AQA A-Level Biology
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Topic 1: Biological molecules
Biological building blocks
3.1.1 - Monomers and polymersLearn how shared molecular units join into polymers, and how condensation and hydrolysis make and break the bonds between them.
3.1.2 - CarbohydratesA potato cell stores starch inside a cellulose wall. Both are chains of glucose, yet one is a compact store and the other a strong wall, and the difference starts at a single carbon atom. You also learn to test for, separate and measure carbohydrates.
3.1.3 - LipidsWhy is butter solid when olive oil pours? How can a bird cross the Pacific on stored fat? Lipid structure explains both, as well as how membranes form and how to test for lipid.
Proteins and enzymes
3.1.4.1 - Protein structureHaemoglobin dissolves and carries oxygen, while collagen forms rope-like fibres, yet both are chains drawn from the same set of twenty amino acids. Follow how sequence becomes shape and shape becomes function, then detect proteins with the Biuret test and separate amino acids by chromatography.
3.1.4.2 - EnzymesLife runs on reactions far too slow without enzymes. This lesson shows how the active site speeds them up, what changes the rate, and how enzymes shape organisms.
RP01 - Rate of an enzyme-controlled reactionTrypsin turns cloudy milk clear, and a stopwatch turns that change into a rate. Plan required practical 1, calculate rates from raw times and graphs, and judge your results.
Nucleic acids and ATP
3.1.5.1 - Structure of DNA and RNADNA and RNA are the information-carrying molecules of every living cell: DNA holds genetic information and RNA transfers it to the ribosomes. Build both from nucleotides, tell apart the bonds along and between strands, and use base pairing to work out sequences and percentages.
3.1.5.2 - DNA replicationA cell copies its DNA before it divides, and each new molecule keeps one old strand. Follow the copying mechanism, track old strands through generations, and see how heavy nitrogen tested the competing models.
3.1.6 - ATPA pump moving ions and a muscle contracting both run on energy from one small molecule. ATP's structure explains how it passes on that energy, and why a cell must keep remaking it.
Water and inorganic ions
3.1.7 - WaterMost of a cell's mass is water. Its dipole and the hydrogen bonds between its molecules explain why water can act as a solvent, a temperature buffer and a coolant, and why it holds together in plants and at water-air surfaces.
3.1.8 - Inorganic ionsInorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations. In human blood plasma, sodium ions outnumber hydrogen ions by over three million to one. Each type of ion has a specific role, depending on its proper...
Topic 2: Cells
Cell structure and study
3.2.1.1 - Eukaryotic cellsA pancreatic cell exports enzymes, a muscle cell contracts and a leaf cell captures light. Learn the structure and function of each organelle, then use them to explain specialised cells and how they build tissues, organs and systems.
3.2.1.2 - Prokaryotic cells and virusesBacteria are living cells with no nucleus; viruses are not cells at all. Learn what each is built from and how to tell them apart from structural evidence.
3.2.1.3 - Studying cellsWhy can a light microscope show a cell but not its ribosomes? Learn to measure cells, judge the detail an image can support, and isolate organelles intact.
Cell division
3.2.2 - Cell divisionEvery cell in your body came from an earlier cell. Follow the DNA through the cell cycle, mitosis and cytokinesis, then see what uncontrolled division causes, how cancer drugs slow it, how prokaryotes divide by binary fission and why viruses do not divide at all.
RP02 - Mitosis in root tipsA stained root-tip squash freezes cells at different moments of the cell cycle. Prepare one, name its stages, and use cell counts and calibrated measurements without mistaking a snapshot for a measure of growth.
Membranes and transport
3.2.3 - Transport across cell membranesA cell stays alive because its membrane lets some substances through and holds others back. You’ll see how the fluid-mosaic structure does this, the five routes across, and how specialised cells speed them up.
RP03 - Water potential of plant tissueOne sucrose concentration leaves a potato chip's mass unchanged. Make a dilution series, plot a calibration curve and use its intercept to find the water potential of the tissue.
RP04 - Membrane permeabilityBeetroot stores a purple pigment behind two membranes, so a solution that turns purple shows they have become more permeable. In this practical, you change one named variable, such as ethanol concentration, and turn that colour into an indirect measure of permeability.
Topic 3: Exchange and transport
Gas exchange
3.3.1 - Surface area to volume ratioAn amoeba takes in oxygen straight through its surface; you could not survive that way. Respiratory gases, nutrients, excretory products and heat all cross an organism's surface, and as size increases, volume outgrows that surface. This one relationship explains flattened bodies, lungs and blood...
3.3.2 - Gas exchangeAn amoeba needs no lungs, an insect pipes air straight to its muscles, and a fish takes oxygen from water. All exchange gases by diffusion, and three features keep that fast: a large surface area, a short diffusion pathway and a maintained concentration gradient. Ventilation helps maintain the gr...
