NEET Previous Year Questions (2016-2024): Photosynthesis in Higher Plants | Biology Class 11 PDF Download

2024

Choose the correct answer from the options given below:
(a) A, B and C only
(b) B, C and D only
(c) C, D and E only
(d) D and E only
Ans: (c)
The dark reactions of photosynthesis, also known as the Calvin cycle, do not directly require light to proceed and hence are termed "dark reactions." The reactions occur in the stroma of chloroplasts and primarily involve the synthesis of organic molecules from carbon dioxide (CO₂). Here's an analysis of the options provided:

A. Light: Not required for the dark reactions themselves; these reactions are light-independent.
B. Chlorophyll: Chlorophyll is essential for the light-dependent reactions of photosynthesis, where it absorbs light energy and helps convert it into chemical energy. It is not used directly in the dark reactions.
C. CO₂: Carbon dioxide is a critical substrate in the dark reactions. It is fixed into organic sugars through a series of enzymatic steps in the Calvin cycle.
D. ATP: Adenosine triphosphate (ATP) is a vital energy carrier generated in the light reactions. It provides the energy required for the synthesis of glucose from CO₂ in the dark reactions.
E. NADPH: Nicotinamide adenine dinucleotide phosphate (NADPH) is another product of the light reactions and acts as a reducing agent, donating electrons during the reduction of CO₂ to form glucose in the Calvin cycle.
Given this understanding, the components required for the dark reaction are CO₂ for carbon fixation, ATP for energy, and NADPH for reducing power. Therefore, the parts necessary from the given list are C, D and E . So, the correct answer to this question is: Option C: C, D, and E only

Q2: How many molecules of ATP and NADPH are required for every molecule of CO₂ fixed in the Calvin cycle? (NEET 2024)
(a) 2 molecules of ATP and 3 molecules of NADPH
(b) 2 molecules of ATP and 2 molecules of NADPH
(c) 3 molecules of ATP and 3 molecules of NADPH
(d) 3 molecules of ATP and 2 molecules of NADPH
Ans: (d)
The Calvin cycle, also known as the Calvin-Benson-Bassham cycle, is the set of chemical reactions that take place in chloroplasts during photosynthesis. The cycle is light-independent because it takes place after the energy has been captured from sunlight. The Calvin cycle uses ATP and NADPH as energy sources, and incorporates CO₂ into organic molecules, eventually producing glucose.

The cycle consists of three main stages:

• Carbon fixation
• Reduction phase
• Regeneration of the ribulose-1,5-bisphosphate (RuBP)

In the Calvin cycle:
Carbon Fixation: Each CO₂ molecule is attached to a five-carbon sugar named ribulose-1,5-bisphosphate (RuBP). This reaction is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The product of this reaction is a six-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).
Reduction Phase: Each 3-PGA is phosphorylated by ATP (consuming 2 ATP molecules total for two 3-PGA molecules) to form 1,3-bisphosphoglycerate. This molecule is then reduced by NADPH (using 2 NADPH molecules in total) to form glyceraldehyde-3-phosphate (G3P). Out of every six G3P formed, one exits the cycle to contribute towards forming glucose, while the rest are recycled to regenerate RuBP.
Regeneration of RuBP: For every three CO₂ molecules fixed, five molecules of G3P are used to regenerate three molecules of RuBP, requiring further ATP input (3 more ATP molecules).
Thus, for each incorporated CO₂ molecule, 3 ATP molecules and 2 NADPH molecules are required:
3 ATP molecules (2 for the reduction of two molecules of 3-PGA into 1,3-bisphosphoglycerate and then one for the regeneration phase of RuBP).
2 NADPH molecules are used to reduce two molecules of 1,3-bisphosphoglycerate to G3P.
Therefore, the correct answer to the question is Option D: 3 molecules of ATP and 2 molecules of NADPH are required for every molecule of CO₂ fixed in the Calvin cycle.

