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NCERT Class 11 Biology Chapter 14 Respiration in Plants
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Respiration in Plants
Chapter: 14
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. Differentiate between
(a) Respiration and Combustion.
Ans. Respiration:
1. It is a controlled biochemical process.
2. It occurs in living cells.
3. ATP is generated.
4. Enzymes are required.
Combustion:
1. It is an uncontrolled physicochemical process.
2. It does not occur in living cells.
3. ATP is not generated.
5. Enzymes are not required.
(b) Glycolysis and Krebs cycle.
Ans. Glycolysis Krebs cycle:
GLYCOLYSIS
(a) It occurs in the cytoplasm of cell.
(b) Both aerobic and anaerobic respiration starts with Glycolysis.
(c) Glucose undergoes partial oxidation to form two molecules of pyruvic acid, 2 NADH and 2 ATP.
Glucose + 2 NAD⁺ + 2 ATP → 2
Pyruvate + 2 NADH + 2 ATP + 2 H⁺
(d) Each NADH is equivalent to 3 ATP so met gain in glycolysis is 8 ATP.
(e) Net ATPs produced = 4 (produced) – 2 (consumed) = 2 ATPs.
(f) The pyruvate may undergo:
(i) Lactic acid fermentation.
(ii) Alcoholic fermentation.
(iii) Aerobic respiration (Krebs cycle).
KREB’S CYCLE (Citric acid cycle / Tricarboxylic acid cycle):
(i) It takes place in the mitochondrial matrix.
(ii) It is complete step wise oxidation of pyruvate to three molecules of CO₂
Pyruvate + 4 NAD⁺ + FAD + ADP + 2 H₂O → 3 CO₂ + 4 NADH + 4 H⁺ + FADH₂ + ATP
(iii) Acetyl CoA is the substrate entrant for Kreb cycle.
(iv) An acceptor molecule of the cycle is oxaloacetate.
(c) Aerobic respiration and Fermentation
Ans. Aerobic respiration and fermentation Aerobic respiration
(i) It is complete oxidation of organic food with oxygen.
(ii) End products are CO₂ + H₂O + 36/38 ATPs
(iii) Aerobic respiration consists of Glycolysis, Citric acid cycle and ETS (both occur in mitochondria). Fermentation ins
(iv) Incomplete oxidation of organic food, under anaerobic respiration.
(v) Glycolysis produces pyruvate which is broken down to form lactic acid/ ethyl alcohol.
(vi) It occurs in bacteria, yeast and striated muscles.
(vii) There is net gain of only 2 ATP for each molecule of glucose.
Q.2. What are respiratory substrates? Name the most common respiratory substrate.
Ans. The compounds oxidised during the process of respiration are called respiratory substrates. Respiratory substrate is most commonly glucose but these can also be proteins, fats or organic acids.
Q.3. Give the schematic representation of glycolysis?
Ans. Do yourself.
Q.4. What are the main steps in aerobic respiration? Where does it take place?
Ans. The major steps in aerobic respiration and the sites are:
1. Glycolysis — Cytoplasm.
2. Krebs cycle — Matrix of mitochondria.
3. Electron system transport — Inner mitochondrial membrane.
4. Oxidative phosphorylation — F0-F1 particles in the inner mitochondrial membrane.
Q.5. Give the schematic representation of an overall view of Krebs cycle.
Ans. Do yourself.
Q.6. Explain ETS.
Ans. Electron Transport Chain (ETC):
(i) Electrons are passed from one carrier to another.
(ii) Complex I to IV is involved in electron transport.
(iii) Complex I is NADH dehydrogenase complex.
• It has two prosthetic groups – FMN (Flavin mononucleotide) and Fe S (Iron Sulphur complex).
(iv) Complex II is ubiquinone (UQ).
(v) Complex III is cytochrome b c₁ complex.
• Cytochrome c is a mobile protein carrier that transfers electrons from complex III to IV.
(vi) Complex IV – Cytochrome c oxidase complex.
• It contains cytochrome a and cytochrome a₃ with two copper center.
