A<unk>  is a substance used in an organism's metabolism or physiology which must be taken in from the environment. Non-autotrophic organisms typically acquire<unk> s by the ingestion of foods. Methods for<unk>  intake vary, with animals and protists having an internal digestive system, while plants digest<unk> s externally and then ingested.
Organic<unk> s include carbohydrates, fats, proteins (or their building blocks, amino acids), and vitamins. Inorganic chemical compounds such as minerals; water, oxygen, and carbon dioxide may also be considered<unk> s.  A<unk>  is essential to an organism if it cannot be synthesized by the organism in sufficient quantities and must be obtained from an external source.<unk> s needed in relatively large quantities are called macronutrients and those needed in relatively small quantities are called micronutrients.
See healthy diet for information on the role of<unk> s in human nutrition.
Nutrient
Biomolecule
Metal
Phytochemical
Biopolymer
Organic compound
Chemical substance
Biological pigment