Maharashtra Board Class 11 Biology Chapter 13 Respiration and Energy Transfer Solutions

Respiration And Energy Transfer Class 13 Exercise Question Answers Solutions Maharashtra Board

Class 11 Biology Chapter 13 Exercise Solutions Maharashtra Board

Biology Class 11 Chapter 13 Exercise Solutions

Exercise 1. Choose Correct Option

Question (A) The reactions of the TCA cycle occur in
(A) ribosomes
(B) grana
(C) mitochondria
(D) endoplasmic reticulum
Answer: (C) mitochondria
In simple words: The Tricarboxylic Acid (TCA) cycle, also known as the Krebs cycle, is a central metabolic pathway for energy production in aerobic organisms, and its reactions primarily take place within the mitochondrial matrix.

🎯 Exam Tip: Students should remember the cellular locations of major metabolic pathways as these are common factual questions in exams.

Question (B) In eukaryotes the complete oxidation of a molecule of glucose results in the net gain of
(A) 2 molecules of ATP
(B) 36 molecules of ATP
(C) 4 molecules of ATP
(D) 38 molecules of ATP
Answer: (D) 38 molecules of ATP
In simple words: Complete oxidation of one glucose molecule in eukaryotes yields a net total of 38 ATP molecules through glycolysis, the Krebs cycle, and oxidative phosphorylation.

🎯 Exam Tip: Quantities of ATP produced in different stages of respiration (glycolysis, oxidative phosphorylation) are frequently tested, so precise memorization is key.

Question (C) Which step of Krebs cycle operates substrate-level phosphorylation?
(A) x-ketoglutarate → succinyl CoA.
(B) Succinyl CoA → succinate
(C) Succinate → fumarate
(D) Fumarate → malate
Answer: (B) Succinyl CoA → succinate
In simple words: Substrate-level phosphorylation in the Krebs cycle occurs during the conversion of succinyl CoA to succinate, directly generating a molecule of GTP (which is equivalent to ATP).

🎯 Exam Tip: Identify the specific reactions within the Krebs cycle that produce ATP/GTP directly, as opposed to generating reducing equivalents like NADH and FADH2.

Exercise 2. Fill In The Blanks With Suitable Words

Question 1.
A. Acetyl CoA is formed from __________ and co-enzyme A.
B. In the prokaryotes __________ molecules of ATP are formed per molecule of glucose oxidised.
C. Glycolysis takes place in __________ .
D. \( \text{F}_1 \)- \( \text{F}_o \) particles participate in the synthesis of __________ .
E. During glycolysis __________ molecules of \( \text{NADH+H}^+ \) are formed.
Answer:
A. pyruvic acid
Β. 2/38
C. cytoplasm
D. ATP
E. 2
[Note: ii. In prokaryotes, during anaerobic respiration 2 ATPs are formed per glucose and 38 ATPs are formed during aerobic respiration.]
In simple words: This question tests fundamental knowledge about the initial and intermediate steps of respiration, including the formation of Acetyl CoA, ATP yield in prokaryotes, location of glycolysis, function of \( \text{F}_1 \)-\( \text{F}_o \) particles, and \( \text{NADH+H}^+ \) production in glycolysis.

🎯 Exam Tip: Memorize the key products, reactants, locations, and ATP/NADH yields for each stage of cellular respiration, including variations in prokaryotes and eukaryotes.

Exercise 3. Answer The Following Questions

Question (A) When and where does anaerobic respiration occur in man and yeast?
Answer:
1. In absence of oxygen, anaerobic respiration takes place in skeletal muscles of man during vigorous exercise.
2. Anaerobic respiration occurs in the cytoplasm of the yeast cell.
In simple words: Anaerobic respiration happens in human skeletal muscles during intense activity when oxygen is scarce, and it occurs in the cytoplasm of yeast cells.

🎯 Exam Tip: Understand the conditions and cellular locations for both aerobic and anaerobic respiration in different organisms, as well as their respective end products.

Question (B) Why is less energy produced during anaerobic respiration than in aerobic respiration?
Answer:
Anaerobic respiration produces less energy because:
1. Incomplete breakdown of respiratory substrate takes place.
2. Some of the products of anaerobic respiration can be oxidised further to release energy which shows that anaerobic respiration does not liberate the whole energy contained in the respiratory substrate.
3. \( \text{NADH}_2 \) does not produce ATP, as electron transport is absent.
4. Only 2 ATP molecules are generated from one molecule of glucose during anaerobic respiration.
In simple words: Anaerobic respiration yields less energy because the breakdown of the respiratory substrate is incomplete, and the electron transport system, which generates most ATP, is absent.