(vii) Oxygen is the final acceptor of electrons. It combines with protons to form water.
Q.7. Distinguish between the following:
(a) Aerobic respiration and Anaerobic respiration.
Ans. Aerobic respiration and Anaerobic respiration
Aerobic respiration-
(i) It is complete oxidation of organic food with oxygen.
(ii) End products are CO₂ + H₂O + 36/38 ATPs
(iii) Aerobic respiration consists of Glycolysis, Citric acid cycle and ETS (both occur in mitochondria).
Anaerobic respiration-
(i) It is incomplete oxidation of organic food without oxygen.
(ii) End products are pyruvate, ethyl alcohol/ lactic acid, CO₂ and 2 ATP.
(b) Glycolysis and Fermentation.
Ans. Glycolysis and Fermentation GLYCOLYSIS
(i) It occurs in the cytoplasm of cell.
(ii) Both aerobic and anaerobic respiration starts with Glycolysis.
(iii) Glucose undergoes partial oxidation to form two molecules of pyruvic acid, 2 NADH and 2 ATP.
Glucose + 2 NAD⁺ + 2 ADP → 2
Pyruvate + 2 NADH + 2 ATP + 2 ATP + 2 H⁺
(iv) Each NADH is equivalent to 3 ATP so net gain in glycolysis is 8 ATP.
(v) et ATPs produced = 4 (produced) 2 (consumed) = 2 ATPs
(vi) The pyruvate may undergo:
Lactic acid fermentation; Alcoholic fermentation or Aerobic respiration (Krebs cycle)
FERMENTATION
(i) Incomplete oxidation of organic food, under anaerobic respiration.
(ii) Glycolysis produces pyruvate which is broken down to form lactic acid/ ethyl alcohol.
(iii) It occurs in bacteria, yeast and striated muscles.
(iv) There is net gain of only 2 ATP for each molecule of glucose.
Q.8. What are the assumptions made during the calculation of net gain of ATP?
Ans. Assumptions made during the calculation of net gain of ATP are:
(a) Various steps of aerobic respiration – glycolysis, TCAcycle, and ETS occur in a sequential and orderly pathway.
(b) NADH produced during glycolysis enters into mitochondria to undergo oxidative phosphorylation.
(c) Glucose molecule is assumed to be the only substrate and no other molecule enters the pathway at intermediate stages.
(d) The intermediates produced during respiration are not utilized in any other process.
Q.9. Discuss “The respiratory pathway is an amphibolic pathway.”
Ans. Respiration is a catabolic process because 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. Proteins are converted into amino acids which enter respiration after deamination.
Respiration is anabolic process because, acetyl CoA is withdrawn from respiratory pathway During synthesis of fatty acids. Respiratory substrates are also withdrawn from respiratory pathway in the synthesis of proteins. Therefore, respiration can be termed as amphibolic pathway as it involves both anabolism and catabolism.
Q.10. Define RQ. What is its value for fats?
Ans. RESPIRATORY QUOTIENT (RQ): It is the ratio of the volume of CO₂ evolved to the volume of O₂ consumed 2 during respiration. It depends on type of substrate used in respiration. RQ = 1 when carbohydrate is used as substrate. RQ is less than 1 for fats.
Q.11. What is oxidative phosphorylation
Ans. OXIDATIVE PHOSPHORYLATION:
(i) It is synthesis of ATP from oxidation of NADH and FADH₂.
(ii) Enzyme required is ATP synthase Complex V of ETC.
(iii) Oxidation of 1 NADH produces ATPs.
(iv) Oxidation of 1 FADH₂ produces ATPs.
Q.12. What is the significance of stepwise release of energy in respiration?
Ans. The significance of stepwise release of energy in respiration:
(i) There is stepwise release of chemical bond energy which can be easily trapped in production of ATP.
(ii) Energy wastage is reduced.
(iii) Various molecules produced during respiration are involved in other biochemical processes.
(iv) The respiratory rates can be controlled by enzymes involved at various steps.
