what is photosynthesis?Photosynthesis converts massive amount of Sunlightinto electrical and then chemical energy. The input iscarbon dioxide (CO2), water (H2O), minerals and light,and the output is carbohydrates (food) that we needfor our nourishment, and oxygen that we need tobreathe. This oxygenic photosynthesis occurs inhigher plants (e.g., rice, maize, wheat, mosses, ferns,forest trees, shrubs, etc); in green, red, brown andyellow algae, and even blue-green cyanobacteria.
Equation of photosynthesis6CO2 + 12H2O + light → C6H12O6 + 6O2 + 6H2O6 molecules of carbon dioxide (6CO2) and 12molecules of water (12H2O) are consumed in theprocess, while glucose (C6H12O6), six molecules ofoxygen (6O2), and six molecules of water (6H2O) areproduced.This equation may be simplified as: 6CO2 + 6H2O +light → C6H12O6 + 6O2.
The set of photosynthetic reactions are arbitrarilydivided into :(1) The light phase (that produces the reducing powerand ATP, the energy currency of life).(2) The dark phase (where the products of light phaseare used to convert CO2 to carbohydrates).Division of photosynthesis
The light phase(occur in the presence of light)It is a photochemical phase. Light reactions occur mostly inthe thylakoid stacks of the grana. Here, sunlight is convertedto chemical energy in the form of ATP (free energy containingmolecule) and NADPH (high energy electron carryingmolecule). Chlorophyll absorbs light energy and starts a chainof steps that result in the production of ATP, NADPH, andoxygen (through the splitting of water). Oxygen is releasedthrough the stomata. Both ATP and NADPH are used in thedark reactions to produce sugar.
(cont.)This process further has two more phases :1.Photolysis of water or hill reaction:Chemical process by which molecules are broken down intosmaller units through the absorption of light.ADP+inorganic phosphate+energy ATP(photophosphoryation)Assimilatory molecules are: NADPH2 andADP2.Formation of assimilating powermolecules:The light reactions result in theformation of the high-energy compoundsATP and NADPH. While these compoundscan be used to drive metabolic processes,one additional critical reaction must occur: the fixation ofcarbon dioxide.
The dark reaction(do not need direct light)It is a biosynthetic phase . Dark reactions occur in the stroma.Carbon dioxide is converted to sugar using ATP and NADPH.This process is known as carbon fixation or the Calvin cycle.Carbon dioxide is combined with a 5-carbon sugar creating a6-carbon sugar. The 6-carbon sugar is eventually broken-downinto two molecules, glucose and fructose. These twomolecules make sucrose or sugar.
summaryIn summary, photosynthesis is a process in which lightenergy is converted to chemical energy and used toproduce organic compounds. In plants,photosynthesis occurs within the chloroplasts.Photosynthesis consists of two stages, the lightreactions and the dark reactions. The light reactionsconvert light into energy (ATP and NADHP) and thedark reactions use the energy and carbon dioxide toproduce sugar.