Question 1

Differentiate between:(a) Respiration and Combustion(b) Glycolysis and Kreb's cycle(c) Aerobic respiration and fermentation

Accepted Answer

(a)                          Respiration Combustion  1. It takes place in living cells only. 1. It does not take place in the living cell. 2. It is carried out with the help of various enzymes. 2. Enzymes are not involved in this process.  3. The oxidation of food and the liberation of energy occur in a step-wise manner. 3. The substances are oxidized spontaneously with sudden release of energy.  4. It occurs at the body temperature of the organism. 4. Sudden release of energy generates high temperature of a fire. 5. 60% of energy escapes as body heat and 40% of energy is packaged directly into new chemical energy (ATP). 5. Energy released in combustion is dissipated as heat and to some extent as light.(b) Glycolysis  Krebs cycle1. It is a linear pathway. 1. It is a cyclic pathway.2. It occurs in the cell cytoplasm.2. It occurs in the mitochondrial matrix.  3. It occurs in both aerobic as well as anaerobic respiration.3. It occurs in aerobic respiration only.4. Net generation of 2 NADH+H+ and 2 ATP molecules occurs on the breakdown of one glucose molecule.4. It produces 6 NADH+H+, 2FADH2​, and 2 ATP molecules on the breakdown of two acetyl-CoA molecules generated after glycolysis of one glucose molecule.   (c) Aerobic respiration Fermentation   1. Oxygen is used for deriving energy.1. Occurs in the absence of oxygen. 2. Occurs in the cytoplasm and mitochondria.  2. Occurs in the cytoplasm. 3. End products are carbon dioxide and water.3. End products are ethyl alcohol and carbon dioxide. 4. Complete oxidation of the respiratory substrate takes place. 4. Incomplete oxidation of the respiratory substrate takes place. 5. About 36 ATP molecules are produced.5. Only 2 ATP molecules are produced.

Question 2

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

Accepted Answer

The compounds oxidised during the process of respiration are called as respiratory substrates. Carbohydrates, especially glucose, act as a respiratory substrate. Fats, proteins, and organic acids can also act as respiratory substrates depending upon the physiological condition of the body of an organism.

Question 3

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

Accepted Answer

The major steps in aerobic respiration and the sites where they occur are listed in the given table : Step Site of occurrence Glycolysis Cytoplasm Kreb's cycle Matrix of mitochondria Electron transport system Inner mitochondrial membrane Oxidative phosphorylation F0 - F1 particles in the inner mitochondrial membrane

Question 4

Explain ETS.

Accepted Answer

ETS or electron transport system is located in the inner mitochondrial membrane. It helps in releasing and utilizing the energy stored in NADH2​ and FADH2​. NADH2​ 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 centres (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. 3 ATP molecules are produced by the oxidation of one molecule of NADH. One molecule of FADH2​, on oxidation, gives 2 ATP molecules.

Question 5

Distinguish between the following:(a) Aerobic respiration and Anaerobic respiration(b) Glycolysis and Fermentation(c) Glycolysis and Citric acid cycle

Accepted Answer

(a) Aerobic Respiration Anaerobic Respiration 1. Aerobic respiration takes place in the presence of free oxygen. 1. Anaerobic respiration takes place in the absence of free oxygen.2. The first step of this process (glycolysis) takes place in the cytoplasm while the second step (Krebs cycle) is carried out in mitochondria.  2.The complete process is carried out outside the mitochondria i.e., in the cytoplasm. 3. Glucose is completely oxidized into carbon dioxide and water. 3. Glucose is incompletely oxidized into carbon dioxide and ethyl alcohol. 4. 38 molecules of ATP are produced by the complete oxidation of one gram-mole of glucose. 4. Only 2 molecules of ATP are formed in this process.(b) Glycolysis Fermentation 1. Glycolysis is a common process during aerobic and anaerobic respiration. 1. Fermentation is a type of anaerobic respiration. 2. Pyruvic acid is produced as its end product. 2. Ethanol or lactic acid is produced as its end product.(c) Glycolysis Citric acid cycle (Krebs cycle) 1. It is a linear pathway. 1. It is a cyclic pathway. 2. It occurs in the cell cytoplasm. 2. It occurs in the mitochondrial matrix. 3. It occurs in both aerobic as well as in anaerobic respiration. 3. It occurs in aerobic respiration only. 4. One glucose molecule breaks down to generate 2 NADH22 and 2 ATP molecules. 4. It produces 6 NADH2, 2 FADH2, and 2 ATP molecules on the breakdown of two acetyl-CoA molecules generated after glycolysis.

Question 6

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

Accepted Answer

For theoretical calculation of ATP molecules, various assumptions are made, which 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) A 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.

Question 7

Discuss the respiratory pathway is an amphibolic pathway.

Accepted Answer

Respiration is generally assumed to be a catabolic process because, during respiration, various substrates are broken down for deriving energy. 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. In a similar manner, proteins are converted into amino acids, which enter respiration after deamination.During synthesis of fatty acids, acetyl-CoA is withdrawn from the respiratory pathway. Also, in the synthesis of proteins, respiratory substrates get withdrawn. Thus, respiration is also involved in anabolism. Therefore, respiration can be termed as the amphibolic pathway as it involves both anabolism and catabolism.

Question 8

Define RQ. What is its value for fats?

Accepted Answer

Respiratory quotient (RQ) or respiratory ratio can be defined as the ratio of the volume of CO2​ evolved to the volume of O2​ consumed during respiration. 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.It can be illustrated through the example of tripalmitin fatty acid, which consumes 145 molecules of O2​ for respiration while 102 molecules of CO2​ are evolved. The RQ value for tripalmitin is 0.7.

Question 9

What is oxidative phosphorylation?

Accepted Answer

Oxidative phosphorylation is a metabolic pathway of generating ATP molecule by phosphorylation (addition of phosphate to an organic compound) of ADP.This process takes place in the mitochondria of a cell during the electron transport chain.The ATP is formed as a result of the transfer of electrons from NADH or FADH2​ to O2​ by a series of electron carriers.

Question 10

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

Accepted Answer

The process of aerobic respiration is divided into four phases – glycolysis, TCA cycle, ETS, and oxidative phosphorylation. It is generally assumed that the process of respiration and production of ATP in each phase takes place in a step-wise manner. The product of one pathway forms the substrate of the other pathway. Various molecules produced during respiration are involved in other biochemical processes. The respiratory substrates enter and withdraw from the pathway on necessity. ATP gets utilized wherever required and enzymatic rates are generally controlled. Thus, the step-wise release of energy makes the system more efficient in extracting and storing energy.

Chapter 14 : Respiration in Plants