GCSE AQA Biology: Complete Topic Guide & Revision Tips

1. Cell Biology

Study the structure and function of cells, cell division, and transport in and out of cells.

• Cells are the basic unit of life; prokaryotic (bacteria) and eukaryotic (plants, animals).
• Animal cells: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes.
• Plant cells: all animal cell parts plus cell wall, chloroplasts, permanent vacuole.
• Specialised cells perform specific functions (e.g., sperm, root hair cells).
• Microscopy is used to observe cell structure.
• Cell division by mitosis produces identical cells for growth and repair.
• Stem cells can differentiate into different cell types.
• Diffusion, osmosis, and active transport move substances in and out of cells.
• Surface area to volume ratio affects the rate of transport.
• Ethical issues surround stem cell use.

2. Organisation

Explore how cells form tissues, organs, and organ systems, focusing on digestion, circulation, and plant transport.

• Cells → tissues → organs → organ systems.
• Enzymes are biological catalysts; affected by temperature and pH.
• The digestive system breaks down food into small molecules.
• The heart pumps blood through the double circulatory system.
• Blood contains red cells, white cells, platelets, plasma.
• Arteries, veins, and capillaries have different structures and functions.
• Coronary heart disease is caused by blocked arteries.
• Health is affected by lifestyle, diet, and disease.
• Plant tissues: epidermal, palisade, spongy mesophyll, xylem, phloem.
• Transpiration and translocation move water and sugars in plants.

3. Infection and Response

Learn about pathogens, the immune system, vaccination, and disease treatment.

• Pathogens include bacteria, viruses, fungi, and protists.
• Diseases can be spread by air, water, or direct contact.
• The body’s defences: skin, mucus, stomach acid, white blood cells.
• White blood cells ingest pathogens, produce antibodies and antitoxins.
• Vaccination stimulates immunity without causing disease.
• Antibiotics treat bacterial infections; resistance is a growing problem.
• Drugs are tested for efficacy, toxicity, and dosage.
• Monoclonal antibodies are used in diagnosis and treatment.
• Plant diseases and defences are also studied.
• Herd immunity protects populations from outbreaks.

4. Bioenergetics

Study photosynthesis and respiration, the processes that provide energy for life.

• Photosynthesis: carbon dioxide + water → glucose + oxygen (needs light and chlorophyll).
• Limiting factors: light, CO₂, temperature, chlorophyll.
• Glucose is used for respiration, making cellulose, amino acids, fats, and oils.
• Respiration releases energy from glucose (aerobic and anaerobic).
• Aerobic respiration uses oxygen; anaerobic does not.
• Anaerobic respiration in muscles produces lactic acid (causes fatigue).
• Oxygen debt is the extra oxygen needed after exercise.
• Fermentation by yeast produces ethanol and CO₂.
• Metabolism is the sum of all chemical reactions in the body.
• Practical: measuring the rate of photosynthesis (e.g., pondweed experiment).

5. Homeostasis and Response

Understand how organisms maintain stable internal conditions and respond to stimuli.

• Homeostasis keeps conditions constant (e.g., temperature, water, blood sugar).
• The nervous system detects and responds to stimuli.
• Reflex actions are automatic and rapid.
• Structure of a neuron: cell body, dendrites, axon.
• Synapses transmit signals between neurons using chemicals.
• The endocrine system uses hormones to control processes.
• Control of blood glucose: insulin and glucagon (pancreas).
• Diabetes is caused by problems with insulin production or response.
• Menstrual cycle controlled by hormones (FSH, LH, oestrogen, progesterone).
• Contraception and fertility treatments manipulate hormones.

6. Inheritance, Variation and Evolution

Explore genetics, natural selection, and the development of new species.

• DNA carries genetic information in chromosomes.
• Genes code for proteins; alleles are different forms of a gene.
• Sexual reproduction produces variation; asexual produces clones.
• Genetic diagrams (Punnett squares) predict inheritance.
• Dominant and recessive alleles affect traits.
• Mutations are changes in DNA; can be beneficial, harmful, or neutral.
• Evolution by natural selection explains adaptation and speciation.
• Selective breeding and genetic engineering modify organisms.
• Fossils provide evidence for evolution.
• Extinction is caused by environmental changes, competition, or new predators.

7. Ecology

Study ecosystems, biodiversity, and the impact of human activity on the environment.

• Habitat: where an organism lives; population: all members of a species in an area.
• Community: all populations in an area; ecosystem: community plus environment.
• Abiotic (non-living) and biotic (living) factors affect organisms.
• Adaptations help organisms survive in their environment.
• Food chains and food webs show energy flow.
• Decomposers break down dead material, recycling nutrients.
• Biodiversity is the variety of living organisms; important for ecosystem stability.
• Human activities (deforestation, pollution, global warming) threaten biodiversity.
• Conservation protects endangered species and habitats.
• Practical: sampling techniques (quadrats, transects) to study populations.

8. Key Concepts in Biology (Combined Science Only)

Fundamental ideas that underpin all biology topics, especially for Combined Science students.

• Cells as the basic unit of life.
• Structure and function of DNA.
• Enzymes as biological catalysts.
• Transport in and out of cells (diffusion, osmosis, active transport).
• Cell division and growth.
• Inheritance and variation.
• Photosynthesis and respiration basics.
• Homeostasis and control systems.
• Interdependence in ecosystems.
• Scientific methods and practical skills.

Further Support

For detailed notes, practice questions, and interactive resources on every GCSE AQA Biology topic, visit TRH Learning.