Overview
This lecture reviews essential topics for AQA GCSE Biology Paper 1, covering cells, organization, infection and response, and bioenergetics, with key practicals and exam knowledge.
Cells and Microscopy
- All living things are made of cells, visible under a light microscope; electron microscopes reveal finer details.
- Magnification = image size ÷ object size; rearrange to find actual size.
- Eukaryotic cells have a nucleus (found in animals/plants); prokaryotic cells (bacteria) do not.
- Both types have a membrane (controls entry/exit), cytoplasm (site of reactions), and ribosomes (protein synthesis).
- Plant cells contain chloroplasts (photosynthesis), a cell wall (cellulose for support), and a permanent vacuole (storage).
- Mitochondria (in eukaryotes) are sites of respiration.
Cell Division and Specialization
- Mitosis is the process where a diploid cell divides into two identical cells for growth and repair.
- Human cells have 23 chromosome pairs (diploid); gametes have 23 chromosomes (haploid).
- Specialized cells perform specific functions; stem cells are unspecialized and can differentiate.
- Stem cells are found in embryos, bone marrow (blood cells), and plant meristems.
Transport Processes in Cells
- Diffusion: movement of particles from high to low concentration, down a gradient, passive process.
- Osmosis: diffusion of water across a semi-permeable membrane.
- Active transport: movement of substances against a concentration gradient using energy, via carrier proteins.
Organization of Living Things
- Tissues are groups of similar cells; tissues form organs; organs work together in organ systems.
- Digestive system: enzymes and bile break down nutrients for absorption.
- Enzymes: biological catalysts with specific active sites; affected by temperature and pH.
- Food tests: iodine for starch, Benedict’s for sugar, Biuret for protein, ethanol for lipids.
Circulatory and Respiratory Systems
- The heart pumps blood in a double circulatory system (to lungs and body).
- Arteries carry blood away from the heart (thick walls); veins return blood (valves and thinner walls); capillaries are one cell thick for exchange.
- Coronary heart disease is caused by blocked arteries; treated by stents, statins, or valve replacements.
Disease and Health
- Non-communicable diseases (e.g., cancer, diabetes) arise from internal or lifestyle causes.
- Communicable diseases are caused by pathogens: viruses, bacteria, fungi, or protists.
- Viruses replicate by injecting genetic material; bacteria release toxins; fungi and protists cause various symptoms.
Immunity and Preventing Disease
- Skin, mucus, and stomach acid defend against pathogens.
- White blood cells: lymphocytes (produce antibodies/antitoxins) and phagocytes (ingest pathogens).
- Vaccines introduce dead/inactive pathogens to stimulate immunity.
- Antibiotics kill bacteria, not viruses; overuse leads to resistance.
- Drug development uses blind/double-blind trials for safety and effectiveness.
Plant Biology
- Leaves carry out photosynthesis; roots absorb water/minerals; xylem (water transport, one way), phloem (food transport, both directions).
- Factors affecting transpiration: temperature, humidity, air movement.
- Structure of a leaf: cuticle, epidermis, mesophyll, vascular bundle, stomata (gas exchange, controlled by guard cells).
Bioenergetics (Photosynthesis & Respiration)
- Photosynthesis (in chloroplasts) requires light; converts CO₂ + water → glucose + O₂; rate limited by light, CO₂, temperature.
- Respiration (mitochondria): aerobic (with oxygen, produces energy); anaerobic (makes lactic acid in animals, ethanol + CO₂ in plants/yeast).
- Metabolism is the sum of all chemical reactions in an organism.
Key Terms & Definitions
- Eukaryotic cell — cell with a nucleus.
- Prokaryotic cell — cell without a nucleus.
- Mitosis — cell division making identical cells.
- Stem cell — undifferentiated cell able to specialize.
- Diffusion — movement of particles down a concentration gradient.
- Osmosis — diffusion of water through a semi-permeable membrane.
- Active transport — energy-driven movement against a gradient.
- Enzyme — protein catalyst with a specific active site.
- Antibody — protein produced by lymphocytes to target antigens.
- Antigen — unique molecule on pathogen's surface.
- Vaccine — dead/inactive pathogen to stimulate immunity.
- Transpiration — water movement through plants and evaporation from leaves.
- Photosynthesis — process using light to make glucose.
- Respiration — energy release from glucose.
Action Items / Next Steps
- Review cell structures, division, and transport processes.
- Practice calculations for magnification and osmosis practicals.
- Revise the functions and tests for enzymes and nutrients.
- Learn the flow of blood through the heart and vessels.
- Study plant structure and processes (photosynthesis, transpiration).
- Prepare for required practicals and be able to analyze results.