Gaseous exchange

Gas exchange is a biological process through which different gases are transferred in opposite directions across a specialized respiratory surface. Gases are constantly required by, and produced as a by-product of, cellular and metabolic reactions, so an efficient system for their exchange is extremely important. It is linked with respiration in animals, and both respiration and photosynthesis in plants, bacteria and some protista.

In respiration, oxygen (O
2) is required to enter cells, while waste carbon dioxide (CO
2) must be excreted. Respiration, which takes place in the has four main steps: glycolysis, pyruvate oxidation, the citric acid cycle and oxidative phosphorylation. During the process of respiration, glucose is broken down into carbon dioxide (CO
2) and water (H
2O), with ATP being produced throughout these steps.

Photosynthesis, is the process by which plants, bacteria and some protista use light energy to produce glucose from CO
2 and O
2. This conversion is facilitated by the green pigment called chlorophyll, found in the chloroplast organ of these organisms.

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