Q3: Given below are two statements:     (NEET 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 :
(a) Both Statement I and Statement II are true
(b) Both Statement I and Statement II are false
(c) Statement I is true but Statement II is false
(d) Statement I is false but Statement II is true
Ans: (c)
In C₃ plant, some O₂ bind to RuBisCO, and hence CO₂ fixation is decreased. Statement II is incorrect, In C4 plants,  photorespiration does not occur. This is because they have a mechanism that increases the concentration of CO2 at the enzyme site. This takes place when the C4 acid from the mesophyll is broken down in the bundle sheath cells to release CO2 – this results in increasing the intracellular concentration of CO2 . In turn, this ensures that the RuBisCO functions as a carboxylase minimising the oxygenase activity.

Q4: The photochemical phase of photosynthesis include:   (NEET 2024)
A. Oxygen release
B. Formation of NADPH
C. Use of ATP
D. Water splitting
E. Carboxylation
Choose the correct answer from the options given below:
(a) C and E only
(b) A, B and D only
(c) B, C and E only
(d) A, B, C and D only
Ans: (b)
The photochemical phase of photosynthesis, also known as the light-dependent reactions, involves the following processes:

• A. Oxygen release: During the photochemical phase, water molecules are split into oxygen, protons, and electrons (this is known as photolysis), releasing oxygen as a byproduct.
• B. Formation of NADPH: In the photochemical phase, electrons from water are passed through the electron transport chain, leading to the formation of NADPH, which is used in the next phase (Calvin cycle).
• D. Water splitting: The splitting of water molecules (photolysis) occurs during the photochemical phase, providing the electrons needed for the electron transport chain.
• C. Use of ATP: While ATP is produced in the photochemical phase via photophosphorylation, its usage occurs primarily in the Calvin cycle (the light-independent phase) rather than in the light-dependent reactions themselves.
• E. Carboxylation: This process, which involves the fixation of CO2 into an organic molecule, occurs in the Calvin cycle (light-independent phase), not in the photochemical phase.

Therefore, the correct answer is (b): A, B, and D only.

Q5: Match List-I with List-II  (NEET 2024)
Choose the correct answer from the options given below:
(a) A-II, B-I, C-IV, D-III
(b) A-IV, B-II, C-I, D-III
(c) A-III, B-I, C-IV, D-II
(d) A-III, B-IV, C-II, D-I
Ans: (c)

• A. C4 Pathway: The C4 pathway involves the enzyme phosphoenolpyruvate carboxylase that fixes carbon into a 4-carbon molecule, phosphoenol pyruvate (III).
• B. Light reaction: In the light reactions of photosynthesis, water is split to release oxygen and protons, which also generates electrons, as shown in the equation 2H₂O → 4H⁺ + O₂ = 4e^- (I).
• C. Photorespiration: This is the process where oxygen is fixed by the enzyme RuBisCO leading to the production of phosphoglycolate (IV).
• D. Calvin cycle: In the Calvin cycle, Ribulose 1,5-bisphosphate (RuBP) is the molecule that reacts with carbon dioxide to form an unstable 6-carbon compound (II).

Thus, the correct match is:

• A-III: C4 Pathway involves phosphoenolpyruvate.
• B-I: Light reaction involves water splitting.
• C-IV: Photorespiration results in phosphoglycolate.
• D-II: Calvin cycle uses Ribulose 1,5-bisphosphate.

Q6: How many molecules of ATP and NADPH are required, respectively, for fixation of every CO2 molecule entering the Calvin cycle?
(a) 2 and 4
(b) 4 and 2
(c) 3 and 2
(d) 2 and 3      (NEET 2024)
Ans: (c)
In the Calvin cycle, for the fixation of one CO₂ molecule, the following are required:

3 ATP molecules:

• One ATP is used to convert 3-phosphoglycerate (3-PGA) into 1,3-bisphosphoglycerate.
• Another ATP is used to convert glycerate-3-phosphate into glyceraldehyde-3-phosphate (G₃P).
• The third ATP is needed for the regeneration of ribulose-1,5-bisphosphate (RuBP) from G₃P.

2 NADPH molecules:

• Two NADPH molecules are used to reduce 1,3-bisphosphoglycerate into glyceraldehyde-3-phosphate (G₃P).

So, for each CO₂ molecule fixed in the Calvin cycle, 3 ATP and 2 NADPH molecules are required.

