Nutrient
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[[Image:Nutrient-cycle_hg.png|thumb|Nutrient cycle in the oceans]]
A '''nutrient''' is food or chemicals that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Non-autotrophic organisms typically acquire nutrients by the ingestion of foods. Methods for nutrient intake vary, with animals and [[protist]]s having an internal digestive system, but plants externally digesting nutrients before ingesting them. The effects of nutrients are [[Dose (biochemistry)|dose-dependent]].
Organic nutrients include [[carbohydrate]]s, [[fat]]s, [[protein]]s (or their building blocks, [[amino acid]]s), and [[vitamin]]s. Inorganic chemical compounds such as [[mineral]]s; [[water]] and [[oxygen]] may also be considered nutrients. A nutrient is [[Essential nutrient|essential]] to an organism if it cannot be synthesized by the organism in sufficient quantities and must be obtained from an external source. Nutrients needed in relatively large quantities are called '''macronutrients''' and those needed in relatively small quantities are called '''[[micronutrient]]s'''.
See [[healthy diet]] for more information on the role of nutrients in human [[nutrition]].
==Types of nutrient==
{{main|Nutrition}}
'''Macronutrients''' are defined in several different ways.
* The [[chemical element]]s humans consume in the largest quantities are [[carbon]], [[hydrogen]], [[nitrogen]], [[oxygen]], [[phosphorus]], and [[sulfur]].
* The classes of [[chemical compound]]s humans consume in the largest quantities and which provide bulk energy are [[carbohydrate]]s, [[protein]]s, and [[fat]]s. [[Water]] and atmospheric [[oxygen]] also must be consumed in large quantities, but are not always considered "food" or "nutrients".
* [[Calcium]], [[salt]] ([[sodium]] and [[chloride]]), [[magnesium]], and [[potassium]] (along with phosphorus and sulfur) are sometimes added to the list of macronutrients because they are required in relatively large quantities compared to other vitamins and minerals. They are sometimes referred to as the [[Dietary mineral|macrominerals]].
The remaining vitamins, minerals, or elements, are called '''[[micronutrients]]''' because they are required in relatively small quantities.
===Substances that provide energy===
* [[Carbohydrate]]s are compounds made up of [[sugar]]s. Carbohydrates are classified by their number of sugar units: [[monosaccharide]]s (such as [[glucose]] and [[fructose]]), [[disaccharide]]s (such as [[sucrose]] and [[lactose]]), [[oligosaccharide]]s, and [[polysaccharide]]s (such as [[starch]], [[glycogen]], and [[cellulose]]).
* [[Protein]]s are [[organic compounds]] that consists of the [[amino acids]] joined by [[peptide bond]]s. The body cannot manufacture some of the [[amino acids]] (termed [[essential amino acids]]); the diet must supply these. In [[nutrition]], proteins are [[protein catabolism|broken down]] through [[digestion]] by [[protease]]s back into free amino acids.
* [[Fat]]s consist of a [[glycerin]] molecule with three [[fatty acid]]s attached. Fatty acids are unbranched [[hydrocarbon]] chains, connected by single bonds alone ([[Saturated fat|saturated fatty acids]]) or by both double and single bonds ([[Unsaturated fat|unsaturated fatty acids]]). Fats are needed to keep [[cell membrane]]s functioning properly, to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids (termed [[essential fatty acids]]) and the diet must supply these.
Fat has an [[energy]] content of 9 kcal/g (~37.7 kJ/g); [[protein]]s and [[carbohydrate]]s 4 kcal/g (~16.7 kJ/g). [[Ethanol]] ([[grain alcohol]]) has an energy content of 7 kcal/g (~29.3 kJ/g).<ref>Coyle EF. 1995. Fat metabolism during exercise. Sports science exchange 8(6):59-65 </ref>
===Substances that support metabolism===
* [[Dietary mineral]]s are generally trace elements, salts, or ions such as copper and iron. Some of these minerals are essential to human metabolism.
