Overview
This lecture reviews the essential topics for AQA GCSE Biology Paper 1, covering cells, organization, infection and response, and bioenergetics.
Cell Structure and Microscopy
- All life consists of cells visible using light or electron microscopes.
- Magnification = image size / object size; use to calculate actual cell size.
- Eukaryotic cells have a nucleus (plants, animals); prokaryotic cells do not.
- Cell membrane is semi-permeable; cell wall provides rigidity in plants and bacteria.
- Key organelles: cytoplasm (site of reactions), mitochondria (respiration), ribosomes (protein synthesis), chloroplasts (photosynthesis), vacuole (plant sap storage).
- Bacteria multiply by binary fission (Triple only).
Practical Techniques and Calculations
- Use aseptic technique in bacteria cultures; calculate area using ΟrΒ² or ΟdΒ²/4.
- Potato osmosis practical: measure mass change and calculate % change for different sugar concentrations.
Cell Division and Specialization
- Eukaryotic nuclei contain chromosomes; humans have 23 pairs (diploid); gametes have 23 chromosomes (haploid).
- Mitosis: genetic material duplicated, nucleus divides, creates two identical cells.
- Specialized cells and stem cells (found in embryos, bone marrow, plant meristems) can differentiate; used in medicine and plant cloning.
Transport in Cells
- Diffusion: passive movement from high to low concentration.
- Osmosis: diffusion of water through a semi-permeable membrane.
- Active transport: moves substances against a concentration gradient using energy.
- Surface area, concentration difference, and temperature affect rates of diffusion/osmosis.
Organization of Living Things
- Cells form tissues, which make organs and organ systems.
- Digestive system: breaks down food with acid, bile, and enzymes.
- Enzymes are biological catalysts specific to substrates; affected by temperature and pH; tested with food tests (iodine, Benedictβs, Biuret, ethanol).
The Circulatory and Respiratory Systems
- Gas exchange in alveoli; oxygen transported by hemoglobin; COβ exhaled.
- Double circulatory system: arteries (away from heart), veins (to heart), capillaries (exchange).
- Arteries have thick walls; veins have valves; capillaries are one cell thick.
- Coronary arteries supply heart; blockages cause CHD; treatments include stents and statins.
Non-Communicable and Communicable Diseases
- Non-communicable: heart disease, diabetes, cancer (benign/malignant).
- Communicable: caused by pathogens (viruses, bacteria, fungi, protists); examples include measles, HIV, salmonella, malaria.
- Body defenses: skin, mucus, stomach acid, white blood cells (lymphocytes produce antibodies/antitoxins; phagocytes ingest pathogens).
Immunity, Vaccination, and Medicines
- Immunity arises after pathogen exposure; vaccines use dead/inert pathogens or mRNA (e.g., COVID-19).
- Antibiotics kill bacteria, not viruses; resistance can develop.
- Drugs are tested in lab, animals, and double-blind human trials.
- Monoclonal antibodies produced from hybrid cells; used in diagnosis and treatment (Triple only).
Plant Structures and Functions
- Leaves: site of photosynthesis and transpiration; regulated by stomata and guard cells.
- Xylem transports water (one direction), phloem transports food (both directions).
- Rate of transpiration increased by higher temperature, decreased humidity, more air movement.
- Plant deficiencies: lack of nitrate (poor protein synthesis), magnesium (chlorosis/leaf yellowing).
Photosynthesis and Respiration
- Photosynthesis: endothermic, in chloroplasts; equation given.
- Limiting factors: temperature, light intensity, COβ concentration.
- Practical: measure oxygen from pondweed; light intensity follows inverse square law.
- Aerobic respiration (with Oβ): releases energy; anaerobic (without Oβ): produces lactic acid or ethanol (fermentation).
- Metabolism: sum of all chemical reactions in an organism.
Key Terms & Definitions
- Eukaryotic cell β cell with nucleus.
- Prokaryotic cell β cell without nucleus.
- Diffusion β movement from high to low concentration.
- Osmosis β diffusion of water through a membrane.
- Mitosis β cell division producing identical cells.
- Active transport β energy-requiring movement against a gradient.
- Enzyme β biological catalyst for reactions.
- Antibody β protein produced by white blood cells to fight pathogens.
- Vaccine β inactive pathogen to stimulate immunity.
- Transpiration β movement of water through plants and evaporation from leaves.
Action Items / Next Steps
- Review practical experiment steps for osmosis, enzyme activity, and photosynthesis.
- Learn and practice key equations (magnification, area, percentage change).
- Memorize definitions and functions of cell structures, enzymes, and transport systems.
- Complete any assigned textbook readings or revision questions on these topics.