Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose. This chemical energy is stored in the bonds of the glucose molecule and is later used by the plant as an energy source.
The process of photosynthesis is commonly represented by the equation:
6CO2 + 6H2O → C6H12O6 + 6O2
6 carbon dioxide + 6 water molecules + light energy → sugar (glucose) + 6 oxygen
This means that the reactants, six carbon dioxide molecules, and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products.
During the process of photosynthesis, carbon dioxide is taken in from the air through small pores called stomata, which are found on the leaves of plants. The carbon dioxide is then used in the Calvin cycle, also known as the light-independent reaction, which occurs in the stroma
In the Calvin cycle, the carbon dioxide is combined with a 5-carbon molecule called ribulose bisphosphate (RuBP) to produce a 6-carbon molecule called 6-phosphogluconate. This reaction is catalyzed by the enzyme RUBISCO.
The 6-phosphogluconate is then converted into glucose through a series of steps involving the transfer of electrons and the addition of hydrogen atoms.
In addition to carbon dioxide, water is also necessary for photosynthesis. Water is taken in by the roots of the plant and transported to the leaves through small tubes called the xylem.
Once in the leaves, the water is used to produce oxygen gas through a process called photolysis, which occurs in the thylakoid membranes of the chloroplasts.
During photolysis, light energy is used to split water molecules into oxygen gas, hydrogen ions, and electrons. The oxygen gas is released into the atmosphere, while the hydrogen ions and electrons are used to produce ATP and NADPH, which are types of energy-carrying molecules.
The production of ATP and NADPH occurs in the thylakoid membranes through a process called light-dependent reactions. In this process, the hydrogen ions and electrons are used to power the synthesis of ATP and NADPH through a process called chemiosmosis.
Once the ATP and NADPH have been produced, they have used in the Calvin cycle to power the synthesis of glucose from carbon dioxide. The glucose is then used by the plant as an energy source or is stored in the form of starch for later use.
In addition to producing glucose and oxygen, photosynthesis also plays an important role in the regulation of atmospheric carbon dioxide levels. As plants convert carbon dioxide into glucose, they remove the carbon dioxide from the atmosphere, helping to regulate the levels of this greenhouse gas.