NIOS Class 12 Biology Chapter 12 Respiration in Plants

NIOS Class 12 Biology Chapter 12 Respiration in Plants Solutions to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Biology Chapter 12 Respiration in Plants Notes and select need one. NIOS Class 12 Biology Chapter 12 Respiration in Plants Question Answers Download PDF. NIOS Study Material of Class 12 Biology Notes Paper 314.

NIOS Class 12 Biology Chapter 12 Respiration in Plants

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Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Biology Chapter 12 Respiration in Plants Solutions, NIOS Senior Secondary Course Biology Solutions for All Chapter, You can practice these here.

Respiration in Plants

Chapter: 12




1. How do plant and other organisms obtain energy for various activities such as growth?

Ans: The plants covert solar energy (sun’s energy) to chemical energy and that is stored it in form of complex organic molecules (food). During respiration, complex organic includes are oxidised and there is release of large amount of energy. It is stored as ATP. The plants use ATP for metabolic activities.

2. Name the energy rich molecule formed during respiration from food.

Ans: In form of ATP.

3. Give two differences between aerobic and anaerobic respiration.

Ans: Difference between Aerobic and Anaerobic Respiration:

S. No.Aerobic RespirationAnaerobic Respiration
1It occurs in presence of O₂. C₆H₁₂O₆ → 6CO₂ + 6H₂O + 60₂ + Energy (38 ATP)It occurs in absence of O₂. C₂H₁₂O₆ → 2 Ethyl alcohol + 2CO₂ +2 ATP(Energy as in yeast) 
2Occurs in cytoplasm; mitochondria (in eukaryotes) and plasma membrane (in prokaryotes).Or 
C₆H₁₂O₆ → 2 Lactic acid + 2ATP(Energy as in muscles)


1. Name the surfaces that help plants in taking up oxygen from the atmosphere.

Ans: The gaseous exchange occurs through general body surface of plants, through stomata and lenticels.

2. Name the process by which oxygen is taken up by the plants from the atmosphere.

Ans: Diffusion.

3. Name the gases given out by plants during daytime and night.

Ans: O₂; CO₂.

4. Why do plants not have any special respiratory organs like animals? Give two reasons.

Ans: (i) The plants have a large surface area to exchange gases from.

(ii) The requirement of plants for oxygen is much less.


1. Why is pyruvic acid converted into alcohol or lactic acid during fermentation?

Ans: (i) In presence of oxygen pyruvic acid is completely broken down to simple forms like CO₂ and H₂O.

2 Pyruvic acid + 6O₂ → 6CO₂ + 6H₂O + 30 ATP 


(8 ATP are obtained from the glycolysis) 

(ii) In absence of O₂, they carry out alcoholic fermentation.

2 Pyruvic acid → 2 Ethyl alcohol + 2CO₂ (carbon-dioxide)

2. Why is there less release of energy during anaerobic respiration?

Ans: It is because the organic molecules are only partially oxidised in anaerobic respiration and much of energy remains in end products like alcohol or lactic acid.

3. List the three phases of aerobic respiration of glucose. Where in the cell do these reactions take place?

Ans: (i) Glycolysis: In cytosol.

(ii) Kreb’s cycle: Matrix of mitochondria.

(iii) E.T.C.: Inner membrane of mitochon-dria.

4. What is the role of O₂ in aerobic respiration?

Ans: Oxygen acts as terminal acceptor of H₂ removed from glucose molecule and gets reduced to water.

5. Name the substrate and product of Kreb’s cycle.

Ans: (i) Substrate: Acetyl CoA.

(ii) Product: 2CO₂, 3NADH, 1FADH₂, 1ATP.

6. How do fatty acids enter Kreb’s cycle?

Ans: The fatty acid undergo ß oxidation and produce acetyl CoA. It can enter Kreb’s cycle.


1. What is the R.Q. for carbohydrates and fats?

Ans: (i) The R.Q. is one (1) for carbohydrates.

(ii) the R.Q. is >1 for fats.

2. What is the effect of high concentration of O₂ on respiration?

Ans: The rate of respiration increases up to a point and beyond this point its rate of increase falls.

3. What is the ideal temperature for the process of respiration?

Ans: 30-35°C. 

4. Define R. Q.

Ans: The R.Q. is defined as “the ratio of volume of CO₂ evolved to volume of O₂ consumed in respiration.” R.Q. gives us an idea of the kind of substrate used for respiration. RQ is respiratory quotient in plants.

5. What is the limiting factor of respiration in dry seeds?

Ans: Water.


