Why Photosynthesis Matters

Challenges to clear

• Advance to the only step that brings carbon INTO living things.
• Follow the carbon all the way round.

The task

Follow a carbon atom out of the air and back again.

What this lesson covers

• Carbon dioxide in the air — About 0.03% of the atmosphere, and the source of every carbon atom in every living body.
• Fixed by green plants — Photosynthesis locks that carbon into glucose. Green plants are the producers — the only entry point for energy and carbon into the living world.
• Passed along the food chain — Herbivores eat the plants, carnivores eat the herbivores. Every consumer is living on carbon and energy that a plant captured first.
• Returned by respiration — Every organism, plant and animal alike, releases CO₂ back to the air as it respires.
• Returned by decomposers — When organisms die, bacteria and fungi break their bodies down and release the carbon again.
• Locked away, and released — Some carbon was buried and became coal and petroleum. Burning fossil fuels returns it far faster than it was stored — which is why the balance of the cycle is shifting.
• And the oxygen — Photosynthesis is also the source of the oxygen every aerobic organism breathes. Both halves of the atmosphere we depend on are maintained by it.

Hint

Photosynthesis and respiration are the two halves of the cycle. In balance they cancel; the burning of fossil fuel is the extra term that breaks the balance.