Direct respiration means exchange of gases without using any special respiratory organ and blood. In case of insects, the tracheal tubes exchange oxygen and carbon dioxide with the haemocoel which then exchange then with tissues

Respiration in Insects

In insects, respiration occurs through a system of specialized tubes called tracheae. These tracheae branch out into smaller tubes called tracheoles, which reach every tissue and cell in the insect's body. The exchange of gases takes place directly between the tracheal tubes and the tissues.

Explanation:

1. Respiratory System of Insects:
Insects do not possess lungs or any specialized respiratory organs like mammals. Instead, they have a network of tracheal tubes that serve as their respiratory system. These tubes start from the surface of the insect's body and extend into the body tissues.

2. Tracheal Tubes:
The tracheal tubes carry oxygen from the outside environment to the tissues and remove carbon dioxide, which is the waste product of cellular respiration. The tubes are lined with a thin, permeable cuticle that allows gas exchange to occur. The tracheal tubes penetrate the insect's body and reach each individual cell, ensuring efficient delivery of oxygen and removal of carbon dioxide.

3. Tracheoles:
The tracheal tubes branch out into smaller tubes called tracheoles. These tracheoles are extremely fine and extend throughout the insect's body tissues, making them very close to the cells. This proximity allows for a more efficient exchange of gases between the respiratory system and the cells.

4. Direct Exchange of Gases:
The exchange of gases in insects occurs directly between the tracheal tubes and the tissues. Oxygen diffuses from the tracheal tubes into the cells, where it is used for cellular respiration. Carbon dioxide, the waste product of cellular respiration, diffuses from the cells into the tracheal tubes for elimination.

5. Tracheal System and Haemocoel:
Option B states that insects exchange gases with the haemocoel, which is incorrect. The haemocoel is the body cavity of insects that contains the circulatory fluid called haemolymph. While the tracheal tubes are in close proximity to the haemolymph, the exchange of gases does not occur directly with it. Instead, the tracheal system directly exchanges gases with the tissues.

Conclusion:
Insects have a unique respiratory system where respiration occurs through tracheal tubes and tracheoles. The exchange of gases takes place directly between these tubes and the tissues. This system allows for efficient gas exchange and ensures that every cell in the insect's body receives oxygen and gets rid of carbon dioxide.