1. Name the products that are produced when RUBP combines with O₂. Name the enzyme that is responsible for this reaction. 

Ans: The products are:

(i) PGA.

(ii) Phospho-glycolate.

2. Give one point of difference bet-ween respiration and photorespiration.

Ans: Difference between Respiration and Photorespiration:

1. It occurs in mitochondria.It involves three, organelles:
(i) chloroplast.
(ii) mitochondria. and 
(iii) peroxisome. 
2. The substrate is glu-cose in it. The substrate is RUBP in it.

(Note: Write any one only).

3. State the conditions under which photorespiration occurs?

Ans: The conditions for photorespiration to occur are the following:

(a) light.

(b) high concentration of O₂. and

(c) low concentration of CO₂.


1. Define respiration.

Ans: The respiration is defined as “the stepwise oxidation of complex organic molecules/ food and the release of energy as ATP.”

2. What is the role of O₂ in electron transport chain (ETC)?

Ans: Role of O₂ in ETC: The hydrogen carried by carriers is carried to cristae of mitochondria undergoes oxidation by using molecular oxygen to release energy in steps. O₂ is the final acceptor of electrons.

3. How many molecules of ATP are released when glucose is oxidised to

(a) CO2 and H₂O?

Ans: 38 ATP.

(b) Ethyl alcohol and CO₂?

Ans: 2 ATP.

4. Write the equation for aerobic respiration.

Ans: Equation for aerobic respiration is: C₆H₁₂O₆ + 60₂ → 6CO₂ + 6H₂O + Energy (38 ATP)

5. Name the end product of electron transport chains.

Ans: ATP and water.

6. Respiration is a continuous process in plants. Then why is it that they give out O₂ and not CO₂ during the day? 

Ans: The oxygen released during photosynthesis is made available for respiration in plants. Rate of photosynthesis is more than rate of respiration. During day plants produce excess O₂. They give out only CO₂ at night when photo-synthesis is stopped.

7. What is the site for:

(a) Glycolysis.

Ans: Cytoplasm of cell.

(b) Krebs cycle.

Ans: Matrix of the mitochondria.

(c) ATP generation by oxidative phosphorylation?

Ans: Inner membrane of mitochondria.

8. What is the fate of pyruvic acid in 

(a) presence. and

(b) absence of oxygen? Write the equations representing the processes.

Ans: (a) 2 Pyruvic acid + 8NAD + 2FAD

+ 2ADP Mitochondrial/Matrix 6CO2 + 2ATP

Occur in Cytosoly of us + 2 PADH₂ + NADH 

(b) 2 Pyruvic acid → 2 Ethanol + CO₂ + 2 ATP   

                            NADH                       (2C₂H₅OH).

Occur in muscle cells NAD⁺

9. What is the significance of stepwise oxidation of organic molecules instead of one step reaction?

Ans: The energy is released in a series of small steps and so there is stepwise oxidation of organic molecules. The stepwise release of chemical bond energy facilitates the utilisation of a relatively higher proportion of that energy gain in ATP synthesis. The some pathway can be used for making intermediates used for making intermediates used in synthesis of other biomolecules as proteins, fats, amino acids, etc.

10. What is the significance of photorespiration?

Ans: Significance of photorespiration: It protects the plants from photooxidative damages by using part of solar energy that may destroy plant pigments.

11. List the substrates that enter and the products produced in

(a) Glycolysis.

Ans: Substrate: Glucose. 

Products: 2 mols of pyruvic acid + 2ATP.

(b) Kreb’s cycle.

Ans: Substrate: Acetyl CoA.

Products: 2CO₂ +3NADH + 1FADH₂ + 1 ATP.

12. How is yeast useful in industry? Give any three examples.

Ans: Yeast in Industry: The fermentation has several applications in industry. Yeast is cultured in huge amounts and used for:

(i) preparing bread, cakes as well as biscuits.

(ii) to prepare wine and other alcoholic drinks.

(iii) to produce vinegar and in tanning of leather.

The ethanol is used to make gasohol (a fuel). Fermentation is used to make dosa, idli, bhatura, etc.

13. How does exchange of respiratory gases take place in plants?

Ans: Exchange of respiratory gases in plants: The plants need O₂ for respiration. The leaves of plants have stomata. Lenticels are found in bark of woody stems for gaseous exchange. The plants take O₂ by diffusion from the atmosphere. The plants do not need oxygen carrier. The O₂ requirement of plants is less as they possess large surface area (leaves) for respiration or to absorb O₂ by diffusion. From atmosphere gas inter into intercellular spaces inside plants. The CO₂ is formed and it diffuses out of plant and used in photosynthesis.

