How often does Respiration in Plants appear in NEET?

Respiration in Plants is a Medium to High Weightage chapter with 3 to 5 questions in most NEET exams. Questions focus on glycolysis intermediates and net ATP, the link reaction, Krebs cycle products per turn, the electron transport chain (Complex I, II, III, IV and ATP synthase), ATP yield per glucose (NCERT 38 ATP), fermentation pathways (alcoholic and lactic acid), respiratory quotient (RQ) values, and the amphibolic nature of the respiratory pathway. Master each phase quantitatively for a strong NEET score.

What is the difference between glycolysis and the Krebs cycle?

Glycolysis takes place in the cytoplasm. It does not need oxygen and breaks one glucose (6C) into two pyruvate (3C). Net products per glucose: 2 ATP and 2 NADH. The Krebs cycle (TCA cycle) takes place in the mitochondrial matrix. It needs oxygen indirectly (because the ETC must run to keep the cycle going). It oxidises acetyl CoA (2C) to 2 CO2. Per turn it produces 3 NADH, 1 FADH2, and 1 GTP (or ATP). Per glucose, 2 turns of the Krebs cycle produce 6 NADH, 2 FADH2, 2 ATP, and 4 CO2.

What is the total ATP yield from one glucose molecule in aerobic respiration?

According to NCERT (theoretical maximum): 38 ATP per glucose. The breakdown is: glycolysis gives 2 ATP (net) + 2 NADH; the link reaction gives 2 NADH (1 per pyruvate, 2 pyruvates per glucose); the Krebs cycle gives 2 ATP + 6 NADH + 2 FADH2. Total reduced coenzymes: 10 NADH + 2 FADH2. Each NADH yields 3 ATP and each FADH2 yields 2 ATP via the ETC and oxidative phosphorylation, giving 30 + 4 = 34 ATP from oxidative phosphorylation. Total: 2 (glycolysis) + 2 (Krebs GTP) + 34 (ETC) = 38 ATP. The actual yield in modern biochemistry is around 30-32 ATP because of proton leak and the cost of the malate-aspartate shuttle, but NEET expects the NCERT value of 38.

What is the difference between aerobic respiration and fermentation?

Aerobic respiration uses oxygen as the final electron acceptor. It completely oxidises glucose to CO2 and H2O, takes place in the cytoplasm + mitochondria, and yields 38 ATP per glucose (NCERT). It involves glycolysis + link reaction + Krebs cycle + ETC. Fermentation does not use oxygen. It is incomplete oxidation. It takes place entirely in the cytoplasm. The only ATP produced is the 2 ATP from glycolysis. The pyruvate is converted to ethanol + CO2 (alcoholic fermentation in yeast like Saccharomyces) or to lactate (lactic acid fermentation in muscles under O2 stress and in Lactobacillus). The point of fermentation is to regenerate NAD+ so that glycolysis can continue.

What is the respiratory quotient (RQ) and what are its values?

The respiratory quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed during respiration: RQ = volume of CO2 evolved / volume of O2 consumed. Standard NEET values: carbohydrates (such as glucose) RQ = 1.0; fats (such as tripalmitin) RQ ≈ 0.7; proteins RQ ≈ 0.9; organic acids (such as malic acid) RQ > 1.0 (typically 1.33 for malic acid); anaerobic respiration RQ = infinity (CO2 is produced but no O2 is consumed). The RQ depends on the substrate being respired. Pure water-loving fatty substrates have lower RQ because they need more oxygen to oxidise.

Why is respiration called an amphibolic pathway?

A pathway is amphibolic when it serves both catabolic (breakdown) and anabolic (synthesis) roles. The respiratory pathway is amphibolic because its intermediates are not just energy currency; they are also building blocks for biosynthesis. For example: acetyl CoA is the precursor for fatty acids, sterols, and ketone bodies; alpha-ketoglutarate gives rise to glutamate and other amino acids; oxaloacetate gives rise to aspartate and other amino acids; pyruvate gives rise to alanine. So the same pathway that breaks down glucose to release energy can also be tapped at any intermediate to build up other biomolecules. Respiration is therefore catabolic and anabolic, hence amphibolic.

Where exactly do the four phases of cellular respiration occur?

Glycolysis occurs in the cytoplasm (cytosol). Link reaction (pyruvate dehydrogenase complex) occurs in the mitochondrial matrix. Krebs cycle (TCA cycle) occurs in the mitochondrial matrix. Electron transport chain and oxidative phosphorylation (ATP synthase) occur on the inner mitochondrial membrane (cristae). Glycolysis is the only phase that does not require mitochondria, which is why anaerobic organisms (those without mitochondria) can still do glycolysis but not the later phases. The inner mitochondrial membrane is folded into cristae to provide a large surface area for the electron transport chain and ATP synthase.

Home

Botany

Respiration in Plants

Respiration in PlantsNEET Botany · Class 11 · NCERT Chapter 14

Overview Notes NEET Questions Interactive Learning

14 NEET previous-year questions on Respiration in Plants, each with the correct answer and a step-by-step solution. Sourced directly from official NEET papers across every booklet code.

PYQ frequency · topic × year

Respiration in Plants

Darker = more questions in our PYQ bank for that topic and year.

Want to time yourself?

Take a free 10-question chapter mock test on Respiration in Plants — no login needed for your first attempt.

Take timed test →

All (14)

Respiration in Plants (14)

Aerobic respiration in plants

Aerobic respiration in animals

Alcoholic fermentation

Lactate fermentation

Solution

Lactate fermentation does not produce $CO_{2}$ ; it converts pyruvate to lactate. In contrast, aerobic respiration and alcoholic fermentation both release $CO_{2}$ as byproducts, so option (d) is correct. NCERT XI chapter Respiration in Plants covers these metabolic pathways.

