Explain oxidative phosphorylation
Describe hydrogen splitting, electron transport, proton pumping, ATP synthesis by chemiosmosis and oxygen reduction to water.
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
Through which enzyme do protons return to the matrix to drive ATP synthesis?
What you will learn
- Trace energetic electrons and proton movement across the inner membrane
- Explain ATP synthesis and the role of oxygen as final electron acceptor
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
During oxidative phosphorylation, hydrogen atoms split into protons and energetic electrons. Electrons pass along the electron transport chain in the inner mitochondrial membrane and release energy. This energy is used to transfer protons across the inner membrane, establishing an electrochemical gradient. Protons return to the matrix by facilitated diffusion through ATP synthase, and this flow provides energy for ATP synthesis. Oxygen is the final electron acceptor and combines with electrons and protons to form water.
Apply it carefully
Keep the direction clear: protons are pumped from the matrix across the inner membrane and return through ATP synthase. Oxygen accepts electrons at the end; it is not the source of the proton gradient. Do not add detailed carrier or ATP synthase structure beyond the syllabus expectations.
Pause and explain
What is the final electron acceptor in aerobic respiration?
Worked example
Why does oxygen have to be available for oxidative phosphorylation to continue?
Show the worked solution
- Identify its place at the end of electron transport.
- It accepts electrons and forms water, allowing the chain to pass electrons onward.
Answer Oxygen is the final electron acceptor. It combines with electrons and protons to form water, allowing electron transport to continue.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Trace the sequence from energetic electrons to ATP synthesis and water formation.
Give me a hint
Include electron flow, proton pumping, ATP synthase and oxygen.
Compare my reasoning
- Electrons pass along the inner-membrane chain and release energy used to pump protons across the membrane.
- Protons flow back through ATP synthase, driving ATP synthesis; oxygen accepts electrons and forms water with protons.
Hydrogen splits into protons and energetic electrons. Electrons pass along the inner-membrane electron transport chain and release energy used to pump protons from the matrix across the membrane. Protons return through ATP synthase, driving ATP synthesis; oxygen accepts electrons and combines with protons to form water.
Look for these in your work
- Electron energy used for proton pumping
- Gradient/direction correct
- ATP synthase role correct
- Oxygen and water included
A membrane becomes freely permeable to protons. Predict how this affects chemiosmotic ATP synthesis and explain why.
Give me a hint
Consider whether a proton gradient can be maintained.
Compare my reasoning
- Protons would cross without being channelled through ATP synthase.
- The gradient dissipates, so less proton flow through ATP synthase is available to drive ATP synthesis.
The proton gradient would dissipate as protons cross the membrane without passing through ATP synthase. Less proton flow would be coupled through ATP synthase, so chemiosmotic ATP synthesis would decrease.
Look for these in your work
- Gradient loss predicted
- ATP synthase coupling considered
- Direction of effect explained
A student says oxygen pumps protons across the inner membrane. Refine the mechanism.
Give me a hint
Separate electron acceptance from energy-driven proton transfer.
Compare my reasoning
- Electron transport releases energy used to pump protons.
- Oxygen accepts electrons at the end and forms water with protons.
Energy released as electrons pass along the transport chain drives proton transfer across the membrane. Oxygen is the final electron acceptor and combines with electrons and protons to form water; it does not pump the protons.
Look for these in your work
- Energy source identified
- Pumping mechanism corrected
- Oxygen role stated
Common mistakes
- Reversing proton movement
- Saying oxygen pumps protons
- Claiming ATP synthase pumps protons outward in this account
What can you explain now?
Through which enzyme do protons return to the matrix to drive ATP synthesis?
Compare with the explanation
ATP synthase
Proton flow through ATP synthase is coupled to phosphorylation of ADP.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
How does electron transport establish a proton gradient that drives ATP synthesis?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.