carbohydrate

The digestion of carbohydrate. The complex polysaccharide starch is broken down into glucose by the enzymes amylase and maltase (secreted by the small intestine).

Chemical compounds composed of carbon, hydrogen, and oxygen, with the basic formula C_m(H₂O)_n, and related compounds with the same basic structure but modified functional groups. They are important to living organisms and, as sugar and starch, are an important part of a balanced human diet, providing energy for life processes including growth and movement. Excess carbohydrate intake can be converted into fat and stored in the body.

The simplest carbohydrates are sugars (monosaccharides, such as glucose and fructose, and disaccharides, such as sucrose), which are soluble compounds, some with a sweet taste. When these basic sugar units are joined together in long chains or branching structures they form polysaccharides, such as starch and glycogen.

The simple sugar called glucose is used in living organisms in respiration to release energy that can be used for life processes. The sugar we use to sweeten foods is a complex sugar called sucrose. Starch is used by plants as a way of storing energy-rich food, and animals that eat plants take advantage of this. It is a common part of the human diet because it is major constituent of wheat, rice, potatoes, and maize. Humans use a carbohydrate called glycogen as an energy store. This is also made from glucose. It is stored in the liver and muscles and can be broken down to supply body cells with glucose. The hormone insulin regulates this process, causing glucose to be taken in the bloodstream to the liver to be converted to glycogen.

Chitin and cellulose Even more complex carbohydrates are known, including chitin, which is found in the cell walls of fungi and the hard outer skeletons of insects, and cellulose, which makes up the cell walls of plants. Cellulose cannot be digested by humans, though it is useful in the diet as fibre.