Why do organisms need carbohydrates?

Maybe the question should be 'What do organisms use carbohydrates for?' Carbohydrates are any biochemical substance that is comprised of sugars. Single sugars, monosaccharides, can be strung into disaccharides of two or more sugar molecules or polysaccharides of thousands of sugar molecules. Sugars are used via cellular respiration to derive energy for the cells and organism as a whole. Most sugars used for energy are monosaccharides. Brain cells only use glucose for energy. Cellular respiration derives energy from monosaccharides like glucose by several stages: Glycolysis The link reaction The Krebs cycle/Citric acid cycle The electron transport pathway All these reactions are very complex and involve many enzymes. Some sugar molecules are attached to cell coats as glycoproteins. Sugar molecules ribose and deoxyribose are involved in the genetic behaviour of cells.