What is photosynthesis?

Photosynthesis is the process by which light energy and carbon dioxide are utilised by plants to produce sugars like glucose. Through two reaction cycles, the light-independent and light-dependent reactions. Photosynthesis takes place in plants within green cells, which contain high numbers of chloroplasts. Chloroplasts are intracellular organelles - small enclosed compartments, that are rich in chlorophyll molecules. Chlorophyll molecules absorb light energy, particularly light in the blue wavelength, primarily through two pigments, photosystem I and photosystem II, which releases high energy electrons. The energy from these high energy electrons is used to produce a highly reduced chemical mediator - NADPH. The energy stored in NADPH is coupled to the reduction of carbon compounds, like ribulose biphosphate, to sugars like glucose. So light energy is used in part of the process, but carbon compounds to be reduced are also required.

     The light-independent reaction, also known as the Calvin cycle, sequesters carbon dioxide into organic carbon compounds. The Calvin cycle traps carbon dioxide in the atmosphere with a 5 carbon compound - ribulose bisphosphate, catalysed by the enzyme RuBisCo. The resulting 6 carbon compound is then further processed by enzymes to form a 3 carbon compound that will form glucose and another 3 carbon compound that will go on to regenerate ribulose bisphosphate, completing the Calvin cycle. Therefore, photosynthesis is the usage of carbon dioxide and light energy to produce sugar.