Q7: Synthesis of ATP linked to development of a proton gradient across a membrane is:  (NEET 2024)
(a) Mass flow hypothesis
(b) Wobble hypothesis
(c) Chemiosmotic hypothesis
(d) Rivet Popper hypothesis
Ans: (c)
The Chemiosmotic hypothesis, proposed by Peter Mitchell, explains how ATP is synthesized in mitochondria and chloroplasts. According to this hypothesis, the energy from electrons moving through the electron transport chain is used to pump protons (H⁺) across a membrane, creating a proton gradient. This proton gradient generates a proton motive force (PMF) that drives ATP synthesis as protons flow back across the membrane through ATP synthase, linking the development of the proton gradient to ATP production.

Q8: Which of the following are required for the light reaction of photosynthesis?     (NEET 2024)
A. CO₂
B. O₂
C. H₂O
D. Chlorophyll 
E. Light 
(a) A , C, D and E only 
(b) C, D and E only 
(c) A and B only
(d) A, C and E only
Ans: (b)

For the light reaction of photosynthesis, the following are required:

• C. H₂O (Water): Water is split in the light reaction to provide electrons, protons, and oxygen (photolysis).
• D. Chlorophyll: Chlorophyll absorbs light energy, which is essential for the light reaction to occur.
• E. Light: Light energy is needed to excite electrons in chlorophyll, initiating the light-dependent reactions.

A. CO₂ and B. O₂ are not required for the light reaction:

• CO₂ is used in the Calvin cycle, which is the light-independent reaction.
• O₂ is produced as a byproduct of the light reaction, but it is not required for the light reaction to occur.

Thus, the correct answer is (b): C, D, and E only.

Q9: Which one of the following products diffuses out chloroplast during photosynthesis?    (NEET 2024)
(a) ADP 
(b) NADPH 
(c) O₂
(d) ATP
Ans: (c)
During photosynthesis, the light reactions occur in the chloroplast, where water (H₂O) is split, releasing oxygen (O₂) as a byproduct. This oxygen is then diffused out of the chloroplast into the surrounding environment.

• ADP, NADPH, and ATP are involved in the light reactions, but they do not diffuse out of the chloroplast. Instead, ADP is converted to ATP in the process, and NADPH is used in the Calvin cycle for carbon fixation.

Thus, the correct answer is (c): O₂.

Q10: Observe the given figure. Identify the different stages labelled with alphabets by selecting the correct option:   (NEET 2024)

(a) A-Carboxylation, B-Regeneration, C-Reduction
(b) A-Reduction, B-Decarboxylation, C-Regeneration 
(c) A-Carboxylation, B-Reduction, C-Regeneration 
(d) A-Reduction, B-Carboxylation, C-Regeneration 
Ans: (c)
Based on the diagram provided:

• A (Carboxylation): This is the step where CO₂ is fixed to Ribulose-1,5-bisphosphate (RuBP), forming an unstable 6-carbon compound which immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA). This process is known as carboxylation.
• B (Reduction): In this stage, ATP and NADPH are used to convert 3-phosphoglycerate (3-PGA) into triose phosphate (G₃P). This is a reduction reaction where electrons are transferred to the molecule.
• C (Regeneration): This step involves the regeneration of Ribulose-1,5-bisphosphate (RuBP) from triose phosphates (G₃P), which is necessary for the Calvin cycle to continue. ATP is used for this regeneration process.

Thus, the correct sequence is:

• A: Carboxylation (CO₂ is added to RuBP)
• B: Reduction (3-PGA is converted to G₃P)
• C: Regeneration (RuBP is regenerated from G₃P)

2023

Q1: How many ATP and NADPH₂ are required for the synthesis of one molecule of Glucose during Calvin cycle? [NEET 2023]
(a) 12 ATP and 12 NADPH₂
(b) 18 ATP and 12 NADPH₂
(c) 12 ATP and 16 NADPH₂
(d) 18 ATP and 16 NADPH₂
Ans: (b)
For every CO₂ molecule entering the Calvin cycle, 3 molecules of ATP and 2 of NADPH₂ are required. To make one molecule of glucose, 6 turns of the cycle are required. Thus, ATP and NADPH₂ molecules required for synthesis of one molecule of glucose during Calvin cycle will be

Q2: The reaction centre in PS II has an absorption maxima at     [2023]
(a) 680 nm
(b) 700 nm
(c) 660 nm
(d) 780 nm
Ans: (a)
In PS-I, the reaction centre chlorophyll a has an absorption peak at 700 nm, while in PS-II, reaction centre has an absorption maxima at 680 nm.

