Explain how glycolysis converts glucose into pyruvate and contributes to ATP production.

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)

1. Glucose (C₆H₁₂O₆) is phosphorylated by ATP to form fructose‑1,6‑bisphosphate, activating the sugar.
2. The 6‑carbon molecule is cleaved into two 3‑carbon triose phosphates (glyceraldehyde‑3‑phosphate).
3. Each triose phosphate loses a hydride ion; the electrons are transferred to NAD⁺, forming NADH.
4. Substrate‑level phosphorylation of the triose phosphates to pyruvate generates a net gain of 2 ATP per glucose.

Examiner tips

  • Use the exact terms: ‘phosphorylated’, ‘fructose‑1,6‑bisphosphate’, ‘triose phosphate’, ‘NAD⁺ → NADH’, ‘substrate‑level phosphorylation’, ‘net gain of 2 ATP’.
  • Show the sequence of steps in order and link each to ATP production or NADH formation.

Mark scheme (4 marks)

  1. Glucose (a 6-carbon molecule) is phosphorylated / activated using ATP, producing hexose bisphosphate
  2. The 6-carbon sugar is split into two 3-carbon molecules (triose phosphate / glyceraldehyde-3-phosphate)
  3. Hydrogen / electrons are removed from triose phosphate and accepted by NAD, producing reduced NAD (NADH)
  4. A net gain of 2 ATP per glucose is produced by substrate-level phosphorylation during the conversion of triose phosphate to pyruvate

Key terms in this question

glycolysis · pyruvate

Related

More Cell respiration questions

▶ Try answering this question with AI marking (free) →