- The chemical reaction that occurs during photosynthesis is simple. The process combines six molecules of water with six molecules of carbon dioxide to produce one molecule of sugar, releasing six molecules of breathable oxygen as waste. The energy needed to break down the water and carbon dioxide molecules is taken from sunlight absorbed by the leaves.
- Photosynthesis occurs inside the cells of a plant's leaves in special organelles, or individual components of a single cell, called chloroplasts. Chloroplasts are so named because they contain the green pigment chlorophyll, which absorbs the majority of the light used in photosynthesis. Although chloroplasts can be found throughout a plant, giving it its green color, they are found in their highest concentration in the leaves. Inside the chloroplasts are structures called thylakoids, the physical site of the photosynthetic reaction.
- There are two types of reactions involved in photosynthesis. In the light-dependent reaction, a chlorophyll molecule absorbs a photon of light, causing it to lose an electron, which is sent through an electron transport chain for use as energy in the light-independent reactions. Ultimately, it regains this electron through photolysis, where it strips an electron from a water molecule. Photolysis breaks the water molecule, releasing a breathable dioxygen molecule (two oxygen atoms) as waste. This oxygen, although waste to the plant, is used by the majority of other organisms on Earth for the process of cellular respiration.
- The electron lost by the chlorophyll in the light-dependent reaction is transported via the NADPH molecule, where the electron is used to reduce (a chemistry term meaning to add electrons) molecules in a process that results in the formation of sugar. Carbon dioxide is drawn from the atmosphere outside of the leaf and captured by proteins that reduce the molecule, breaking it down and combining the carbon with hydrogen and oxygen to produce sugar molecules, which the plant stores as food.
- Water is constantly both being used in the photosynthetic reactions as well as being evaporated by the heat of the sunlight. However, this water loss is necessary for the plant to absorb more water through the roots. Water is transported through tubes within the plant's stems from the roots to the leaves. Because water is cohesive, meaning its molecules tend to stick to each other, when water evaporates through the leaf it draws up the entire column of water in the tubes. In the roots, water is drawn from the soil into the plant through cohesion as well. Evaporation creates the pressure needed to draw water into the plant as well as up the height of the plants stem, or even a tree's trunk.
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