Explain the mechanism of photosynthesis?
Answers
Photosynthesis: It is a metabolic process where light energy is converted to chemical energy. It is the source of all living matter and biological energy.
Chlorophyll and other accessory pigments are situated in the thylakoid membranes of the chloroplast. These membranes organise to form Reaction Centres called Photosystem - I and Photosystem - II.
Light Reaction:This reaction takes place in the presence of light, in the Grana region of the chloroplast. It is a photochemical reaction. Light energy is absorbed by all the pigments of the chloroplast. (Like Chlorophyll, Xanthophyll, Carotene etc). But as the other pigments cannot use this energy, they transfer the absorbed energy to the pigment chlorophyll, which is the reaction centre.
When the chlorophyll molecules absorb light energy, its electrons get excited and are displaced from their normal orbit and in a very short span of time (10-10 seconds) of this state, this energy is utilised to form ATP and NADPH2. Then the electron deficient chlorophyll performs the photolysis of water, spiltting water molecule into H+ + OH- ions. Both the systems PS I and PS II play an important role in light reaction which involves release of O2 from H2O and formation of energy rich molecules (ATP and NADPH2). This process happens due to cyclic and Non-Cyclic Photophosphorylation.
Photophosphorylation: The energy obtained in the movement of protons is used to produce ATP. Cyclic photophosphorylation, when PS I is activated by light, electrons in chlorophyll get energised and go through different steps to form ATP molecule.
Non-Cyclic Photophosphorylation: It results in the photolysis of water releasing O2
and in the formation of ATP and NADPH2 molecules, involving both PS I and PS II.
2 H2O → 2 H+ + 2 OH- 2 H+ Protons reduce NADP to form NADPH2.
2 OH- → 2 (OH) + 2 e- (these electrons are transferred to PS II)
2 OH → H2O + O
At the end of light reaction, energy is trapped in ATP and NADPH2; which are essential for reduction of carbon dioxide in the dark reaction.
The photosystems represents an aggregate of a large number of pigment molecules which are connected together by an electron transport system.
Dark Reaction: It takes place in the presence of light as well as in the absence of light; in the stroma region of the chloroplast. It is a thermo - chemical reaction. Light is not absorbed in this reaction, thus called as dark reaction. CO2 enters into the process of photosynthesis in this phase. It is used to synthesise sugars. It is a reduction reaction the ATP and NADPH2 molecules formed at the end of the light reaction are utilised in the dark reaction.
Here, CO2 -------> complex organic substances.
One molecule of CO2 is transferred to a five carbon sugar with two Phosphates Attached to it called Ribulose - 1, 5 - diphosphate which results in the formation of a six carbon sugar phosphate (it is highly unstable), which splits into 2 PGA molecules.
CO2 + RuDP → 6 Carbon compound---> (Splits)2 Molecules of 3 - Phospho glyceric acid (PGA)
This 3 - Phosphoglyceric acid undergoes a series of reactions and is converted into glyceraldehyde-3-phosphate, which is later converted into glucose.
Scientist: Melvin Calvin: (April 8, 1911- January 8, 1997) He was American Chemist, most famed for discovering the Calvin Cycle. His full name is Melvin Cllis Calvin. He worked along with Andrew Benson and James Basshan. He was awarded the 1961 Nobel Prize in Chemistry.
Using the carbon-14 isotope as a tracer, Calvin and his team mapped the complete route that carbon travels through a plant during Photosynthesis.
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Answer:
Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.