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Topic Question Set

Q 1 :    

Given below are two statements:                 [2024]

Statement I: In C3 plants, some O2 binds to RuBisCO, hence CO2 fixation is decreased.
Statement II: In C4 plants, mesophyll cells show very little photorespiration while bundle sheath cells do not show photorespiration.

In the light of the above statements, choose the correct answer from the options given below:

  • Both Statement I and Statement II are true.

     

  • Both Statement I and Statement II are false

     

  • Statement I is true but Statement II is false.

     

  • Statement I is false but Statement II is true. 

     

(3)

RuBisCO enzyme shows affinity for both CO2and O2 molecules. The relative concentration of these determines which of the two will bind to the enzyme. In C3 plants, sometimes O2 does bind to RuBisCO which reduces CO2 fixation and the plant enters the pathway of photorespiration. C4 plants lack the process called photorespiration.

 

Q 2 :    

Given below are two statements:         [2023]

Statement I: RuBisCO is the most abundant enzyme in the world.
Statement II: Photorespiration does not occur in C4 plants.

In the light of the above statements, choose the most appropriate answer from the options given below:

  • Statement I is correct but Statement II is incorrect.

     

  • Statement I is incorrect but Statement II is correct.

     

  • Both statements I and II are correct

     

  • Both statements I and II are incorrect

     

(3)

Ribulose Bisphosphate Carboxylase-Oxygenase (RuBisCO) is the most abundant protein in the whole of the biosphere. C4 plants lack photorespiration as they have a mechanism that increases the concentration of CO2 at the enzyme site, so RuBisCO does not bind to oxygen.

 

Q 3 :    

The oxygenation activity of RuBisCO enzyme in photorespiration leads to the formation of      [2020]

  • 2 molecules of 3-C compound

     

  • 1 molecule of 3-C compound

     

  • 1 molecule of 6-C compound

  • 1 molecule of 4-C compound and 1 molecule of 2-C compound

     

(2)

During photorespiration in C3 plants, some O2 does bind to RuBisCO and RuBP instead of being converted to 2 molecules of PGA. It binds with  O2 to form one molecule of phosphoglycerate (3 Carbon) and phosphoglycolate (2 Carbon).

 

Q 4 :    

The process which makes a major difference between C3 and C4 plants is         [2016]

  • glycolysis

     

  • Calvin cycle

     

  • photorespiration

     

  • respiration

     

(3)

Photorespiration is the light-dependent process of oxygenation of ribulose bisphosphate (RuBP) and release of carbon dioxide by the photosynthetic organs of a plant. It leads to the oxidation of a considerable amount of photosynthetic products to CO2 and H2O without the production of useful energy. Photorespiration occurs only in C3 plants because, at high temperature and high oxygen concentration, RuBP carboxylase changes to RuBP oxygenase. Photorespiration is wasteful.