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


' Respiration in Plants' chapter in NCERT Solutions for class 11 Biology syllabus talks about the mechanism where the food materials breakdown inside the cell to release energy, which is also technically called cellular respiration, and how the energy released is trapped for the Synthesis of ATP. Also elaborated are topics, like Glycolysis, which answers a question - "Do Plants Breathe"?, Aerobic Respiration, Fermentation, Respiratory Quotient, Amphibolic Pathway, and The Respiratory Balance Sheet. Understanding of all these topics is a must for comprehensive learning, So, read below.

  • Answering the question - 'Do Plants Breathe'?
  • Glycolysis
  • Fermentation
  • Aerobic Respiration
  • The Respiratory Balance Sheet
  • Amphibolic Pathway
  • Respiratory Quotient

This chapter is the gateway to cellular respiration, which deals with the mechanism of food disintegration inside the cells to discharge energy. ATP, which are the energy boosters for a cell, is synthesized through the released energy, which for this purpose is trapped. The process of breathing, under this topic, has been linked with the cycle of the release of energy from food. The oxidation of certain macromolecules that is known as 'food' is the source of all the energy required to perform any activity.


Q1. Differentiate between

  1. Respiration and Combustion








It takes place inside the living cells


it is a non-cellular process


It is a biochemical process


It is a chemical process


Energy is released in steps as chemical bonds are broken into  steps


Energy is released in a single step as all chemical reactions take place simultaneously


Most of the energy is in the form of ATP


ATP formation does not occur


It requires enzymes


It is a non-enzymatic process


  1. Glycolysis and Krebs cycle





Krebs cycle


Glycolysis takes place inside the cytoplasm


It occurs inside mitochondria.


It is a straight or linear pathway


It is a cyclic process


This process is common to both aerobic and anaerobic respiration


This process occurs only in aerobic respiration


It breaks down one molecule of glucose into two molecules of pyruvate


It breaks down pyruvate completely into carbon dioxide, energy and water


It consumes two ATP molecules


It does not consume ATP


(c) Aerobic respiration and Fermentation


Aerobic respiration


It is an intracellular process.

Fermentation can occur both intracellularly and extracellularly.

It is not economically exploited

It is economically exploited in production of wine, bread etc

its uses oxygen to breakdown a respiratory substrate

It is an enzyme controlled breakdown and transformation of organic nutrients.


Q2. What are respiratory substrates? Name the most common respiratory substrate.


Respiratory substrates are those organic substances that are oxidized during respiration to liberate energy inside the living cells. The common respiratory substrates are carbohydrates, proteins, fats, and organic acids.


Q3. Give the systematic representation of glycolysis?


Schematic representation of glycolysis is as follows:


Q4. What are the main steps in aerobic respiration? Where does it take place?


The main steps of aerobic respiration are as follows:

  1. Glycolysis- Cytoplasm
  2. Krebs cycle- Matrix of mitochondria
  3. Electron transport system- Inner mitochondrial membrane
  4. Oxidative phosphorylation- Oxysome in the inner mitochondrial membrane.


Q5. Give the schematic representation of an overall view of Krebs' cycle.


Schematic representation of the Krebs cycle


Q7. Distinguish between the following:

  1. Aerobic respiration and Anaerobic respiration


Aerobic respiration

Anaerobic respiration

It occurs in the presence of O₂ 

It occurs in the absence of O₂ 

It involves the exchange of gases between the organism and the environment.

The exchange of gases is absent.

It occurs in the cytoplasm and mitochondria

It only occurs in the cytoplasm.

It always releases carbon dioxide and water as the end product.

End products vary.


  1. Glycolysis and Fermentation





It is the first step of respiration which occurs without the requirement of oxygen and is common to both aerobic and anaerobic modes of respiration


It is anaerobic respiration or respiration which does not require oxygen.


Glycolysis produces pyruvic acid


Fermentation produces different products such as ethanol and lactic acid.


It produces two molecules of NADH per glucose molecule


It uses NADH produced during glycolysis.


c. Glycolysis and Citric acid Cycle





Citric acid cycle


It takes place inside the cytoplasm


It takes place in mitochondria

It is the first step of respiration in which glucose is broken down to the level of pyruvate.

It is the second step of respiration wherein an active acetyl group is broken down completely


Q8. What are the assumptions made during the calculation of the net gain of ATP?


The assumptions made during the calculation of net gain of ATP are as follows:

  1. It is assumed that various parts of aerobic respiration such as glycolysis, TCA cycle, and ETS occur in a sequential and orderly pathway.
  2. NADH produced during the process of glycolysis enters into mitochondria to undergo oxidative phosphorylation.
  3. The glucose molecule is assumed to be the only substrate while it is assumed that no other molecule enters the pathway at intermediate stages.
  4.  The intermediates produced during respiration are not utilized in any other process.

