Turning Energy Into Sugar
Most plants produce their own food through a process called photosynthesis. During photosynthesis, light energy is converted to chemical energy and stored in the bonds of sugar. Light energy is usually taken from the sun, but can also be obtained through artificial lighting. Light rays are absorbed through the leaves of the plant by the plant's chlorophyll. Chlorophyll are the pigments that give leaves their green color. The chlorophyll captures the sun’s energy. With the help of carbon dioxide (taken from the air) and water (absorbed through the plant's roots), the chlorophyll turns the energy of the sun into sugar.
Making Use of the Sugar
The sugar that is created from the chlorophyll of the plant is transported through tubes in the leaves to the roots, stems and fruits of the plant. Some of the sugar is used immediately by the plant for energy while some is stored away as starch (carbohydrates). Some of the sugar is used to develop plant tissue called cellulose. Later, when the plant is in need of food, it draws upon the energy from the stored carbohydrates. Animals and humans can receive energy, also, from the stored sugar by consuming the plant or its products. This process is called respiration.
The Complexity of Photosynthesis
Photosynthesis may seem like a simple process, but it is actually quite complex. It occurs in two stages called "light reactions" and "dark reactions." Light reactions occur in the presence of light. It is during this stage that sunlight (or artificial light) is converted to chemical energy in the form of ATP (free energy-containing molecule) and NADPH (high-energy electron-carrying molecule). Chlorophyll absorbs light energy and begins the process that result in the production of ATP and NADPH. Oxygen is also produced through the splitting of water and released through the stomata. Stomata are pores in the underside of the leaves.
Dark reactions do not require direct light, but usually occur during daylight hours. This reaction occur mostly in the thylakoid stacks of the grana (membranes where the clorophyll molecules reside). From there, it continues in the stroma, where enzymes take the carbon from carbon dioxide and combine it with hydrogen and oxygen to make carbohydrate molecules. Carbon dioxide is converted to sugar using ATP and NADPH. This process is known as carbon fixation or the Calvin cycle.
Benefits of Photosynthesis
Plants play an important role in the circle of life. The energy that is absorbed through the plant is converted into sugars, starches and high-energy carbohydrates that benefit the plant, humans and animal life. Photosynthesis is a controlling factor for the environment. Through the process of photosynthesis, carbon dioxide is removed from the atmosphere and replaced with oxygen. Human and animal life depend on oxygen for survival just as plants depend upon photosynthesis for their survival. Understanding how a plant produces its own food through photosynthesis is a step towards understanding how all life is intertwined and dependant upon one another.