1. In living organisms, respiration occurs at two levels:
- At the body level, where oxygen and carbon dioxide are exchanged with the environment.
- At the cellular level, where food molecules are oxidized to release energy.
2. Carbohydrates, especially glucose, are the main source of energy. Glucose is oxidized step-by-step in cells to form ATP, the energy currency of the cell. This process is known as cellular respiration.
3. Cellular respiration occurs in two ways:
- Aerobic respiration (with oxygen), where glucose is completely broken down in three steps.
- Anaerobic respiration (without oxygen), where glucose is partially broken down.
