NCERT Solutions for Class 11 Biology Chapter 14 Respiration in Plants
These Solutions are part of NCERT Solutions for Class 11 Biology. Here we have given NCERT Solutions for Class 11 Biology Chapter 14 Respiration in Plants.
(a) Respiration and Combustion
(b) Glycolysis and Krebs’ cycle
(c) Aerobic respiration and Fermentation
(a) Differences between respiration and combustion are as follows :
(b) Differences between glycolysis and krebs’ cycle are as follows :
(c) Differences between aerobic respiration and fermentation are as follows :
What are respiratory substrates ? Name the most common respiratory substrate.
The compounds that are oxidised during the process of respiration process are known as respiratory substrates. Usually carbohydrates are oxidised to release energy, but proteins, fats and even organic acids can be used as respiratory substrates in some plants, under certain conditions.
Give the schematic representation of glycolysis.
What are the main steps in aerobic respiration ? Where does it take place ?
In aerobic respiration which takes place within the mitochondria, the final product of glycolysis, pyruvate is transported from the cytoplasm into the mitochondria.
The crucial events in aerobic respiration are:
• The complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules of C02.
• The passing on of the electrons removed as part of the hydrogen atoms to molecular 02 with simultaneous synthesis of ATP.
• The first process takes place in the matrix of the mitochondria while the second process is located on the inner membrane of the mitochondria.
• Pyruvate, which is formed by the glycolytic catabolism of carbohydrates in the cytosol, after it enters mitochondrial matrix undergoes oxidative decarboxylation by a complex set of reactions catalysed by pyruvic dehydrogenase. The reactions catalysed by pyruvic dehydrogenase require the participation of several coenzymes, including NAD+ and Coenzyme A.
During this process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid (produced from one glucose molecule during glycolysis).
The acetyl CoA then enters a cyclic pathway, tricarboxylic acid cycle, more commonly called as Krebs’ cycle.
Give the schematic representation of an overall view of Krebs’ cycle.
Electron Transport System (ETS)
- ETS occurs in the electron transport particles (ETP) on the inner surface of the inner membrane of mitochondria.
- It is a metabolic pathway through which electron passes from one carrier to another.
- Electrons from NADH produced in the mitochondrial matrix during citric acid cycle are oxidised by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone located within the inner membrane.
- Ubiquinone also receives reducing equivalents via FADH2 generated during the oxidation of succinate by succinate dehydrogenase (complex II).
- The reduced ubiquinone, called ubiquinol, is then oxidised by transfer of electrons to cytochrome c, cytochrome bc1 – complex (complex III).
- Cytochrome c acts as a mobile carrier between complex III and complex IV.
- Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a, and two copper centres.
- When the electrons are pass from one carrier to another carrier via complex I to IV in the electron transport chain, they are coupled to ATP synthase (complex V) for the formation of ATP from ADP and iP.
- Oxygen functions as the terminal acceptor of electrons and is reduced to water along with the hydrogen atoms. It drives whole process by removing hydrogen from system.
- In respiration, energy of oxidation-reduction utilised for the production of proton gradient. So the process is called as oxidative phosphorylation.
- Higher proton concentration in the outer chamber causes the protons to pass inwardly into matrix or inner chamber causes the protons to pass inwardly into matrix or inner chamber through the inner membrane.
- The energy of the proton gradient is used in attaching a phosphate radicle to ADP by high energy bond.
- Oxidation of one molecule of NADH2 produces 3 ATP molecules while a similar oxidation of FADH2 forms 2 ATP molecules.
- ATP synthase (complex V) helps in ATP synthesis. It consists two major components F1 andFo.
- F1 (head piece) is a peripheral membrane protein complex and contains the site for ATP synthesis while Fo is an integral membrane protein complex that forms channel through which protons cross the inner membrane.
- For each ATP produced, 2H+ passes through Fo from the intermembrane space to the matrix down the electrochemical proton gradient.
