NCERT Solutions Class 11 Biology Chapter 14

NCERT Solutions for Class 11 Biology Chapter 14

We all know that energy is required to carry out our daily activities. Do plants, on the other hand, require energy? Is it true that plants breathe, and if so, what is the purpose of breathing? All of these may appear to be unrelated at first, but they are all related to the ‘Respiration’ process that our NCERT Class 11 Biology Chapter 14 deals with. The chapter also has to practice questions at the end to help students revise the learned concepts.

If students are looking for accurate answers to these practice questions, they are at the right place. Extramarks offers NCERT Solutions for Class 11 Biology Chapter 14 Respiration in Plants that are carefully curated by the subject-matter experts to provide answers to all the questions given in Chapter 14 of the NCERT Biology textbook. These are written as per the latest CBSE curriculum and guidelines to guide the students in their studies. 

NCERT Solutions for Class 11 Biology Chapter 14 – Respiration in Plants

NCERT Solutions Class 11 Biology Chapter 14 by Extramarks have answers to all the NCERT textbook questions. The solutions are written in a straightforward and structured manner so that students do not have any confusion in understanding the concept or explanation given for that question

Access NCERT Solutions for Class 11 Biology Chapter 14 – Respiration in Plants

NCERT Solutions for Class 11 Biology Chapter 14 – Respiration in Plants

Respiration in Plants Class 11 NCERT Solutions 

Chapter 14 of Class 11 Biology explains cellular respiration in plants and how it results in the release of energy through the disintegration of food within the cells. The chapter will also help students in understanding the process of respiration carried out in living beings. Here’s a detailed breakdown of the topics covered in Class 11 Biology Chapter 14:

Section Number Section Title
14.1 Do Plants Breathe?
14.2 Glycolysis
14.3 Fermentation
14.4 Aerobic Respiration
14.4.1 Tricarboxylic Acid Cycle
14.4.2 Electron Transport System (ETS) and Oxidative Phosphorylation
14.5 The Respiratory Balance Sheet
14.6 Amphibolic Pathway
14.7 Respiratory Quotient


14.1 Do Plants Breathe?

Plants require oxygen to respire, but the process emits carbon dioxide as a by-product. Plants, unlike humans and animals, lack specialised structures for gas exchange, but they do have stomata (found in leaves) and lenticels (found in stems) that are actively involved in the process. Thus, this section deals with plant respiration, types of respiration, and the respiratory quotient.

14.2 Glycolysis

Glycolysis is the partial oxidation of glucose or a similar hexose sugar into two molecules of pyruvic acid via an enzyme-mediated reaction that releases ATP, NADH and water. The process occurs in a cell’s cytoplasm and does not require oxygen. It can be found in both aerobic and anaerobic bacteria. 

14.3 Fermentation

In this process, incomplete oxidation of glucose is achieved, under anaerobic conditions. A series of reactions take place in the process that result in the conversion of carbon dioxide to ethanol. This section discusses yeast fermentation and how pyruvic acid is converted to ethanol and CO2.

14.4 Aerobic Respiration

This section explains aerobic respiration, which involves the oxidation of glucose to produce energy. The complete oxidation of organic substances is also discussed in the section.

14.4.1 Tricarboxylic Acid Cycle

This section deals with the tricarboxylic acid cycle, also known as the Krebs cycle, and terminal oxidation in detail. The TCA cycle is a type of tricarboxylic cycle. The matrix of mitochondria is where the second stage of cellular respiration takes place. 

14.4.2 Electron Transport System (ETS) and Oxidative Phosphorylation

The section introduces students to the electron transport system, which is a metabolic pathway in which an electron moves from one carrier to another inside the inner mitochondrial membrane, and oxidative phosphorylation. It uses the energy of oxidation-reduction to create the proton gradient needed for phosphorylation.

14.5 The Respiratory Balance Sheet

Calculating the gain of ATP for each glucose molecule oxidised is possible, but in practice, this is only a theoretical question. There are a few factors that it depends on. This section deals with how to calculate the amount of ATP released during glucose oxidation. 

