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C1.2.16 (HL)—Oxygen as terminal electron acceptor

Oxygen accepts electrons at the end of the electron transport chain and combines with protons to form water, supporting usable cellular work and measurable biological activity.

Syllabus
First assessment 2025
Objective
C1.2.16
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2023
Most common paperPaper1
Typical marks1–5

Common command terms

  • Identify
  • Describe

Recent exam appearances

May 2023Paper1 ["HL"] · TZ226[ 1 ]C1.2.16 (HL)—Oxygen as terminal electron acceptor
May 2021Paper1 ["HL"] · TZ230[ 1 ]C1.2.16 (HL)—Oxygen as terminal electron acceptor
November 2018Paper2 ["HL"] · TZ06(b)[ 5 ]C1.2.16 (HL)—Oxygen as terminal electron acceptor
November 2016Paper1 ["HL"] · TZ030[ 1 ]C1.2.16 (HL)—Oxygen as terminal electron acceptor
Practice this objective

Coverage 2016–2023 · Updated 15 Jul 2026

Concept essentials

  • Oxygen is the final electron acceptor in the electron transport chain.
  • Oxygen combines with electrons and protons to form water.
  • Oxygen allows reduced carriers to be reoxidized.
  • Aerobic respiration depends on oxygen for sustained electron flow.
ConceptIB Biology HL