Alveolus - GCSE Biology Definition

An alveolus is a small air sac found in the lungs, important for gas exchange for respiration. These tiny sac-like structures are located at the end of bronchioles. They are where oxygen from inhaled air passes into the blood, while carbon dioxide moves into the alveoli from the blood to be exhaled. Alveoli have very thin walls and are surrounded by capillaries, which enable efficient gas exchange due to their close contact with the air sacs. Their large number and combined surface area are vital for effective gas exchange, making them an essential part of the human respiratory system studied in GCSE Biology.