BIOLOGY WITH HAMZA · MDCAT REVISION
Bioenergetics
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Locate each stage of aerobic respiration in a eukaryotic cell.
- Track the different roles of ATP, NADH, FADH₂ and oxygen.
- Explain chemiosmosis and the reduced yield of anaerobic pathways.
Core notes
- Glycolysis supplies pyruvate, a little ATP and reduced NAD.
- The Krebs cycle mainly loads electron carriers.
- Electron transport builds the proton gradient used by ATP synthase.
- Fermentation regenerates NAD so glycolysis can continue without oxygen.
Read, cover and redraw
ATP activates a six-carbon sugar.
One six-carbon molecule becomes two three-carbon units.
Electrons reduce NAD to NADH.
ATP forms and two pyruvate remain.
Written recall
1. Why does blocking the electron-transport chain eventually slow the Krebs cycle?
2. What is the immediate purpose of fermentation?
3. Where are protons pumped?
4. Can ATP form without ATP synthase?
5. Does oxygen consumption alone measure ATP output?
Apply the idea
1. During glycolysis, one glucose molecule leads to the formation of four ATP molecules, while two ATP molecules are invested. What is the net ATP gain from glycolysis of three glucose molecules?
- 6 ATP
- 2 ATP
- 12 ATP
- 18 ATP
My answer: _____ Reason: ____________________________________
2. In isolated mitochondria supplied with substrate and oxygen, a treatment produces the pattern below. Which action best explains it?
| Measurement | Before treatment | After treatment |
|---|---|---|
| Oxygen consumption | 100 | 150 |
| ATP synthesis | 100 | 20 |
- Blocking every electron transfer to oxygen
- Making the inner membrane more permeable to protons
- Removing all respiratory substrate
- Increasing the amount of ATP already present
My answer: _____ Reason: ____________________________________
3. Why can muscle cells continue glycolysis for a time when pyruvate is converted to lactate?
- Lactate supplies oxygen to mitochondria
- Lactate directly produces most cellular ATP
- The reaction regenerates NAD⁺ needed in glycolysis
- The reaction replaces all enzymes of glycolysis
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. NADH and FADH₂ cannot be efficiently oxidised, so oxidised NAD and FAD become limiting for Krebs-cycle dehydrogenation reactions.
2. To regenerate oxidised NAD, allowing glycolysis and its small ATP yield to continue.
3. From the matrix toward the intermembrane space.
4. Yes, through substrate-level phosphorylation.
5. No. Coupling efficiency also matters.
Applied questions
1. A — The net gain is 4 − 2 = 2 ATP per glucose. Three glucose molecules therefore yield a net six ATP in glycolysis.
2. B — A proton leak dissipates the gradient without ATP synthase. Electron transfer and oxygen use can continue or rise, while ATP synthesis falls.
3. C — Reduction of pyruvate oxidizes NADH to NAD⁺. This supports the oxidation step in glycolysis, allowing its substrate-level ATP formation to continue.