Photosynthesis is one of the most important biological processes on Earth. It is the process by which plants, algae, and certain bacteria convert light energy from the sun into chemical energy stored as glucose. This process requires three main inputs: sunlight, water, and carbon dioxide. The outputs are glucose, which serves as food for the plant, and oxygen, which is released into the atmosphere as a byproduct.
The first step of photosynthesis is light absorption. This occurs in specialized organelles called chloroplasts, which are found in plant cells. Chloroplasts contain a green pigment called chlorophyll that captures light energy. Chlorophyll primarily absorbs red and blue wavelengths of light, while reflecting green light, which is why plants appear green to our eyes. The absorbed light energy is then used to power the chemical reactions of photosynthesis.
In the second step, light energy is used to split water molecules in a process called photolysis. This reaction breaks down water into oxygen gas, protons, and electrons. The oxygen is released as a byproduct into the atmosphere. In the third step, the electrons from water splitting, along with the captured light energy, are used to create energy-rich molecules called ATP and NADPH. These molecules serve as energy carriers that will power the next stage of photosynthesis.
In the fourth step, called the Calvin Cycle, the energy stored in ATP and NADPH is used to convert carbon dioxide from the atmosphere into glucose. This process occurs in the stroma of the chloroplast and is also known as carbon fixation. Finally, in step five, glucose is produced as the end product. This glucose serves multiple purposes: it can be used immediately for energy, stored for later use, or converted into other organic compounds needed for plant growth and development. The overall equation for photosynthesis shows six molecules of carbon dioxide and water being converted into one molecule of glucose and six molecules of oxygen.