Respiration in insects is called direct because
| 1. | the cells exchange O2/CO2 directly with the air in the tubes |
| 2. | the tissues exchange O2/CO2 directly with coelomic fluid |
| 3. | the tissues exchange O2/CO2 directly with the air outside through body surface |
| 4. | tracheal tubes exchange O2/CO2 directly with the haemocoel with tissues which then exchange with tissues |
