The term carbohydrates (or sugars) refers to a group of polyhydroxy aldehydes or ketones. This means that a carbohydrate molecule contains several hydroxyl groups and either an aldehyde or a ketone group (see below). Carbohydrates are produced from carbon dioxide and water by plants through the process of photosynthesis. The primary function of the carbohydrates in living organisms is as an energy source. Many of them are easily digested by animals where they are converted back into carbon dioxide and water, with a concurrent release of energy.
Carbohydrates can be classified as simple or complex. Simple carbohydrates, often called monosaccharides or simple sugars, cannot be broken down into smaller carbohydrate molecules. Complex carbohydrates can be broken down into smaller carbohydrate units through a process known as hydrolysis. Examples of common carbohydrates are shown in the table below. You can click on the name of the carbohydrate if you wish to see its structure.