CBSE - X - Biology - Life Processes
mechanism of photosynthesis explain
Two main phases are involved in the mechanism of photosynthesis:light dependent phase and light independent phase.
Light dependent phase
Light-dependent phase is also known as the Hill reaction or photochemical reaction. This phase occurs in the thylakoids of the chloroplast.
Major events occuring in this phase are:
1.Activation of chlorophyll- On exposure to light, chlorophyll becomes excited and absorbs photons to get activated.
2.Photolysis of water- Energy absorbed is used in the splitting of water molecules into hydrogen ion (H+) and hydroxide ion (OH−). During this process, electrons are released.
3.Production of reducing agent- NADP (nicotinamide dinucleotide phosphate) picks up the hydrogen ion and is reduced to NADPH.
4.Formation of molecular oxygen- Hydroxide ion is oxidised to hydrogen peroxide which decomposes to form molecular oxygen (O2). Molecular oxygen is released during photosynthesis.
5.Photophosphorylation- Electrons are used in converting ADP (adenosine diphosphate) into energy-rich compound ATP (adenosine triphosphate) by adding one phosphate group.The process of addition of phosphate is called phosphorylation. Because the energy used comes from light, it is also called photophosphorylation.
Light Independent Phase
This phase is also known as the Calvin cycle or biosynthetic phase. It occurs in the stroma of the chloroplast. This phase occurs simultaneously with the light-dependent reaction.
Major event occuring in this stage is:
1.Formation of glucose- Carbon dioxide is converted into glucose by using ATP and NADPH produced during the light reaction
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