Respiration is the process by which living cells release energy from food (glucose). It should not be confused with breathing — respiration is a chemical process inside every cell.
Aerobic Respiration
Aerobic respiration uses oxygen and releases a large amount of energy.
It takes place in the mitochondria of cells. Most organisms (including humans) use aerobic respiration for their daily energy needs.
Anaerobic Respiration
Anaerobic respiration occurs without oxygen and releases a small amount of energy. It takes place in the cytoplasm.
- In animals (during hard exercise): Glucose → Lactic acid + Energy. The build-up of lactic acid causes muscle cramps and fatigue.
- In plants and yeast: Glucose → Ethanol + Carbon dioxide + Energy. This is called fermentation, used in brewing and baking.
Comparing Aerobic and Anaerobic Respiration
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Oxygen needed? | Yes | No |
| Energy released | Much (about 38 ATP) | Little (about 2 ATP) |
| End products | CO₂ and water | Lactic acid (animals) or ethanol + CO₂ (yeast) |
| Where in cell | Mitochondria | Cytoplasm |
Gaseous Exchange
Breathing brings oxygen into the lungs and removes carbon dioxide. In humans, gaseous exchange occurs in the alveoli (tiny air sacs) of the lungs, which have thin walls and a large surface area for efficient diffusion.
Summary
Respiration releases energy from glucose. Aerobic respiration (with oxygen) releases much energy and produces CO₂ and water. Anaerobic respiration (without oxygen) releases little energy and produces lactic acid (animals) or ethanol and CO₂ (yeast).
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