🎯 Exam Tip: Focus on the efficiency difference between aerobic and anaerobic respiration, specifically mentioning the incomplete breakdown of glucose and the absence of the electron transport chain in the latter.

Question (C) Which is the site for ETS in mitochondrial respiration?
Answer:
The inner mitochondrial membrane is the site for ETS in mitochondrial respiration.
In simple words: The Electron Transport System (ETS) in mitochondria is located on the inner mitochondrial membrane.

🎯 Exam Tip: Knowing the precise locations of key respiratory processes within the cell (e.g., inner mitochondrial membrane for ETS, cytoplasm for glycolysis) is vital for objective and short answer questions.

Question (D) Which compound is the terminal electron acceptor in aerobic respiration?
Answer:
Molecular oxygen is the terminal electron acceptor in aerobic respiration.
In simple words: In aerobic respiration, molecular oxygen acts as the final acceptor of electrons at the end of the electron transport chain.

🎯 Exam Tip: The role of oxygen as the terminal electron acceptor is a fundamental concept in aerobic respiration and a common exam question.

Question (E) What is RQ.? What is its value for fats?
Answer:
1. Respiratory quotient (R.Q.) or respiratory ratio is the ratio of volume of \( \text{CO}_2 \) released to the volume of \( \text{O}_2 \) consumed in respiration.
2. \( \text{R.Q.} = \frac{\text{Volume of CO}_2 \text{ released}}{\text{Volume of O}_2 \text{ consumed}} \)
In simple words: The Respiratory Quotient (RQ) indicates the ratio of carbon dioxide produced to oxygen consumed during respiration; for fats, its value is generally less than 1.

🎯 Exam Tip: Understand the definition of RQ and know the typical RQ values for different respiratory substrates (carbohydrates, fats, proteins) and their implications.

Question (F) What are respiratory substrates? Name the most common respiratory substrate.
Answer:
Respiratory substrates are the molecules that are oxidized during respiration to release energy which can be used for ATP synthesis. Carbohydrates, fats and proteins are the common respiratory substrate. Glucose is the most common respiratory substrate.
In simple words: Respiratory substrates are the energy-rich molecules, such as carbohydrates, fats, and proteins, that are broken down during respiration to produce ATP, with glucose being the most common.

🎯 Exam Tip: Define respiratory substrates and be able to list examples, emphasizing glucose as the primary one, is a basic but important concept.

Question (G) Write explanatory notes on:

Question (i) Glycolysis
Answer:
Glycolysis is a process where glucose is broken down into two molecules of pyruvic acid, hence called glycolysis (glucose-breaking). It is common to both aerobic and anaerobic respiration. It occurs in the cytoplasm of the cell. It involves ten steps. Glycolysis consists of two major phases:
1. Preparatory phase (1-5 steps).
2. Payoff phase (6-10 steps).
1. Preparatory phase:
a. In this phase, glucose is phosphorylated twice by using two ATP molecules and a molecule of fructose 1,6-bisphosphate is formed.
b. It is then cleaved into two molecules of glyceraldehyde-3-phosphate and dihydroxy acetone phosphate. These two molecules are 3-carbon carbohydrates (trioses) and are isomers of each other.
c. Dihydroxy acetone phosphate is isomerised to second molecule of glyceraldehyde-3-phosphate.
d. Therefore, two molecules of glyceraldehyde-3- phosphate are formed.
e. Preparatory phase of glycolysis ends.
2. Payoff phase:
a. In this phase, both molecules of glyceraldehyde-3-phosphate are converted to two molecules of 1,3- bisphoglycerate by oxidation and phosphorylation. Here, the phosphorylation is brought about by inorganic phosphate instead of ATP.
b. Both molecules of 1, 3-bisphosphoglycerate are converted into two molecules of pyruvic acid through series of reactions accompanied with release of energy. This released energy is used to produce ATP (4 molecules) by substrate-level phosphorylation.
In simple words: Glycolysis is the initial ten-step breakdown of glucose into two molecules of pyruvic acid, occurring in the cytoplasm and consisting of a preparatory phase that consumes ATP and a payoff phase that generates ATP and \( \text{NADH+H}^+ \).

🎯 Exam Tip: Be able to outline the key steps of glycolysis, distinguish between its preparatory and payoff phases, and recall its location and net energy yield.

