C4.2.21 Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis Notes

The Role of Photosynthesis in Producing Oxygen

1. A key step in photosynthesis is the release of oxygen, which occurs during photolysis in the light-dependent reactions.
2. Oxygen is produced when water molecules are split using light energy, catalyzed by the oxygen-evolving complex in photosystem II.

Aerobic Respiration Depends on Photosynthesis

1. Oxygen in the atmosphere is continually replenished by photosynthesizing autotrophs, making it available for aerobic respiration.
2. Without photosynthesis, atmospheric oxygen levels would drop, making aerobic respiration unsustainable for heterotrophs.

Photosynthesis Relies on Carbon Dioxide from Respiration

1. Respiration by heterotrophs releases carbon dioxide, which autotrophs absorb and use in the Calvin cycle to synthesize glucose.
2. Without this constant supply of carbon dioxide, the rate of photosynthesis would decline, as carbon dioxide is often a limiting factor for photosynthesis.

Global Carbon Fluxes

1. It is estimated that terrestrial ecosystems fix approximately 120 gigatonnes of carbon per year through photosynthesis, and nearly the same amount is released back into the atmosphere through respiration.
2. These massive exchanges of carbon dioxide and oxygen sustain life on Earth by maintaining a dynamic balance between the two processes.

Interdependence of Photosynthesis and Respiration

1. Autotrophs and heterotrophs are interconnected through the cycling of oxygen and carbon dioxide:
   1. Autotrophs produce oxygen, supporting respiration in heterotrophs.
   2. Heterotrophs release carbon dioxide, fueling photosynthesis in autotrophs.