What are two functions of carbohydrates?
The main function of carbohydrates in a living organism is to supply energy for life processes. When food is consumed by animals, one of the ultimate products of digestion is glucose, a carbohydrate that is carried to all the organism's cells. Once inside the cell, it is broken down in a process called cellular respiration. In simplified form, this means that carbohydrates and oxygen result in energy for the cell, with carbon dioxide and water as the resulting products of the reaction. Plants perform cellular respiration, but they also perform the "opposite" reaction of photosynthesis. Plants use carbon dioxide and water, plus the energy of the sun (or in some specialized cases, chemical energy) to build carbohydrates and release oxygen.
Other molecules can also be broken down in a living organism to supply energy; a supply of carbohydrates prevents proteins from being broken down for energy production. Carbohydrates are stored as glycogen if there is an excess.
Carbohydrates are structural parts of DNA/RNA. They are also part of the cell membrane, involved in cell recognition by other cells; ie, so that the organism's immune response recognizes cells as being part of the organism, and not an unwanted bacteria or fungus.