Question

Assertion :In Periplanata Americana opening and closing of stigmata is influenced by $C{O}_2$ tension in haemolymph and oxygen tension in the tracheae. Reason: The air enters into tracheoles and oxygen from the air is taken into the cells and $C{O}_2$ is released into haemolymph.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

The respiratory system of cockroach consists of a series of rigid tubes, called trachea connected to the exterior via pairs of openings called spiracles. Air enters the system via the spiracles. The tracheal branches entering into an organ end in a special cell called tracheole.

Insects lose most of their water through the spiracles. They do not have much water to lose as they are small. Therefore, insects typically only open their spiracles when they need more oxygen. An increase in carbon dioxide, a product of respiration, also causes the spiracles to open more. The expulsion of carbon dioxide from the body of the cockroach occurs in bursts when the spiracles are open.

When air enters the tracheoles, due to its high partial pressure, oxygen diffuses faster into the tissues. At the same time the carbon dioxide, instead of passing into the tracheal system, goes into the haemolymph. Carbon dioxide goes more quickly into the haemolymph due to its greater solubility in it.

So, the answer is A.