Mass transport
3.3.4.1 - Mass transport in animalsDiffusion alone is too slow to supply a large animal, so mammals pump blood. This lesson follows oxygen from haemoglobin through the heart and vessels to the fluid around cells, then covers cardiac data, evidence on cardiovascular disease and pulse investigations.
RP05 - Dissecting an exchange or transport systemA real heart shows what a flat diagram can't: how thin a valve is, how much thicker one ventricle is, how the main arteries cross. You will dissect safely, read each structure as evidence of function, draw what you see, and transfer the method to lungs, gills, insects and plants.
3.3.4.2 - Mass transport in plantsPlants have no heart or pump, yet water reaches their highest leaves and sucrose reaches their roots and fruits. Xylem carries water and dissolved mineral ions from roots to leaves by a passive, tension-driven mechanism. Phloem carries organic solutes such as sucrose from sources to sinks by pres...
Topic 4: Genetic information and diversity
Genetic information and variation
3.4.1 - DNA, genes and chromosomesDNA stores the instructions for polypeptides in its base sequence, yet most of a human cell's DNA does not code for polypeptides. This lesson covers how DNA is organised, packaged and read.
3.4.2 - DNA and protein synthesisMuscle and pancreas cells carry the same genes yet make different proteins. Follow a protein-coding gene from DNA through RNA to a polypeptide, then test that explanation with codon tables and experimental data.
3.4.3 - Genetic diversity from mutation and meiosisTwo human parents could produce about 70 trillion chromosome combinations in their children, before crossing over adds more. Mutation creates new alleles; meiosis and random fertilisation reshuffle existing ones.
3.4.4 - Genetic diversity and adaptationWhy do antibiotics stop working? Follow how mutation, selection and reproduction change allele frequencies, compare directional and stabilising selection, and explain how adaptations build up.
RP06 - Aseptic technique and antimicrobialsA clear ring around a paper disc is this practical's result, and a stray microorganism can spoil it. Run a fair aseptic disc test, judge what zones prove, then count living bacteria by serial dilution and read their growth on a log scale.
Species and biodiversity
3.4.5 - Species and taxonomyWhat makes two organisms one species? Breeding, not looks. Follow how species are named, how courtship acts as a species check, and how molecules test a classification based on ancestry.
3.4.6 - Biodiversity within a communityTwo fields can hold the same 25 plant species and still differ hugely in diversity. Learn the number that shows it, how far to trust it, and how to weigh farming against conservation.
3.4.7 - Investigating diversityCompare genetic diversity through characteristics and through DNA, mRNA and protein sequences. Then sample at random and describe your data with charts, means and standard deviations, without claiming more than they show.
Topic 5: Energy transfers
Photosynthesis
3.5.1 - PhotosynthesisPhotosynthesis transfers light energy into chemical energy in two linked stages. The light-dependent reaction makes ATP and reduced NADP; the light-independent reaction, or Calvin cycle, uses them to make carbohydrate from carbon dioxide. Trace that link and limiting-factor questions become a sea...
RP07 - Chromatography of leaf pigmentsSeparate the pigments hidden in a leaf, explain why they travel different distances, and judge what your results can and cannot prove.
RP08 - Dehydrogenase activity in chloroplastsMeasure how a named factor, here light intensity, affects electron transfer in a chloroplast extract, and learn how far that result can be taken.
Respiration
3.5.2 - RespirationRespiration transfers energy from glucose and other substrates to ATP, one controlled step at a time. Glycolysis comes first, pyruvate then follows an aerobic or an anaerobic route, and most ATP in aerobic respiration is made at the very end, by oxidative phosphorylation.
RP09 - Respiration rate in single-celled organismsYou can't see yeast respire, but you can time a blue dye losing its colour as respiration reduces it. This required practical investigates how a named variable affects the respiration rate of cultures of single-celled organisms, with yeast and temperature as the worked case.
Energy and nutrients in ecosystems
3.5.3 - Energy and ecosystemsFollow the chemical energy in plant and animal biomass to calculate production, explain losses between trophic levels and judge how farming changes energy transfer. Measurements only become comparable when their area, time and units are clear.
3.5.4 - Nutrient cyclesOrganisms cannot make nitrogen or phosphorus atoms, so life depends on reusing them. Follow both elements through soil, microbes, plants and animals, then see how harvesting removes them and how fertilisers can damage rivers and lakes.
Topic 6: Responses and homeostasis
Responses and receptors
3.6.1.1 - Survival and responseA woodlouse has no plan, a seedling has no nerves, and your hand leaves a hot pan before you decide to move it. Each is a simple response that raises the chance of survival. This lesson covers taxes and kineses, IAA-controlled plant growth, the three-neurone reflex and how to investigate IAA.