Question (ii) Write explanatory notes on: Fermentation by yeast
Answer:
Alcoholic fermentation is a type of anaerobic respiration where the pyruvate is decarboxylated to acetaldehyde. The acetaldehyde is then reduced by \( \text{NADH+H}^+ \) to ethanol and Carbon dioxide. Since ethanol is produced during the process, it is termed alcoholic fermentation.
In simple words: Fermentation by yeast is an anaerobic process where pyruvate is converted into acetaldehyde, then reduced by \( \text{NADH+H}^+ \) to ethanol and \( \text{CO}_2 \).

🎯 Exam Tip: For fermentation, focus on the starting substrate, key intermediate, final products, and the specific role of \( \text{NADH+H}^+ \) in the process.

Question (iii) Write explanatory notes on: Electron transport chain
Answer:
1. \( \text{NADH}_2 \) and \( \text{FADH}_2 \) produced during glycolysis, connecting link reaction and Krebs cycle are oxidized with the help of various electron carriers and enzymes.
2. These carriers and enzymes are arranged on inner mitochondrial membrane in the form of various complexes as complex I, II, III, VI and V.
3. \( \text{NADH+H}^+ \) is oxidised by NADH dehydrogenase (complex I) and it's electrons are transferred to ubiquinone (coenzyme Q-CoQ) present on inner membrane of mitochondria. Reduced ubiquinone is called as ubiquinol.
4. \( \text{FADH}_2 \) is oxidised by complex II (Succinate dehydrogenase) and these electrons are also transferred to CoQ.
5. During oxidation of \( \text{NADH+H}^+ \) and \( \text{FADH}_2 \), electrons and protons are released but only electrons are canned forward whereas protons are released into outer chamber of mitochondria (intermembrane space).
6. Ubiquinol is oxidised by complex-III (Cytochrome bc1 complex) and it's electrons are transferred to cytochrome C. Cytochrome C is a small, iron-containing protein, loosely associated with inner membrane. It acts as a mobile electron carrier, transferring the electrons between complex III and IV.
7. Cytochrome C is oxidised by complex IV or cytochrome C oxidase consisting of cytochrome a and \( \text{a}_3 \). Electrons are transferred by this complex to the molecular oxygen. This is terminal oxidation.
8. Reduced molecular oxygen reacts with protons to form water molecule called as metabolic water.
9. Protons necessary for this are channelled from outer chamber of mitochondria into inner chamber by \( \text{F}_o \) part of oxysome (complex V) present in inner mitochondrial membrane.
10. This proton channelling by \( \text{F}_o \) is coupled to catalytic site of \( \text{F}_1 \) which catalyses the synthesis of ATP from ADP and inorganic phosphate. This is oxidative phosphorylation.
11. As transfer of protons is accompanied with synthesis of ATP, this process is named as 'Chemiosmosis' by Peter Mitchell.
Significance of ETS:
1. Major amount of energy is generated through ETS or terminal oxidation in the form of ATP molecules.
2. Per glucose molecule 38 ATP molecules are formed, out of which 34 ATP molecules are produced through ETS.
3. Oxidized coenzymes such as \( \text{NAD}^+ \) and \( \text{FAD} \) are regenerated from their reduced forms (\( \text{NADH+H}^+ \) and \( \text{FADH}_2 \)) for recycling.
4. In this process, energy is released in a controlled and stepwise manner to prevent any damage to the cell.
5. ETS produces water molecules.
In simple words: The Electron Transport Chain (ETC) is a series of protein complexes on the inner mitochondrial membrane that uses electrons from \( \text{NADH+H}^+ \) and \( \text{FADH}_2 \) to pump protons, creating a gradient that drives ATP synthesis through chemiosmosis, ultimately leading to terminal oxidation where oxygen accepts electrons to form water and generate significant energy.

🎯 Exam Tip: For the ETC, understand the sequence of electron carriers, the role of oxygen, the generation of the proton gradient, and how chemiosmosis links to ATP synthesis; mentioning Peter Mitchell is a bonus point.

