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

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    1. Differentiate between:

    (a) Respiration and Combustion.

    (b) Glycolysis and Kreb’s cycle.

    (c) Aerobic respiration and Fermentation.

    Ans. (a) Respiration and combustion:

    Respiration Combustion
    1. It is a biochemical process.
    It is a physicochemical process.
    1. It occurs in the living cells.
    It does not occur in the living cells.
    1. ATP is generated.
    ATP is not generated.
    1. Enzymes are required.
    Enzymes are not required.
    1. It is a biologically-controlled process
    It is an uncontrolled process.

    (b) Glycolysis and Krebs’ cycle:

    Glycolysis Kreb’s cycle
    1. It is a linear pathway.
    ItIt is a cyclic pathway.
    1. It occurs in the cell cytoplasm.
    It occurs in the mitochondrial matrix.
    1. It occurs in both aerobic as well as anaerobic respiration.
    It occurs in aerobic respiration only.
    1. Net Generation of 2NADH + H+ and 2ATP molecules occurs on the breakdown of one glucose molecule.
    It produces 6NADH + H+, 2FADH2, and 2ATP molecules on the breakdown of two acetyl-CoA molecules generated after glycolysis of one glucose molecule.

    (c) Aerobic respiration and fermentation:

    Aerobic Respiration Fermentation
    1. Oxygen is used for deriving energy.
    Occurs in the absence of oxygen.
    1. Occurs in the cytoplasm and mitochondria.
    Occurs in the cytoplasm.
    1. End products are carbon dioxide and water.
    End products are ethyl alcohol and carbon dioxide.
    1. Complete oxidation of the respiratory substrate takes place.
    Incomplete oxidation of the respiratory substrate takes place.
    1. About 36 ATP molecules are produced.
    Only 2 ATP molecules are produced.

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

    Ans. 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.

    3. Give the schematic representation of glycolysis.

    Ans. Schematic representation of glycolysis is given as:

    Respiration in Plantsanns3

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

    Ans. The main steps of aerobic respiration and occurence there are as follows:

    1. Glycolysis— Cytoplasm

    2. Krebs cycle— Matrix of mitochondria

    3. Electron transport system— Inner mitochondrial membrane

    4. Oxidative phosphorylation— Oxysomes in the inner mitochondrial membrane.

    5. Give the schematic representation of an overall view of Kreb’s cycle.

    Ans. Schematic presentation of Krebs’s cycle:

    Respiration in Plantsans5

    6. Explain ETS.

    Ans. ETS or electron transport system is located in the inner mitochondrial membrane. It helps in releasing and utilizing the energy stored in NADH + H+ and FADH2. NADH + H+, which is formed during glycolysis and citric acid cycle, gets oxidized by NADH dehydrogenase (complex I).

    The electrons so generated get transferred to ubiquinone through FMN. In a similar manner, FADH2 (complex II) generated during citric acid cycle gets transferred to ubiquinone. The electrons from ubiquinone are received by cytochrome bc1 (complex III) and further get transferred to cytochrome c. The cytochrome c acts as a mobile carrier between complex III and cytochrome c oxidase complex, containing cytochrome a and a3, along with copper centers (complex IV).

    During the transfer of electrons from each complex, the process is accompanied by the production of ATP from ADP and inorganic phosphate by the action ATP synthase (complex V). The amount of ATP produced depends on the molecule, which has been oxidized. 2 ATP molecules are produced by the oxidation of one molecule of NADH. One molecule of FADH2, on oxidation, gives 3 ATP molecules.

    Respiration in Plantsans6

    7. Distinguish between the following:

    (a) Aerobic respiration and Anaerobic respiration.

    (b) Glycolysis and Fermentation.

    (c) Glycolysis and Citric acid Cycle.

    Ans. (a) Aerobic respiration and Anaerobic respiration:

    Aerobic Respiration Anaerobic Respiration
    1. It uses oxygen for deriving energy.
    It occurs in the absence of oxygen.
    1. It occurs in cytoplasm and mitochondria.
    It occurs in cytoplasm.
    1. The end products of aerobic respiration are carbon dioxide and water.
    The end products of fermentation are ethyl alcohol and carbon-dioxide and Lactic acid depending upon organism.
    1. Complete oxidation of respiratory substrate takes place.
    Incomplete oxidation of respiratory substrate takes place.
    1. 36-38 ATP molecules are produced.
    Only 2 ATP molecules are produced.

    (b) Glycolysis and Fermentation:

    Glycolysis Fermentation
    1. Glycolysis is a common process during aerobic and anaerobic respiration.
    Fermentation is a type of anaerobic respiration.
    1. Pyruvic acid is produced as its end product.
    Ethanol or lactic acid is produced as its end product.

    (c) Glycolysis and citric acid cycle:

    Glycolysis Citric acid Cycle (Kreb’s cycle)
    1. It is a linear pathway.
    It is a cyclic pathway.
    1. It occurs in the cell cytoplasm.
    It occurs in the mitochondrial matrix.
    1. It occurs in both aerobic as well as in anaerobic respiration.
    It occurs in aerobic respiration only.
    1. One glucose molecule breaks down to generate 2 NADH + H+ and 2 ATP molecules.
    It produces 6 NADH + H+, 2 FADH2, and 2 ATP molecules on breakdown of two acetyl-coA molecules generated after glycolysis of are glucose molecule.

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

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

    (a) It is assumed that various parts of aerobic respiration such as glycolysis, TCA cycle, and ETS occur in a sequential and orderly pathway.

    (b) NADH produced during the process of glycolysis enters into mitochondria to undergo oxidative phosphorylation.

    (c) The glucose molecule is assumed to be the only substrate while it is assumed that no other molecule enters the pathway at intermediate stages.

    (d) The intermediates produced during respiration are not utilized in any other process.

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

    Ans. 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. Therefore, respiration can be termed as an amphibolic pathway as it involves both anabolism and catabolism.

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

    Ans. The RQ (respiratory quotient) is the volume of carbon dioxide liberated over the volume of oxygen absorbed during respiration. The respiratory quotient is also called the respiratory ratio. RQ for various respiratory substrates is as follows:

    Carbohydrates- 1

    Fat - 0.7

    Organic acids- more than 1

    Proteins - less than 1

    11. What is oxidative phosphorylation?

    Ans. The conversion of ADP to ATP by an electron transport mechanism is known as oxidative phosphorylation. When hydrogen protons travel through the inner mitochondrial membrane, phosphorylation occurs via the ATP synthetase complex. The energy required for phosphorylation comes from the oxidation-reduction reactions that occur during respiration. As a result, the process is called oxidative phosphorylation.

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

    Ans. Significance of step-wise release of energy in respiration:

    (a) The step-wise release of chemical bond energy is very easily trapped in forming ATP molecules.

    (b) Cellular temperature is not allowed to rise.

    (c) Wastage of energy is reduced.

    (d) There are several intermediate compounds which can be used in production of a number of biochemicals.

    (e) Through their metabolic intermediates, different substances can undergo respira-tory catabolism.

    (f) Each step of respiration is controlled by its own enzyme. The activity of different enzymes can be enhanced or inhibited by specific compounds.

    This helps in controlling the rate of respiration and the amount of energy liberated by it.

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