Q3: Which of the following combinations is required for chemiosmosis?   (NEET 2023)
(a) Proton pump, electron gradient, NADP synthase.
(b) Membrane, proton pump, proton gradient, ATP synthase.
(c) Membrane, proton pump, proton gradient, NADP synthase.
(d) Proton pump, electron gradient, ATP synthase.
Ans: (b)
Chemiosmosis is the process through which ATP is generated in the light reactions of photosynthesis and cellular respiration. The following are required for chemiosmosis:

• Membrane: A membrane (e.g., thylakoid membrane in chloroplasts or inner mitochondrial membrane) is essential for establishing the proton gradient.
• Proton pump: Proteins in the membrane, such as those in the electron transport chain, actively pump protons (H⁺) across the membrane, creating a proton gradient.
• Proton gradient: This gradient of protons across the membrane is what drives the synthesis of ATP.
• ATP synthase: This enzyme allows protons to flow back across the membrane through a channel, and the energy released is used to synthesize ATP from ADP and inorganic phosphate.

Thus, (b) is the correct combination required for chemiosmosis.

Q4:  Match List - I with List - II     (NEET 2023)

Choose the correct answer from the options given below:
(a) (A) III, (B) II, (C) IV, (D) I
(b) (A) III, (B) I, (C) IV, (D) II
(c) (A) III, (B) II, (C) I, (D) IV
(d) (A) IV, (B) III, (C) II, (D) I
Ans: (a)
Here is the correct matching based on the pigment colors:

• (A) Chlorophyll a: This pigment absorbs light most efficiently and reflects blue-green light, so it corresponds to (III).
• (B) Chlorophyll b: This pigment assists in photosynthesis by absorbing yellow-green light, so it corresponds to (II).
• (C) Xanthophyll: This pigment absorbs light and reflects yellow light, so it corresponds to (IV).
• (D) Carotenoids: These pigments reflect yellow to yellow-orange light, so they correspond to (I).

Thus, the correct match is:

• (A) III: Chlorophyll a reflects blue-green light.
• (B) II: Chlorophyll b reflects yellow-green light.
• (C) IV: Xanthophyll reflects yellow light.
• (D) I: Carotenoids reflect yellow to yellow-orange light.

Q5: Given below are two statements:    (NEET 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:
(a) Statement I is correct but Statement II is incorrect
(b) Statement I is incorrect but Statement II is correct
(c) Both Statement I and Statement II are correct
(d) Both Statement I and Statement II are incorrect
Ans: (c)

• Statement I: RuBisCO is indeed the most abundant enzyme on Earth. It plays a crucial role in the Calvin cycle by fixing carbon dioxide (CO₂) into ribulose-1,5-bisphosphate (RuBP). Due to its widespread presence in plants, algae, and cyanobacteria, it is considered the most abundant enzyme.
• Statement II: Photorespiration is a process where RuBisCO fixes oxygen instead of carbon dioxide, leading to a less efficient form of photosynthesis. However, in C₄ plants, the enzyme PEP carboxylase fixes carbon dioxide first, reducing the occurrence of photorespiration. Although it is minimized, photorespiration can still occur in C4 plants under certain conditions (e.g., extreme heat or high oxygen concentrations), but it is much less than in C3 plants.

Thus, both statements are correct in the context:

• RuBisCO is the most abundant enzyme (Statement I).
• Photorespiration is largely minimized in C4 plants (Statement II).

So, the answer is (c).

