While animals and fungus get energy secondhand, by digesting the remains of animals or plants, plants use a process called photosynthesis to produce energy directly from the sun. The plant uses leaves to capture and biochemically process the raw energy from sunlight, or artificial light, into several chemicals that make it possible for the plant to live, grow and reproduce.
The aim of photosynthesis is to produce energy for the plant, and this energy comes primarily in the form of the enzyme ATP. ATP, or adenosine triphosphate, is a necessary product for all living things and the energy used in cellular reactions and interactions. In animals, ATP is stored in muscle tissue, but plants have no use for muscle tissue and instead store ATP in the same chloroplasts that are used to help harvest energy from the sun. ATP is both used and produced in photosynthesis and is necessary in both in the photophosphorylation process, which produces ATP, and the Calvin cycle, which produces sugars to store the energy gains made from photosynthesis. Single cell protists such as algae store ATP in the mitochondria of the cell.
One of the most beneficial byproducts of photosynthesis is oxygen. Of course animals such as humans require oxygen to breath and this life-sustaining substance is released as a waste product from the photosynthesis process. As a plant takes in sunlight and begins the photosynthetic process, it also takes in six molecules of H20, or water, and six molecules of CO2, or carbon dioxide, which it uses in the production of each molecule of sugar. The sugar is used to trap the ATP enzyme and store energy for later use, but since each sugar molecule only requires six molecules of oxygen, six molecules of O2 oxygen are left over. As the sugar is produced, the oxygen is released through small pores in the plant's chloroplasts called stoma.
Like the fat reserves of an animal, sugar, in the form of glucose along with fructose and other sugars, act as the long term energy storage system for plants and ensure that a plant will not simply dry up or die on the first cloudy day, cold night or dry spell. Sugar is also used in the production of flowers and fruits in many plants. Sugar is created in the Calvin cycle near the end of the photosynthesis process, sometimes referred to as the dark stage since it takes place after the collection of sunlight.