WBI14 Energy, Environment, Microbiology and Immunity

Lessons in WBI14

1. Photosynthesis overview and ATP
   6CO2 + 6H2O → C6H12O6 + 6O2. Light splits water; hydrogen reduces CO2 and energy is stored in glucose; O2 comes from water. ATP hydrolysis gives immediate energ
2. The light-dependent reactions
   Light excites electrons in chlorophyll; their energy along the electron transport chain makes ATP (via H+ and ATP synthase). Non-cyclic: PSII to PSI, makes ATP,
3. The light-independent reactions (Calvin cycle)
   CO2 + RuBP (RuBisCO) → 2 GP; GP reduced to GALP using ATP and reduced NADP; most GALP regenerates RuBP. 6 turns per glucose, using 18 ATP and 12 reduced NADP.
4. Chloroplasts, pigments and spectra
   Thylakoids (grana) hold photosystems for the light-dependent reactions; the stroma holds Calvin cycle enzymes, DNA and ribosomes. Action spectrum matches absorp
5. Core practical 10: factors affecting photosynthesis
   Measure gas from pondweed in a photosynthometer while changing one factor. Light intensity ∝ 1/d²; V = πr²l. A plateau means another factor is now limiting.
6. Productivity and energy transfer
   NPP = GPP - R. Efficiency = energy transferred / energy available x 100. Energy is lost through parts not eaten, faeces, excretion and respiration (heat).
7. Ecosystems, distribution and the niche
   Population = one species; community = all species; ecosystem = community plus abiotic environment. Distribution depends on biotic and abiotic factors; each spec
8. Core practical 11: ecology of a habitat
   Random quadrats compare areas (t-test); belt transects study gradients (Spearman's rank). Measure density, percentage cover or frequency, plus abiotic factors a
9. Succession
   Pioneers colonise bare ground, form soil and change conditions; seral stages follow until a stable climax community. Secondary succession starts with soil prese
10. Evidence for climate change and its limits
    Direct evidence: temperature records, Mauna Loa CO2 (about 313 ppm in 1958, about 432 ppm in May 2026), ice cores. Indirect: pollen in peat bogs, tree rings. Ex
11. The greenhouse effect, carbon cycle and sustainability
    Greenhouse gases absorb re-emitted infrared; human CO2 and methane enhance the effect. Photosynthesis removes CO2; respiration, decomposition and combustion ret
12. Climate change, temperature and Q10 (Core practical 12)
    Warming shifts ranges poleward and uphill, changes the timing of life cycles and can alter sex ratios. Q10 = rate at (t + 10) / rate at t, about 2 for many enzy
13. Evolution and speciation
    Evolution = change in allele frequency through mutation and natural selection. Reproductive isolation stops gene flow. Allopatric: geographical separation; symp
14. Culturing and counting microorganisms
    Aseptic technique: flame loops and bottle necks, work near a Bunsen, tape lids, incubate at 25 °C, autoclave. Growth: haemocytometer count, dilution plating (co
15. The bacterial growth curve (Core practical 13)
    Lag, log (exponential), stationary, death. N = N0 x 2ⁿ. k = (log10 N - log10 N0) / (0.301 t) generations per hour; mean generation time = 1/k. CP13 measures gr
16. Bacteria and viruses: structure and life cycles
    Bacteria: prokaryotic cells with circular DNA, plasmids, 70S ribosomes and a peptidoglycan wall. Viruses: DNA or RNA in a capsid, some enveloped. Lytic cycle ma
17. How tuberculosis and HIV cause disease
    TB: droplets, engulfed by macrophages but survives (waxy wall), walled off in granulomas, latent until immunity weakens. HIV: gp120 binds CD4 on T helper cells,
18. Barriers and non-specific defences
    Barriers: skin, mucus and cilia, stomach acid, lysozyme, natural flora, clotting. Inflammation: histamine causes vasodilation and leaky capillaries. Phagocytes
19. The specific immune response: B cells and T cells
    APCs display antigens; T helper cells bind, clone and release cytokines; T killer cells destroy infected cells; B cells clone into plasma cells (antibodies) and
20. Types of immunity and the evolutionary race
    Active (own antibodies and memory cells, slow but lasting) vs passive (given antibodies, fast but short). Natural vs artificial. Vaccines give artificial active
21. Antibiotics and hospital-acquired infections
    Bactericidal kills (penicillin weakens cell walls); bacteriostatic stops growth (tetracycline blocks 70S ribosomes). Resistance arises by mutation and natural s
22. Core practical 14: the effect of antibiotics on bacteria
    Make a bacterial lawn, add antibiotic discs plus a sterile-water control, incubate at 25 °C, then measure zones of inhibition: area = πr². Zone size also depend
23. PCR, gel electrophoresis and DNA profiling
    PCR: denature about 95 °C, anneal primers about 55 °C, extend with Taq polymerase at 72 °C; 2ⁿ copies after n cycles. Electrophoresis: negative DNA moves to th
24. Decomposition and estimating time of death
    Decomposers secrete enzymes, absorb products and respire, returning CO2. Time of death: body cooling, rigor mortis (starts about 1 to 2 h, full by about 12 h, g

Next exams for WBI14

• January 2027: Mon 18 Jan 2027, morning, 1h 45m
• Summer 2027: Mon 24 May 2027, afternoon, 1h 45m

From Pearson's final timetables. All exam dates. Always confirm your entries with your exams officer.