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

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Chapter 14 - Respiration in Plants Exercise 238

Solution 1

(a) Respiration and Combustion:

Respiration

Combustion

  1. It is a biochemical process.
  2. Temperature remains low.
  3. It takes place in living cells.
  4. Most of the energy is entrapped in the phosphate bonds of ATP. 
  1. It is a physicochemical process.
  2. Temperature rises considerably.
  3. It is a non-cellular process.
  4. No ATP is formed. 

 

(b) Glycolysis and Kreb's cycle:

Glycolysis

Kreb's cycle

  1. It occurs inside the cytoplasm.
  2. It is a straight or a linear pathway.
  3. It is the first step of respiration in which glucose is broken down to the level of pyruvate.
  4. The net gain of energy is equal to 8 molecules of ATP. 
  1. It operates inside the mitochondria.

 

  1. It is a cyclic pathway.
  2. It is the second step in respiration where an active acetyl group is broken down completely.
  3. The net gain of energy is equal to 24 molecules of ATP. 

 

(c) Aerobic respiration and Fermentation:

Aerobic respiration

Fermentation

  1. It involves the exchange of gases.
  2. It occurs in the presence of oxygen.
  3. Respiratory material is completely oxidised.
  4. The end products are inorganic. 
  1. It does not involve the exchange of gases.
  2. It occurs in the absence of oxygen.
  3. Respiratory material is incompletely broken.
  4. At least one of the end products is organic. 

 

Solution 2

The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio.

 Ncert Solutions Cbse Class 11-science Biology Chapter - Respiration In Plants

The value of respiratory quotient depends on the type of respiratory substrate. Its value is one for carbohydrates. However, it is always less than one for fats as fats consume more oxygen for respiration than carbohydrates.

For example, RQ value for tripalmitin is 0.7 which consumes 145 molecules of O2 for respiration while 102 molecules of CO2 are evolved.

RQ of fats:

 Ncert Solutions Cbse Class 11-science Biology Chapter - Respiration In Plants

 

 


Solution 3

Conversion of ADP to ATP by the electron transport system in aerobic respiration is called oxidative phosphorylation. The process of phosphorylation occurs in the inner mitochondrial membrane when hydrogen protons pass through the ATP synthetase complex. The energy required for phosphorylation comes from the oxidation-reduction process in respiration, and therefore, the process is called oxidative phosphorylation. 

Solution 4

Step-wise release of energy is accompanied by conservation of energy in a large number of ATP molecules. A single molecule of glucose breaks down to release carbon dioxide and water and results in the formation of 36 molecules of ATP. If energy will be released at one go, then most of it will be lost in the form of heat. Cells should be in a position to utilise all the energy to synthesise something. Thus, step-wise release of energy in respiration is more efficient in conservation of energy and release of more ATP.


Solution 5

Compounds which are oxidised during respiration to liberate energy inside the living cells are called respiratory substrates. Glucose is the most common respiratory substrate.

Solution 6

Ncert Solutions Cbse Class 11-science Biology Chapter - Respiration In Plants 


Solution 7

The following are the main steps in aerobic respiration: 

  1. Glycolysis: It is the breakdown of glucose to pyruvic acid and occurs inside the cytosol of cytoplasm.
  2. Oxidative decarboxylation of pyruvic acid to acetyl coenzyme-A: It occurs inside the mitochondrial matrix.
  3. Tricarboxylic acid cycle or Kreb's cycle: It occurs inside the mitochondrial matrix.
  4. Electron transport system and oxidative phosphorylation which occur in the inner mitochondrial membrane involving ATP synthase complex.

Aerobic respiration occurs in mitochondria.

Solution 8

Ncert Solutions Cbse Class 11-science Biology Chapter - Respiration In Plants 


Solution 9

An electron transport system (ETS) is a series of coenzymes and cytochromes which take part in the passage of electrons from a chemical to its ultimate acceptor.