14.6 Amphibolic Pathway 

Students will learn about the amphibolic pathway, which includes anabolism (synthesis) and catabolism (breaking down) within a living being.

14.7 Respiratory Quotient

This section deals with the respiratory quotient, which is the ratio of carbon dioxide produced to oxygen consumed in respiration over time. It’s also called the respiratory ratio. This ratio is determined by the respiratory substrate used during respiration.

NCERT Solutions for Class 11 Biology Chapter 14 Respiration in Plants

By referring to NCERT Solutions for Class 11 Biology Chapter 14, students will be able to answer tricky questions in exams in a better manner. Since they are curated by experts, Extramarks Solutions are accurate and reliable. 

Division of Marks for Respiration in Plants Class 11 NCERT

This chapter is a part of Unit 4 that has a weightage of 18 marks in exams. So a simple 1-mark question or a complex 5-mark question can be expected from this chapter. 

Advantages of NCERT Solutions for Class 11 Biology Chapter Respiration in Plants

The advantages of referring to the NCERT Solutions of Class 11 Biology Chapter 14 are as follows:  

  • They have been prepared as per the latest syllabus prescribed by CBSE. 
  • The use of easy and simple language in the study materials and detailed explanations will make the topics easy to understand.
  • These NCERT Solutions have answers written thoroughly so that students do not need to refer to help books.

Q.1 Differentiate between

(a) Respiration and Combustion

(b) Glycolysis and Krebs’ cycle

(c) Aerobic respiration and Fermentation F



Respiration Combustion
1. It occurs within living cells only. It does not occur inside a living system.
2. It requires enzymes. It does not require enzymes.
3. It occurs in a highly regulated mode under controlled condition. It is non-regulated and uncontrolled.
4. It produces energy equivalents in the form of high energy ATP molecules. It produces energy in terms of heat and light only.


Glycolysis Krebs’ Cycle
1. It occurs in the cytoplasm. It occurs in the mitochondria.
2. It is a non-cyclic process. It is a cyclic process.
3. It is common in both aerobic and anaerobic respiration. It takes place only in aerobic respiration.
4. Less productive in terms of ATP and NADP generation. Produces 8 ATP molecules from one glucose molecule Produces 15 ATP molecules from one molecule of Acetyl CoA


Aerobic respiration Fermentation
1. It occurs in the presence of molecular oxygen only. It does not require molecular oxygen.
2. It takes place in both cytoplasm and mitochondria. It takes place only in the cytoplasm.
3. It is highly efficient and produces 38 ATP molecules per molecule of glucose. It is non-economical, produces only 2 molecules of ATP per molecule of glucose
4. The final products formed from one glucose molecule are carbon dioxide and water. The final products formed from one glucose molecule are ethyl alcohol and carbon dioxide

Q.2 What are respiratory substrates? Name the most common respiratory substrate.


The complex organic compound that gets oxidized in the cell during respiration to release large amounts of energy is called respiratory substrate. Under normal condition, glucose is the most common respiratory substrate which is a carbohydrate along with six carbon atoms.

Q.3 Give the schematic representation of glycolysis?


Schematic representation of glycolysis:

Q.4 What are the main steps in aerobic respiration? Where does it take place?


The four main steps of aerobic respiration are as follows:

S.No Steps of aerobic respiration Site of occurrence in the cell
1. Glycolysis Cytoplasm
2. Krebs’ Cycle Mitochondrial matrix
3. Electron transport chain Inner membrane of mitochondria
4. Oxidative phosphorylation F0-F1 particle of cristae present in the inner membrane of mitochondria

Q.5 Give the schematic representation of an overall view of Krebs’ cycle.

Schematic representation of Krebs’ cycle:

Q.6 Explain ETS.


The electrons removed from the substrates of glycolysis and the Krebs’ cycle are stored in the reduction equivalents, namely NADH2 and FADH2. This energy is released when NADH2 and FADH2 are oxidized by passing their electrons to a chain of electrons carrier complex called Electron transport system, present in the inner membrane of mitochondria. These complexes transfer the electron through a series of redox reactions with high energy electrons entering the system and low-energy electrons leaving the system. The energy released through this process is utilized to pump out protons which develop a proton gradient (Proton motive force) across the inner membrane. This proton motive force is utilized by ATP synthase to generate high energy ATP molecules at 3 different sites.