Q6: Which of the following statements is incorrect?    (NEET 2023)
(a) Grana lamellae have both PS I and PS II
(b) Cyclic photophosphorylation involves both PS I and PS II
(c) Both ATP and NADPH + H⁺ are synthesized during non-cyclic photophosphorylation
(d) Stroma lamellae lack PS II and NADP reductase
Ans: (b)

• Statement 1: Grana lamellae (the thylakoid stacks) contain both Photosystem I (PS I) and Photosystem II (PS II). This is correct because the light reactions of photosynthesis occur in these grana and involve both photosystems.
• Statement 2: Cyclic photophosphorylation involves only Photosystem I (PS I). In this process, electrons from PS I are cycled back through the electron transport chain, generating ATP but not NADPH. Photosystem II (PS II) is not involved in cyclic photophosphorylation.
• Statement 3: In non-cyclic photophosphorylation, both ATP and NADPH + H⁺ are produced. This process involves both PS I and PS II, where PS II generates electrons and PS I is involved in the reduction of NADP⁺ to NADPH.
• Statement 4: Stroma lamellae (the connecting membrane between thylakoid stacks) indeed lack PS II and NADP⁺ reductase, but they do have components like ATP synthase that are involved in ATP synthesis.

Thus, the incorrect statement is Statement 2, because cyclic photophosphorylation only involves PS I, not both PS I and PS II.

2022

Q1: When one CO₂ molecule is fixed as one molecule of triose phosphate, which of the following photochemically made, high energy chemical intermediates are used in the reduction phase? [NEET 2022 Phase 2]
(a) 2 ATP + 2 NADPH
(b) 1 ATP + 1 NADPH
(c) 1 ATP + 2 NADPH
(d) 2 ATP + 1 NADPH
Ans: (a)
In the Calvin cycle, during the reduction phase, two molecules of ATP and two molecules of NADPH are required to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P), which is the precursor for glucose and other carbohydrates.

Q2: Identify the correct statements regarding chemiosmotic hypothesis:       [NEET 2022 Phase 2]
(a) Splitting of the water molecule takes place on the inner side of the membrane.
(b) Protons accumulate within the lumen of the thylakoids.
(c) Primary acceptor of electron transfers the electrons to an electron carrier.
(d) NADP reductase enzyme is located on the stroma side of the membrane.
(e) Protons increase in number in stroma.
Choose the correct answer from the options given below:
(a) (b), (c) and (e)
(b) (a), (b) and (e)
(c) (a), (b) and (d)
(d) (b), (c) and (d)
Ans: (c)

• Primary acceptor of electron transfers its electron not to an electron carrier but to an H carrier.
• Protons increase in number in lumen of the thylakoid not in stroma.

Q3: Given below are two statements:      [NEET 2022 Phase 1]
Statement I: The primary CO₂ acceptor in C₄ plants is phosphoenolpyruvate and is found in the mesophyll cells.
Statement II: Mesophyll cells of C₄ plants lack RuBisCo enzyme.
In the light of the above statements, choose the correct answer from the options given below:
(a) Both Statement I and Statement II are correct
(b) Both Statement I and Statement II are incorrect
(c) Statement I is correct but Statement II is incorrect
(d) Statement I is incorrect but Statement II is correct
Ans: (a)
The primary CO₂ acceptor is a 3-carbon molecule, phosphoenol pyruvate (PEP) and is present in the mesophyll cells.
Mesophyll cells of C₄ plants lack RuBisCO enzyme.

Q4: Which one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis? It involves:
(a) Breakdown of proton gradient
(b) Breakdown of electron gradient
(c) Movement of protons across the membrane to the stroma
(d) Reduction of NADP to NADPH₂ on the stroma side of the membrane [NEET 2022 Phase 1]
Ans: (b)
Chemiosmosis requires a membrane, a proton pump, a proton gradient and ATP synthase. Energy is used to pump protons across a membrane to create a gradient or a high concentration of protons within the thylakoid lumen.
The NADP reductase enzyme is located on the stroma side of the membrane. Along with the electrons that come from the acceptor of electrons of PS I, protons are necessary for reduction of NADP⁺ to NADPH + H⁺.
The process does not involve breaking of electron gradient.

