.

Immobilised enzymes are attached to a support, allowing reuse and continuous processes, and are used in lactose-free milk production.

Metabolic pathways are sequences of enzyme-catalysed reactions; a missing enzyme blocks the pathway and may cause a genetic disease such as phenylketonuria.

Coenzymes such as NAD and FAD carry electrons and hydrogen between reactions in respiration and photosynthesis.

Enzyme inhibitors can be reversible or irreversible; heavy metal ions often denature enzymes irreversibly.

Allele frequency is the proportion of one allele among all alleles at a locus in a population.

Hardy-Weinberg equilibrium assumes a large population, random mating, no mutation, no migration and no selection.

Genetic drift has a larger effect in small populations, where chance can remove alleles regardless of fitness.

Founder effect occurs when a small group colonises a new area, carrying only part of the original gene pool.

Pedigree analysis: an affected child from unaffected parents indicates a recessive allele; affected parents with an unaffected child indicates dominance.

Amniocentesis and chorionic villus sampling test fetal cells for chromosomal and genetic disorders.

Carrier testing identifies heterozygous individuals who do not show a recessive disorder.

Multiple alleles and codominance explain the ABO blood group system with alleles IA, IB and i.

Producers convert light energy to chemical energy; consumers transfer energy through trophic levels with about 10% efficiency.

Decomposers break down dead organic matter, releasing mineral ions and carbon dioxide back to the environment.

The nitrogen cycle: nitrogen fixation by Rhizobium and lightning, nitrification by nitrifying bacteria, denitrification by denitrifying bacteria.

The carbon cycle includes photosynthesis, respiration, decomposition, combustion and ocean dissolution.

The phosphorus cycle has no significant gaseous phase; phosphorus is released by weathering and recycling of organic matter.

Energy is lost at each trophic level through respiration, excretion and uneaten parts.

Food webs are more realistic than food chains because they show multiple feeding relationships.

Keystone species have a disproportionate effect on community structure relative to their abundance.

Light microscopes resolve about 200 nm; electron microscopes resolve much smaller structures but require dead, dehydrated specimens.

Magnification is the degree of enlargement; resolution is the ability to distinguish two close points.

Organelles: nucleus holds DNA, mitochondria carry out aerobic respiration, ribosomes synthesise proteins, chloroplasts carry out photosynthesis.

The cell surface membrane is a phospholipid bilayer with embedded proteins, described by the fluid mosaic model.

Plant cells have a cellulose cell wall, chloroplasts and a large permanent vacuole; animal cells lack these.

The Golgi apparatus modifies and packages proteins into vesicles for secretion.

Lysosomes contain hydrolytic enzymes that digest worn-out organelles and ingested material.

Cell fractionation uses differential centrifugation to separate organelles by density.

Gas exchange surfaces have a large area, thin barrier, moist surface and a maintained concentration gradient.

Insects use tracheae and spiracles; fish use gills with counter-current flow of water and blood to maximise oxygen uptake.

Counter-current flow in fish gills means water and blood flow in opposite directions, maintaining a diffusion gradient along the whole gill.

Mammalian lungs contain alveoli with a large total surface area and a rich capillary network.

Ventilation in mammals is driven by pressure changes from the diaphragm and intercostal muscles.

Breathing rate and depth increase during exercise to remove CO2 and supply more O2.

Smoking damages alveoli (emphysema), reduces surface area and increases diffusion distance.

Plants exchange gases through stomata and lenticels; the leaf's flat shape maximises surface area for light and gas exchange.

FSH and LH are gonadotrophins released by the anterior pituitary; oestrogen and progesterone are ovarian hormones.

Oestrogen has a positive feedback effect on LH before ovulation, causing the LH surge.

Progesterone maintains the uterus lining and inhibits FSH and LH during pregnancy.

In-vitro fertilisation involves hormonal stimulation, egg collection, fertilisation outside the body and embryo transfer.

Clomifene is used to stimulate ovulation in some fertility treatments.

Contraception can be hormonal (pills, implants) or barrier (condoms, diaphragms) or surgical (vasectomy, tubal ligation).