Distinguish between the following:
(a) Aerobic respiration and anaerobic respiration.
(b) Glycolysis and fermentation.
(c) Glycolysis and citric acid cycle.
Differences between aerobic respiration and anaerobic respiration are as follows :
Differences between glycolysis and fermentation are as follows :
Differences between glycolysis and citric acid cycle are as follows :
What are the assumptions made during calculation of net gain of ATP ?
The calculations of net gain of ATP for every glucose molecule oxidised is made on certain assumptions that are as follows:
• There is a sequential, orderly pathway functioning, with one substrate forming the next and with glycolysis, TCA cycle and ETS pathway following one after another.
• The NADH synthesized in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.
Discuss “The respiratory pathway is an amphibolic pathway”.
- Glucose is the favoured substrate for respiration. All carbohydrates are usually first converted into glucose before they are used for respiration.
- Respiration involves breakdown as well as synthesis of substrates, the respiratory process involves both catabolism and anabolism.
- Glucose breakdown to release energy. This is called catabolism. Many compounds are also withdrawn from respiratory pathway for the synthesis new substrates (for example acetyl CoA is withdrawn from pathway to synthesis fatty acids when needed).
- This is called anabolism. Thus respiratory pathway involves in both anabolism and catabolism So it is called as an amphibolic pathway.
Define RQ. What is its value for fats ?
The ratio of the volume of C02 evolved to the
volume of 02 consumed is respiration is called respiratory quotient (RQ) or respiratory ratio.
What is oxidative phosphorylation ?
- Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP).
- During oxidative phosphorylation, electrons are transferred from electrons donors to electron acceptors such as oxygen, in redox reactions.
- These redox reactions release energy, which is used to form ATP.
- In eukaryotes, these redox reactions are carried out by a series of five protein complexes within mitochondria.
- When the electrons pass from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase (complex V) for the production of ATP from ADP and inorganic phosphate.
- The number of ATP molecules synthesised depends on the nature of the electron donor. Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that of one molecule of FADH2 produces 2 molecules of ATP.
Oxygen acts as the final hydrogen acceptor.
- Unlike photophosphorylation where it is the light energy that is utilised for the production of proton gradient required for phosphorylation, in respiration it is the energy of oxidation-reduction utilised for the same process.
- It is for this reason that the process is called oxidative phosphorylation.
What is the significance of step-wise release of energy in respiration ?
During oxidation within a cell, all the energy contained in respiratory substrates is not released free into the cell, or in a single step.
It is released in a series of slow step-wise reactions controlled by enzymes, and it is trapped as chemical energy in the form of ATP. Hence, it is important to understand that the energy released by oxidation in respiration is not used directly but is used to synthesise ATP, which is broken down whenever (and wherever) energy needs to be utilised. Hence, ATP acts as the energy currency of the cell.
This energy trapped in ATP is utilised in various energy- requiring processes of the organisms, and the carbon skeleton produced during respiration is used as precursors for biosynthesis of other molecules in the cell.
VERY SHORT ANSWER QUESTIONS
Which organic compound acts as link between glycolysis and Kreb’s cycle?
Acetyl Co-A acts as link between glycolysis and Krebs cycle.
Name the final acceptor of electron in ETC.
Oxygen is the electron acceptor of ETC.
Function of oxygen in aerobic respiration:
(i) It acts as the final electron acceptor.
(ii) It drives the whole process by removing hydrogen from the system.
Function of oxygen in aerobic respiration:
(i) It acts as the final electron acceptor.
(ii) It drives the whole process by removing hydrogen from the system.
What term is given to the reduced ubiquinone?
Ubiquinol is a reduced form of ubiquinone.
Where does the electron transport system operate in the mitochondria?
Phosphofructokinase catalyses the formation of fructose 1, 6 bisphosphate from fructose 6- phosphate.
Give the function of phosphofructokinase in glycolysis.
Hexokinase-helps in phosphorylation of glucose.
Name the enzyme that catalyses phosphorylation of glucose.
