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oxygen
Oxygen accepts electrons at the end of the aerobic respiratory chain.
O Level · English Medium · Cambridge · Biology
Nutrition, transport and respiration
Connect nutrition, transport and respiration without confusing breathing with energy release.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
Digestion breaks large food molecules into absorbable forms. Transport moves materials between tissues. Aerobic respiration transfers energy through reactions using oxygen; breathing ventilates lungs and is a different process. Plants also respire, including when they photosynthesise.
Worked example
The simplified aerobic equation is glucose + oxygen → carbon dioxide + water. In humans, oxygen diffuses from alveolar air into blood, then is transported to tissues. The equation describes chemistry, not the act of inhaling.
- Track a named substance through the system.
- Identify the exchange surface and gradient.
- Connect transport to cellular reactions.
Stretch example
Water movement through xylem is linked to evaporation from leaves and cohesion of water. Phloem translocation transports assimilates between sources and sinks; it is not simply “food always moves downward”.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
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haemoglobin
Oxygen binds to haemoglobin in red blood cells.
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yes
Plant cells also need energy transfer through respiration.
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A large surface area supports gas exchange by diffusion.
Connect surface area with exchange, not active pumping of oxygen.
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Ventilation moves air in and out; cellular respiration comprises metabolic reactions transferring energy.
Name the different processes and locations.
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xylem
Xylem vessels provide the main pathway.
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It consumes or stores assimilates supplied from a source such as a photosynthesising leaf.
Use source-sink reasoning rather than a fixed direction.
Transport explanation
Draw one human and one plant transport pathway.
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- Label the transported substance.
- Connect exchange and transport.
- Separate the model from medical advice.
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