I85PREP
⌘ K
Basque PAU Biology study materials
Basque PAU Biology study resources

Basque PAU Biology: Metabolism: Catabolism, Anabolism, Respiration and Photosynthesis

Basque PAU Biology · Work through your exam, one topic at a time.

All guide sections

Metabolism: Catabolism, Anabolism, Respiration and Photosynthesis

The metabolism domain of the Basque PAU Biology exam tests how cells obtain and use energy. You need to locate glycolysis, the Krebs cycle, oxidative phosphorylation and photosynthesis in the cell, compare aerobic and anaerobic pathways, and explain how enzyme kinetics and regulation control metabolic rate.

Catabolism and respiration

  • Glycolysis occurs in the cytosol and yields ATP and NADH.
  • The link reaction and Krebs cycle occur in the mitochondrial matrix and produce NADH, FADH2, ATP and CO2.
  • Oxidative phosphorylation occurs on the inner mitochondrial membrane; electrons pass along the chain and chemiosmosis drives ATP synthase. Oxygen is the terminal electron acceptor.
  • Fermentation regenerates NAD+ so glycolysis can continue; it does not increase ATP yield beyond glycolysis.

Anabolism and photosynthesis

  • The light reactions occur in thylakoid membranes and produce ATP and NADPH; water is the electron donor and O2 is released.
  • The Calvin cycle occurs in the stroma and fixes CO2 using ATP and NADPH.
  • Photosynthesis stores energy; respiration releases it. The overall equations are complementary but not simple reverses.

Enzyme kinetics

  • Rate rises with substrate concentration until Vmax; Km indicates affinity.
  • Temperature and pH affect rate; excessive heat denatures enzymes.
  • Allosteric regulation and feedback inhibition adjust pathway activity.

Worked example

One glucose molecule is oxidised. Using a school-text yield of 30 ATP and ΔG for ATP hydrolysis of −30.5 kJ/mol, the energy captured is 30 × 30.5 = 915 kJ/mol. Glucose oxidation releases about 2870 kJ/mol, so efficiency is 915 ÷ 2870 ≈ 0.319, or 31.9%. Using 38 ATP gives 1159 ÷ 2870 ≈ 40.4%. State which yield your syllabus uses; the reasoning matters more than the exact textbook maximum.

Traps

  • The light reactions do not fix CO2; the Calvin cycle does.
  • O2 released in photosynthesis comes from water, not CO2.
  • Fermentation does not produce 30–38 ATP; it only regenerates NAD+.
  • The Krebs cycle itself produces little ATP directly; most ATP comes from oxidative phosphorylation.
  • A high Km means lower affinity, not higher affinity.