This set of Class 11 Biology Chapter 13 Multiple Choice Questions & Answers (MCQs) focuses on “Photorespiration”.
1. Which of these cannot help us differentiate between C3 and C4 plants?
a) Carbon dioxide acceptor molecule
b) Presence of Kranz anatomy
c) Photorespiration
d) Number of chloroplasts
View Answer
Explanation: C4 plants differ in various ways from C3 plants. They show Kranz anatomy. C4 plants lack photorespiration but C3 plants have a high rate of photorespiration and they do not show Kranz anatomy.
2. What is the first step of the Calvin pathway?
a) Regeneration
b) Reduction
c) CO2 fixation
d) Synthesis of sugar
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Explanation: The first step of the Calvin pathway or the Calvin cycle is the carbon dioxide fixation step. Carbon dioxide is fixed with the help of a carbon dioxide acceptor molecule, such as RuBP or PEP.
3. Which of these take place in the first step of the Calvin pathway?
a) 3 molecules of 2PGA are formed
b) RuBisCO combines with CO2
c) RuBP and CO2 give PGA
d) RuBP acts as a catalyst
View Answer
Explanation: The first step of the Calvin pathway or the Calvin cycle is the carbon dioxide fixation step. The carbon dioxide acceptor molecule RuBP combines with carbon dioxide to give 2 molecules of 3PGA.
4. Which of these is true regarding carbon dioxide fixation?
a) RuBP and CO2 give PGA
b) RuBisCO combines with CO2
c) 3 molecules of 2PGA are formed
d) RuBP acts as a catalyst
View Answer
Explanation: The first step of the Calvin pathway is the carbon dioxide fixation step. The carbon dioxide acceptor molecule RuBP combines with carbon dioxide to give 2 molecules of 3PGA with RuBisCO as the catalyst.
5. Complete the reaction.
RuBP + CO2 →
a) 3 × 3PGA
b) 2 × 3PGA
c) 2 × 3PGA + RuBisCO
d) 3 × 3PGA + RuBisCO
View Answer
Explanation: The given reaction is that of the first step of the Calvin cycle, carbon dioxide fixation. RuBP combines with carbon dioxide to form two molecules of 3PGA. RuBisCO is an enzyme that catalyses the reaction.
6. What is the most abundant enzyme in the world?
a) Papain
b) Alpha amylase
c) RuBisCO
d) Horse radish peroxidase
View Answer
Explanation: RuBisCO or Ribulose-1,5-bisphosphate carboxylase oxygenase is the most abundant enzyme in the world. It catalyses the formation of 3PGA from RuBP and carbon dioxide.
7. What does the name RuBisCO imply?
a) Its active site can bind to oxygen and carbon dioxide
b) It leads to the combination of oxygen and carbon dioxide
c) It uses carbon and oxygen to breakdown sugar
d) It uses carbon and oxygen to breakdown RuBP
View Answer
Explanation: RuBisCO or Ribulose-1,5-bisphosphate carboxylase oxygenase is the most abundant enzyme in the world. The active site of RuBisCO can bind to both oxygen and carbon dioxide. It has a higher affinity for carbon dioxide.
8. What factor determines the binding of carbon dioxide to the active site of RuBisCO?
a) Intensity of sunlight
b) Number of chloroplasts
c) Opening and closing of stomata
d) Relative O2 and CO2 concentration
View Answer
Explanation: The active site of RuBisCO can bind to both oxygen and carbon dioxide. It has a higher affinity for carbon dioxide. Hence, the relative concentrations of carbon dioxide and oxygen decide the binding of carbon dioxide.
9. Why is carbon dioxide fixation decreased in some C3 plants?
a) Phosphoglycerate formation
b) Unavailability of RuBP
c) Oxygen binds to RuBisCO
d) Oxygen binds to RuBP
View Answer
Explanation: The active site of RuBisCO can bind to both oxygen and carbon dioxide. When oxygen binds to RuBisCO, carbon dioxide fixation is reduced as the active site of RuBisCO is not able to bind to carbon dioxide.
10. When CO2: O2 is approximately 1, RuBisCO has a lower affinity for CO2. True or false?
a) True
b) False
View Answer
Explanation: RuBisCO or Ribulose-1,5-bisphosphate carboxylase oxygenase catalyses the formation of 3PGA from RuBP and carbon dioxide during Calvin cycle. RuBP is the primary carbon dioxide acceptor molecule.
11. What is formed when the active site of RuBisCO binds to oxygen?
a) ATP
b) OAA
c) PGA
d) Phosphoglycolate
View Answer
Explanation: When oxygen binds to RuBisCO, carbon dioxide fixation is reduced as the active site of RuBisCO is not able to bind to carbon dioxide. Phosphoglycerate and phosphoglycolate are formed instead.
12. Which of these is not true regarding photorespiration?
a) ATP is not synthesized
b) 1 molecule of phosphoglycerate is formed
c) 1 molecule of PGA is formed
d) The active site of RuBisCO binds to oxygen
View Answer
Explanation: During the process of photorespiration, the active site of RuBisCO binds to oxygen. ATP and sugars are not formed. Instead of PGA, 1 molecule of phosphoglycerate and phosphoglycolate are formed.
13. Which of these are synthesized during photorespiration?
a) NADPH
b) ATP
c) CO2
d) Sugars
View Answer
Explanation: During the process of photorespiration, the active site of RuBisCO binds to oxygen. ATP is not formed but is utilized. NADPH and sugars are not synthesized. Carbon dioxide is released as a result of this process.
14. Which of these is a 2-carbon molecule?
a) Phosphoglycolate
b) OAA
c) PGA
d) Malic acid
View Answer
Explanation: Phosphoglycolate is a 2-carbon compound formed during the process of photosynthesis. Malic acid and oxaloacetic acid (OAA) are 4-carbon compounds while PGA is a 3-carbon compound.
15. Why is the productivity of C4 plants better than that of C3 plants?
a) C4 plants show Kranz anatomy
b) C4 plants lack photorespiration
c) C4 plants show high phosphoglycerate formation
d) C4 plants show high phosphoglycolate formation
View Answer
Explanation: The productivity of C4 plants better than that of C3 plants as C4 plants lack photorespiration. C4 plants do not show phosphoglycerate and phosphoglycolate formation, unlike C3 plants.
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