Carbon, hydrogen and oxygen are some of the most abundant elements in the Earth. That is most likely the primary reason that most organic compounds are built by them. The advantage of carbon is that it is possible to make infinite chains with it. Depends on the other elements binding to the carbon atoms the molecule would show different features. There are three most abundant organic molecule types which are carbohydrates, fatty acids and amino acids. The energy cycle of all living organisms include building carbon chains to store energy at first and then removing carbon atoms from the chains to convert the energy for use in other chemical reactions. In practice all three types of molecules are suitable for that purpose. However fatty acids are not water soluble and needs to be carried by proteins which is not that efficient. Amino acids on the other hand contain nitrogen which would create the side product NH3(Ammonia) when broken down, which is poisonous because its acidic nature. Therefore, carbohydrates are the only option for an efficient energy chain. Monosaccharides as the most basic form of carbohydrates, are the base compound of all energy chain of all living on Earth.
To an organism that relies on glucose, monosaccharides provide the body with energy that is very vital for growth and maintenance of metabolic functions such as cellular respiration. Monosaccharides are the building blocks of disaccharides like common sugar.