Respiration in insects Is called direct because

Options

A. the cells exchange `O_(2)//CO_(2)` directly with the air in the tubes
B. the tissues exchange `O_(2)//CO_(2)` directly with coelomic fluid
C. the tissues exchange `O_(2)//CO_(2)` directly with the air outside through body surface
D. tracheal tubes exchange `O_(2)//CO_(2)` directly with the haemocoel which then exchange with tissues

Explanation

### Step-by-Step Solution:

1. **Understanding Insect Respiration**: Insects have a unique respiratory system that differs from that of mammals. Instead of lungs, they utilize a system of tubes.

2. **Tracheal System**: The respiratory system of insects consists of a network of tubes called tracheae. These tubes branch out throughout the insect's body and are responsible for transporting air directly to the tissues.

3. **Spiracles**: The tracheal tubes open to the outside of the insect's body through small openings called spiracles. These spiracles allow atmospheric air to enter the tracheal system.

4. **Direct Gas Exchange**: The key feature of insect respiration is that oxygen (O2) and carbon dioxide (CO2) are exchanged directly between the air in the tracheae and the cells of the insect. This means that there is no intermediary fluid (like blood) involved in the gas exchange process.

5. **Conclusion**: Because of this direct exchange of gases between the air and the cells through the tracheal system, respiration in insects is termed "direct respiration."

### Final Answer:
Respiration in insects is called direct because it involves the direct exchange of oxygen and carbon dioxide between the air in the tracheal tubes and the insect's cells, without the need for a circulatory fluid.

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