RP10 - Animal responses in a choice chamber or mazeIn this required practical you test how one environmental variable affects an animal's movement, using either a choice chamber or a maze. Chi-squared then shows whether the difference could be chance, and the evidence sets how much you can claim about behaviour.
3.6.1.2 - ReceptorsReceptors turn a specific stimulus into an electrical signal. See how in the Pacinian corpuscle, how the pigments and wiring of rods and cones shape vision, and how to test skin sensitivity.
3.6.1.3 - Control of heart rateThis lesson follows the wave of electrical excitation that starts each heartbeat, then shows how receptors and the autonomic nervous system change how often it happens, and how to measure the result.
Nervous coordination and effectors
3.6.2.1 - Nerve impulsesA nerve impulse arrives at full size because the axon rebuilds it on the way. Trace how ion gradients produce it, why myelin speeds it up, and how the refractory period limits its frequency.
3.6.2.2 - Synaptic transmissionAn action potential cannot cross a chemical synapse, so a chemical neurotransmitter carries its effect over the gap. Use that step to explain one-way transmission, summation, inhibition, muscle stimulation and drug effects.
3.6.3 - Skeletal muscleSkeletal muscles are the effectors that turn nerve impulses into movement. Follow one movement down to myosin heads pulling on actin, then see why some fibres tire sooner and how to study muscle.
Homeostasis and control
3.6.4.1 - Homeostasis and negative feedbackLearn why mammals keep temperature, pH and glucose stable, how negative feedback corrects a change, and how to tell it from positive feedback.
3.6.4.2 - Control of blood glucoseBlood glucose rises after a meal and falls during a fast, yet it stays within narrow limits. Learn how the liver and three hormones hold it there, what fails in diabetes, and how to judge glucose data and claims about Type II diabetes.
RP11 - Glucose calibration curveA Benedict's colour only hints at how much glucose a sample holds. Make a dilution series, build a colorimetric calibration curve and use it to estimate the glucose in an unknown ‘urine’ sample, then judge how far to trust the answer.
3.6.4.3 - Control of blood water potentialBlood water potential stays steady because the kidneys return most of the water they filter. Follow blood and filtrate through a nephron, then see how the medullary gradient and ADH set how much water stays in the body.
Topic 7: Genetics, evolution and ecosystems
Inheritance and populations
3.7.1 - InheritanceHow can two green-podded pea plants produce a yellow-podded offspring? Follow alleles from parents through gametes to offspring, and you can predict the ratios of a cross or work backwards from them.
3.7.2 - Populations and allele frequenciesYou can't see a recessive allele hidden in a heterozygote, but you can calculate how common it is, and judge when survey data justify that estimate.
Ecosystems
3.7.4 - Populations in ecosystemsWhat stops a population growing for ever, and how do you count animals that won't stay still? Learn what limits populations, how to estimate them, how communities change and how to judge conservation evidence.
RP12 - Species distribution and environmental factorsDoes a plant really thin out with distance from a path? Investigate how a named environmental factor is associated with one species' distribution: pair field measurements, choose an analysis and state what the evidence can establish. This lesson supports Required Practical 12; completing its writ...
Topic 8: Gene expression
Mutations and gene expression
3.8.1 - Mutations and protein structureOne changed base in the β-globin gene can cause sickle-cell disease, while another can leave the polypeptide untouched. Trace any gene mutation from DNA to polypeptide, and use a supplied genetic code to predict what it does.
3.8.2.1 - Cell specialisation and stem cellsCells with essentially the same genes do very different jobs. Learn how gene expression causes this, what stem cells can become, and how to weigh stem-cell treatments.
3.8.2.2 - Regulating transcription and translationA cell can control a gene at several stages, from access to its DNA to the survival of its mRNA. Learn each control, then use data to separate observation from mechanism and genes from environment.
3.8.2.3 - Gene expression and cancerTumours develop when the controls on cell division fail. Learn how faulty genes, methylation and oestrogen cause this, and how to judge evidence about risk and cure.
Genomes and biotechnology
3.8.3 - Using genome projectsGenome projects read an organism's complete DNA base sequence. See how it is rebuilt from fragments, how a simple genome can lead to a vaccine, and why a human genome is much harder to turn into a proteome.
3.8.4.1 - Recombinant DNA technologyRecombinant DNA technology moves a gene from one organism into another, where it can be expressed. Follow the route from obtaining and copying the gene to finding the cells that carry it, then weigh who gains, who bears the risks and who owns the result.
3.8.4.2 - DNA probes and genetic screeningOne changed base in an allele can cause a heritable condition or make a standard drug dose harmful. This lesson shows how labelled DNA probes find such differences between people, and how the results guide genetic counselling and personalised medicine.
3.8.4.3 - Genetic fingerprintingGenetic fingerprinting compares DNA between samples. Some parts of the genome vary a lot between individuals, so amplifying, separating and visualising those regions gives a pattern of bands that is very unlikely to be identical in two unrelated people.