How Does Energy Flow Through Living Systems?

Energy in living organisms flows through chemical reactions. Each step in chemical reaction involves conversion of a set of substances, known as the reactants, into specific products. During chemical reactions, energy stored in chemical bonds is transferred to other, newly created chemical bonds.

All living organisms require capturing, store and utilizing energy to perform the functions of life. These processes are achieved through cellular chemical processes. Exothermic reactions discharge energy, while endothermic reactions take in energy for a reaction to occur. In plants, chemical reactions involve the process by which plant cells convert sunlight energy into chemical energy that supports plant growth and other processes. Carbon dioxide combines with simple sugars to produce complex carbohydrates in a process known as photosynthesis.

The sum of cell chemical reactions in living things is known as metabolism and occurs in two phases. Catabolism reactions break down molecules into simpler molecules. Anabolism, on the other hand, constructs larger molecules. Generally, catabolism produces chemical energy, while anabolism requires chemical energy. Essentially, chemical energy in all living organisms is essentially stored in the form of a molecule known as Adenosine Tri-phosphate. ATP may be transformed into Adenosine di-phosphate in a process that involves loss of a phosphate group and the discharge of stored chemical energy. ADP may be converted back to ATP when a cell has excessive energy.