8. Explain with the help of Chemical reaction the process of photosynthesis. (5M)
Answers
Answer:Photosynthesis is a physiological process by which plant cells containing chlorophyll produce food in the form of carbohydrates by using carbon dioxide, water and light energy. Oxygen is released as a by-product. The chemical equation for photosynthesis is
Two main phases are involved in the mechanism of photosynthesis:
Light-dependent Phase
Light-independent Phase
Light-dependent Phase
The light-dependent phase is also known as Hill reaction or photochemical reaction.
This phase takes place in the thylakoids of the chloroplast.
Activation of Chlorophyll
On exposure to light, chlorophyll becomes excited and absorbs photons (a photon is the smallest unit of light energy) to get activated.
Photolysis of Water
Energy absorbed is used in splitting of water molecules into hydrogen ion (H+) and hydroxide ion (OH−). During this process, electrons are released.
Production of Reducing Agent
NADP, i.e. nicotinamide dinucleotide phosphate, picks up the hydrogen ion and is reduced to NADPH.
Formation of molecular oxygen
Hydroxide ion is oxidised to hydrogen peroxide which decomposes to form molecular oxygen (O2). Molecular oxygen is released during photosynthesis.
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. Since the energy used comes from light, it is also called photophosphorylation.
Light-independent Phase
This phase is also known as Calvin cycle or biosynthetic phase. It occurs in the stroma of chloroplasts.
This phase occurs simultaneously with the light-dependent reaction.
The time gap between the two phases is less than one thousandth of a second.
Formation of Glucose
Carbon dioxide is converted into glucose by usingATP and NADPH produced during the light reaction.
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