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

2024

Q1: Identify the step in tricarboxylic acid cycle, which does not involve oxidation of substrate.     (NEET 2024)
(a) Malic acid → Oxaloacetic acid
(b) Succinic acid → Malic acid
(c) Succinyl-CoA → Succinic acid
(d) Isocitrate → α-ketoglutaric acid
Ans: (c)
The tricarboxylic acid cycle (TCA cycle), also known as the Krebs cycle or citric acid cycle, is a series of enzyme-catalyzed chemical reactions that form a key part of aerobic respiration in cells. This cycle is primarily used to generate high-energy electron carriers and carbon dioxide. Most of the steps in the TCA cycle involve the oxidation of the substrate, where electrons are transferred to NAD+ to form NADH or to FAD to form FADH2.

Each option provided corresponds to a step in the TCA cycle:

Option A: Malic acid → Oxaloacetic acid involves the enzyme malate dehydrogenase, where malate is oxidized to oxaloacetate. NAD+ is reduced to NADH in this process, indicating an oxidation reaction.
Option B: Succinic acid → Malic acid is not a direct step in the TCA cycle. Instead, succinic acid is first converted to fumarate by succinate dehydrogenase, involving the reduction of FAD to FADH2, then fumarate is hydrated to malate by fumarase. Both involve transformations but particularly the conversion of succinate to fumarate involves oxidation.
Option C: Succinyl-CoA → Succinic acid involves the conversion of Succinyl-CoA to Succinic acid catalyzed by succinyl-CoA synthetase. In this process, a high-energy thioester bond in Succinyl-CoA is broken to release a molecule of coenzyme A (CoA) and produce succinate. This step does not involve the transfer of electrons or the reduction of NAD+ or FAD; rather, it's coupled with the phosphorylation of GDP to GTP (or ADP to ATP in some organisms), which is a substrate-level phosphorylation.
Option D: Isocitrate →α-ketoglutaric acid involves the enzyme isocitrate dehydrogenase that catalyzes the oxidative decarboxylation of isocitrate into alpha-ketoglutarate. NAD+ is reduced to NADH, showing that this step involves oxidation.

Therefore, the correct answer is Option C (Succinyl-CoA → Succinic acid). This is the step in the TCA cycle that does not involve the oxidation of the substrate but instead involves substrate-level phosphorylation, which is associated with the energy conversion of GTP formation rather than an electron transfer process.

Q2: Match List I with List II     (NEET 2024)

Choose the correct answer from the options given below:
(a) A-I, B-II, C-III, D-IV
(b) A-II, B-I, C-IV, D-III
(c) A-III, B-IV, C-I, D-II
(d) A-IV, B-III, C-II, D-I
Ans: (b)
To correctly match the given processes in List I with their locations in List II, let's go through each item:

Citric Acid Cycle (A) occurs in the mitochondrial matrix. This process, also known as the Krebs cycle, takes place in the matrix of mitochondria where enzymes for the cycle are located.

Glycolysis (B) takes place in the cytoplasm of the cell. It is the process of breaking down glucose into pyruvate, generating small amounts of energy (ATP) and does not involve the mitochondria.

Electron Transport System (C) occurs at the inner mitochondrial membrane. This is where the electron transport chains are located and where ATP is produced by oxidative phosphorylation.

Proton Gradient (D) is involved in the creation of ATP and is formed across the intermembrane space of the mitochondria. Protons (H+ ions) are pumped from the mitochondrial matrix to the intermembrane space, creating a gradient that drives ATP synthesis.

Now using the above information, let's match these with the correct options:
A. Citric Acid Cycle - II. Mitochondrial Matrix
B. Glycolysis - I. Cytoplasm
C. Electron Transport System - IV. Inner Mitochondrial Membrane
D. Proton Gradient - III. Intermembrane Space of Mitochondria

Comparing these to the options provided:

Option A: A-I, B-II, C-III, D-IV - Incorrect
Option B: A-II, B-I, C-IV, D-III - Correct
Option C: A-III, B-IV, C-I, D-II - Incorrect
Option D: A-IV, B-III, C-II, D-I - Incorrect

Therefore, Option B is the correct match: A-II, B-I, C-IV, D-III

2023

Q1:  Which of the following combinations is required for chemiosmosis?        (NEET 2023)
(a) Membrane, proton pump, proton gradient, NADP synthase
(b) Proton pump, electron gradient, ATP synthase
(c) Proton pump, electron gradient, NADP synthase
(d) Membrane, proton pump, proton gradient, ATP synthase
Ans: (d)
Chemiosmosis is a process by which ATP (adenosine triphosphate) is produced in the cell. It relies on a concentration gradient of protons (H+ ions) across a membrane. The proton gradient is created by a proton pump. As protons flow back across the membrane, down their concentration gradient, they pass through a protein complex called ATP synthase, which uses the energy of the proton flow to produce ATP.

