Carbohydrates are an essential food and energy source for all life.
Plants form simple carbohydrates as sugars from carbon dioxide and water and then link these simple sugars into long-chain carbohydrates for future energy release.
Animal creatures, including humans, consume carbohydrates as food, and the digested carbohydrates can serve either as an immediate energy source or become reconstituted as a stored energy reserve.
The word carbohydrate implies hydrated carbon, which these molecules are. Carbon atoms link as the backbone structure for carbohydrates, and hydrogen and oxygen atoms bond both to carbon and to each other. Glucose and fructose are the basic simple carbohydrate molecules formed by plants. Each has 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Glucose can bond to itself, forming maltose, a double-glucose or disaccharide molecule. Glucose can bond also to fructose, forming a second type of disaccharide, sucrose.
All of these compounds are made by plants and are stored in plants as mono-sugars or di-sugars.
Plants also form and store longer chains of glucose. These chains are “starch,” and starch is simply a glucose polymer, meaning a larger polysaccharide of linked glucose molecules. Formed starch resides in plants as an energy store for the plant’s life during nocturnal respiration events. Starch is broken down again to the basic glucose sugar in plants as necessary for the plant’s energy needs.
Most plants form starch polymers. Plant starch takes two basic forms: a linear helix of glucose molecules linked in a chain or a chain of glucose with multiple side branches. Both are digestible by animals and humans.
The digestion and assimilation of carbohydrates by animals and humans is straightforward. All carbohydrates must be broken down to the basic glucose and fructose components before their absorption from the intestine can occur. This process is “digestion,” and digestion requires enzymes. Carbohydrate digesting enzymes abide in saliva, in pancreas secretions. and are also bound to the inner intestinal cell lining. These enzymes cleave starches, maltose, and sucrose to the basic monosaccharide: glucose and fructose. Glucose and fructose are then absorbed and transported in the blood stream to the liver and other organs.
Glucose and fructose can re-polymerize in our tissues into polymer carbohydrates. Glycogen is the starch created from these two simple sugars, and glycogen becomes an energy reserve in animals and humans, abiding in the liver and in muscles for eventual breakdown into glucose during periods of fasting. Glucose thus continues to serve as the universal cell energy source whether the creature is fasting or eating.
How fascinating it is that plant life and animal life share carbohydrate molecules as energy sources. Only plants can synthesis a carbohydrate molecule from “scratch” – i.e. from carbon, hydrogen, and oxygen atoms. Animal and plant life use glucose as the basic energy source for cell life, but the animal must ingest glucose and fructose either as simple sugars or as starch polymers to acquire the life-essential glucose molecule.