The formation of acetyl CoA takes place in the mitochondrial matrix.
Where does the formation of acetyl CoA take place in a cell?
The first step in Krebs cycle is the condensation of acetyl group (acetyl CoA) with oxaloacetic acid (OAA) to form citric acid and release the Coenzyme A.
What is the first step of reaction in TCA cycle?
Fatty acids may be converted to acetyl CoA before they from the respiratory substrates.
What happens to fatty acids before they form the respiratory substrates?
Name the oxidative pathway through which intermediate metabolites of glucose, fatty acids and amino acids are finally oxidised.
36 ATP/38 ATP molecules are obtained in the process of respiration and it is related to the aerobic respiration type.
How many ATP molecules are obtained in the process of respiration?
The two molecules obtained by the actions of aldolase from fructose -1,6-biphosphete are :- Glyceraldehyde 3-phosphete and Dihyroxy acetone-3-phosphate.
What are the two molecules obtained by the action of aldolase from fructose -1, -6- biphosphate?
ATP is produced.
SHORT ANSWER QUESTIONS
How is proton gradient established?
Proton gradient is established by passing proton (H+) from the matrix across the inner mitochondrial membrane into intermembrane space with the energy released during electron transfers in ETC.
Describe the steps in the formation of lactic acid from pyruvic acid.
Pyruvic acid is catalysed by the enzyme lactic dehydrogenase. NADH formed in glycolysis is used up for the reduction.
How is ATP formed by the energy released during the electron transport system in mitochondria?
ATP formations require enzyme called ATP synthase. It has two component F0– F1. ATP- synthase become active in ATP formation when concentration of H+ on Fo side is higher than F| side. Fligher proton concentration in outer chamber cause the proton to pass inner chamber. F1 particle induced by flow of proton through Fo channel. The energy of proton gradient attaches the phosphate radicle to ADP. This produces ATP.
Give a detailed account on the net gain of ATP at different stage of respiration.
In most eukaryotic cells 2 molecules of ATP are required for transporting NADH produced in glycolysis to mitochondria for further oxidation. Hence net gain of ATP is 36 molecules.
Enumerate the functions of ATP.
Functions of ATP :-
(i) ATP functions as universal energy carrier of living systems.
(ii) ATP stores small packets of energy in its molecules.
(iii) It is mobile in the cell. Therefore, it reaches all parts of cell away from the region of ATP synthesis.
(iv) It activates a number of chemicals by functioning as phosphorylating agent.
(v) ATP provides energy for muscle contraction.
(vi) It is involved in transport of substances against concentration gradient.
Where is cytochrome c located? What is its function?
Cytochrome c is located on the outer surface of the inner mitochondrial membrane. It acts as a mobile carrier for the transfer of electrons between complex III and complex IV of the electron transport system.
Define respiratory quotient.
Respiratory quotient is defined as the ratio of the volume of carbondioxide evolved to the volume of oxygen consumed in respiration.
What is oxidative phosphorylation?
The whole process by which oxygen effectively allows the production of ATP by phosphorylation of ADP is called oxidative phosphorylation.
The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration. Why is there anaerobic respiration even in organisms that live in aerobic condition like human beings and angiosperms?
Aerobic organisms do face situations where oxygen availability is little. For example, overworked muscles do not receive enough oxygen during strenuous exercise. Similarly deep seated tissues of angiosperms do not receive enough oxygen through diffusion from outside. In such situations only anaerobic respiration can help in survival of the tissue.
Comment on the statement- “Respiration is an energy producing process but ATP is used in some steps of the process”.
ATP is required in all those reactions where phosphorylative activation of substrate is required. Therefore, despite producing energy (as ATP), respiration requires ATP in certain steps, e.g., glucose —> glucose 6-phosphate, fructose 6-phosphate —fructose 1, 6- bisphosphate.
LONG ANSWER QUESTIONS
Explain the major steps in Krebs’ cycle. Why is this cycle also called citric acid cycle?
