Editing Carbohydrate (section)

===Use in living organisms===
Monosaccharides are the major fuel source for [[metabolism]], and glucose is an energy-rich molecule utilized to generate ATP in almost all living organisms.  Glucose is a high-energy substrate produced in plants through photosynthesis by combining energy-poor water and carbon dioxide in an endothermic reaction fueled by solar energy.  When monosaccharides are not immediately needed, they are often converted to more space-efficient (i.e., less water-soluble) forms, often [[polysaccharide]]s.  In animals, glucose circulating the blood is a major metabolic substrate and is oxidized in the mitochondria to produce ATP for performing useful cellular work.  In humans and other animals, serum glucose levels must be regulated carefully to maintain glucose within acceptable limits and prevent the deleterious effects of hypo- or hyperglycemia.  Hormones such as insulin and glucagon serve to keep glucose levels in balance: insulin stimulates glucose uptake into the muscle and fat cells when glucose levels are high, whereas glucagon helps to raise glucose levels if they dip too low by stimulating hepatic glucose synthesis.  In many animals, including humans, this storage form is [[glycogen]], especially in liver and muscle cells. In plants, [[starch]] is used for the same purpose. The most abundant carbohydrate, [[cellulose]], is a structural component of the [[cell wall#plant cell walls|cell wall]] of plants and many forms of algae. [[Ribose]] is a component of [[RNA]]. [[Deoxyribose]] is a component of [[DNA]]. [[Lyxose]] is a component of lyxoflavin found in the human [[heart]].<ref>{{cite encyclopedia |title=lyxoflavin |url=http://www.merriam-webster.com/medical/lyxoflavin |dictionary=Merriam-Webster |access-date=February 26, 2014 |archive-date=October 31, 2014 |archive-url=https://web.archive.org/web/20141031135041/http://www.merriam-webster.com/medical/lyxoflavin |url-status=live }}</ref> [[Ribulose]] and [[xylulose]] occur in the [[pentose phosphate pathway]]. [[Galactose]], a component of milk sugar [[lactose]], is found in [[galactolipid]]s in [[cell membrane#lipids|plant cell membranes]] and in [[glycoprotein]]s in many [[biological tissue|tissues]]. [[Mannose]] occurs in human metabolism, especially in the [[glycosylation]] of certain proteins. [[Fructose]], or fruit sugar, is found in many plants and humans, it is metabolized in the liver, absorbed directly into the intestines during [[digestion]], and found in [[semen]]. [[Trehalose]], a major sugar of insects, is rapidly hydrolyzed into two glucose molecules to support continuous flight.