Important Questions Class 11 Biology Chapter 12 Respiration in Plants
Important Questions Class 11 Biology Chapter 12 Respiration in Plants
Respiration in Plants is Chapter 12 of Class 11 Biology. Respiration is the process by which a cell breaks down food, such as glucose, to release energy. This energy is stored in a molecule called ATP (adenosine triphosphate). The chapter explains glycolysis, fermentation, the Krebs cycle, the Electron Transport System (ETS), oxidative phosphorylation, the respiratory quotient (RQ) and why respiration is called an amphibolic pathway.
This page gives 12 important questions from Respiration in Plants with clear answers prepared by Extramarks experts. The questions cover the proton gradient, the ETS diagram, the difference between aerobic and anaerobic respiration, the net gain of ATP and the Krebs cycle. Students can use them for school tests and CBSE (Central Board of Secondary Education) exam revision, and teachers and parents can use them for quick practice.
Important Questions Class 11 Biology Chapter 12 Respiration in Plants
Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Respiration in Plants
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Q1. By which process proton gradient is established?
Answer: By passing protons from the matrix across the inner mitochondrial membrane into inner-membrane space with the energy released during electron transfer over ETS.
Q2. Show the diagrammatic representation of ETS.
Answer: The diagrammatic representation of the Electron Transport System (ETS), present on the inner mitochondrial membrane, is given below:
Electrons move from Complex I and Complex II to Complex III through ubiquinone (Q), and then to Complex IV through cytochrome c. The proton gradient formed across the inner mitochondrial membrane is used by ATP synthase (Complex V) to make ATP.
Q3. Explain ETS.
Answer: The electrons removed from the substrates of glycolysis and the Krebs’ cycle are stored in the reduction equivalents, namely NADH2 and FADH2. This energy is released when NADH2 and FADH2 are oxidized by passing their electrons to a chain of electrons carrier complex called Electron transport system, present in the inner membrane of mitochondria. These complexes transfer the electron through a series of redox reactions with high energy electrons entering the system and low-energy electrons leaving the system. The energy released through this process is utilized to pump out protons which develop a proton gradient (Proton motive force) across the inner membrane. This proton motive force is utilized by ATP synthase to generate high energy ATP molecules at 3 different sites.
Process: The NADH2 produced during the citric acid cycle are oxidized by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone which gets reduced. Ubiquinone also receives reducing equivalents via FADH2 (complex II). The reduced ubiquinone (ubiquinol) is then re-oxidized by transferring its electrons to cytochrome c via cytochrome bc1 complex (complex III). The electron is transferred from complex III to complex IV through cytochrome C which is a mobile carrier present in the inner membrane. Complex IV is called cytochrome C oxidase complex and consists of cytochromes a-a3, and two copper centers.
Q4. A toxic compound was introduced in an experiment which selectively inhibited cytochrome oxidase in the inner
mitochondrial membrane. Despite normal glycolysis and Krebs cycle activity, ATP production fell sharply and NADH
accumulated.
(a) Which specific step in aerobic respiration was blocked and how did it impact electron transport?
(b) Why did ATP production drop even though earlier steps were unaffected?
(c) How does the chemiosmotic hypothesis explain ATP synthesis under normal conditions?
Answer: a. The toxic compound inhibited cytochrome oxidase (Complex IV), the final enzyme in the electron transport chain (ETC) located in the inner mitochondrial membrane. This step is crucial because it transfers electrons to oxygen, the final electron acceptor, forming water. By blocking this step, the entire electron flow through the ETC halts, preventing the regeneration of NAD⁺ and FAD, which are needed for continuous operation of the Krebs cycle and glycolysis.
b. Although glycolysis and the Krebs cycle were still active initially, ATP production dropped sharply because the electron transport chain is the site of oxidative phosphorylation, which accounts for the majority of ATP yield in aerobic respiration (about 34 out of 38 ATP molecules). Without the ETC, the proton gradient across the inner mitochondrial membrane cannot be established, and thus ATP synthase cannot function efficiently.
c. Under normal conditions, the chemiosmotic hypothesis explains ATP synthesis by stating that electron transport drives the pumping of protons (H⁺ ions) into the intermembrane space, creating an electrochemical gradient. The return flow of protons through ATP synthase releases energy that is used to convert ADP into ATP. When the ETC is blocked, this proton motive force cannot be generated, effectively halting ATP synthesis.