Krebs cycle : This process occurs in the mitochondrial matrix.
Major steps of krebs cycle are as follows :
- Acetyl Co-A, formed by the oxidative decarboxylation of pyruvic acid enters the Krebs’ cycle.
- It combines with oxalo acetic acid (OAA), a 4C-compound, to form a 6C-compound, citric acid; the reaction is catalysed by citrate synthase.
- Citrate is then isomerised into isocitrate.
- Isocitrate is converted into oxalosuccinic acid in the presence of NAD and isocitrate dehydrogenase.
- Oxalosuccinic acid is then decarboxylated into a-ketoglutaric acid (KG), in the presence of a decarboxylase enzyme.
- a-ketoglutaric acid is converted into succinyl Co-A in the presence of NAD,Co- A and enzyme a-ketoglutarate dehydrogenase.
- When succinyl Co-A is converted into succinic acid, one molecule of GTP is formed and Co-A is released.
- In the remaining part of the cycle, succinic acid is converted into OAA, so that the citric acid cycle can continue to operate.
- During this cycle three molecules of NAD and one molecule of FAD are reduced to NADH and FADH respectively.
- This cycle is called as citric acid cycle because the first product is citric acid which is 3-C compound.
Name the end product of glycolysis. Where is it produced in the cell? Discuss oxidative decarboxylation.
Glycolysis results in the formation of two molecules of pyruvic acid, NADH and ATP. It occurs in the cytosol of the cell.
Aerobic oxidation : One of the three carbons of pyruvic acid is oxidised to carbon dioxide in the reaction called oxidative decarboxylation. Pyruvic acid is first decarboxylated and then oxidised by the enzyme pyruvic dehydrogenase. The two-carbon units are readily accepted by coenzyme-A (Co-A) to form acetyl Co-A. The summary of the reaction is given in the following equation :
Thus, pyruvic acid enters Krebs cycle as acetyl Co-A. Krebs’ cycle occurs in the mitochondrial matrix.
Acetyl Co-A, formed by the oxidative decarboxylation of pyruvic acid enters the Krebs’ cycle.
Represent schematically the interrelationship among metabolic pathways in a plant, showing respiration mediated breakdown of different organic compounds.
Schematic representation among metabolic pathways showing respiration mediated breakdown of different organic molecules to C02 and H20:
How do plants manage exchange of gases? Give an overview of respiration in plants.
Plants, unlike animals, have no specialised organs for gaseous exchange but they have stomata and lenticles for this purpose. There are several reasons why plants can get along without respiratory organs.
- Each plant part takes care of its own gas- exchange needs. There is very little transport of gases from one plant part to another.
- Plants do not present great demands for gas exchange. Roots, stems and leaves respire at lower rate than animals do.
- Only during photosynthesis, large volumes of leases exchanged and, each leaf is well adapted to take care of its own needs during these periods.
- When cells perform photosynthesis, availability of 02 is not a problem in these cells since 02 is released
- The distance that gases must diffuse even in large, bulky plants is not great. Each living cell in a plant is located quite close to the surface of the plant.
- Even in woody stems, the ‘living’ cells are organised in thin layers inside and beneath the bark. They also have openings called lenticels. The cells in the interior are dead and provide only mechanical support.
- Thus, most cells of a plant have attest a part of their surface in contact with air. This is also facilitated by the loose packing of parenchyma cells in leaves, stems and roots, which provide an interconnected network of air spaces.
- The complete combustion of glucose, which produces C02 and H20 as end products, yields energy. Most of the energy is given out as heat.
C6H12°6 + 6°2 >6C02+6H20 + Energy
- If this energy is to be useful to the cell, it should be able to utilise it to synthesis other molecules that the cell requires.
- The strategy that the plant cell uses is to catabolise the glucose molecule in such a way that not all the liberated energy goes out as heat.
- The key is to oxidise glucose not in one step but in several small steps enabling some steps to be just large enough so that the energy released can be coupled to ATP synthesis.
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