A Level Biology Practice Exam 2025 - Free A Level Biology Practice Questions and Study Guide

The primary function of alveoli in respiration is to perform gas exchange between air and blood. Alveoli are tiny, sac-like structures in the lungs that provide a large surface area for efficient gas exchange. They are surrounded by a network of capillaries, where oxygen from the air inside the alveoli diffuses into the bloodstream, and carbon dioxide, a waste product of metabolism, diffuses from the blood into the alveoli to be expelled during exhalation. This process is essential for maintaining the body’s oxygen levels and for getting rid of carbon dioxide, which is vital for homeostasis. The structure of the alveoli, with their thin walls and extensive surface area, maximizes the efficiency of this exchange, making them crucial for respiratory function.