Excretion is necessary to remove waste by-products created during chemical reactions involving carbon sources and oxygen, which are often harmful or useless to the body’s cells.

Organisms vary in complexity and metabolic requirements, leading to different nutritional strategies. Depending on their biochemical composition and energy needs, organisms may utilize various types of carbon-based food sources and employ different mechanisms for obtaining and processing nutrients.

Energy for maintenance processes is obtained from external sources through the process of nutrition, where organisms consume food to extract energy-rich molecules that can be used for cellular activities.

Examples of autotrophs include green plants, algae, and certain bacteria that are capable of photosynthesis or chemosynthesis to produce their own food.

Autotrophs are organisms that can produce their own food using simple inorganic sources such as carbon dioxide and water, while heterotrophs rely on consuming complex substances from other organisms for energy and materials.