Cell respiration
Cell respiration is the process in which cells release energy from food. Living cells need energy for growth, movement and repair. In respiration, glucose reacts with oxygen to release energy, and the waste products are carbon dioxide and water.
Key idea
glucose + oxygen → carbon dioxide + water + energy
Respiration happens in every living cell, all day and all night. This is why we keep breathing even when we sleep — our cells always need oxygen.
Photosynthesis
Photosynthesis is the process by which green plants make their own food. It happens in the chloroplast, which contains green chlorophyll. The plant uses carbon dioxide and water, and with the energy from sunlight it makes glucose and releases oxygen.
Key idea
carbon dioxide + water → (sunlight, chlorophyll) → glucose + oxygen
How they balance each other
These two processes are opposite but connected. Plants make oxygen and food; animals and plants use that oxygen and food to release energy.
| Respiration | Photosynthesis | |
| Uses | oxygen + glucose | carbon dioxide + water |
| Makes | carbon dioxide + water | glucose + oxygen |
| Energy | releases | stores (from sunlight) |
Remember
- All living cells respire; only green plants photosynthesise.
- Respiration releases energy; photosynthesis stores energy from sunlight.
- Together they keep oxygen and carbon dioxide balanced in the air.