Free The Interrelationship Between Photosynthesis and Respiration OCR A Level Biology revision notes – covering specification point 5.2.1 (a).
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Photosynthesis and respiration are interdependent processes.
Carbon dioxide and water, which are products of respiration, are the raw materials for photosynthesis.
Glucose and oxygen, which are products of photosynthesis, are the raw materials for aerobic respiration.
As a result, the same substances are continuously recycled between the two processes.
The overall equations for photosynthesis and aerobic respiration show this interrelationship:
Photosynthesis:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy absorbed by chlorophyll)
Aerobic respiration:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (energy released as ATP)
The Compensation Point
The compensation point is the light intensity at which the rate of photosynthesis equals the rate of respiration. At this point, there is no net gain or loss of carbohydrate in the plant.
Comparing Photosynthesis and Aerobic Respiration
Due to the shared principles by which photosynthesis and aerobic respiration work (such as such as oxidation–reduction reactions, electron transport chains, and chemiosmosis), questions comparing the two processes are common and likely.
The table below compares the key features of photosynthesis and respiration:
| Feature | Photosynthesis | Respiration |
|---|---|---|
| Overall purpose | Converts light energy into chemical energy (glucose) | Transfers chemical energy (glucose) into ATP |
| Reactants | CO₂ + H₂O | Glucose + O₂ |
| Products | Glucose + O₂ | CO₂ + H₂O + ATP |
| Organelle(s) | Chloroplast | Mitochondria and cytoplasm |
| Coenzymes |
|
|
| Chemiosmosis | Thylakoid membrane | Inner mitochondrial membrane |