MDCAT Bioenergetics Complete Guide 2026 — ATP, Photosynthesis & Respiration
Premeth Team
Meth Experts
Bioenergetics contributes 6–8 of the 81 MDCAT Biology MCQs — roughly 9% of the Biology section. The chapter is dense but reliably predictable: ATP structure, glycolysis, Krebs cycle, electron transport, photosynthesis light + dark reactions.
- Estimated MCQs — 6–8 of 81 Biology MCQs
- ATP yields to memorise — Glycolysis: 2; Krebs: 2 (per pyruvate); ETC: ~34
- Total ATP per glucose — 38 (theoretical) / ~30–32 (actual)
- Photosynthesis stages — Light-dependent (thylakoid) + Light-independent / Calvin (stroma)
Source: PMDC MDCAT 2026 syllabus; UHS Biology Bioenergetics MCQ analysis 2008–2024.
ATP — The Cell's Energy Currency
- Structure — Adenine + Ribose (= adenosine) + 3 phosphate groups
- Energy release — hydrolysis of terminal phosphate yields ~7.3 kcal/mol
- ATP ↔ ADP cycle — ATP → ADP + Pi (energy released) / ADP + Pi → ATP (energy invested)
Cellular Respiration — 3 Stages
- 1. Glycolysis — cytoplasm. Glucose (6C) → 2 Pyruvate (3C). Net 2 ATP, 2 NADH.
- 2. Krebs (citric acid / TCA) cycle — mitochondrial matrix. Each pyruvate → CO2. Per cycle: 3 NADH, 1 FADH2, 1 ATP (GTP).
- 3. Electron transport chain (ETC) + oxidative phosphorylation — inner mitochondrial membrane. NADH/FADH2 → ATP via chemiosmosis. ~34 ATP / glucose.
Photosynthesis — 2 Stages
- Light-dependent reactions — in thylakoid membrane. Splits H2O (photolysis), produces O2, ATP, NADPH. Photosystem II then I.
- Calvin cycle (light-independent / dark reactions) — in stroma. Fixes CO2 via RuBisCO, uses ATP & NADPH to build glucose.
- Net equation — 6CO2 + 6H2O + light → C6H12O6 + 6O2
Trap MCQs PMDC Keeps Asking
- “Where does the oxygen released in photosynthesis come from?” — H2O, not CO2. From photolysis.
- “Net ATP gain in glycolysis?” — 2 (4 produced − 2 used in priming).
- “Final electron acceptor in ETC?” — Oxygen (forms H2O).
- “Site of Krebs cycle?” — mitochondrial matrix, NOT inner membrane.
- “Anaerobic glycolysis yield?” — 2 ATP only (no Krebs, no ETC).
FAQ
Q: How many ATP per glucose — 36 or 38?
Theoretical: 38. In humans/most eukaryotes the actual yield is ~30–32 due to membrane transport costs. PMDC accepts 38 for textbook MCQs.
Q: Difference between NADH and NADPH?
NADH = cellular respiration; NADPH = photosynthesis (and reduction biosynthesis).
Q: Which chapter does Bioenergetics overlap with?
Cell Structure (mitochondria + chloroplasts) and Bio Molecules (enzymes, carbohydrates).
Bioenergetics is dense but ROI-positive: ~9% of Biology marks for ~10% of Biology study time. Drill our Bioenergetics chapter page and pair with Cell Biology.
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