Relate mitochondrial structure to respiration
Use mitochondrial membranes, cristae and matrix to explain the locations and functions of aerobic respiration stages.
A Level; Cambridge International Biology 9700, 2028–2030. Written practice is self-checked; practical investigations need supervised work and human subject-teacher review remains pending.
Before you begin
- ATP transfers energy for cellular work, and enzymes control metabolic reactions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Where is the mitochondrial matrix?
What you will learn
- Identify mitochondrial compartments relevant to respiration
- Relate structure to stage location without overclaiming
Locate the four stages of aerobic respiration
| Feature | Meaning |
|---|---|
| Glycolysis | Cytoplasm · glucose to pyruvate |
| Link reaction | Mitochondrial matrix · acetyl-CoA formation |
| Krebs cycle | Mitochondrial matrix · oxaloacetate regenerated |
| Oxidative phosphorylation | Inner mitochondrial membrane · electron transport and chemiosmosis |
Build the explanation
A mitochondrion has an outer membrane and an inner membrane surrounding the matrix. The inner membrane is folded into cristae, increasing its surface area. Glycolysis takes place in the cytoplasm, the link reaction and Krebs cycle in the matrix, and oxidative phosphorylation on the inner membrane. The membrane can maintain a proton gradient between the intermembrane space and matrix, while the matrix contains enzymes for the link reaction and Krebs cycle.
Apply it carefully
A diagram or electron micrograph shows structure, not every molecule's activity. A greater inner-membrane surface can provide more area for oxidative-phosphorylation components, but a micrograph alone does not measure ATP production. Label the matrix, inner membrane, cristae and intermembrane space accurately.
Pause and explain
Why are cristae relevant to oxidative phosphorylation?
Worked example
Which mitochondrial feature provides the membrane surface for oxidative phosphorylation?
Show the worked solution
- Identify the membrane where the electron transport chain occurs.
- The inner membrane and its cristae provide this surface.
Answer The inner mitochondrial membrane, folded into cristae.
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Relate three mitochondrial structures to stages of aerobic respiration.
Give me a hint
Match the matrix and inner membrane to their reactions.
Compare my reasoning
- Matrix: link reaction and Krebs cycle.
- Inner membrane/cristae: oxidative phosphorylation and proton-gradient maintenance.
The mitochondrial matrix contains enzymes for the link reaction and Krebs cycle. The inner membrane, folded into cristae, supports electron transport, proton-gradient formation and oxidative phosphorylation.
Look for these in your work
- Matrix stages correct
- Inner-membrane stage correct
- Cristae function linked
An electron micrograph has many inner-membrane folds. What can be inferred about potential surface area, and what cannot be concluded from the image alone?
Give me a hint
Distinguish structural inference from a measurement of function.
Compare my reasoning
- Cristae increase inner-membrane area.
- The image alone cannot establish respiration rate or ATP output.
The cristae increase the available inner-membrane surface for oxidative-phosphorylation components. The image alone does not show the rate of respiration or the amount of ATP produced.
Look for these in your work
- Surface-area inference valid
- Functional limit stated
A toxin makes the inner mitochondrial membrane leaky to protons. Explain one structural reason this matters to respiration.
Give me a hint
Connect membrane integrity to the proton gradient.
Compare my reasoning
- The inner membrane normally separates compartments and maintains a proton gradient.
- Leakiness dissipates the gradient and reduces chemiosmotic ATP synthesis.
The inner membrane separates the matrix from the intermembrane space, allowing a proton gradient to form. If it becomes leaky, the gradient dissipates and less proton flow is coupled through ATP synthase, reducing ATP synthesis by chemiosmosis.
Look for these in your work
- Compartment barrier named
- Gradient role stated
- ATP consequence reasoned
Common mistakes
- Putting the Krebs cycle on cristae
- Treating micrograph appearance as a direct respiration measurement
- Confusing matrix with intermembrane space
What can you explain now?
Where is the mitochondrial matrix?
Compare with the explanation
Inside the inner mitochondrial membrane
The matrix contains enzymes for the link reaction and Krebs cycle.
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Make it stick
How do the matrix and inner mitochondrial membrane support different respiration stages?
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