NEET UG Biology Photosynthesis MCQs

 

Green plants make their own food by photosynthesis. During this process carbon dioxide form the atmosphere is taken in by leaves through stomata and used for making carbohydrates, principally glucose and starch. Photosynthsis takes place only in the green parts of the plants, mainly the leaves. Within the leaves, the mesophyll cells have a large number of chloroplasts that are responsible for CO₂ fixation. Within the chloroplasts, the membranes are sites for the light reaction, while the chemosynthetic pathway occurs in the stroma. photosynthesis has two stages the light reaction and the carbon fixing reations. in the light reaction the light energy is absorbed by the pigments present in the antenna and funnelled to special chlorophyll a molecules called reaction centre chlorophylls there are two photosystems, PS I and PS II. PS I has a 700 nm absorbing chlorophyll a P700 molecule at its reaction center, while PS II has a P680 reaction centre that absorbs red loght at 680 nm After absorbing light, electrons are excited and transferred through PS II and PS I and finally to NAD forming NADH. during this process a proton gradient due to movement through the thylakoid The breakdown of the protons gradient due to movement through the F0 part of the ATPase enzyme releases enough energy for synthesis of ATP splitting of water molecles is associated with PS II resulting in the release of O₂, protons and transfer of electrons to PS II In the carbon fixation cyale, CO₂ is added by the enzyme, RuBisCO, to a 5 carbon compound RuBP that is converted to 2 molecules of 3- carbon PGA. this is then converted to sugar by the Calvin cycle, and the RuBp is regenerated. During this process ATP and NADPH synthesised in the light reaction are utilsed RuBisCO also catalyses a wasteful oxygenation reaction in C₃ plants: Photorespiration Some tropical plants show a special type of photosynthesis called C₄ pathway in these plants the first product of CO₂ fixation that takes place in the mesophyll, is a 4-carbon compound. in the bundle sheath cells the Calvin pathway is carried out for the synthesis of carbohydrates.

 

(a) synthesis of ATP during photosynthesis

(b) release of water during photosynthesis

(c) carbon fixation during photosynthesis

(d) capture light energy during photosynthesis

 

(A) Park and Biggins (B) Meyers and French

(C) Willstatter and Stahi (D) Arnon and Benson

 

(A) phytol (B) porphyrin (C) pyrrol (D) none above