Question

Choose the correct answer from the alternatives given. What are the respiratory organs in the cockroach?
(a) Lung
(b) Trachea
(c) Skin
(d) None of these

Answer 1

Hint: Insect respiratory system is not the same as the respiratory system in humans. The respiratory system in cockroaches is highly efficient but there are no lungs. Instead, they draw in air through external valves called spiracles and transport them directly to the cells through a tube-like structure. Spiracles capture the oxygenated air and transfer to the tube- like structure which distributes the oxygen to the cells of the cockroach.

Complete step by step answer:
In cockroaches, breathing occurs through small openings on the sides of its body called spiracles. When air enters into its respiratory system, spiracles serve as muscular valves paving the way to the internal respiratory system. The respiratory organ of the cockroach is a dense array of a network of air tubes found in the internal system known as tracheae. Tracheae are known to balance the pressure inside the system. There are ten pairs of spiracles, which are present on the lateral side of the body. Each spiracle is oval in shape and bounded by an annular sclerite having a filtering apparatus formed by the bristles to eliminate dust particles from inflowing air. Three longitudinal tracheal trunks are present on each side of the abdominal cavity. Alternate contraction and relaxation of tergo- sternal muscles bring about the changes in the diameter of the tracheae so that the air is forced in and out of tracheal tubes through the spiracles. The working of spiracles is under the control of the central nervous system.
So, the correct answer is 'Trachea'.

Additional Information:
- During the intake of air, the muscles relax to open anterior four pairs of spiracles, through which air reaches in.
- During expiration, the abdominal muscles contract to drive air out of tracheal space.
- When oxygen- rich air enters into the body of a cockroach via spiracles into the tracheal tubes, it diffuses into various tissues and cells of the body.
- Likewise, carbon dioxide- rich air passes into the trachea and moves to the outwards through the spiracles.

Note:
- Cockroaches can close all the spiracles and may suspend their respiration for a considerable period of time.
- The opening and closure of the spiracles depend upon the carbon dioxide concentration.
- The concept of the respiratory system of the cockroach is similar to that of human beings in the way that spiracles act as nostrils, the trachea is common in both, and tracheoles act as alveoli in humans.