Explain how the products of glycolysis are used in subsequent stages of aerobic cell respiration to produce ATP.

IB DP Biology Standard Level (2023 syllabus) — C1.2 Cell respiration · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Glycolysis produces pyruvate and NADH. The pyruvate enters the mitochondria where it is converted to acetyl‑CoA for the Krebs cycle. Both glycolysis and the Krebs cycle generate reduced NADH and, in the Krebs cycle, FADH₂. These electron carriers donate electrons to the electron transport chain on the inner mitochondrial membrane. The energy released by electron transfer pumps protons across the membrane, creating a proton gradient. ATP synthase uses this gradient (chemiosmosis) to synthesise ATP – the process of oxidative phosphorylation.

Examiner tips

Use the exact terms – pyruvate, acetyl‑CoA, NADH, FADH₂, electron transport chain, chemiosmosis, ATP synthase.
Show the flow from glycolysis → mitochondria → Krebs cycle → ETC → ATP synthesis.
Mention the proton gradient and its role in driving ATP synthase.
Keep the answer concise – 4 marks only.

Common mistakes

Confusing NAD⁺ with NADH, or omitting FADH₂.
Failing to mention the proton gradient or ATP synthase.
Using vague terms like ‘energy’ instead of ‘electron transport chain’ or ‘oxidative phosphorylation’.

Mark scheme (4 marks)

Glycolysis produces pyruvate (and reduced NAD / NADH), which enters the mitochondrial matrix for the link reaction / Krebs cycle
In the link reaction / Krebs cycle, pyruvate / acetyl CoA is further oxidised, releasing CO₂ and producing more reduced NAD (and reduced FAD)
Reduced NAD (and reduced FAD) produced in glycolysis and the Krebs cycle donate electrons to the electron transport chain on the inner mitochondrial membrane
Energy released from electron transport drives the pumping of protons (H⁺) across the inner membrane, creating a gradient that powers ATP synthase to synthesise ATP (oxidative phosphorylation / chemiosmosis)

Key terms in this question

glycolysis