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

2024

Q1: Which of the following are required for the dark reaction of photosynthesis?     (NEET 2024)
A. Light
B. Chlorophyll
C. CO_{2
D. ATP
E. NADPH}

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 areCO₂ 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 giver below :
(a) Both Statement [ 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, photorespiration does not occur in C₄ plants as they lack RuBisCO in mesophyll. Hence statement I is the only correct option.

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.

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)
The reduction step of Calvin cycle involves utilisation of two molecules of ATP for phosphorylation and two molecules of NADPH for reduction per molecule of CO₂ fixed. 

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.