2.2 | Movement and Exchange of Gases in the Human Body

• The air inhaled into the alveolus has a higher concentration of oxygen compared to the concentration of oxygen in the blood. Therefore, oxygen will diffuse through the wall of the alveolus into the walls of the capillaries and into the blood.

• In red blood cells, there is a dark red-coloured compound known as haemoglobin. Haemoglobin will combine with oxygen to form oxyhaemoglobin which is an unstable compound and bright red in colour.

Haemoglobin + oxygen <--------> Oxyhaemoglobin

• Blood with oxyhaemoglobin is transported from the lungs to the heart and pumped to the other parts of the body.

• When the blood reaches the area around the body cells that has a low concentration of oxygen, the oxyhaemoglobin being an unstable compound will decompose to release oxygen molecules and change back into haemoglobin.

Oxyhaemoglobin → haemoglobin + oxygen

• In the body cells, the diffused oxygen oxidises glucose molecules into carbon dioxide, water and energy through the process of cellular respiration as summarised in the following chemical equation.

Glucose + oxygen → carbon dioxide + water + energy

• Carbon dioxide released by the cells diffuses into the blood capillaries and is transported to the alveolus to be removed during exhalation.