ANATOMY

Detailed explanation-1: -And the fact that they are permeable means that it is much easier for the gases to diffuse from the capillaries into the cells and vice versa. We have therefore determined that the correct answer is (E). It is important for capillaries to have thin, permeable walls to allow substances to diffuse into and out of cells.

Detailed explanation-2: -The walls of the alveoli and capillaries are permeable. What does this mean? substances can pass through them.

Detailed explanation-3: -In a process called diffusion, oxygen moves from the alveoli to the blood through the capillaries (tiny blood vessels) lining the alveolar walls. Once in the bloodstream, oxygen gets picked up by the hemoglobin in red blood cells.

Detailed explanation-4: -The capillary wall is a one-layer tissue so thin that gas and other items (eg oxygen, water, proteins and fats) can pass through them driven by pressure differences. Waste items such as carbon dioxide and urea can move back into the blood to be carried away for removal from the body.

Detailed explanation-5: -The alveoli are where the lungs and the blood exchange oxygen and carbon dioxide during the process of breathing in and breathing out. Oxygen breathed in from the air passes through the alveoli and into the blood and travels to the tissues throughout the body.