Q2: Match List I with List II :       (NEET 2023)

Choose the correct answer from the options given below :
(a) A – III, B – IV, C – II, D – I
(b) A – II, B – IV, C – I, D – III
(c) A – III, B – I, C – II, D – IV
(d) A – II, B – IV, C – III, D – I

Ans: (d)

• Pyruvate, which is formed by the glycolytic catabolism of carbohydrates in the cytosol, after it enters mitochondrial matrix undergoes oxidative decarboxylation by a complex set of reactions catalyzed by pyruvate dehydrogenase.
• The scheme of glycolysis was given by Gustav Embden, Otto Meyrhof and J. Parnas, and is often referred to as the EMP pathway.
• In electron transport system, the energy of oxidation-reduction is utilized for the production of proton gradient required for phosphorylation, thus, this process is also called oxidative phosphorylation.
• The TCA (tricarboxylic acid cycle) starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to yield citric acid. The reaction is catalysed by the enzyme citrate synthase. Thus, option (C) is correct.

Q3: Melonate inhibits the growth of pathogenic bacteria by inhibiting the activity of       (NEET 2023)
(a) Amylase
(b) Lipase
(c) Dinitrogenase
(d) Succinic dehydrogenase
Ans: (d)

• Melonate is a known inhibitor of the enzyme succinic dehydrogenase, which is involved in the citric acid cycle (also known as the Krebs cycle or TCA cycle), an essential metabolic pathway in many organisms, including bacteria.
• By inhibiting succinic dehydrogenase, melonate can disrupt the normal metabolism of pathogenic bacteria and inhibit their growth.

2022

Q1: What amount of energy is released from glucose during lactic acid fermentation?       (NEET 2022 Phase 1)
(a) More than 18%
(b) About 10%
(c) Less than 7%
(d) Approximately 15%

Ans: (c)
Less than seven percent of the energy in glucose is released during lactic acid fermentation and not all of it is trapped as high energy bonds of ATP.

Q2: What is the net gain of ATP when each molecule of glucose is converted to two molecules of pyruvic acid?       (NEET 2022 phase 1)
(a) Six
(b) Two
(c) Eight
(d) Four
Ans: (b)
During glycolysis, total 4 ATPs are produced from one glucose molecule with a net gain of 2 ATPs.

Q3: The number of time(s) decarboxylation of isocitrate occurs during single TCA cycle is       (NEET 2022 phase 2)
(a) Four
(b) One
(c) Two
(d) Three
Ans: (c)
During TCA cycle, 6-C compound isocitrate is converted into succinyl CoA, a 4-C compound by removing two CO₂ molecules.
The steps are as follows -

2021

Q1: Which of the following statements is incorrect?       (NEET 2021)
(a) ATP is synthesized through complex V.
(b) Oxidation-reduction reactions produce proton gradient in respiration.
(c) During aerobic respiration, the role of oxygen is limited to the terminal stage.
(d) In ETC (Electron Transport Chain), one molecule of NADH+H+ gives rise to 2ATP molecules, and one FADH2 gives rise to 3 ATP molecules.
Ans: (d)

• During respiration, process of ATP synthesis is explained by chemiosmotic model. it says that a proton gradient is required for ATP synthesis that is established by oxidation-reduction reactions.
• In ETC, one NADH + H⁺ produces 3 ATP while one FADH₂ produces 2 ATP molecules. NADH and FADH₂ are two different types of electron donors. They differ in the ways they feed electron during electron transport chain. NADH feeds its electrons into the electron transport chain at the beginning (Complex I). FADH₂ feeds into the electron transport chain at Complex II (at a lower energy level down the chain). The high energy electrons from NADH have sufficient energy to result in 3 ATP whereas the lower energy electrons in FADH₂ have energy for 2 ATP production.
• ATP is synthesized via complex V.
• In ETS, oxygen acts as terminal electron acceptor.

2020

Q1: The number of substrate level phosphorylations in one turn of citric acid cycle is:       (NEET 2020)
(a) Two
(b) Three 
(c) Zero
(d) One
Ans: (d)
One substrate level phosphorylation in one turn of citric acid cycle as per following reaction:

2019

Q1: Conversion of glucose to glucose-6-phosphate, the first irreversible reaction of glycolysis, is catalysed by       (NEET 2019)
(a) Phosphofructokinase
(b) Aldolase
(c) Hexokinase
(d) Enolase
Ans: (c)
Hexokinase catalyse the conversion of Glucose to Glucose-6 phosphate. It is the first step of activation phase of glycolysis.

