Define excretion.

Hint: The ways in which the organs systems comprising the organs, tissues and cells along with biomolecules work together to complete a specific goal is referred to as physiological processes. They involve smaller chemical and physical mechanisms that combine to form the bigger physiological process. Excretion is also a physiological process.

Complete answer:
• Excretion is one of the most important physiological processes seen in all living organisms. The process of eliminating the metabolic wastes from the body is defined as excretion.
• People usually confuse excretion as only the faecal matter which is a type or a part of the excretory system. The major organs involved in excretion are kidneys, liver, lungs and the skin.
• The kidney is the most important excretory organ in the body. The kidney is involved in excreting wastes and extra fluids from the body. Apart from this, the kidneys also remove acids produced by different cells and maintain a healthy balance of the salts, water and minerals (like Ca, Na, K etc) in the blood.
• The liver is involved in excreting wastes like cholesterol, vitamins, hormones through the bile.
• The lungs are involved in excreting the wastes such as carbon dioxide and water.
• Skin is involved in excreting dissolved wastes in the form of sweat. Sweat glands are responsible for the secretion of sweat.

Note: Excretion is a process that can be confused with secretion, where certain substances are produced and put out of the cell to perform certain tasks. Sweat is a form of secretion and excretion. As a secretion, it is involved in pheromone release and helps in temperature control. And as excretion, it removes excess water and salts.