Q5. Differentiate between FAD and NAD.
Answer:
| FAD | NAD |
|---|---|
| Flavin adenine dinucleotide | Nicotinamide adenine dinucleotide |
| Its oxidation along ETC produces 2 ATP. | Its oxidation along ETC produces 3 ATP. |
Q6. What is the significance of step-wise release of energy in respiration?
Answer: Carbohydrates, proteins, fats and organic acids are used as respiratory substrates and oxidation of these compounds releases energy in the cell. However, the energy released is not dissipated freely in the cell. In other words, it does not occur in one step. Instead, it is released in a series of slow step-wise reactions controlled by enzymes and is trapped in the form of ATP. This prevents the sudden increase in the temperature and avoids wastage of energy. This holds a lot of significance as ATP which stores the energy can be broken down whenever and wherever it is needed in the various energy-requiring processes of the organisms.
Q7. What is oxidative phosphorylation?
Answer: The metabolic pathway that uses the energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP) is called oxidative phosphorylation. Almost all the forms of life on earth use a range of different nutrients to carry out oxidative phosphorylation to produce the molecule that supplies energy to metabolism i.e. ATP. This is a very efficient process of energy generation.
This process requires the presence of oxygen in the system. Oxygen drives the whole process as it removes hydrogen from the system and acts as the final hydrogen acceptor. During oxidative phosphorylation, electrons are transferred from electron donors like NADH2 to electron acceptors such as oxygen. These redox reactions release energy, which is used to form ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within mitochondria, whereas, in prokaryotes, these proteins are located in the cells' inner membranes. These linked sets of proteins are called electron transport chains. It is the energy of the oxidation-reduction process that is used for the production of proton gradient required for phosphorylation and thus, this process is called oxidative phosphorylation.
Q8. Define RQ. What is its value for fats?
Answer: Complete oxidation of substrates during aerobic respiration requires oxygen and apart from energy, carbon dioxide is produced as the by-product. The ratio of the volume of CO2 released to the volume of O2 consumed during complete oxidation of one molecule of a substrate in a given period of time at standard temperature and pressure is called the respiratory quotient (RQ).
For example, during aerobic respiration of one molecule of glucose, 6 molecules of CO2 are released and 6 molecules of O2 are consumed. Thus RQ for glucose is 1.
RQ value for fats: Fats need more oxygen molecule than carbohydrate (glucose) for complete oxidation through aerobic respiration, due to which the value of RQ for fat is always less than 1.
For example, when fatty acid tripalmitin is used as a substrate, 145 molecules of O2 are consumed whereas 102 molecules of CO2 are produced, the RQ value is 0.7.
Q9. Discuss “The respiratory pathway is an amphibolic pathway.”
Answer: The process of metabolism involves both anabolic and catabolic reactions. Anabolism is the synthesis of complex macromolecules like lipids and proteins from simple molecules like glycerol and amino acid respectively. On the other hand, catabolism includes the breakdown of macromolecules into simple molecules so that they can enter in the respiratory pathway as a substrate for the release of energy. If fatty acids are used as a respiratory substrate they are broken down to glycerol and acetyl CoA. Glycerol gets converted to 3-phosphoglyceraldehyde (PGAL) and enters in glycolysis while Acetyl CoA directly enters in Krebs’ cycle. However, when an organism needs to synthesize fatty acids, acetyl CoA is withdrawn from the above-said pathway and is made available for catabolic reaction. Similarly, when proteins are used as a substrate, they are first broken down to amino acid, which in turn, depending on their structure, gets converted into different intermediates of Krebs’ cycle. At the time of need, the same molecules are withdrawn to synthesize new proteins. Most of these reactions are reversible and depending on the requirement, the cell uses the respiratory substrate in the process of anabolism or catabolism. Thus, the respiratory pathway is known as the amphibolic pathway rather than only a catabolic pathway.