2018

Q1: What is the role of NAD⁺ in cellular respiration?       (NEET 2018)
(a) It functions as an enzyme.
(b) It functions as an electron carrier.
(c) It is a nucleotide source for ATP synthesis.
(d) It is the final electron acceptor for anaerobic respiration.
Ans: (b)
NAD+ act as an electron carrier in cellular respiration.

Q2: Which of these statements is incorrect?       (NEET 2018)
(a) Enzymes of TCA cycle are present in mitochondrial matrix.
(b) Glycolysis occurs in cytosol.
(c) Glycolysis operates as long as it is supplied with NAD that can pick up hydrogen atoms.
(d) Oxidative phosphorylation takes place in outer mitochondrial membrane.
Ans: (d)
Oxidative phosphorylation takes place in inner mitochondrial membrane via F0 – F1 particles.

2017

Q1: Which statement is wrong for Krebs’ cycle?       (NEET 2017)
(a) There is one point in the cycle where FAD⁺ is reduced to FADH₂.
(b) During conversion of succinyl CoA to succinic acid, a molecule of GTP is synthesised.
(c) The cycle starts with condensation of acetyl group (acetyl CoA) with pyruvic acid to yield citric acid.
(d) There are three points in the cycle where NAD⁺ is reduced to NADH⁺ H⁺.
Ans: (c)
Krebs cycle begins with condensation of acetyl CoA (2C) with oxaloacetic acid (4C) to form citric acid (6C).

2016

Q1: Which of the following biomolecules is common to respiration-mediated breakdown of fats, carbohydrates and proteins?       (NEET 2016 Phase 2)
(a) Glucose-6-phosphate
(b) Fructose 1, 6-bisphosphate
(c) Pyruvic acid
(d) Acetyl CoA
Ans: (d)
Carbohydrates are usually first converted into glucose before they are used for respiration. Fats are broken down into glycerol and fatty acids first. If fatty acids were to be respired they would first be degraded to acetyl CoA and enter the pathway. Glycerol would enter the pathway after being converted to 3-phosphoglyceraldehyde (PGAL). The proteins are degraded by proteases to individual amino acids (after deamination) and depending on their structure enter the pathway within the Krebs’ cycle or as pyruvate or acetyl CoA. Thus, acetyl CoA is the common metabolite of all the three (carbohydrates, proteins and fats).

Q2: Oxidative phosphorylation is       (NEET 2016)
(a) Formation of ATP by transfer of phosphate group from a substrate to ADP 
(b) Oxidation of phosphate group in ATP
(c) Addition of phosphate group to ATP
(d) Formation of ATP by energy released from electrons removed during substrate oxidation.
Ans: (d)

• Oxidative phosphorylation is the synthesis of energy rich ATP molecules with the help of energy liberated during oxidation of reduced co-enzymes (NADH, FADH₂) produced in respiration. The enzyme required for this synthesis is called ATP synthase. It is located in F₁ or head piece of F₀ – F₁ or elementary particles present in the inner mitochondrial membrane.
• F₁ particle is capable of ATP synthesis. ATP synthase becomes active in ATP formation only when there is a proton gradient having higher concentration of H⁺ or protons on the F0 side as compared to F₁ side. This higher concentration creates an electric potential across the mitochondrial membrane. The proton gradient and membrane electric potential together form proton motive force (PMF). The flow of protons through the F0 channel which induces F₁ particle to function as ATP synthase. The energy of the proton gradient is used in attaching a phosphate radicle to ADP by high-energy bond. This produces ATP.

2015

Q1: Cytochromes are found in      (NEET / AIPMT 2015 Cancelled Paper)
(a) cristae of mitochondria
(b) lysosomes
(c) matrix of mitochondria
(d) outer wall of mitochondria.
Ans: (a)
Cytochromes are fond in mitochondria. These are located on the inner membrane of mitochondria and are related with phosphorylation.

2014

Q1: In which one of the following processes CO₂ in not released?       (NEET 2014 / AIPMT 2014)
(a) Aerobic respiration in plants
(b) Aerobic respiration in animals
(c) Alcoholic fermentation
(d) Lactate fermentation
Ans: (d)
Lactic acid fermentation: It occurs in lactic acid bacteria (Lactobacillus) and muscles (Human). Pyruvic acid produced in glycolysis is reduced by NADH₂ to form lactic acid without producing carbon dioxide.