Chapter 14 Respiration in Plants Solutions
Question - 1 : - Differentiate between
(a) Respiration and Combustion
(b) Glycolysis and Krebs’ cycle
(c) Aerobic respiration and Fermentation
Answer - 1 : -
(a) Respirationand combustion
| Respiration | Combustion |
| 1. | It is a biochemical process. | 1. | It is a physiochemical process. |
| 2. | It occurs in the living cells. | 2. | It does not occur in the living cells. |
| 3. | ATP is generated | 3. | ATP is not generated |
| 4. | Enzymes are required | 4. | Enzymes are not required |
| 5. | It is a biologically-controlled process. | 5. | It is an uncontrolled process. |
(b) Glycolysis andKrebs cycle
| Glycolysis | 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 and anaerobic respiration. | 3. | It occurs in aerobic respiration. |
| 4. | It generates 2 NADH2 and 2 ATP molecules on the breakdown of one glucose molecule. | 4. | It produces 6 NADH2, 2FADH2, and 2 ATP molecules on the breakdown of two acetyl-CoA molecules. |
(c) Aerobicrespiration and fermentation
| 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.
Answer - 2 : -
The compounds oxidised during the process of respiration are called respiratory substrates. Carbohydrates, especially glucose, act as respiratory substrates. Fats, proteins, and organic acids also act as respiratory substrates.
Question - 3 : - Give the schematic representation of glycolysis?
Answer - 3 : - 
Question - 4 : - What are the main steps in aerobic respiration? Where does it take place?
Answer - 4 : -
The major steps in aerobic respiration and the sites where they occur are listed in the given table.
| Step | Site of occurrence |
| 1. | Glycolysis | 1. | Cytoplasm |
| 2. | Krebs cycle | 2. | Matrix of mitochondria |
| 3. | Electron transport system | 3. | Inner mitochondrial membrane |
| 4. | Oxidative phosphorylation | 4. | F0-F1 particles in the inner mitochondrial membrane |
Give the schematic representation of an overall view of Krebs cycle.
Answer - 5 : - 
Question - 6 : - Explain ETS.
Answer - 6 : -
ETS or electron transport system is locatedin the inner mitochondrial membrane. It helps in releasing and utilizing the energystored in NADH+H+ and FADH2. NADH+ H+, which is formed during glycolysis and citric acidcycle, gets oxidized by NADH dehydrogenase (complex I). The electrons so generatedget transferred to ubiquinone through FMN. In a similar manner, FADH2 (complex II) generated during citric acidcycle gets transferred to ubiquinone. The electrons from ubiquinone arereceived by cytochrome bc1 (complex III) and further get transferredto cytochrome c. The cytochrome c acts as a mobile carrier between complex III andcytochrome c oxidase complex, containing cytochrome a and a3, along with copper centres (complex IV).
During the transfer of electrons from each complex, theprocess is accompanied by the production of ATP from ADP and inorganicphosphate by the action ATP synthase (complex V). The amount of ATP produceddepends on the molecule, which has been oxidized. 2 ATP molecules are producedby the oxidation of one molecule of NADH. One molecule of FADH2, on oxidation, gives 3 ATP molecules.
Distinguish between the following:
(a) Aerobic respiration and Anaerobic respiration
(b) Glycolysis and Fermentation
(c) Glycolysis and Citric acid Cycle
Answer - 7 : -
(a) Aerobic respiration andAnaerobic respiration
| Aerobic respiration | Anaerobic respiration |
| 1. | It uses oxygen for deriving energy. | 1. | It occurs in the absence of oxygen. |
| 2. | It occurs in cytoplasm and mitochondria. | 2. | It occurs in cytoplasm. |
| 3. | The end products of aerobic respiration are carbon dioxide and water. | 3. | The end products of fermentation are ethyl alcohol and carbon-dioxide. |
| 4. | Complete oxidation of respiratory substrate takes place. | 4. | Incomplete oxidation of respiratory substrate takes place. |
| 5. | 36-38 ATP molecules are produced. | 5. | Only 2 ATP molecules are produced. |
(b) Glycolysis andFermentation
| Glycolysis | | Fermentation |
| 1. | Glycolysis occurs 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 andcitric acid cycle
| 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 and anaerobic respiration. | 3. | It occurs in aerobic respiration. |
| 4. | One glucose molecule breaks down to generate 2 NADH2 and 2 ATP molecules. | 4. | It produces 6 NADH2, 2 FADH2, and 2 ATP molecules on breakdown of two acetyl-coA molecules. |
Question - 8 : - What are the assumptions made during the calculation of net gain of ATP?
Answer - 8 : -
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) 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 - 9 : - Discuss “The respiratory pathway is an amphibolic pathway.”
Answer - 9 : -
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 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 amphibolic pathway as it involves both anabolism and catabolism.
Question - 10 : - Define RQ. What is its value for fats?
Answer - 10 : -
Respiratory quotient (RQ) or respiratoryratio can be defined as the ratio of the volume of CO2 evolvedto the volume of O2 consumed during respiration. The value ofrespiratory quotient depends on the type of respiratory substrate. Its value isone for carbohydrates. However, it is always less than one for fats as fatsconsume more oxygen for respiration than carbohydrates.
It can be illustrated through the example of tripalmitinfatty acid, which consumes 145 molecules of O2 forrespiration while 102 molecules of CO2 areevolved. The RQ value for tripalmitin is 0.7.