Question 1

How many turns of Calvin cycle are required for the formation of three molecules of glucose ?

Accepted Answer

One turn of the Calvin cycle fixes one molecule of CO_2. To synthesize one molecule of glucose (C_6H_ 12 O_6), six molecules of CO_2 are required. Thus, six turns of the Calvin cycle are required to produce one molecule of glucose. For the formation of three molecules of glucose, the number of turns required is 3 6 = 18. Answer: 18

Question 2

Photorespiration reaction catalyzed by RuBisCo is shown below : RuBP + O_2 3-Phosphoglycerate + X Identify “X” from the given options :

Accepted Answer

In photorespiration, the enzyme RuBisCo acts as an oxygenase. It catalyzes the oxygenation of Ribulose-1,5-bisphosphate (RuBP) to form one molecule of a 3-carbon compound, 3-phosphoglycerate, and one molecule of a 2-carbon compound, 2-phosphoglycolate. The reaction is: RuBP + O_2 3-Phosphoglycerate + 2-Phosphoglycolate Thus, the product X is 2-Phosphoglycolate. Answer: 2-Phosphoglycolate

Question 3

Which of the following statements regarding photorespiration are correct ? (a) Do not occur in C3 plants (b) CO_2 is consumed and O_2 is generated (c) Phosphoglycolate is formed (d) No synthesis of AT

Accepted Answer

Photorespiration occurs primarily in C3 plants, making statement (a) incorrect. During photorespiration, O_2 is consumed and CO_2 is released, making statement (b) incorrect. In the first step of photorespiration, RuBP binds with O_2 to form one molecule of phosphoglycerate and one molecule of phosphoglycolate, making statement (c) correct. Photorespiration is a wasteful process where there is no synthesis of ATP or NADPH; instead, it consumes ATP, making statement (d) correct. Therefore, only s

Question 4

Which pigment has absorption peak at 700 nm in the photosynthetic reaction centre PS I (P700) ?

Accepted Answer

In the light reaction of photosynthesis, the reaction centre of Photosystem I (PS I) consists of a specific molecule of chlorophyll a. This chlorophyll a molecule has an absorption peak at 700 nm, which is why it is designated as P700. In contrast, the reaction centre of Photosystem II (PS II) is a chlorophyll a molecule with an absorption peak at 680 nm, known as P680. Answer: Chlorophyll a

Question 5

How many ATP and NADPH molecules are required to make one molecule of glucose through the Calvin pathway ?

Accepted Answer

In the Calvin cycle, the fixation of one molecule of CO_2 requires 3 ATP and 2 NADPH molecules. To synthesize one molecule of glucose, 6 molecules of CO_2 must be fixed. Total ATP required = 6 3 = 18 ATP. Total NADPH required = 6 2 = 12 NADPH. Answer: 18 ATP and 12 NADPH

Question 6

Find the incorrect statement(s) about photosynthesis from the following : A. The water splitting complex is associated with PS I. B. C _4 plants use the C _3 pathway of CO _2 fixation as the main bios

Accepted Answer

Statement A is incorrect because the water splitting complex is associated with PS II, not PS I. Statement B is correct because the Calvin cycle ( C _3 pathway) is the main biosynthetic pathway for all plants, including C _4 plants. Statement C is correct because C _4 plants have a mechanism that increases the concentration of CO _2 at the enzyme site, preventing RuBisCO from acting as an oxygenase, thus avoiding photorespiration. Statement D is incorrect because Kranz anatomy is a characteristi

Question 7

The enzyme required for carboxylation in the Calvin cycle is :

Accepted Answer

The Calvin cycle is the primary pathway for carbon fixation in plants. The first step of the Calvin cycle is carboxylation, where carbon dioxide is added to a five-carbon acceptor molecule, Ribulose-1,5-bisphosphate (RuBP). This reaction is catalyzed by the enzyme Ribulose bisphosphate carboxylase-oxygenase, commonly known as RuBisCO. Hexokinase is an enzyme involved in glycolysis. PEP carboxylase is the primary carboxylating enzyme in the C4 pathway. Carboxypeptidase is a proteolytic enzyme inv

Question 8

Select the correct sequence of experiments that led to a gradual understanding of photosynthesis in green plants.