* [[Vitamin]]s are organic compounds essential to the body. They usually act as [[coenzyme]]s or [[cofactor (biochemistry)|cofactors]] for various proteins in the body.
* [[Water]] is an essential nutrient and is the [[solvent]] in which all the chemical reactions of life take place.
==Nutrients and plants==
{{main|Plant nutrition|Fertilizer}}
[[Image:Intertidal greenalgae.jpg|thumb|400px|right|The strip of a green alga (''Enteromorpha'') along this shore indicates that there is a nearby source of nutrients (probably nitrates or ammonia from a small estuary).]]
The chemical elements consumed in the greatest quantities by plants are [[carbon]], [[hydrogen]], and [[oxygen]]. These are present in the environment in the form of [[water]] and [[carbon dioxide]]; energy is provided by [[sunlight]]. [[Nitrogen]], [[phosphorus]], [[potassium]], and [[sulfur]] are also needed in relatively large quantities. Together, these are the elemental '''macronutrients''' for plants, often represented by the [[Acronym and initialism|acronym]] CHNOPS. Usually they are sourced from inorganic (e.g. [[carbon dioxide]], [[water]], [[nitrate]], [[phosphate]], [[sulfate]]) or organic (e.g. [[carbohydrate]]s, [[lipid]]s, [[protein]]s) [[chemical compound|compounds]], although elemental [[diatomic molecule]]s of nitrogen and (especially) oxygen are often used.
Other chemical elements are also necessary to carry out various life processes and build structures; see [[fertilizer]] and [[micronutrient]] for more information.
Some of these are considered macronutrients in certain organisms. The acronym C. HOPKiN'S CaFe Mg (to be used as C. Hopkins coffee mug) is used by some students to remember the list as: Carbon, Hydrogen, Oxygen, Phosphorus, Potassium (K), Nitrogen, Sulfur, Calcium, Iron (Fe), and Magnesium (Mg). Silicon, chloride, sodium, copper, zinc, and molybdenum are sometimes also included, but are in other cases considered micronutrients.
Oversupply of plant nutrients in the environment can cause excessive plant and [[algae]] growth. [[Eutrophication]], as this process is called, may cause imblances in population numbers and other nutrients that can be harmful to certain species. For example, an [[algal bloom]] can deplete the [[oxygen]] available for fish to breathe. Causes include [[water pollution]] from [[sewage]] or [[runoff]] from farms (carrying excess agricultural fertilizer). Nitrogen and phosphorus are most commonly the [[limiting factor]] in growth, and thus the most likely to trigger eutrophication when introduced artificially.
==Essential and non-essential nutrients==
{{main|Essential nutrient}}
Nutrients are frequently categorized as essential or nonessential. [[Essential nutrient]]s are unable to be synthesized internally (either at all, or in sufficient quantities), and so must be consumed by an organism from its environment.
For humans, these include [[essential fatty acids]], [[essential amino acids]], [[vitamins]], and certain [[dietary minerals]]. [[Oxygen]] and [[water]] are also essential for human survival, but are generally not considered "food" when consumed in isolation.
Humans can derive energy from a wide variety of [[fat]]s, [[carbohydrate]]s, [[protein]]s, and [[ethanol]], and can synthesize other needed amnio acids from the essential nutrients.
Non-essential nutrients can still have a significant impact on health, whether beneficial or toxic. For example, most [[dietary fiber]] is not absorbed by the human digestive tract, but is important in digestion and absorption of otherwise harmful substances. Interest has recently increased in [[phytochemical]]s, which include many non-essential nutrients which may have health benefits.
==References==
* Donatelle, Rebecca J.2008. ''Health: The Basics, 8th edition''. Benjamin Cummings, ISBN 978-0321523020
* Whitney, Elanor and Sharon Rolfes. 2007. ''Understanding Nutrition, 11th edition''. Wadsworth Publishing ISBN 978-0495116868
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==See also==
* [[Ecological sanitation]]
* [[Nutrient density]]
[[Category:Chemical oceanography]]
[[Category:Ecology]]
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[[Category:Edaphology]]
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