Define excretion.

Excretion is a biological process by which living organisms, including humans, eliminate waste products and harmful substances from their bodies. This process is essential for maintaining a stable internal environment, known as homeostasis, and for preventing the accumulation of toxic or unnecessary compounds that could interfere with proper bodily functions.

In animals, including humans, excretion primarily involves the removal of metabolic waste products generated during cellular activities. These waste products may include carbon dioxide, urea, ammonia, excess salts, and other compounds that result from the breakdown of nutrients and the functioning of various physiological processes.

Excretion occurs through specific organs and systems that are adapted to eliminate waste. In humans, these organs include the kidneys, which filter blood to remove waste and excess substances, and the lungs, which expel carbon dioxide through respiration. The skin also plays a role in excretion by eliminating certain waste products through sweat.

Overall, excretion is a crucial biological process that helps maintain the proper functioning of organisms by ensuring the removal of waste products that could otherwise be harmful if allowed to accumulate.