Carbohydrates, monosaccharides and sugars

Sugars are synthesized by green plants from C02 and H20 in the presence of sunlight. Approximately 200 000 million tonnes of carbon dioxide are taken in by plants from the atmosphere each year. In this process 130 000 million tonnes of oxygen are produced, along with 50 000 million tonnes of organic matter. 

The sugar molecules contain many asymmetric carbon atoms. They are therefore optically active and have both d and l isomers. There are 16 optically active aldehyde hexoses alone. Some of them are of value to us in our metabolism and others not. Glucose is the most useful hexose. Our bodies are very selective in what chemicals they use and reject unsuitable ones. 

Sometimes two sugar molecules join up to form a disaccharide. One well-known disaccharide is called sucrose, C F On, formed from one molecule of glucose 

---