2021

Q1: The first stable product of CO₂ fixation in sorghum is:     [NEET 2021]
(a) Succinic acid
(b) Phosphoglyceric acid
(c) Pyruvic acid
(d) Oxaloacetic acid
Ans: (d)

• Sorghum is a C₄ plant. The first stable product of CO₂ fixation in Sorghum is oxaloacetic acid.
• The first stable product in C₃ cycle is 3-phosphoglyceric acid.
• Pyruvic acid is the end product of glycolysis.
• Succinic acid is an intermediate product in krebs cycle.

Q2: Which of the following statements is incorrect?     [NEET 2021]
(a) Grana lamellae have both PSI and PS II.
(b) Cyclic photophosphorylation involves both PS I and PS II.
(c) Both ATP and NADPH+H⁺ are non-cyclic synthesized during photophosphorylation.
(d) Stroma lamellae have PS I only and lack NADP reductase.
Ans: (b)

• Cyclic photophosphorylation involves only PS I. Cyclic photophosphorylation is a process in which an electron expelled by the excited photocentre is returned to it after passing through a series of electron carriers. The excited electron does not pass on to NADP+ but is cycled back to the PS I complex through the electron transport chain.

  Non-cyclic photophosphorylation involves both photosystems I and II. The electron follows a non-cyclic pathway in it. The representation of it is also called Z scheme.

• Both PS I and PS II are found on grana lamellae whereas stroma lamellae have PS I only and lack NADP reductase.

2020

Q1: The oxygenation activity of RuBisCo enzyme in photorespiration leads to the formation of:     [NEET 2020]
(a) 1 molecule of 6-C compound
(b) 1 molecule of 4-C compound and 1 molecule of 2-C compound
(c) 2 molecules of 3-C compound
(d) 1 molecule of 3-C compound
Ans: (d)
In photorespiration, O₂ binds to RubisCo. As a result RuBP instead to being converted to 2 molecules of PGA bind with O₂ to form one molecule each of phosphoglycerate (3 carbon compound) and phosphoglycolate (2 carbon compound). 

Q2: In light reaction, plastoquinone facilitates the transfer of electrons from:     [NEET 2020]
(a) PS-I to NADP+
(b) PS-I to ATP synthase
(c) PS-II to Cytb₆f complex
(d) Cytb₆complex to PS-I
Ans: (c)
After excitement, e^– is passed from PS-II (P680) to primary electron acceptor (Pheophytin). From primary e^– acceptor, e^– is passed to plastoquinone. Plastoquinone (PQ) in turn transfer its e^– to Cytb₆f complex. Therefore plastoquinone facilitates the transfer of electrons from PS-II to Cytb₆f complex. 

2018

Q1: Which of the following is not a product of light reaction of photosynthesis?     [NEET 2018]
(a) ATP
(b) NADH
(c) NADPH
(d) Oxygen
Ans: (b)
Both ATP and NADPH + H⁺ are synthesized by electron flow in light reaction, and O₂ is also a product of non-cyclic photoposphorylation. 

2017

Q1: With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct?    [NEET 2017]
(a) Increasing atmospheric CO₂ concentration up to 0.05% can enhance CO₂ fixation rate.
(b) C₃ plants respond to higher temperature with enhanced photosynthesis while C₄ plants have much -lower temperature optimum.
(c) Tomato is a greenhouse crop which can be grown in CO₂-enriched atmosphere for higher yield.
(d) Light saturation for CO₂ fixation occurs at 10% of full sunlight.
Ans: (b) 
C₄ plants respond to higher temperature with enhanced photosynthesis while C₃ plants have lower temperature optimum.

Q2: Phosphoenol pyruvate (PEP) is the primary CO₂ acceptor in    [NEET 2017]
(a) C₄ plants
(b) C₂ plants
(c) C₃ and C₄ plants
(d) C₃ plants.
Ans: (a)
In the mesophyll cells cytoplasm of C₄ plants like sugarcane, maize, sorghum etc. PEP is 3C compound which serves as primary CO₂ acceptor. 

2016

Q1: The process which makes major difference between C₃ and C₄ plants is     [ NEET 2016 Phase 2]
(a) Glycolysis
(b) Calvin cycle
(c) Photorespiration
(d) Respiration
Ans: (c)
Photorespiration is the light dependent process of oxygenation of ribulose biphosphate (RuBP) and release of carbon dioxide by the photosynthetic organs of a plant. It leads to oxidation of 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 absent in C₄ plants. Peroxisome and mitochondria are required for completing the process.