Q10. What are the assumptions made during the calculation of net gain of ATP?
Answer: Many assumptions have been made in order to calculate the net gain of ATP from one molecule of glucose. This is required as the cellular system is very complex where numerous biochemical reactions take place simultaneously. The assumptions are as follows: All the steps of aerobic respiration (glycolysis, TCA cycle, ETS and oxidative phosphorylation) take place in sequential order where the product of the first step enters the subsequent step as a substrate.
The NADH synthesized in glycolysis enters in the mitochondria and produces ATP through oxidative phosphorylation.
The intermediates formed in various steps of aerobic respiration are not utilized in any other metabolic pathways other than subsequent steps of respiration.
The glucose molecule is the only substrate and no other molecule enters as an intermediate substrate in the process.
Q11. Distinguish between the following:
(a) Aerobic respiration and Anaerobic respiration
(b) Glycolysis and Fermentation
(c) Glycolysis and Citric acid Cycle
Answer: (a) Aerobic respiration and Anaerobic respiration
| S. No. | Aerobic respiration | Anaerobic respiration |
|---|---|---|
| 1. | It occurs only in the presence of molecular oxygen. | It occurs in the absence of molecular oxygen. |
| 2. | It is highly efficient and produces 38 ATP molecules. | It is less efficient and generates only 2 ATP molecules. |
| 3. | It takes place in both cytoplasm and mitochondria. | It takes place in the cytoplasm only. |
| 4. | It is a multistep process having glycolysis, Krebs’ cycle, and ETS. | It is not a multistep process. |
| 5. | It produces carbon dioxide and water as the by-product. | It produces ethyl alcohol and carbon dioxide as a by-product. |
(b) Glycolysis and Fermentation
| S. No. | Glycolysis | Fermentation |
|---|---|---|
| 1. | It is a common step in both aerobic and anaerobic respiration. | It is strictly an anaerobic mode of respiration. |
| 2. | It results in the production of pyruvic acid. | It produces ethyl alcohol. |
| 3. | Net gain is 8 ATP molecules. | Net gain is 2 ATP molecules. |
| 4. | The product of glycolysis is used as an intermediate in Krebs’ cycle. | The product of fermentation (ethyl alcohol) is not used by cells further. |
(c) Glycolysis and Citric acid Cycle
| S. No. | Glycolysis | Citric acid Cycle |
|---|---|---|
| 1. | It occurs in the cytoplasm. | It occurs in the mitochondria. |
| 2. | It is a non-cyclic process. | It is a cyclic process. |
| 3. | It is common in both aerobic and anaerobic respiration. | It takes place only in aerobic respiration. |
| 4. | It produces 8 ATP molecules from one molecule of glucose. | It produces 15 ATP molecules from one molecule of Acetyl CoA. |
Q12. Give the schematic representation of an overall view of Krebs’ cycle.
Answer: Schematic representation of Krebs’ cycle:
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Q.1 Mineral enters a plant mainly by?
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Ans
Active transport is the mediated process of moving particles across a biological membrane against a concentration gradient.
Q.2 Essential micronutrients are also known as?
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Ans
A trace element is a chemical element that is needed in minute quantities for the proper growth, development, and physiology of the organism. A trace element is also referred to as a micronutrient.
Q.3 An essential element
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Ans
Essential element are chemical nutrient that is vital for the successful growth and development of plant.
Q.4 Major nitrogen fixation is carried out by
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Ans
Symbiotic bacteria carries out major nitrogen fixation. These bacteria live in symbiosis with another organism or each other.
Q.5 Hydroponics is a technique of growing plants in
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Ans
Nutrient solution.
Hydroponics is a method of growing plants using mineral nutrient solutions, without soil.