(c) Explain the mechanism of photosynthesis.In 100 words.
Answers
The process of photosynthesis is considered as an oxidation-reduction reaction activated by light absorbed by chlorophyll or certain other substances (e.g., phycocyanin, fucoxanthol), resulting in the evolution of oxygen from water and in the formation of reduced carbon compounds (e.g., carbohydrate) from carbon dioxide.
The organisation of the reaction in the cell is not yet understood-the poor photosynthetic activity of light absorbed by chlorophyll in certain red algae may be indicative of a change in this organisation.
When chloroplasts are isolated from the cell they are able to catalyse the photochemical reduction of certain hydrogen acceptors with evolution of oxygen from water, but they are unable to reduce carbon dioxide.
Analysis of the path of carbon in the green plant cell, both in the light and in the dark, has been made possible by the use of radioactive carbon dioxide.
A large number of intermediates in the metabolism of the cell have been identified, but as yet convincing evidence regarding the specific part played by any of these compounds in a particular metabolic process is lacking.
The metabolic system of the cell may be analysed in terms of a number of separate processes, but it seems probable that these may have many steps in common.
The reactions which must be unique to photosynthesis are those reactions involving at most two light quanta per hydrogen atom transferred which result in the formation of a hydrogen donor capable of reducing carbon dioxide.
Comparative studies of the rate of photosynthesis and of the rate of individual steps, as represented for example by the chloroplast reaction and by tracer studies, present the most promising approach to the physiology of photosynthesis.
Hope it helps..
Answer:
Explanation:
The process of photosynthesis can be divided into two main phases:
Light reaction (or light dependent reaction)
Dark reaction (or light independent reaction)
Light reaction
It occurs in the grana present in chloroplast. During light reaction, chlorophyll absorbs light energy in the form of photons. Actually, light is emitted in the form of ‘packets of energy’ called photons. The light energy absorbed by chlorophyll is used to do following reactions:
1. Formation of ATP
ATP is the main energy source of a cell. Its full form is Adenosine Tri Phosphate. A molecule of ATP is formed by combining inorganic phosphate with ADP (Adenosine DiPhosphate) in the presence of energy.
ADP + phosphate + energy Formation of ATP ATP
This ATP is used as a source of energy during dark reaction.
2. Photolysis of water
The process of decomposition of water into hydrogen and oxygen by light energy absorbed by chlorophyll is called photolysis. The oxygen produced by the photolysis of water is released into the air as a byproduct of photosynthesis.
H2O Photolysis of water 2H+ + 1/2O2 + 2e-
It should be noted that oxygen released during photosynthesis comes from water.
3. Formation of NADPH (reduced Nicotinamide Adenine Dinucleotide Phosphate)
The hydrogen ions (H+) released during second reaction reduces the NADP (Nicotinamide Adenine Dinucleotide Phosphate) into NADPH in the presence of energy.
NADP + Hydrogen + Energy ⇒ NADPH NADPH
NADPH is also used during dark reaction.
Dark reactions (light independent reactions)
In dark reactions, the ATP molecule and NADPH produced during light reaction, are used in the matrix (or stroma) of chloroplast to make carbohydrates from carbon dioxide. In this process, carbon dioxide enters into a cycle of reactions in the presence of a substance called RuDP (Ribulose DiPhosphate) and enzymes. At the end of the cycle, carbohydrate is synthesized and ribulose diphosphate is regenerated.
RuDP + CO2 + NADPH +ATPFormation of NADPH RuDP + Carbohydrate + NADP +ADP+phosphate
This cycle of reactions is called Calvin-Benson cycle because it was discovered by Melvin Calvin and Andy Benson.