A plant takes in sunlight, water, and the air you breathe out, and builds sugar while releasing the oxygen you breathe in. Photosynthesis stores the Sun's energy; respiration — in the plant and in you — spends it back out again.
Two halves of one cycle
Photosynthesis lets plants capture light energy: using sunlight, carbon dioxide, and water, chloroplasts build glucose and release oxygen. Cellular respiration runs the reverse in the mitochondria of nearly all cells: glucose and oxygen are broken down to release usable energy (ATP), giving off carbon dioxide and water.
The products of photosynthesis (glucose + O₂) are the inputs of respiration, and vice versa. Together they cycle energy and matter through ecosystems.
Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Respiration reverses it to release ATP.
- Note that a plant releases oxygen in daylight.
- Ask which process consumes that oxygen.
- Connect the plant's output to the animal's (and plant's own) respiration.
What you should see: Oxygen released by photosynthesis is consumed during respiration — the two processes feed each other.