Organs of Respiration in Plants & Animals

Respiration is the process whereby organisms transport oxygen from the outside atmosphere to the cells in their tissues. Cellular respiration, by contrast, is the process through which sugars and fats are broken down in cells to yield energy.

Types

• Plants exchange gases like carbon dioxide and oxygen through tiny pores in the underside of their leaves; these pores are called stomata. Animals, by contrast, use several different types of organs for gas exchange in respiration. Mammals like humans use specialized organs called lungs; fish, by contrast, use gills, and many small organisms like insects use tracheal systems. Some small organisms in aquatic habitats can even perform gas exchange through their skin.

Function

• Tracheal systems in insects branch throughout the organism's body, conveying oxygen to almost every cell. The gills of fish and the lungs of most large organisms, by contrast, participate in gas exchange with the blood, which conveys the oxygen away from the lungs to the cells of the body. Plants do not have specialized organs for gas exchange; the simple mechanism of diffusion through the stomata is sufficient to meet their needs.

Fun Fact

• Gills are much more efficient than lungs because they use countercurrent exchange; the deoxygenated blood flows in the opposite direction to water flowing through the gills, so fish can extract a high percentage of the oxygen in the water. Birds achieve improved efficiency with air sacs positioned above and below their lungs; these air sacs pump air through the lungs so that air flows through continuously, making gas exchange more efficient in birds than in humans.