The placenta secretes hCG, which maintains the corpus luteum and progesterone production in early pregnancy.

Menstruation occurs when progesterone falls and the uterus lining breaks down.

Antigens are molecules on the surface of pathogens that trigger an immune response; antibodies bind specifically to antigens.

Phagocytes engulf pathogens by phagocytosis; lymphocytes provide specific immunity.

Memory cells give a faster and larger secondary response, which is the basis of vaccination.

Active immunity involves the body producing its own antibodies; passive immunity involves receiving antibodies, giving short-term protection.

Vaccines contain weakened or inactivated pathogens, antigens or toxoids that stimulate an immune response without causing disease.

Antibiotics target bacterial structures; misuse promotes antibiotic resistance.

Hygiene, clean water, sanitation and vector control reduce disease transmission.

Epidemiological studies identify risk factors by comparing disease frequency between exposed and unexposed groups.

Evidence for evolution includes fossils, comparative anatomy, embryology and molecular sequences.

The fossil record shows a sequence of organisms over geological time, with simpler forms generally older.

Homologous structures indicate common ancestry; analogous structures indicate convergent evolution.

Natural selection acts on phenotypic variation; individuals with advantageous alleles survive and reproduce more.

Mutation is the ultimate source of new alleles; recombination and gene flow redistribute them.

Reproductive isolation prevents gene flow between populations and allows speciation.

Allopatric speciation involves geographical separation; sympatric speciation occurs without geographical separation.

Artificial selection by humans produces breeds and varieties with selected traits, demonstrating selection in practice.

During exercise, heart rate, stroke volume and breathing rate increase to deliver more oxygen and remove CO2.

Anaerobic respiration in muscle produces lactate, which contributes to fatigue and an oxygen debt that must be repaid after exercise.

Training increases stroke volume and capillary density and improves oxygen uptake.

Blood pressure is affected by cardiac output and peripheral resistance; high salt intake and obesity raise blood pressure.

BMI = mass in kg ÷ (height in m)², used as a crude indicator of body mass status.

Smoking increases the risk of coronary heart disease by damaging artery linings and promoting plaque formation.

Regular exercise reduces the risk of type 2 diabetes, cardiovascular disease and obesity.

Hydration and thermoregulation are important during exercise; sweating cools the body but loses water and salts.

Genetic screening identifies individuals at risk of inherited disorders, allowing informed decisions and early treatment.

Gene therapy aims to replace or supplement a defective allele, but delivery and immune response remain challenges.

Genetically modified crops can have higher yield or pest resistance, but raise concerns about gene flow and biodiversity.

Stem cells are undifferentiated cells that can differentiate into specialised cell types and are used in research and therapy.

Ethical issues in genetics include consent, confidentiality, genetic discrimination and designer babies.

DNA profiling is used in forensic identification and paternity testing.

Cloning raises ethical concerns about animal welfare and the status of cloned offspring.

Regulation of genetic technology varies between countries and involves risk assessment and public consultation.

Population size is affected by birth rate, death rate, immigration and emigration.

Carrying capacity is the maximum population size an environment can sustain indefinitely.

Density-dependent factors include food supply, disease and predation; density-independent factors include fire and drought.

Intraspecific competition occurs between members of the same species; interspecific competition occurs between different species.

Predator-prey cycles show lagged oscillations in population size.

Competitive exclusion occurs when two species compete for the same limiting resource and one outcompetes the other.

A community is all the populations of different species living and interacting in a habitat.

An ecosystem includes the community and the abiotic environment interacting together.

Fermenters maintain optimal temperature, pH, oxygen and nutrient levels for microbial growth and product formation.

Penicillin is produced by the fungus Penicillium in controlled fermentation.

Immobilised enzymes are used in continuous processes such as lactose-free milk and high-fructose syrup production.

Genetic engineering of bacteria to produce human insulin avoids reliance on animal sources.

PCR amplifies DNA in vitro using primers and a heat-stable polymerase.

Gel electrophoresis separates DNA fragments by size for analysis and profiling.

Monoclonal antibodies are used in pregnancy tests, diagnosis and targeted therapy.

