In which of the following parts of organisms, the process of gaseous exchange during respiration does not take place?

The correct answer is B, Bronchi of humans. The bronchi only carry air between the windpipe and the lungs; their walls are too thick for oxygen and carbon dioxide to pass into the blood, so no gas exchange happens there. In humans air moves through the nose, pharynx, larynx and trachea, which divides into two bronchi; these branch into bronchioles that end in tiny balloon-like sacs called alveoli. The alveoli have very thin walls wrapped in a dense network of capillaries, and it is here that oxygen enters the blood and carbon dioxide leaves it. The passages before the alveoli are called the conducting zone and are sometimes described as dead space. Option A is wrong because the moist, thin skin of the earthworm is its respiratory surface, rich in blood vessels. Option C is wrong because Pila, the apple snail, is aquatic and breathes through gills that exchange gases with water. Option D is wrong because the alveoli are the actual site of gas exchange in human lungs. Exam tip: trachea → bronchi → bronchioles carry air; alveoli exchange gases; earthworm breathes through skin.