The passage of electrons from one enzyme or cytochrome to the next is accompanied with the loss of energy at each step. At each step, the electron carriers include flavins, iron sulphur complexes, quinones and cytochromes. The inner mitochondrial membrane possesses five complexes. Complex V is connected with ATP synthesis. Complexes I to IV are involved in electron transport. These complexes are arranged in a definite sequence in the inner mitochondrial membrane. Reduced coenzymes transfer their electrons and protons through the electron transport system in the following manner:

  1. Transfer of hydrogen from NADH + H+ to metalloflavoprotein-FMN (flavin mononucleotide). The FMN gets reduced to FMNH2 and the coenzyme NADH+H+ gets oxidised to NAD+. Oxidation of NADH occurs by complex I.
  2. Reduced FMN (i.e. FMNH2) then transfers its electrons to Fe-S protein (iron sulphur protein) and 2 H+ into the inner membrane space.
  3. The reduced Fe-S protein then transfers its electrons to ubiquinone (UQ). The UQ takes two electrons from Fe-S protein and two protons (2 H+) from the matrix to become UQH2.
  4. Reduced ubiquinone (UQH2) then transfers its electrons to cytochrome b and 2 H+ to the other side into the inner membrane space. The FADH2 reduced in Krebs cycle also enters through complex II into electron transport system by transferring its 2 H to UQ. The UQ is reduced to UQH2.
  5. NADH+H+, reduced in the glycolysis also enters into electron transport system. The NADH reduces a flavoprotein containing NADH-dehydrogenase located on the outer surface of inner mitochondrial membrane.
  6. The reduced flavoprotein (FPH2) then enters into the main pathway by transferring 2 H to UQ. The reduced UQ then transfers its electrons to complex III and 2 H+ to the outer side.
  7. Reduced cytochrome b then transfers its electrons to Fe-S protein. The Fe3+-S is converted to Fe2+-S. This protein that transfers electrons to UQ which also takes 2 H+ from inner matrix to become UQH2.
  8. The reduced UQ (i.e. UQH2) transfers its electrons to cytochrome c1 and a third pair of H+ is transported outwardly.
  9. Reduced cytochrome c1 then reduced cytochrome c by transferring its electrons.
  10. The electrons from cytochrome c are then transferred to O2 via cyt a and cyt a3.

Ncert Solutions Cbse Class 11-science Biology Chapter - Respiration In Plants 

Solution 10

(a) Aerobic respiration and Anaerobic respiration:

Aerobic respiration

Anaerobic respiration

  1. It occurs in the presence of oxygen.
  2. It involves the complete breakdown of respiratory material.
  3. The end products are carbon dioxide and water.
  4. It involves the exchange of gases.
  1. It occurs in the absence of oxygen.
  2. It involves the incomplete breakdown of gases.
  3. The end products are ethanol and carbon dioxide.
  4. It does not involve the exchange of gases.

 

(b) Glycolysis and Fermentation:

Glycolysis

Fermentation

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

 ii. It produces pyruvic acid.

 

 

 iii. It produces two molecules of NADH per glucose molecule.

 iv. It forms 2 ATP molecules per glucose molecule.

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

 

 

 

 

 

 ii. It produces different products such as ethanol and lactic acid.

 iii. It generally utilises NADH produced during glycolysis.

 iv. It does not produce ATP.

 

(c) Glycolysis and Citric acid cycle:

Glycolysis

Citric acid cycle

  1. It occurs inside the cytoplasm.
  2. It is a straight or linear pathway.
  3. It is the first step of respiration in which glucose is broken down to the level of pyruvate.
  4. The net gain of energy is equal to 8 ATP.

 i. It operates inside the mitochondria.

 

 ii. It is a cyclic pathway.

 iii. It is the second step in respiration where an active acetyl group is broken down completely.

 iv. The net gain of energy is equal to 24 molecules of ATP.

 


Solution 11

The assumptions made during the calculation of net gain of ATP are

  1. NADH produced inside mitochondria helps in the synthesis of 3 ATP molecules during its oxidation.
  2. FADH2 produced inside mitochondria forms 2 ATP molecules during its oxidation.
  3. NADH formed during glycolysis sends its reducing power into mitochondria through the shuttle system.
  4. It forms 3 ATP in the malate-aspartate shuttle (heart, liver and kidney) and 2 ATP in the glycerol phosphate shuttle (muscles and nerve cells). 
Solution 12

The respiratory pathway breaks down the organic substances like carbohydrates, fats, proteins etc. to release energy. Such a process is considered catabolic in nature. The respiratory process which acts as a catabolic pathway for respiratory substrates also acts as an anabolic pathway for the synthesis of various metabolic products and secondary metabolites. The respiratory pathway, therefore, acts as a catabolic as well as an anabolic pathway. Thus, the respiratory pathway is considered an amphibolic pathway. 


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