1.6Unit 1 — Cell Biology
Respiration — SQA National 5 Biology — SQA National 5 Biology Revision Notes & Topical Questions
5 min read 2 parts Lesson 6 of 6
Section 1 of 2Cellular respiration and ATP
- Respiration is a series of enzyme-controlled chemical reactions that breakdown glucose to release chemical energy stored in the form of ATP (Adenosine Triphosphate):
- ADP + Inorganic Phosphate (Pi) + Energy ⇌ ATP
- Cellular processes requiring ATP energy:
- Muscle cell contraction and movement.
- Cell division (mitosis).
- Protein synthesis at ribosomes.
- Active transport of ions against concentration gradients.
- Transmission of electrical nerve impulses.
Section 2 of 2Aerobic respiration vs Fermentation
| Feature | Aerobic Respiration | Fermentation in Animal Cells | Fermentation in Plant & Yeast Cells |
|---|---|---|---|
| Oxygen requirement | Requires oxygen | Absence of oxygen | Absence of oxygen |
| Stage 1: Glycolysis | Occurs in cytoplasm: Glucose broken into 2 pyruvate molecules, yielding 2 ATP | Occurs in cytoplasm: Glucose broken into 2 pyruvate molecules, yielding 2 ATP | Occurs in cytoplasm: Glucose broken into 2 pyruvate molecules, yielding 2 ATP |
| Stage 2: Fate of Pyruvate | Occurs in mitochondria: Pyruvate completely broken down to CO2 and H2O, yielding many ATP (approx. 36 ATP) | Occurs in cytoplasm: Pyruvate is converted to lactate (lactic acid); no further ATP produced | Occurs in cytoplasm: Pyruvate is converted to ethanol and CO2; no further ATP produced |
| Total ATP yield per glucose | Large yield (~38 ATP) | Small yield (2 ATP only) | Small yield (2 ATP only) |
| Reversibility | Irreversible overall | Reversible (when oxygen returns, lactate converts back to pyruvate) | Irreversible (CO2 gas diffuses away) |
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