14. Define R.Q. What is its significance?

Ans. R.Q.: It is defined as “the ratio of O₂ consumed and to the ratio of CO₂ released during respiration”.

R.Q. = Volume of CO₂ evolved / Volume of O₂ consumed

Significance: The rate of respiration is dependent upon the type of substrate used in respiration. For fats >1 since more energy is released.

15. Mention the significance of TCA cycle.

Ans: Significance of TCA cycle:

(i) Major pathway for release of reduced coenzymes and energy in controlled way.

(ii) Common pathway for oxidative breakdown of fatty acids, CHO and amino acids, etc.

(iii) For synthesis of biomolecules, several intermediates are provided by TCA cycle.

16. Why does fermentation yield less energy than aerobic respiration?

Ans: The fermentation yields less energy because there is partial decomposition of substrate used in respiration. It occurs under insufficient supply of oxygen. The regeneration of NAD does not yield ATP because the electrons are not transported to O₂ in membranes of mitochondria.

17. List any two important contributions of PPP in a cell.

Ans: PPP in a cell: Its two contributions include:

(a) Release of pyruvic acid in plant cells.

(b) Release of ATP in plant in plant cells for various metabolic activities.

18. What are the three major phases of glycolysis?

Ans: There are three major phases of glycolysis: The glycolysis can be subdivided into three major phases: 

(i) Phosphorylation of glucose to fructose 1,6 diphosphate. It refers “to the activation of glucose” 2ATPs are used in it.

(ii) The splitting of this compound into two 3- carbon sugar phos-phates, that are interconvertible.

(iii) Oxidation by dehydrogenation: Every 3-C sugar phos-phate is oxidised by removal of hydrogen, producing a reduced NAD which is NADH and formation of 2ATPs.

19. What is the importance of Kreb’s cycle?

Ans: Importance of Kreb’s Cycle:

(i) It provides several intermediate compounds required to synthesise other bimolecules nucleotides, amino acids, chlorophyll and fats.

20. Differentiate between aerobic and anaerobic respiration.

Ans: Difference between Aerobic and Anaerobic Respiration:

Aerobic RespirationAnaerobic Respiration
1. Occurs in presence of O₂ It Occurs in 2 steps: glycolysis and Kreb’s only.Occurs in absence of O₂. It occurs in cytoplasm only.
2. Complete oxidation of glucose takes place. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + E (38 ATP) Incomplete oxidation of glucose occurs.C₆H₁₂O₆ → 2C₂H₅ OH + 2CO₂+ 2ATP

21. Why is photorespiration a waste-ful reaction?

Ans: The photorespiration is a wasteful process: The photorespiration is light dependent uptake of O₂ and release of CO₂ by photo-synthetic system.

RUBP + CO2 Rubisco/Enzyme (3-PGA) → Calvin cycle

It occurs in C₄ plant. No energy-rich compound formed in it. Half of photosynthetically fixed CO₂ is lost by photorespiration. It is a loss to net productivity of green plants (C₃ plants).

22. What is respiratory chain or ETC? What is its significance?

Ans: Respiration Chain or ETC (Electron Transport Chain): It occurs as given below:

(a) Hydrogen carriers move to inner mitochondrial membrane that has folds (cristae). The cristae increase surface area of mitochondria.

(b) The hydrogen carried to cristae under. goes stepwise oxidation and molecular oxygen is used with release of energy in a series of small steps.

(c) Some of the energy is used to form ATP from ADP and inorganic/phosphate or Pi. It is known as oxidative phosphorylation.

(d) In these reactions hydrogen is split into H+ and electrons (e-¹), that are accepted by a series of hydrogen or electron carriers ending with oxygen. This whole series of carriers respiratory chain.

(e) Hydrogen or electrons at a higher energy level are passed from one carrier to the other next (moving downhill in energy terms) till they reach oxygen, (Final acceptor of electrons) and is reduced to water (H₂O).

(f) At every transfer, certain amount of energy is released and in some of the transfers, it is used to make ATP (adenosine triphosphate).

Fig. 12.2. Mitochondrial respiratory chain.

23. Discuss the site of Pentose Phosphate Pathway in a cell.

Ans: The pentose phosphate pathway takes place in the cytosol of the cell, the same location as glycolysis. The two most important products from this process are the ribose-5-phosphate sugar used to make DNA and RNA, and the NADPH molecules which help with building other molecules.

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