Photosynthesis is the fundamental biological process that sustains life on Earth by converting light energy into stored chemical energy. This process is performed by plants, algae, and certain bacteria, known as autotrophs because they produce their own food. The energy captured fuels the growth and metabolism of these organisms, forming the base of nearly every food web.
The Primary Inputs: Carbon Dioxide and Water
The two primary reactants required for photosynthesis are carbon dioxide (CO2) and water (H2O). Carbon dioxide is acquired directly from the atmosphere as a gas, while water is typically absorbed from the soil or the organism’s environment. These molecules serve as the raw materials that are chemically rearranged during the light-driven process.
The reaction also requires an external energy source, which is provided by light, most often sunlight. Light energy is necessary to initiate the conversion, but it is not considered a material reactant because it is not consumed or transformed into the final molecular products. Light drives the chemical change, starting when it is absorbed by chlorophyll, the pigment that gives plants their green color.
How Plants Gather These Essential Components
Plants have specialized structures designed to efficiently capture both water and carbon dioxide. Water is primarily absorbed from the soil through the roots. It is then transported upward through the xylem, a specialized vascular tissue, moving to the stems and leaves where photosynthesis occurs. This system ensures a continuous supply of water to the cells performing the conversion.
Carbon dioxide is taken in directly from the air through microscopic pores called stomata. These small openings are typically found on the underside of leaves, allowing for gas exchange. The stomata are regulated by guard cells, which open and close to balance CO2 intake with minimizing water loss through evaporation. Once inside the leaf, the carbon dioxide diffuses into the chloroplasts where the chemical reactions take place.
The Final Products of the Reaction
After the reactants are acquired and light energy is captured, the photosynthetic process creates two main products. The first product is glucose (C6H12O6), a simple sugar molecule that serves as the plant’s food source. The chemical energy from the light is stored within the molecular bonds of this sugar, which the plant uses immediately for energy or links together to form complex carbohydrates like starch for storage.
The second product is molecular oxygen (O2), which is released back into the atmosphere as a byproduct. This gas results from water molecules being split during the light-dependent stage of photosynthesis. The release of oxygen is important for aerobic life on Earth.