Overview
This lecture reviews all major topics for AQA GCSE Combined Science Biology Paper 1, covering cells, organisation, infection, and bioenergetics, with definitions, processes, and key experiments.
Cell Structure and Specialization
- Eukaryotic cells have a nucleus, cell membrane, cytoplasm, ribosomes, and mitochondria; plant cells also have a cell wall, chloroplasts, and a vacuole.
- The nucleus controls cell activity and contains genetic material; mitochondria are the site of aerobic respiration.
- Prokaryotic cells (bacteria) lack a nucleus and membrane-bound organelles; DNA is in a circular chromosome, with plasmids for extra genes.
- Cell specialization allows cells to carry out specific functions, e.g., sperm (tail, mitochondria), nerve cells (branched), muscle cells (mitochondria, ribosomes).
- Stem cells can differentiate into specialized cells; embryonic stem cells are pluripotent, adult stem cells are multipotent.
Transport in Cells
- Diffusion moves particles from high to low concentration without energy.
- Osmosis is the diffusion of water through a partially permeable membrane, from dilute to concentrated solutions.
- Active transport moves substances from low to high concentration using energy and carrier proteins.
Microscopy and Cell Division
- Light microscopes have lower magnification/resolution than electron microscopes.
- Magnification = image size ÷ actual size; ensure unit consistency.
- Mitosis produces two identical diploid cells for growth/repair.
Biological Organisation
- Cells form tissues, tissues form organs, and organs form organ systems.
- Example: the leaf contains epidermis, palisade mesophyll (photosynthesis), spongy mesophyll (gas exchange), xylem, and phloem.
Digestion and Enzymes
- Enzymes are biological catalysts made of protein; each has a specific active site.
- Amylase breaks down starch, protease breaks proteins into amino acids, lipase breaks lipids into fatty acids/glycerol.
- Bile (from liver) emulsifies fats and neutralizes stomach acid.
Circulatory and Respiratory Systems
- Arteries carry blood away from the heart (thick walls), veins return blood (valves), capillaries exchange substances (one cell thick).
- Red blood cells carry oxygen; white blood cells fight infection; platelets clot blood; plasma carries substances.
- The heart has a double circulatory system with valves, atria, ventricles, and a pacemaker.
Health, Disease, and Immunity
- Health includes physical and mental well-being; disease can be communicable or non-communicable.
- Risk factors: smoking (lung disease), obesity (diabetes), alcohol (liver/brain issues), carcinogens (cancer).
- Communicable diseases: measles, HIV, TMV (viruses); salmonella, gonorrhoea (bacteria); rose black spot (fungus); malaria (protist).
- The immune system uses barriers (skin, mucus), white blood cells (phagocytosis, antibodies).
- Vaccination builds immunity by introducing antigens to stimulate antibody/memory cell production.
Drug Development
- Drugs are tested for toxicity, stability (preclinical), then side effects, efficacy, and dosage (clinical, with double-blind and placebo trials).
- Peer review checks validity; monitoring continues post-licensing.
Bioenergetics
- Photosynthesis stores energy in glucose; word and symbol equations must be accurate.
- Limiting factors: light, COâ‚‚, temperature, chlorophyll.
- Respiration (aerobic uses oxygen; anaerobic doesn’t): releases energy for life processes.
- Anaerobic respiration in yeast is fermentation; in muscles, it forms lactic acid and leads to oxygen debt.
Key Terms & Definitions
- Eukaryotic cell — cell with a nucleus and organelles.
- Prokaryotic cell — cell without a nucleus or membrane-bound organelles.
- Diffusion — movement of particles from high to low concentration.
- Osmosis — movement of water across a partially permeable membrane.
- Active transport — movement of substances against the concentration gradient using energy.
- Enzyme — protein that catalyzes a biological reaction.
- Vaccination — introducing antigens to stimulate immunity.
Action Items / Next Steps
- Review required practicals: microscopy, osmosis, enzyme activity, food tests, photosynthesis.
- Memorize key equations (e.g., magnification, percentage change).
- Complete any assigned readings or textbook exercises on today’s topics.