NCERT
SOLUTIONS
CLASS - 11th
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Class : 11th
Subject : Biology
Chapter : 14
Chapter Name : Respiration in Plants
Q1 Differentiate between
(a) Respiraüon and Combustion
(b) Glycolysis and Krebs' cycle
(c) Aerobic respiration and Fermentation
Answer. (a) Respiration and combustion
(b) Glycolysis and Krebs' cycle
(c) Aerobic respiration and Fermentation
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Q2 What are respiratory substrates? Name the most common respiratory substrate.
Answer. 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.
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Q3 Give the schematic representation of glycolysis?
Answer.
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Q4 What are the main steps in aerobic respiration? Where does it take place?
Answer. The major steps in aerobic respiration and the sites where they occur are listed in the
given table.
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Q5 Give the schematic representation of an overall view of Krebs cycle.
Answer.
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Q6 Explain ETS.
Answer. ETS or electron transport system is located in the inner mitochondrial membrane. It helps
in releasing and utilizing the energy stored in NADH + H and F ADH . NADH + H , which is
+
2
+
formed during glycolysis and citric acid cycle, gets oxidized by NADH dehydrogenase (complex l).
The electrons so generated get transferred to ubiquinone through FMN. In a similar manner,
F ADH (complex II) generated during citric acid cycle gets transferred to ubiquinone. The
2
electrons from ubiquinone are received by cytochrome bcl (complex Ill) and further get transferred
to cytochrome c. The cytochrome c acts as a mobile carrier between complex Ill and cytochrome c
oxidase complex, containing cytochrome a and a3, along with copper centres (complex 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. 2 ATP molecules are produced by the
oxidation of one molecule of NADH. One molecule of F ADH , on oxidation, gives 3 ATP
2
molecules.
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Q7 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
(b) Glycolysis and Fermentation
(c) Glycolysis and Citric acid Cycle
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Q8 What are the assumptions made during the calculation of net gain of ATP?
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) 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.
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Q9 Discuss "The respiratory pathway is an amphibolic pathway."
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 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.
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Q10 De ne RQ. What is its value for fats?
Answer. Respiratory quotient (RQ) or respiratory ratio can be de ned 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 molecules of CO₂ are evolved. The RQ value for tripalmitin is 0.7.
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Q11 What is oxidative phosphorylation?
Answer. Oxidative phosphorylation is a process in which electrons are transferred from electron
donors to oxygen, which acts as electron acceptor. The oxidation-reduction reactions are involved
in the formation of proton gradient. The main role in oxidative phosphorylation is played by the
enzyme ATP synthase (complex V). This enzyme complex consists of FO and Fl components. The
Fl headpiece is a peripheral membrane protein complex and contains the site for ATP synthesis
from ADP and inorganic phosphate. FO component is a part of membrane protein complex, which
acts as a channel for crossing of the protons from inner mitochondrial membrane to the
mitochondrial matrix. For every two protons passing through FO-FI complex, synthesis of one ATP
molecule takes place.
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Q12 What is the signi cance of stepwise release of energy in respiration?
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 stepwise 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
pathway on necessity. ATP gets utilized wherever required and enzymatic rates are generally
controlled. Thus, the stepwise release of energy makes the system more ef cient in extracting and
storing energy.
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