Excretion

Excretion is the way living things get rid of waste from their bodies. This is important for staying healthy. If waste builds up, it can hurt the body. In animals with a backbone, like humans, this happens mainly in the lungs, kidneys, and skin.

For example, humans get rid of urine, a kind of waste made in the kidneys, through a tube called the urethra. Tiny single-celled organisms release their waste through their outer surface. Mammals, including humans, also get rid of solid waste called feces through the anus.

When our cells use energy in a process called cellular respiration, they make waste products like carbon dioxide, water, salts, urea, and uric acid. Getting these wastes out of the body is called excretion, and it is done by special organs known as the excretory system.

Processes across various types of life

Plants

In green plants, oxygen is made during photosynthesis and leaves the plant through tiny openings called stomata. Some plants also release materials like resin, saps, and latex. These are pushed out by pressure inside the plant. When leaves fall off from deciduous plants, this is also a way they get rid of waste.

Animals

Animals get rid of waste materials such as carbon dioxide, ammonia, urea, uric acid, guanine, and creatine. The liver and kidneys help remove these from the blood, and they leave the body in urine and feces.

Aquatic animals often release ammonia directly into the water. On land, animals change ammonia-like compounds into materials like urea, which are less harmful. This process helps keep the body safe.

Birds

Birds get rid of nitrogen waste as uric acid in a paste form. This helps save water and makes it easier to store in the egg. Many seabirds can also remove salt through special glands in their noses, releasing it through their beak.

Insects

In insects, tiny tubes called Malpighian tubules help remove waste. The waste moves into these tubes and then goes to the intestines, where it leaves the body together with other materials.

The material that leaves the body may be called ejecta.