Explain how the structure of the mitochondrion is related to its function in aerobic cellular respiration.

IB DP Biology Standard Level (2023 syllabus) — B2.2 Organelles and compartmentalisation · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The outer membrane encloses the organelle, creating a distinct internal compartment that separates the reactions of aerobic respiration from the cytoplasm.
The inner membrane is highly folded into cristae, which greatly increases the surface area available for the electron transport chain, oxidative phosphorylation and ATP synthase.
The intermembrane space allows a proton (H⁺) gradient to be established, driving ATP synthesis via ATP synthase (chemiosmosis).
The matrix contains enzymes for the Krebs cycle and link reaction, and also contains mitochondrial DNA and ribosomes, allowing the organelle to produce some of its own proteins.

Examiner tips

Use the exact terms: outer membrane, inner membrane, cristae, intermembrane space, matrix, electron transport chain, chemiosmosis, ATP synthase.
Show the link between structure and function for each part – e.g. cristae increase surface area for ETC.
Mention the role of mitochondrial DNA and ribosomes in protein synthesis.
Keep the answer concise and structured in four clear points.

Common mistakes

Confusing the inner membrane with the outer membrane or omitting the cristae.
Failing to mention the proton gradient or chemiosmosis.
Not stating that the matrix contains enzymes for the Krebs cycle.

Mark scheme (4 marks)

The outer membrane encloses the organelle, creating a distinct internal compartment that separates the reactions of aerobic respiration from the cytoplasm.
The inner membrane is highly folded into cristae, which greatly increases the surface area available for the electron transport chain / oxidative phosphorylation / ATP synthase.
The intermembrane space (between the two membranes) allows a proton / H⁺ gradient to be established, which drives ATP synthesis via ATP synthase / chemiosmosis.
The matrix contains enzymes for the Krebs cycle / link reaction, and also contains mitochondrial DNA and ribosomes, allowing the organelle to produce some of its own proteins.

Key terms in this question

mitochondrion