Accepted Answer

Joseph Priestley (1770) performed experiments that revealed the essential role of air in the growth of green plants. Jan Ingenhousz (1779) showed that sunlight is essential to the plant process and that only the green parts of the plants release oxygen. Julius von Sachs (1854) provided evidence for the production of glucose when plants grow. T.W. Engelmann (1843-1909) described the first action spectrum of photosynthesis, which roughly resembles the absorption spectra of chlorophyll a and b. The

Question 9

Match List I with List II: array |l|l|l|l| & List - I & & List - II \ A . & Chlorophyll a & (i) & Yellow-green \ B. & Chlorophyll b & (ii) & Yellow \ C. & Xanthophylls & (iii) & Blue-green \ D. &

Accepted Answer

A chromatographic separation of the leaf pigments shows that the colour that we see in leaves is not due to single pigment but due to four pigments. array |l|l|l|l| Chlorophyll a & Bright or blue-green in the chromatogram \ Chlorophyll b & Yellow-green \ Xanthophylls & Yellow \ Carotenoids & Yellow to Yellow-orange \ array

Question 10

Which of the following statements about RuBisCO is true?

Accepted Answer

Carboxylation is the most crucial step of the Calvin cycle where CO _2 is utilised for the carboxylation of RuBP. This reaction is catalysed by enzyme RuBP carboxylase. Since this enzyme also has an oxygenase activity, RuBisCO has higher affinity for carbon dioxide than oxygen.

Question 11

Which of the following are required for the light reaction of Photosynthesis? A. CO _2 B. O _2 C. H _2 O D. Chlorophyll E. Light Choose the correct answer from the options given below:

Accepted Answer

For the process of light reaction, water, light and chlorophyll are required. CO _2 is used during the second stage of photosynthesis i.e. dark reaction. Oxygen is a product of light reaction formed by photolysis of water.

Question 12

Which of the following are required for the dark reaction of photosynthesis? A. Light B. Chlorophyll C. CO _2 D. ATP E. NADPH Choose the correct answer from the options given below:

Accepted Answer

For dark reaction of photosynthesis there are the requirement of . array l CO _2 \ ATP \ NADPH array ]

Question 13

Given below are two statements: Statement I: In C _3 plants, some O _2 binds to RuBisCO, hence CO _2 fixation is decreased. Statement II: In C _4 plants, mesophyll cells show very little photorespirat

Accepted Answer

In C _3 plant, some O _2 bind to RuBisCO, and hence CO _2 fixation is decreased. Statement II is incorrect, photorespiration does not occur in C _4 plants as they lack RuBisCO in mesophyll. Hence statement I is the only correct option.

Question 14

How many molecules of ATP and NADPH are required for every molecule of CO _2 fixed in the Calvin cycle?

Accepted Answer

For fixation of 1 molecule of CO _2 in Calvin cycle 3 ATP molecules and 2 NADPH molecules are required.

Question 15

Observe the given figure. Identify the different stages labelled with alphabets by selecting the correct option.

Accepted Answer

The calvin cycle proceeds in three stages: (A) Carboxylation, during which CO _2 combines with ribulose-1,5-bisphosphate. (B) Reduction, during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH. (C) Regeneration during which the CO _2 acceptor ribulose-1,5-bisphosphate is formed again so that the cycle continues.

Question 16

Which one of the following products diffuses out of the chloroplast during photosynthesis?

Accepted Answer

Product of light reaction are ATP, NADPH and O _2. Of these O _2 diffuses out of the chloroplast while ATP and NADPH are used to drive the processes leading to synthesis of food, more accurately, sugars.

Photosynthesis in Higher Plants — Previous Year Questions & Solutions