Carbohydrates Carbohydrates are very much essential to life and occur in all plants and animals. Through photosynthesis, plants convert CO2 and H2O into carbohydrates mainly cellulose, starch and sugars. Cellulose is the building block of rigid cell walls and woody tissues in plants. Starch is the storage form of carbohydrates for later use as food or energy source. Some plants (cane and sugar beets) produce sucrose (table sugar). Glucose is an essential component of blood. Two other sugars ribose and 2-dexoyribose are components of RNA and DNA. Other carbohydrates are important components of coenzymes, antibiotics, cartilage, bacterial cell wall and mammalian cell membranes. Thus carbohydrates provide us all the three basic needs like food, cloth and shelter. All carbohydrates contain number of hydroxyl groups and carbonyl group (aldehyde or ketone). Thus carbohydrates are defined as “Polyhydroxy aldehydes or polyhydroxy ketones and other compounds which give these on hydrolysis are called carbohydrates”.