Q2: Water vapour comes out from the plant leaf through the stomatal opening. Through the same stomatal opening, carbon dioxide diffuses into the plant during photosynthesis. Reason out the above statements using one of following options:    [NEET 2016 Phase 1]
(a) The above processes happen only during night time.
(b) One process occurs during day time and the other at night.
(c) Both processes cannot happen simultaneously.
(d) Both processes can happen together because the diffusion coefficient of water and CO₂ is different.
Ans: (d)
In actively growing plants, water is continuously evaporating from the surface of leaf cells through stomatal opening exposed to air. This is called transpiration. Through the same stomatal opening carbon dioxide diffuses into the plant during photosynthesis. Simultaneously as both are the process of simple diffusion occurs in order of diffusion pressure gradient or diffusion coefficient.

Q3: In a chloroplast, the highest number of protons are found in    [NEET 2016 Phase 1]
(a) Intermembrane space
(b) Antennae complex
(c) Stroma
(d) Lumen of thylakoids
Ans: (d)
Proton concentration is higher in the lumen of thylakoid due to photolysis of water, H⁺ pumping and NADP reductase activity in stroma. During the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to pH 4.

Q4: Emerson’s enhancement effect and Red drop have been instrumental in the discovery of    [NEET 2016 Phase 1]
(a) Photophosphorylation and cyclic electron transport
(b) Oxidative phosphorylation
(c) Photophosphorylation and non-cyclic electron transport
(d) Two photosystems operating simultaneously
Ans: (d)

• Emerson et al. (1957) found that if light of shorter wavelengths was provided at the same time as the longer red wavelengths, photosynthesis was even faster than the sum of the two rates with either colour alone. This synergism or enhancement became known as the Emerson enhancement effect. 
• The two separate groups of pigments or photosystems cooperate in photosynthesis-long red wavelengths are absorbed only by one photosystem, called photosystem 1 (PS I) and the second photosystem, photosystem II (PS II), absorbs wavelengths shorter than 690 nm, and for maximum photosynthesis wavelengths absorbed by both systems must function together. 
• The two photosystems normally cooperate to cause photosynthesis at all wavelengths shorter than 690 nm, because both photosystems absorb those wavelengths. The importance of Emerson’s work is that it suggested the presence of two distinct photosystems.

Q5: Water-soluble pigments found in plant cell vacuoles are  [NEET 2016 Phase 1] 
(a) Xanthophylls
(b) Chlorophylls
(c) Carotenoids
(d) Anthocyanins
Ans: (d)
Many leaves produce water-soluble vacuolar pigments, which are stored within cell vacuoles (microscopic water sacs within each cell). Two major classes of leaf vacuolar pigments are anthocyanins and betalains.

Q6: A plant in your garden avoids photorespiratory losses, has improved water use efficiency, shows high rates of photosynthesis at high temperatures and has improved efficiency of nitrogen utilisation. In which of the following physiological groups would you assign this plant?     [NEET 2016 Phase 1] 
(a) CAM
(b) Nitrogen fixer
(c) C₃
(d) C₄
Ans: (d)
C₄ plants are adapted to hot and dry climate and lack photorespiration due to Kranz anatomy and have Greater productivity of biomass.

2015

Q1: Chromatophores take part in:    [NEET 2015 / AIPMT 2015 ]
(a) Growth
(b) Movement
(c) Respiration
(d) Photosynthesis
Ans: (d)
Chromatophores play an important role in the process of photo synthesis. They contain pigments and are found in blue green algae.

Q2: In photosynthesis, the light-independent reactions take place at:  [NEET 2015 / AIPMT 2015 ] 
(a) Photosystem-I
(b) Photosystem-II
(c) Stromal matrix
(d) Thylakoid lumen
Ans: (c)
 In photosynthesis, light-independent reactions are known as dark reactions. They take place in the stromal matrix of chloroplast where all the enzymes required for the reaction are present. This process does not depend directly on the presence of light but is dependent on the products of light reaction i.e., ATP and NADPH. The dark reaction occur through Calvin cycle.