| External respiration | Internal respiration |
| 1. Intake of air from the outside into the body and release of air from the body to outside is called external respiration. | 1. Exchange of gases between cells and tissue fluid is called internal respiration. |
| 2. External respiration occurs between cells and the external environment. | 2. Internal respiration occurs only in the cells of the body. |
| 3. It involves processes of inspiration and expiration. | 3. It involves movement of O2 from blood into tissue fluid and movement of CO2 from tissue. |
| 4. External respiration involves breathing and gaseous exchange. | 4. Internal respiration involves neither breathing nor gaseous exchange. |
| 5. Oxygen combines with haemoglobin in external respiration. | 5. Chemical reactions occur in the cells to form energy. |