Biofuels from fermentation of plant material offer renewable energy but compete with food production.

Auxins promote cell elongation and are redistributed in response to light and gravity.

Phototropism is growth towards light caused by auxin accumulating on the shaded side.

Geotropism: roots grow downwards (positive) and shoots grow upwards (negative) due to auxin distribution.

Gibberellins promote stem elongation, seed germination and fruit growth.

Abscisic acid promotes stomatal closure and seed dormancy under stress.

Ethene promotes fruit ripening and leaf fall.

Apical dominance is the suppression of lateral buds by auxin from the shoot tip.

Commercial uses of plant hormones include rooting powders, fruit ripening control and weed control.

Digestion breaks large insoluble molecules into small soluble ones for absorption.

Carbohydrases break down carbohydrates; proteases break down proteins; lipases break down lipids.

Bile emulsifies fats and neutralises stomach acid, aiding lipase action.

Villi in the small intestine increase surface area for absorption and have a rich blood supply.

Mechanical digestion by teeth and peristalsis increases surface area for enzyme action.

A balanced diet provides carbohydrates, proteins, lipids, vitamins, minerals, fibre and water.

Deficiency diseases include scurvy (vitamin C), rickets (vitamin D) and anaemia (iron).

Obesity and high saturated fat intake are linked to cardiovascular disease.

Excretion removes metabolic waste such as CO2, urea and excess salts.

The kidney nephron filters blood at the glomerulus and reabsorbs useful substances in the tubules.

Ultrafiltration occurs because high pressure forces small molecules out of the glomerulus into the capsule.

Selective reabsorption of glucose and water occurs in the proximal tubule.

ADH increases water reabsorption in the collecting duct, producing concentrated urine.

The loop of Henle creates an osmotic gradient in the medulla, enabling water reabsorption.

Dialysis removes waste products when kidney function fails.

Kidney transplants require matching tissue and immunosuppressive drugs.

Aerobic respiration uses oxygen and glucose to produce CO2, water and ATP.

Anaerobic respiration produces less ATP and lactate or ethanol.

Gas exchange in single-celled organisms occurs by diffusion across the cell surface.

Insects use tracheae; fish use gills; mammals use lungs.

The rate of diffusion depends on surface area, concentration gradient, diffusion distance and temperature.

Plants use stomata for gas exchange and close them to reduce water loss.

Respiration rate can be measured by CO2 production or oxygen consumption.

Anaerobic respiration in yeast is used in bread making and brewing.

A hypothesis is a testable statement based on observation or prior knowledge.

A control group provides a baseline for comparison and does not receive the treatment.

Randomisation reduces bias in assigning treatments or selecting samples.

Repeat measurements improve reliability and allow calculation of means and ranges.

A correlation describes a relationship between variables but does not prove causation.

Statistical tests such as chi-squared and t-tests assess whether differences are significant.

Ethical approval is required for studies involving humans or animals.

Peer review checks the validity of scientific claims before publication.

Biodiversity includes species diversity, genetic diversity and ecosystem diversity.

Species richness is the number of species in an area; evenness describes relative abundance.

Simpson's index of diversity ranges from 0 to 1, with higher values indicating greater diversity.

Habitat destruction is the main cause of biodiversity loss.

Conservation strategies include protected areas, corridors, seed banks and captive breeding.

Sustainable management balances resource use with conservation.

Invasive species can outcompete native species and reduce biodiversity.

International agreements aim to protect endangered species and habitats.

Glycolysis occurs in the cytoplasm and produces pyruvate, ATP and NADH.

The Krebs cycle occurs in the mitochondrial matrix and produces reduced coenzymes and CO2.

The electron transport chain produces most ATP via oxidative phosphorylation.

Photosynthesis occurs in chloroplasts; light reactions in thylakoids, Calvin cycle in stroma.

Chlorophyll absorbs red and blue light and reflects green.

Limiting factors of photosynthesis include light intensity, CO2 and temperature.

Respiratory quotient indicates the substrate being respired.

ATP is the universal energy currency of cells.

