CBSE Class 10 Answered

Insects have evolved a very simple tracheal system that relies on a network of small tubes that channel O₂ directly to the different parts of the body.The tracheal system is composed of chitin-ringed tubes called tracheae that connect directly to the air through openings in the body wall called spiracles. The tracheae branch into smaller and smaller tubes, called tracheoles, that eventually terminate on the plasma membrane of every cell in the insect's body. The tips of the tracheoles are closed and contain fluid. Air enters the tracheae through the spiracles and travels through the tracheoles to the fluid-filled tips, where oxygen diffuses directly from the tracheoles into the cells, and CO₂ diffuses from the cells into the tracheoles.Because the tracheal tubes carry oxygen from the air directly to the cells, insects don't need to carry oxygen in their hemolymph, like mammals do in their blood. So in insects, gasesous exchange does not use any intermediate respiratory pigment or pumping organ. The trachea carry the oxygen directly from the atmosphere to the tissues.