Question (H) How are glycolysis, TCA cycle and electron transport chain-linked? Explain.
Answer:
Glycolysis, TCA cycle and electron transport chain are linked in the following manner:
1. The coenzymes are initially present in the form of \( \text{NAD}^+ \) and \( \text{FAD}^+ \) which latter get reduced to \( \text{NADH+H}^+ \) and \( \text{FADH+H}^+ \) by accepting the hydrogen from organic substrate during glycolysis, link reaction and Krebs cycle.
2. During glycolysis, glucose is oxidised to two molecules of pyruvic acid with net gain 2 molecules of \( \text{NADH+H}^+ \).
3. This pyruvic acid undergoes link reaction to form two molecules of acetyl CoA and two molecules of \( \text{NADH+H}^+ \).
4. Acetyl CoA, thus formed enters into the Krebs cycle and it gets completely oxidised to \( \text{CO}_2 \) and \( \text{H}_2\text{O} \); with a net gain of 6 \( \text{NADH+H}^+ \) and 2 \( \text{FADH+H}^+ \) are formed.
5. During ETS, reduced coenzymes are reoxidized to \( \text{NAD}^+ \) and \( \text{FAD}^+ \) with a net gain of 34 ATPs. The ATPs thus formed are used during glycolysis.
6. The oxidized \( \text{NAD}^+ \) and \( \text{FAD}^+ \) will again accept the hydrogen from organic substrate. Thus, reduced coenzymes are converted back to their oxidized forms by dehydrogenation to keep the process going.
In simple words: Glycolysis, the TCA cycle, and the electron transport chain are interconnected through the production and regeneration of coenzymes like \( \text{NADH+H}^+ \) and \( \text{FADH+H}^+ \), which carry electrons to the ETS for efficient ATP synthesis, linking all stages of aerobic respiration.

🎯 Exam Tip: Focus on how reduced coenzymes (\( \text{NADH+H}^+ \), \( \text{FADH}_2 \)) generated in glycolysis and the TCA cycle feed into the ETS, illustrating the sequential and integrated nature of these pathways.

Question (I) How would you demonstrate that yeast can respire both aerobically and anaerobically?
Answer:
Respiration in yeast can be demonstrated with the help of an experiment.
Anaerobic respiration in yeast:
1. A pinch of dry baker's yeast suspended in water containing 10ml of 10% glucose in a test tube (test tube A).
2. The surface of the liquid is covered with oil to prevent entry of air and the test tube is closed tightly with rubber stopper to prevent leakage.
3. One end of a short-bent glass tube is inserted through it to reach the air inside the tube.
4. Other end of the glass tube is connected by a polyethylene or rubber tubing to another bent glass tube fitted into a stopper.
5. The open end of the glass tube (delivery tube) is dipped into lime water containing in a test tube (Tube B).
6. Stoppers of both the tubes are fitted tightly to prevent leakage of gases. First test tube is placed in warm water (37° C-38° C) in a beaker.
7. Lime water gradually turns milky, indicating the evolution of carbon dioxide from the yeast preparation.
8. Level of the lime water in the delivery tube does not rise, showing that there is no decline in volume of gas in test tube A and consequently no utilization of oxygen by yeast. Preparation is stored for a day or two.
9. When we open the stopper of tube A we will notice a smell of alcohol indicating the formation of ethanol.
10. From this activity it may be inferred that yeast respires anaerobically to ferment glucose to ethanol and carbon dioxide.
Aerobic respiration in yeast: Experiment explained can be carried out for demonstrating aerobic respiration in yeast.
1. If the level of the lime water in the test tube B rises, indicating intake of oxygen, hence the level of volume of gas rises.
2. The preparation tube is stored for a day or two, if no smell of alcohol is noticed it indicates that the yeast respires aerobically.
In simple words: Yeast respiration can be demonstrated by setting up two experiments: one for anaerobic conditions (sealed tube with oil layer, \( \text{CO}_2 \) production, alcohol smell) and another for aerobic conditions (open to air, oxygen intake, no alcohol smell), allowing observation of different end products.

🎯 Exam Tip: When describing experiments, clearly state the setup, observations, and inferences for both aerobic and anaerobic conditions, highlighting the key indicators like \( \text{CO}_2 \) production, oxygen consumption, and product identification.

Question (J) What is the advantage of step wise energy release in respiration?
Answer:
In ETS energy is released in step wise manner to prevent damage of cells.
1. A stepwise release of the chemical bond energy facilitates the utilization of a relatively higher proportion of that energy in ATP synthesis.
2. Activities of enzymes for the different steps may be enhanced or inhibited by specific compounds. This provides a means of controlling the rate of the pathway and the energy output according to need of the cell.
3. The same pathway may be utilized for forming intermediates used in the synthesis of other biomolecules like amino acids.
In simple words: Stepwise energy release in respiration prevents cellular damage by releasing energy gradually, allows for more efficient ATP synthesis, provides regulatory control over the metabolic pathway, and generates intermediates for synthesizing other biomolecules.

