Photosynthesis is the process plants and some algae use to convert light energy to chemical energy stored as sugar. Plants need only carbon dioxide (CO2) and water (H2O) for photosynthesis to work. This occurs in plant leaves, specifically the leaf cells' chloroplasts. Chloroplasts are full of chlorophyll, a green pigment key to photosynthesis. The energy stored during photosynthesis starts the flow of energy and carbon down the food chain. All the energy we consume through food is a direct or indirect result of the energy stored by photosynthesis.
The formula that describes photosynthesis is 6CO2 + 6H20 + light energy = C6H1206 + 602. What this chemical equation means is that photosynthesis combines light energy with six molecules of carbon dioxide and six molecules of water to produce six molecules of oxygen and a molecule of sugar.
Photosynthesis is divided into two main stages: light reaction and dark reaction. The light reaction converts light energy into adenosine triphosphate (ATP) and other components needed in the dark stage. This step occurs in the thylakoid membrane, a membrane found inside chloroplasts.
The dark reaction employs ATP and other products created in the light reaction to transform CO2 into sugar. This happens within the plant's stoma and does not need light. The main cycle in this stage is called the Calvin cycle, which has three main stages. Stage one, also called carbon fixation phase, is when CO2 is added to a ribulose bisphosphate (RuBP), a five-carbon sugar. In stage two ATP is used used to convert the product of stage one into sugar. The third stage, or regeneration phase, again uses ATP to regenerate the reserve levels of RuBp in the cell, completing the cycle .
ATP is an essential component in the process of photosynthesis. Biologists consider it the currency of life, because it is cell's favorite source of energy to do just about anything, from moving muscles to enabling respiration.
Plants use light energy to start the photosynthesis process and fuel the storage of energy in sugars. Light is divided into various colors with their characteristic wavelengths; each wavelength absorbed by a different pigment. Chlorphylls (a certain kind of pigment) take in blue and red light while carotenoids (another type of pigment) use blue-green light. However, green and yellow light is not absorbed efficiently by plants and is reflected by leaves, which is why plants are green.