Process: The NADH2 produced during the citric acid cycle are oxidized by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone which gets reduced. Ubiquinone also receives reducing equivalents via FADH2 (complex II). The reduced ubiquinone (ubiquinol) is then re-oxidized by transferring its electrons to cytochrome c via cytochrome bc1 complex (complex III). The electron is transferred from complex III to complex IV through cytochrome C which is a mobile carrier present in the inner membrane. Complex IV is called cytochrome C oxidase complex and consists of cytochromes a-a3, and two copper centers.

Q.7 Distinguish between the following:

(a) Aerobic respiration and Anaerobic respiration

(b) Glycolysis and Fermentation

(c) Glycolysis and Citric acid Cycle



Aerobic respiration Anaerobic respiration
1 It occurs only in the presence of molecular oxygen. It occurs in the absence of molecular oxygen.
2. It is highly efficient and produces 38 ATP molecules. It is less efficient and generates only 2 ATP molecules.
3. It takes place in both cytoplasm and mitochondria. It takes place in the cytoplasm only.
4. It is a multistep process having glycolysis, Krebs’ cycle, and ETS. It is not a multistep process.
5. It produces carbon dioxide and water as the by-product. It produces ethyl alcohol and carbon dioxide as a by-product.


Glycolysis Fermentation
1. It is a common step in both aerobic and anaerobic respiration. It is strictly an anaerobic mode of respiration.
2. It results in the production of pyruvic acid. It produces ethyl alcohol.
3. Net gain is 8 ATP molecules. Net gain is 2 ATP molecules.
4. The product of glycolysis is used as an intermediate in Krebs’ cycle. The product of fermentation (ethyl alcohol) is not used by cells further.


Glycolysis Citric acid Cycle
1. It occurs in the cytoplasm. It occurs in the mitochondria.
2. It is a non-cyclic process. It is a cyclic process.
3. It is common in both aerobic and anaerobic respiration. It takes place only in aerobic respiration.
4. It produces 8 ATP molecules from one molecule of glucose. It produces 15 ATP molecule from one molecule of Acetyl CoA.

Q.8 What are the assumptions made during the calculation of net gain of ATP?


Many assumptions have been made in order to calculate the net gain of ATP from one molecule of glucose. This is required as the cellular system is very complex where numerous biochemical reactions take place simultaneously. The assumptions are as follows:

  1. All the steps of aerobic respiration (glycolysis, TCA cycle, ETS and oxidative phosphorylation) take place in sequential order where the product of the first step enters the subsequent step as a substrate.
  2. The NADH synthesized in glycolysis enters in the mitochondria and produces ATP through oxidative phosphorylation.
  3. The intermediates formed in various steps of aerobic respiration are not utilized in any other metabolic pathways other than subsequent steps of respiration.
  4. The glucose molecule is the only substrate and no other molecule enters as an intermediate substrate in the process.

Q.9 Discuss “The respiratory pathway is an amphibolic pathway.”


The process of metabolism involves both anabolic and catabolic reactions. Anabolism is the synthesis of complex macromolecules like lipids and proteins from simple molecules like glycerol and amino acid respectively. On the other hand, catabolism includes the breakdown of macromolecules into simple molecules so that they can enter in the respiratory pathway as a substrate for the release of energy. If fatty acids are used as a respiratory substrate they are broken down to glycerol and acetyl CoA. Glycerol gets converted to 3-phosphoglyceraldehyde (PGAL) and enters in glycolysis while Acetyl CoA directly enters in Krebs’ cycle. However, when an organism needs to synthesize fatty acids, acetyl CoA is withdrawn from the above-said pathway and is made available for catabolic reaction. Similarly, when proteins are used as a substrate, they are first broken down to amino acid, which in turn, depending on their structure, gets converted into different intermediates of Krebs’ cycle. At the time of need, the same molecules are withdrawn to synthesize new proteins. Most of these reactions are reversible and depending on the requirement, the cell uses the respiratory substrate in the process of anabolism or catabolism. Thus, the respiratory pathway is known as the amphibolic pathway rather than only a catabolic pathway.