Q9. Discuss "The respiratory pathway is an amphibolic pathway."


 An amphibolic pathway refers to a pathway in which both catabolic and anabolic reactions take place. The products of some reactions are used to synthesize other products. Carbohydrates are broken down to glucose before entering respiratory pathways. Fats get converted into fatty acids and glycerol whereas fatty acids get converted into acetyl CoA before entering the respiration. Similarly, proteins are converted into amino acids, which enter respiration after deamination. During the synthesis of fatty acids, acetyl CoA is withdrawn from the respiratory pathway. Also, in the synthesis of proteins, respiratory substrates get withdrawn. Thus, respiration involves both anabolism and catabolism in anabolism. Therefore, respiration can be termed as an amphibolic pathway as it involves both anabolism and catabolism.


Q10. Define RQ. What is its value for fats?


The respiratory quotient is defined as the ratio of the volume of CO_{2}  evolved to the volume of O_{2} consumed during respiration. The value of the respiratory quotient depends on the type of respiratory substrate. The value of RQ for various respiratory substrates is as follows:

Carbohydrates- 1

Fat - 0.7

Organic acids- more than 1

 Proteins - less than 1


Q11. What is oxidative phosphorylation?


Oxidative phosphorylation is the synthesis of energy-rich ATP molecules with the help of energy liberated during oxidation of reduced coenzymes ( NADH and FADH2 ) produced in respiration. The enzyme required for the synthesis is called ATP synthase. It is the fifth complex of ETS. During this process, several oxidation-reduction reactions occur and lead to the generation of a proton gradient. The enzyme ATP synthase (complex V) consists of F_{0} and F_{1} components. The Fl headpiece is a peripheral membrane protein complex and contains the site for ATP synthesis from ADP and inorganic phosphate whereas the F_{0} the component is a part of the membrane protein complex, which acts as a channel for the crossing of the protons from the inner mitochondrial membrane to the mitochondrial matrix. For every two protons passing through F_{0}-F_{1} complex synthesis of one ATP molecule takes place.


Q12. What is the significance of the step-wise release of energy in respiration?


The process of respiration takes place in a stepwise manner including steps like glycolysis, TCA cycle, ETS, and oxidative phosphorylation. During respiration, the production of ATP also in each phase takes place in a stepwise manner. The products formed in one step of respiration become the substrate of the other pathway. Various molecules produced during respiration are involved in other biochemical processes also. Different respiratory substrates enter and withdraw from the pathway on necessity. The ATP also gets utilized wherever required and the rate of reactions of enzymes are also controlled. Therefore, the stepwise release of energy makes the system more efficient in extracting as well as storing energy.


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Also See    
NCERT Solutions for Class 11 Biology Chapter 1 - The Living World NCERT Solutions for Class 11 Biology Chapter 2 - Biological Classification NCERT Solutions for Class 11 Biology Chapter 3 - Plant Kingdom
NCERT Solutions for Class 11 Biology Chapter 4 - Animal Kingdom NCERT Solutions for Class 11 Biology Chapter 5 - Morphology of Flowering Plants NCERT Solutions for Class 11 Biology Chapter 6 - Anatomy of Flowering Plants
NCERT Solutions for Class 11 Biology Chapter 7 - Structural Organization in Animals NCERT Solutions for Class 11 Biology Chapter 8 - Cells: The Unit of Life NCERT Solutions for Class 11 Biology Chapter 9 - Biomolecules
NCERT Solutions for Class 11 Biology Chapter 10 - Cell Cycle and Division NCERT Solutions for Class 11 Biology Chapter 11 - Transport in Plants NCERT Solutions for Class 11 Biology Chapter 12 - Mineral Nutrition
NCERT Solutions for Class 11 Biology Chapter 13 - Photosynthesis in Higher Plants NCERT Solutions for Class 11 Biology Chapter 15 - Plant Growth and Development NCERT Solutions for Class 11 Biology Chapter 16 - Digestion and Absorption
NCERT Solutions for Class 11 Biology Chapter 17 - Breathing and Exchange of Gases NCERT Solutions for Class 11 Biology Chapter 18 - Body Fluids and Circulation NCERT Solutions for Class 11 Biology Chapter 19 - Excretory Products and their Elimination
NCERT Solutions for Class 11 Biology Chapter 20 - Locomotion and Movement NCERT Solutions for Class 11 Biology Chapter 21 - Neural Control and Coordination NCERT Solutions for Class 11 Biology Chapter 22 - Chemical Coordination and Integration

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