Lesson 5 of 6 / Photosynthesis and respiration
Use oxygen at the end of electron transfer
Why does oxygen availability affect ATP supply?
In this lesson: Identify oxidative-phosphorylation inputs, products and mitochondrial location.
About 5 min
The key ideaReduced carriers are oxidised, oxygen accepts electrons to form water, and energy transfer supports ATP formation from ADP and phosphate.
Explore the idea
Oxygen keeps electron transfer going
The membrane system couples energy transfer to ATP formation. Oxygen is the final acceptor and contributes to water; it is not simply converted into carbon dioxide.
Original functional schematic. The three blocks are not named or counted electron-transfer complexes; detailed machinery and ATP totals are outside this H1 requirement.
Original models of required stage inputs and outputs. Shapes are not full chemical formulae; exact pathway ATP yields are not required here.
Explanation
Oxidative phosphorylation occurs at the inner mitochondrial membrane. Reduced NAD and reduced FAD supply electrons to electron-transfer components and are oxidised back to NAD and FAD. These carriers can then participate again in earlier stages.
Energy released through electron transfer is coupled to ATP formation from ADP and inorganic phosphate. H1 requires the connection and overall inputs and products, not names of the electron-transfer complexes or a detailed ATP-synthase mechanism.
Oxygen is the final electron acceptor and combines with electrons and hydrogen ions to form water. Removing oxygen prevents sustained transfer to this final acceptor, reducing the ability to regenerate oxidised carriers and maintain this ATP supply.
The main stage-level inputs are reduced carriers, oxygen, ADP and phosphate; products include oxidised carriers, water and ATP. Oxygen is not required because it is transformed into carbon dioxide: the oxygen-consumption and carbon-dioxide-release steps are different.
Step by step
- 1
Oxidise the carriers
Reduced NAD and FAD donate electrons and are regenerated in oxidised form.
- 2
Couple energy transfer to ATP
ADP and phosphate are used to form ATP.
- 3
Accept electrons at the end
Oxygen contributes to water formation, allowing sustained flow.
Worked example
Why earlier stages can slow
Explain why lack of oxygen can eventually affect the link reaction and Krebs cycle even though oxygen is not their direct reactant.
One way to explain it
Without a final electron acceptor, sustained oxidation of reduced carriers is restricted. Less oxidised NAD and FAD is regenerated for earlier reactions, so their continued operation is limited.
Why this answer works
- Trace the recycling of carriers between stages.
- Distinguish direct use of oxygen from indirect dependence on it.
Is this true? "Respiratory oxygen is changed directly into the carbon dioxide breathed out."
Oxygen acts as the final electron acceptor and forms water. Carbon dioxide is released from carbon-containing respiratory substrates in earlier stages.