Overview
This lecture covers the core content for AQA A-level Biology Paper 1, including biological molecules, cell structure, transport mechanisms, immunity, and the basics of genetics, biodiversity, and evolution.
Biological Molecules: Carbohydrates, Lipids, Proteins, Nucleic Acids
- Monomers (e.g., glucose, amino acids, nucleotides) join to form polymers by condensation (releases water).
- Hydrolysis splits polymers into monomers using water.
- Carbohydrates: monosaccharides (glucose, fructose, galactose), disaccharides (maltose, lactose, sucrose), polysaccharides (starch, cellulose, glycogen).
- Starch/glycogen store energy; cellulose provides structure; glycogen is in animals.
- Lipids: triglycerides (energy store, saturated/unsaturated), phospholipids (cell membranes with hydrophilic heads, hydrophobic tails).
- Proteins: polymers of amino acids, structure determined by primary, secondary, tertiary, and quaternary levels; enzymes lower activation energy via induced fit model.
Biochemical Tests
- Starch: iodine turns from orange-brown to blue-black.
- Reducing sugars: Benedict's + heat yields green/yellow/orange/brick-red.
- Non-reducing sugars: acid hydrolysis, neutralize, then Benedict's test.
- Proteins: Biuret turns from blue to purple.
- Lipids: dissolve in ethanol, add water—white emulsion forms.
Nucleic Acids and ATP
- DNA: double helix of deoxyribose, phosphate, bases A, T, C, G (A-T, C-G), joined by phosphodiester bonds.
- RNA: single strand, ribose, A, U, C, G, shorter than DNA.
- DNA replicates by semi-conservative method using DNA helicase & DNA polymerase.
- ATP: energy molecule, made by condensation (ADP + Pi), releases energy by hydrolysis.
Water and Inorganic Ions
- Water: metabolite, solvent, high heat capacity, high latent heat, cohesion.
- Ions: H+ (pH/enzymes), Fe2+ (hemoglobin), Na+ (co-transport), PO4 3- (DNA/ATP).
Cell Structure & Methods of Study
- Organelles: nucleus (DNA, transcription), RER (protein synthesis), SER (lipids), Golgi (modification), lysosomes (enzymes), mitochondria (respiration), ribosomes (protein synthesis), vacuole (plants), chloroplasts (photosynthesis), cell wall, plasma membrane.
- Prokaryotes: small, no nucleus, circular DNA, 70S ribosomes, cell wall of murein.
- Viruses: genetic material, capsid, attachment proteins, replicate in hosts.
- Microscopes: optical (light, lower resolution/color), electron (higher resolution/black & white, no living samples).
- Cell fractionation: cold, isotonic, buffered; separates by density via centrifugation.
Cell Division
- Mitosis: one division, diploid, genetically identical cells (growth/repair).
- Binary fission (prokaryotes): replicate DNA, split cytoplasm.
- Viruses: inject genetic material into host for replication.
Membranes and Transport
- Fluid mosaic model: phospholipid bilayer with proteins, glycoproteins, glycolipids.
- Diffusion: passive, high to low concentration.
- Facilitated diffusion: via protein channels/carriers.
- Osmosis: water moves from higher to lower water potential.
- Active transport: uses ATP and carrier proteins, moves substances against gradient.
- Co-transport: e.g., absorption of glucose with Na+ in the ileum.
Immunity
- Lymphocytes identify self/non-self via surface proteins (antigens).
- Phagocytosis: non-specific engulf and destroy.
- T lymphocytes: cell-mediated response, differentiate into helper, cytotoxic, or memory T cells.
- B lymphocytes: humoral response, differentiate into plasma cells (antibodies) or memory B cells.
- Immunity: active (own antibodies/memory), passive (antibodies received).
- Vaccines trigger memory cell formation; herd immunity protects vulnerable.
- HIV destroys helper T cells—leads to AIDS.