Q.10 Define RQ. What is its value for fats?


Complete oxidation of substrates during aerobic respiration requires oxygen and apart from energy, carbon dioxide is produced as the by-product. The ratio of the volume of CO2 released to the volume of O2 consumed during complete oxidation of one molecule of a substrate in a given period of time at standard temperature and pressure is called the respiratory quotient (RQ).

For example, during aerobic respiration of one molecule of glucose, 6 molecules of CO2 are released and 6 molecules of O2 are consumed. Thus RQ for glucose is 1.

RQ value for fats: Fats need more oxygen molecule than carbohydrate (glucose) for complete oxidation through aerobic respiration, due to which the value of RQ for fat is always less than 1.

For example, when fatty acid tripalmitin is used as a substrate, 145 molecules of O2 are consumed whereas 102 molecules of CO2 are produced, the RQ value is 0.7.

Q.11 What is oxidative phosphorylation?


The metabolic pathway that uses the energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP) is called oxidative phosphorylation. Almost all the forms of life on earth use a range of different nutrients to carry out oxidative phosphorylation to produce the molecule that supplies energy to metabolism i.e. ATP. This is a very efficient process of energy generation.

This process requires the presence of oxygen in the system. Oxygen drives the whole process as it removes hydrogen from the system and acts as the final hydrogen acceptor. During oxidative phosphorylation, electrons are transferred from electron donors like NADH2 to electron acceptors such as oxygen. These redox reactions release energy, which is used to form ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within mitochondria, whereas, in prokaryotes, these proteins are located in the cells’ inner membranes. These linked sets of proteins are called electron transport chains. It is the energy of the oxidation-reduction process that is used for the production of proton gradient required for phosphorylation and thus, this process is called oxidative phosphorylation.

Q.12 What is the significance of step-wise release of energy in respiration?


Carbohydrates, proteins, fats and organic acids are used as respiratory substrates and oxidation of these compounds releases energy in the cell. However, the energy released is not dissipated freely in the cell. In other words, it does not occur in one step. Instead, it is released in a series of slow step-wise reactions controlled by enzymes and is trapped in the form of ATP. This prevents the sudden increase in the temperature and avoids wastage of energy. This holds a lot of significance as ATP which stores the energy can be broken down whenever and wherever it is needed in the various energy-requiring processes of the organisms.

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FAQs (Frequently Asked Questions)

1. What kind of assumptions are made when calculating ATP's net gain?

Calculating the net addition of ATP for each oxidized glucose particle is possible; however, this is merely a hypothetical exercise. These assumptions can be based on specific suspicions that: 

  • There is a sequential, methodical pathway in operation, with one substrate shaping the next, and with glycolysis, TCA cycle, and ETS pathway moving in a steady progression into the mitochondria and undergoing oxidative phosphorylation.
  • At any of the intermediate stages, only glucose is breathed; no other optional substrates enter the pathway.

However, in an actual living framework, these kinds of assumptions are rarely true; all pathways are active at the same time and do not always occur in the same order; substrates enter and exit pathways as needed; ATP is used as needed; enzymatic rates are constrained by various methods. As a result, during an oxygen-consuming breath of one atom of glucose, there can be a net increase of 36 ATP particles.

2. What concepts can I learn from the NCERT Solutions for Class 11 Biology Chapter 14?

The concepts explained in Chapter 14 of Class 11 Biology are – “Do Plants Breathe?”, Glycolysis, Fermentation, Aerobic Respiration, The Respiratory Balance Sheet, Amphibolic Pathway and Respiratory Quotient. 

3. Is it necessary to practise all the NCERT questions at the end of each chapter?

 The questions listed at the end of each chapter in NCERT textbooks are crucial not only for exams but also for a better understanding of the concepts. These questions have been designed to assess students’ comprehension and knowledge of the topics covered in the chapter. So after reading the chapter and understanding it, you must practise all the NCERT questions at the end of each chapter.