Photosynthesis in Plants

In green plants, water is the hydrogen donor and it undergoes oxidation to produce oxygen. Photosynthesis occurs in two stages, viz. light reaction and dark reaction. The light reaction is light-dependent. Light energy is captured in this stage and is utilised to make the energy-storage molecules ATP and NADPH. Dark reaction is lightindependent reaction. Dark reaction is utilised to capture and reduce carbon dioxide. Dark reaction doesn‟t mean that it happens in the absence of light. Importance of photosynthesis: 1. Synthesis – mechanism of synthesising organic compounds from inorganic raw materials. 2. Conversion of radiant energy – Changes radiant energy into chemical energy. 3. Producers – Only the plants & some lower organisms have the ability to synthesise organic substances from inorganic substances, hence called as producers. 4. Plant products – A number of useful products are obtained from plants which are synthesised by plants through photosynthesis – fire-wood, timber, oils, gums, resisns, rubber, tannins, drugs, fibres, etc. 5. Fossil fuels – Coal, natural gas & petroleum have been formed inside earth through action of heat & pressure over organic matter a product of photosynthesis which got buried due to various changes in the crust of earth. 6. Carbon dioxide – Helps keep the concentration of carbon dioxide nearly constant due to its utilisation during photosynthesis. 7. Oxygen – Almost the whole atmospheric oxygen originated due to photosynthetic activity of past plants. Photosynthesis maintains the atmospheric oxygen content nearly constant.