Genotype is the genetic makeup; phenotype is the observable characteristic.

Homozygous individuals have two identical alleles; heterozygous individuals have two different alleles.

Dominant alleles are expressed when present; recessive alleles are expressed only when homozygous.

Punnett squares predict offspring ratios from parental genotypes.

A monohybrid cross of heterozygotes gives a 3:1 phenotype ratio.

Codominance and incomplete dominance produce intermediate or combined phenotypes.

Sex-linked traits are carried on sex chromosomes and show different patterns in males and females.

Test crosses determine unknown genotypes.

Variation within populations arises from mutation and sexual reproduction.

Natural selection acts on variation, favouring individuals with advantageous traits.

Over generations, allele frequencies change and populations adapt to their environment.

Fossils provide evidence of past life and evolutionary change.

Homologous structures show common ancestry; analogous structures show convergent evolution.

Speciation occurs when populations become reproductively isolated.

Antibiotic resistance is a modern example of natural selection.

Artificial selection by humans demonstrates selective breeding.

Pollution can be air, water or land based and affects organisms and ecosystems.

Eutrophication results from excess nutrients causing algal blooms and oxygen depletion.

Acid rain forms from sulfur dioxide and nitrogen oxides and damages ecosystems.

The greenhouse effect is enhanced by CO2 and methane emissions.

Deforestation reduces carbon storage and increases erosion.

Conservation and sustainable management aim to reduce human impact.

Recycling and renewable energy reduce resource depletion.

Environmental impact assessments predict and mitigate damage.

Mitosis produces genetically identical cells for growth and repair.

Meiosis produces haploid gametes with genetic variation.

Crossing over and independent assortment increase genetic variation.

Cancer results from uncontrolled cell division due to mutations in genes controlling the cell cycle.

Tumours can be benign or malignant; malignant tumours invade and spread.

Risk factors for cancer include smoking, radiation and some viruses.

Treatment options include surgery, chemotherapy and radiotherapy.

Screening and early detection improve outcomes.

The nervous system uses electrical impulses for rapid responses.

The endocrine system uses hormones for slower, longer-lasting responses.

Reflex actions are rapid, automatic responses that protect the body.

Synapses transmit impulses between neurones using neurotransmitters.

The brain coordinates responses and processes information.

Hormones are secreted by glands and travel in the blood to target organs.

Negative feedback maintains stable internal conditions.

The hypothalamus links the nervous and endocrine systems.

Quadrats sample populations in a habitat and allow estimation of density.

Transects show how species distribution changes along a gradient.

Random sampling avoids bias in ecological studies.

Mark-recapture estimates population size using marked and recaptured individuals.

Abiotic factors such as light, temperature and soil affect distribution.

Biotic factors include competition, predation and disease.

Food chains and webs show feeding relationships and energy flow.

Pyramids of number, biomass and energy represent trophic levels.

Pathogens include bacteria, viruses, fungi and protoctists.

The body has non-specific defences such as skin, mucus and phagocytes.

Specific immunity involves lymphocytes and antibodies.

Vaccination provides active immunity and protects populations through herd immunity.

Antibiotics treat bacterial infections but not viral infections.

Lifestyle factors such as diet, exercise and smoking affect health.

Non-communicable diseases include cardiovascular disease, diabetes and cancer.

Public health measures reduce disease transmission.

DNA structure and replication are fundamental to inheritance.

The genetic code is transcribed into mRNA and translated into proteins.

Mutations can alter protein structure and function.

Genetic engineering transfers genes between organisms.

PCR amplifies DNA for analysis.

Gel electrophoresis separates DNA fragments by size.

Genetic profiling has forensic and medical applications.

Ethical considerations accompany genetic technologies.

Plants transport water and minerals in xylem and sugars in phloem.

Transpiration is driven by evaporation and cohesion-tension.

Stomata regulate gas exchange and water loss.

Animals transport oxygen and nutrients via circulatory systems.

Gas exchange surfaces are adapted for efficient diffusion.

Homeostasis maintains internal stability in animals and plants.

Hormones regulate growth, reproduction and responses.

Environmental factors influence physiological processes.