Overview
This lecture is a comprehensive summary of key topics for AQA GCSE Biology Paper 1, covering cells, organization, infection and response, and bioenergetics for both combined and separate science students.
Cells and Microscopy
- All living things are made of cells, visible with light and electron microscopes (electron microscopes have higher resolution).
- Magnification = image size ÷ object size; actual size = image size ÷ magnification.
- Eukaryotic cells (plants, animals) have nuclei; prokaryotic (bacteria) do not.
- Cell structures: cell membrane (controls passage), cell wall (rigidity), cytoplasm (chemical reactions), mitochondria (respiration), ribosomes (protein synthesis), chloroplasts (photosynthesis), and permanent vacuole (stores sap in plants).
- Bacteria reproduce by binary fission (triple only).
- Aseptic techniques prevent contamination during bacterial culture practicals.
Cell Division and Specialisation
- Human cells are diploid (23 pairs chromosomes); gametes are haploid (23 chromosomes).
- Mitosis creates identical cells for growth/repair: DNA duplicates, nucleus divides.
- Specialized cells (nerve, muscle), stem cells (unspecialized) found in embryos, bone marrow, and plant meristems.
- Stem cells treat diseases—ethical considerations discussed.
- Plant cloning prevents extinction or creates desirable crops.
Transport in Cells
- Diffusion: passive movement from high to low concentration.
- Osmosis: diffusion of water across a membrane; practical involves potato in sugar solution.
- Active transport: uses energy to move substances against the gradient (e.g., minerals into root hair cells).
- Increased concentration difference, temperature, or surface area increases diffusion/osmosis rates.
Organisation in Multicellular Organisms
- Cells form tissues, tissues form organs, organs form organ systems.
- Digestive system: breaks down food using acid, bile (neutralizes acid, emulsifies fats), and enzymes.
- Enzymes: biological catalysts, work on substrate via lock and key model, optimal at specific temperature/pH; denature if conditions extreme.
- Food tests: iodine for starch, Benedict's for sugar, Biuret for protein, ethanol for lipids.
Circulatory and Respiratory Systems
- Breathing provides oxygen for respiration; gas exchange in alveoli (large surface area).
- Oxygen binds to hemoglobin, transported to cells; CO₂ diffuses into lungs and is exhaled.
- Heart: double circulatory system, right side pumps to lungs, left to body; arteries (away), veins (towards), capillaries (exchange).
- CHD: fatty deposits block coronary arteries; treated by stents/statins/valve replacements.
- Blood: contains plasma, red and white cells (immunity), platelets (clotting).
Non-communicable and Communicable Diseases
- Non-communicable: arise from internal factors (heart disease, diabetes, cancer).
- Communicable: caused by pathogens (virus, bacteria, fungi, protists).
- Viruses reproduce inside cells; bacteria release toxins.
- Body defenses: skin, mucus, acid, enzymes, white blood cells (lymphocytes, phagocytes).
- Immunity from memory cells after infection or vaccination.
Infection, Vaccination, and Drug Development
- Vaccines: dead/inactive pathogens induce immunity without illness.
- Antibiotics treat bacterial infections, not viruses; resistance is a concern.
- Drug testing: tissue/animal/human trials, blind/double-blind trials avoid bias.
- Triple only: monoclonal antibodies from cloned cells for treatment/diagnosis.
Plant Structure and Function
- Photosynthesis in chloroplasts: light energy converts CO₂ and water into glucose and O₂.
- Transpiration: water movement via xylem; affected by temperature, humidity, air movement.
- Phloem transports sugars (translocation).
- Leaf structure: waxy cuticle (prevents water loss), epidermis, palisade mesophyll (photosynthesis), spongy mesophyll (gas exchange), guard cells control stomata.
- Deficiencies: lack of nitrates stunts growth, lack of magnesium causes chlorosis (yellowing).
Bioenergetics and Metabolism
- Photosynthesis: an endothermic reaction, rate limited by temperature, CO₂, light.
- Practical: measure O₂ from pondweed, rate increases with light; light intensity follows inverse square law.
- Aerobic respiration: uses oxygen, produces CO₂ and water; anaerobic (no O₂) produces lactic acid (humans) or ethanol/CO₂ (plants/yeast).
- Metabolism: sum of all chemical reactions including respiration, synthesis, and breakdown.
Key Terms & Definitions
- Eukaryotic cell — Cell with a nucleus.
- Prokaryotic cell — Cell without a nucleus.
- Diffusion — Movement from high to low concentration without energy.
- Osmosis — Diffusion of water through a semi-permeable membrane.
- Active transport — Movement against concentration gradient using energy.
- Enzyme — Biological catalyst that speeds up reactions.
- Antigen — Molecule on pathogen recognized by immune system.
- Antibody — Protein made by lymphocytes binding to antigens.
- Vaccine — Dead/inert pathogen to trigger immunity.
- Stent — Tube to keep arteries open.
- Transpiration — Loss of water vapor from plant leaves.
- Photosynthesis — Conversion of CO₂ and water into glucose using light.
- Metabolism — All chemical reactions in a cell/organism.
Action Items / Next Steps
- Review all practicals: microscopy, osmosis, enzyme activity, photosynthesis.
- Learn key equations: magnification, area of circles, percentage change.
- Memorize functions of organelles, systems, enzymes, and plant structures.
- Complete any assigned past papers or quizzes on these topics.