Which of the following respiratory systems is not closely associated with a blood supply?

Options

A. Vertebrate lungs
B. Fish gills
C. Tracheal systems of insects
D. Outer skin of earthworm

Explanation

To determine which respiratory system is not closely associated with a blood supply, we can analyze the respiratory systems of various organisms:

1. **Human Respiratory System**: In humans, the respiratory system is closely linked to the circulatory system. The lungs contain alveoli, which are highly vascularized structures where gas exchange occurs. Oxygen from the air enters the blood, and carbon dioxide from the blood is expelled into the lungs. Thus, the human respiratory system is closely associated with blood supply.

2. **Fish Gills**: Fish use gills for respiration, which extract dissolved oxygen from water. Gills are also highly vascularized, allowing for efficient gas exchange. The oxygen absorbed by the gills is transported by the blood to body tissues. Therefore, fish gills are also closely associated with blood supply.

3. **Earthworm Skin**: Earthworms respire through their skin (cutaneous respiration). The skin is moist and has a rich blood supply that facilitates gas exchange. Oxygen diffuses into the blood, and carbon dioxide diffuses out. Thus, the skin of earthworms is also associated with blood supply.

4. **Insect Tracheal System**: Insects, such as cockroaches, have a unique respiratory system known as the tracheal system. This system consists of a network of tubes (tracheae) that directly deliver oxygen to tissues without the need for a circulatory system to transport it. Air enters through openings called spiracles and travels through the tracheae, where oxygen diffuses directly into the cells. Therefore, the tracheal system is not closely associated with a blood supply.

**Conclusion**: The respiratory system that is not closely associated with a blood supply is the **tracheal system of insects**.