Only (d)

Only (a)

(a), (c) and (d)

(b) and (c)

Solution

In Human RBCs, nucleus degenerates during maturation which provide more space for oxygen carrying pigment (Haemoglobin). It lacks most of the cell organelles including mitochondria so respires anaerobically.

There are three points in the cycle where NAD + is reduced to NADH + H+

There is one point in the cycle where FAD + is reduced to FADH2

During conversion of succinyl CoA to succinic acid, a molecule of GTP is synthesised

The cycle starts with condensation of acetyl group (acetyl CoA) with pyruvic acid to yield citric acid

Solution

Krebs cycle starts with condensation of acetyl CoA (2C) with oxaloacetic acid (4C) to form citric acid (6C).

It is a nucleotide source for ATP synthesis.

It functions as an electron carrier.

It functions as an enzyme.

It is the final electron acceptor for anaerobic respiration.

Solution

NAD $^{+}$ functions as an electron carrier in cellular respiration, accepting electrons and hydrogen to form NADH. This is a key step in the electron transport chain, as described in NCERT XI chapter Respiration in Plants, so option (b) is correct.

Chlamydiasis

Gonorrhea

Genital warts

Genital herpes

Solution

Factual NCERT

0.09

0.9

0.7

0.07

Solution

Ref. XI NCERT Chapter- 14, Page No. 237

Breakdown of proton gradient

Breakdown of electron gradient

Movement of protons across the membrane to the stroma

Reduction of NADP to NADPH2 on the stroma side of the membrane

Solution

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.

Four

Six

Two

Eight

Solution

During glycolysis, total 4 ATPs are produced from one glucose molecule with a net gain of 2 ATPs.

Approximately 15%

More than 18%

About 10%

Less than 7%

Solution

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.

Cofactor inhibition

Feedback inhibition

Competitive inhibition

Enzyme activation

Solution

Correct answer is option (3) because malonate shows close structural similarity with the substrate and it competes with the substrate for the substrate binding site of the enzyme succinic dehydrogenase. Option (1), (2) and (4) are incorrect as enzyme activation, co-factor inhibition are not showing structural similarity with substrate.

Malic acid → Oxaloacetic acid

Succinic acid → Malic acid

Succinyl-CoA → Succinic acid

Isocitrate → α-ketoglutaric acid

Solution

Oxidation involves the loss of electrons (often as part of hydrogen) from a molecule, leaving to an increase in its oxidation state. This process is typically associated with the transfer of electrons to an electron acceptor which is reduced in the process. The conversion of succinyl CoA to succinic acid does not involve oxidation of substrate.

A-I, B-II, C-III, D-IV

A-II, B-I, C-IV, D-III

A-III, B-IV, C-I, D-II

A-IV, B-III, C-II, D-I

Solution

Citric acid cycle occurs in mitochondrial matrix. Glycolysis occurs in cytosol in most of the organism. Electron transport system is present in the inner mitochondrial membrane. Proton gradient is formed across the intermembrane space of mitochondria.

Cytochrome $b c_{1}$

Succinate dehydrogenase

Cytochrome c oxidase

NADH dehydrogenase

Solution

Complex II of the mitochondrial electron transport chain is also known as succinate dehydrogenase. This enzyme catalyzes the oxidation of succinate to fumarate and transfers electrons to ubiquinone. NCERT XI chapter Respiration in Plants identifies this enzyme as Complex II, so option (b) is correct.

RuBisCo

Carbonic anhydrase

Succinate dehydrogenase

Catalase

Solution

In peroxidase and catalase, which catalyze the breakdown of hydrogen peroxide to water and oxygen, haem is the prosthetic group and it is part of the active site of the enzymes.

Zinc is the cofactor in enzyme carbonic anhydrase.

RuBisCo is the most abundant protein in whole of the biosphere.

Succinate is the substrate of enzyme succinic dehydrogenase.

Respiration in PlantsNEET Botany · Class 11 · NCERT Chapter 14

More NEET questions, next chapter

Track Your NEET Score Across All 90 Chapters

Respiration in PlantsNEET Botany · Class 11 · NCERT Chapter 14

1NEET 2014Medium4 bookletsIn which one of the following processes CO 2 is not released ?

2NEET 2017Medium5 bookletsAdult human RBCs are enucleate. Which of the following statement(s) is/are most appropriate explanation for this feature? (a) They do not need to reproduce (b) They are somatic cells (c) They do not metabolize (d) All their internal space is available for oxygen transport

3NEET 2017Medium5 bookletsWhich statement is wrong for Krebs' cycle?

4NEET 2018Medium20 bookletsWhat is the role of NAD + in cellular respiration ?

5NEET 2019Medium4 bookletswhich of the following sexually transmit diseases is not completely curable?

6NEET 2019Medium3 bookletsRespiratory Quotient (RQ) value of tripalmitin is:

7NEET 2022Medium24 bookletsWhich one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis? It involves:

8NEET 2022Medium24 bookletsWhat is the net gain of ATP when each molecule of glucose is converted to two molecules of pyruvic acid?

9NEET 2022Medium24 bookletsWhat amount of energy is released from glucose during lactic acid fermentation?

10NEET 2024Medium24 bookletsInhibition of Succinic dehydrogenase enzyme by malonate is a classical example of:

11NEET 2024Medium24 bookletsIdentify the step in tricarboxylic acid cycle, which does not involve oxidation of substrate.

13NEET 2025Medium4 bookletsThe complex II of mitochondrial electron transport chain is also known as

14NEET 2025Medium4 bookletsWhich one of the following enzymes contains 'Haem' as the prosthetic group?

More NEET questions, next chapter

Track Your NEET Score Across All 90 Chapters