Photosynthesis is the process of transforming sunlight into chemical energy by storing it in the bonds of glucose or sugar. This process occurs in plants, bacteria and some protists, or algae to produce sugar as food. The chlorophyll present in leaves of photosynthetic plants captures energy from sunlight and converts it to carbohydrates. Photosynthesis uses carbon dioxide (CO2) and water as raw material to produce sugar and release oxygen as a byproduct.
Photosynthesis takes place primarily in leaves and stems. The typical leaf includes the upper and lower epidermis, vascular bundles, mesophyll and stomate, or plant pores. The upper and the lower epidermis serve as a protection to the leaf. The stomates are pores in the lower epidermis that act as a passage for CO2 and air to pass. The vascular bundles move water, minerals and nutrients around the plant. The mesophyll contains chloroplast in its thylakoid membrane. This is the place where photosynthesis occurs.
Occurrence of Chemical Reaction
The overall chemical reaction under photosynthesis can be written as "6H2O + 6CO2 -----> C6H12O6+ 6O2." The process occurs in two stages. The first stage is the reaction of light used to form high energy molecules. The energy harvested in the light reaction is stored in cells in the form of a chemical named as ATP, or adenosine triphosphate. The second stage of photosynthesis is called the Calvin Cycle Reaction.
Calvin Cycle Reaction
In this part of the reaction, chemical energy stored at ATP is used to produce sugar from CO2 through enzymatic, or enzyme reactions. Initially, CO2 reacts with a five-carbon compound called, ribulose bisphosphate (RuBP), catalyzed by the enzyme carboxylase oxygenase to produce a stable, three-carbon compound called as phosphoglycerate (PGA). Energy captured in ATP converts PGA into glyceraldehyde 3-phosphate (G3P) which is converted to other organic compounds.
Factors Limiting Photosynthesis
Photosynthesis is highly determined by the factors such as light intensity, soil nutrients, water availability, temperature and concentration of carbon dioxide in the atmosphere. Decrease in the water level reduces moisture from soil and close the stomata. This limits the diffusion of carbon dioxide and affects the photosynthesis.