- Monoclonal antibodies: used for targeted therapy, diagnosis (ELISA; pregnancy tests).
- Ethical issues: animal use for antibody production.
Gas Exchange & Transport
- Surface area to volume ratio: smaller organisms rely on diffusion; larger need specialized systems.
- Human lungs: alveoli (gas exchange), intercostal/diaphragm muscles (ventilation).
- Insects: tracheal system with spiracles, tracheae, tracheoles.
- Fish: gills (countercurrent exchange, large SA).
- Plants: leaf structure (stomata, mesophyll), adaptations in xerophytes.
Digestion & Absorption
- Carbs digested by amylase, maltase; proteins by endopeptidases, exopeptidases, dipeptidases; lipids by lipase, bile salts (emulsification).
- Absorption: villi/microvilli increase SA; co-transport for glucose/amino acids.
Circulatory System
- Double circulatory system: pulmonary + systemic.
- Heart: atria, ventricles, valves (prevent backflow), coronary arteries.
- Blood vessels: arteries (thick walls), capillaries (exchange), veins (valves).
- Cardiac cycle: diastole, atrial systole, ventricular systole.
- Tissue fluid: ultrafiltration at arteriole end, reabsorption at venule end, lymphatic system.
Plant Transport
- Transpiration: loss of water vapor through stomata; cohesion, adhesion, root pressure move water up xylem.
- Translocation: phloem transports sugars; source-to-sink via hydrostatic pressure/concentration gradients.
Genetics and Variation
- Eukaryotic vs prokaryotic DNA: linear/chromosomal vs circular, histone-associated vs not.
- Genes: DNA sequences for polypeptides or functional RNA; locus = gene location.
- Genetic code: degenerate, universal, non-overlapping.
- Transcription (DNA to mRNA, splicing removes introns), translation (mRNA to protein).
- Mutations: substitution/deletion (frameshift), chromosome mutation (nondisjunction/polyploidy/aneuploidy).
- Variation via meiosis: independent assortment, crossing over.
- Mitosis vs meiosis: mitosis for identical diploid, meiosis for diverse haploid cells.
Evolution, Selection & Biodiversity
- Genetic diversity: number of alleles in a population; enables natural selection.
- Natural selection: advantageous alleles become frequent.
- Directional selection: shifts trait mean; stabilizing selection: favors average.
- Species: can breed to produce fertile offspring; courtship ensures species recognition.
- Classification: phylogenetic trees, hierarchy (domain, kingdom, phylum...).
- Biodiversity: habitat, genetic, species; measured by species richness/index of diversity (D).
- DNA/amino acid sequencing more accurate than appearance for relatedness.
- Farming practices can reduce biodiversity; compromises needed.
Key Terms & Definitions
- Condensation reaction — joins molecules, forms bond, releases water.
- Hydrolysis — breaks bonds using water.
- Glycosidic bond — linkage between carbohydrate monomers.
- Ester bond — linkage in lipids.
- Peptide bond — linkage between amino acids.
- Osmosis — diffusion of water from high to low water potential.
- Antigen — molecule triggering immune response.
- Antibody — protein binding specific antigen.
- Semi-conservative replication — new DNA has one original, one new strand.
- Active immunity — produced by own immune system.
- Passive immunity — receives antibodies from another source.
- Genetic code — sequence of bases coding for amino acids: degenerate, universal, non-overlapping.
- Genome — complete set of genes.
- Proteome — all proteins a cell can produce.
- Transpiration — loss of water vapor from plant leaves.
- Translocation — transport of sugars in phloem.
- Biodiversity — variety of life; measured by index of diversity (D).
Action Items / Next Steps
- Complete any set homework or practice questions on lecture topics.
- Review detailed diagrams of organelles, heart, lung, leaf, and exchange surfaces.
- Memorize key definitions and biochemical test steps.
- Practice calculations (e.g., magnification, cardiac output, index of diversity).
- Prepare for mock or actual exams by revisiting challenging sections.