Because they toxin material which are not useful for our body so they are execrt out

Excretion is the removal of useless substances and substances present in excess.

Excretion is an essential process in living organisms that helps maintain homeostasis by removing waste products from the body. It involves the elimination of substances that are not required by the body or are present in excess. This ensures the proper functioning and health of the organism.

Key Points:
- Excretion is the process of eliminating waste materials from the body.
- It helps in maintaining the internal environment of the body by removing harmful substances.
- The main purpose of excretion is to get rid of waste products that are produced as a result of metabolic processes.
- Excretion involves the removal of substances that are not required by the body or are present in excess.
- It plays a crucial role in maintaining the balance of various substances in the body, such as water, electrolytes, and nitrogenous waste products.
- Excretion helps in regulating the pH level of the body by removing excess acids or bases.
- The organs involved in excretion include the kidneys, lungs, liver, skin, and intestines.
- The kidneys are the primary organs of excretion in humans and are responsible for filtering waste products from the blood and producing urine.
- The lungs excrete carbon dioxide, a waste product of cellular respiration, through the process of breathing.
- The liver excretes bile, a waste product produced during the breakdown of hemoglobin and other substances.
- The skin excretes sweat, which contains water, salts, and urea.
- The intestines excrete undigested food materials through feces.
- Excretion is a continuous process that helps in maintaining the overall health and well-being of the organism.

Conclusion:
Excretion is a vital process that involves the removal of useless substances and substances present in excess from the body. It ensures the proper functioning and health of the organism by maintaining the internal environment and eliminating waste products.