Mitochondria are compartmentalized organelles whose cristae, matrix, membranes, and intermembrane space support efficient aerobic respiration and ATP production in cells.
Coverage 2013–2025 · Updated 15 Jul 2026
A mitochondrion's double membrane creates a small intermembrane space, a highly folded inner membrane and a separate matrix, each adapted for aerobic ATP production.
Cristae provide a large area for electron-transport chains and ATP synthase. Proton pumping into the small intermembrane space rapidly builds an electrochemical gradient; proton return through ATP synthase drives ATP formation.
The matrix concentrates enzymes and substrates for the link reaction and Krebs cycle, while transport proteins regulate entry of pyruvate and movement of required metabolites across membranes.
A mitochondrion in a high-energy cell can have extensive cristae, accommodating more electron-transfer and ATP-synthase complexes when oxygen and respiratory substrates are available.
Cristae increase capacity but do not guarantee ATP production: oxygen, substrates, ADP, phosphate and functioning electron carriers are also required.
This objective is assessed through structured response, commonly using Draw / Explain / Label.
Draw / Explain / Label / Describe / Outline / Identify
Build the answer around this relationship: Cristae increase inner membrane surface area for electron transport and ATP synthase.
Naming mitochondrial structures without linking them to respiration or ATP production.
Representative question
Explain the relationship between the structure of the mitochondrion and its function.
HL structure-function answers should link organelle compartments to the process they support. Mitochondria use cristae, intermembrane space, and matrix; chloroplasts use thylakoid membranes, thylakoid space, and stroma. Protein export is a route: rough ER makes entry-pathway proteins, Golgi modifies and sorts, vesicles bud and fuse with targets.