🎯 Exam Tip: Emphasize the efficiency of energy capture and the cellular control mechanisms enabled by the gradual release of energy in respiration, rather than a single explosive release.

Question (K) Explain ETS.
Answer:
1. \( \text{NADH}_2 \) and \( \text{FADH}_2 \) produced during glycolysis, connecting link reaction and Krebs cycle are oxidized with the help of various electron carriers and enzymes.
2. These carriers and enzymes are arranged on inner mitochondrial membrane in the form of various complexes as complex I, II, III, VI and V.
3. \( \text{NADH+H}^+ \) is oxidised by NADH dehydrogenase (complex I) and it's electrons are transferred to ubiquinone (coenzyme Q-CoQ) present on inner membrane of mitochondria. Reduced ubiquinone is called as ubiquinol.
4. \( \text{FADH}_2 \) is oxidised by complex II (Succinate dehydrogenase) and these electrons are also transferred to CoQ.
5. During oxidation of \( \text{NADH+H}^+ \) and \( \text{FADH}_2 \), electrons and protons are released but only electrons are canned forward whereas protons are released into outer chamber of mitochondria (intermembrane space).
6. Ubiquinol is oxidised by complex-III (Cytochrome bc1 complex) and it's electrons are transferred to cytochrome C. Cytochrome C is a small, iron-containing protein, loosely associated with inner membrane. It acts as a mobile electron carrier, transferring the electrons between complex III and IV.
7. Cytochrome C is oxidised by complex IV or cytochrome C oxidase consisting of cytochrome a and \( \text{a}_3 \). Electrons are transferred by this complex to the molecular oxygen. This is terminal oxidation.
8. Reduced molecular oxygen reacts with protons to form water molecule called as metabolic water.
9. Protons necessary for this are channelled from outer chamber of mitochondria into inner chamber by \( \text{F}_o \) part of oxysome (complex V) present in inner mitochondrial membrane.
10. This proton channelling by \( \text{F}_o \) is coupled to catalytic site of \( \text{F}_1 \) which catalyses the synthesis of ATP from ADP and inorganic phosphate. This is oxidative phosphorylation.
11. As transfer of protons is accompanied with synthesis of ATP, this process is named as 'Chemiosmosis' by Peter Mitchell.
Significance of ETS:
1. Major amount of energy is generated through ETS or terminal oxidation in the form of ATP molecules.
2. Per glucose molecule 38 ATP molecules are formed, out of which 34 ATP molecules are produced through ETS.
3. Oxidized coenzymes such as \( \text{NAD}^+ \) and \( \text{FAD} \) are regenerated from their reduced forms (\( \text{NADH+H}^+ \) and \( \text{FADH}_2 \)) for recycling.
4. In this process, energy is released in a controlled and stepwise manner to prevent any damage to the cell.
5. ETS produces water molecules.
In simple words: The Electron Transport System (ETS) is where the energy from \( \text{NADH+H}^+ \) and \( \text{FADH}_2 \) is used to create a proton gradient across the inner mitochondrial membrane, driving the synthesis of most cellular ATP through oxidative phosphorylation, with oxygen acting as the final electron acceptor.

🎯 Exam Tip: A comprehensive explanation of ETS requires detailing the roles of electron carriers, proton pumping, chemiosmosis, and the final ATP production, along with its overall significance in energy generation.

Question (L) Discuss "The respiratory pathway is an amphibolic pathway”.
OR
Question (M) Why is Krebs cycle referred as amphibolic pathway?
Answer:
1. Respiration is considered as a catabolic process; however, it is not entirely correct in case of Krebs cycle.
2. Many reactions of Krebs cycle involve oxidation of acetyl CoA to release energy and \( \text{CO}_2 \).
3. However, the breakdown of respiratory substrates provides intermediates like a-ketoglutarate, oxaloacetate are used as precursors for synthesis of fatty acids, glutamic acid and aspartic acid respectively.
4. Thus, as the same respiratory process acts as catabolic as well as anabolic pathway for synthesis of various intermediate metabolic products, it is called amphibolic pathway.
In simple words: The Krebs cycle is considered amphibolic because it not only breaks down molecules (catabolic) to release energy but also provides intermediates for the synthesis of new biomolecules (anabolic), thus participating in both breakdown and buildup processes.

🎯 Exam Tip: To explain 'amphibolic pathway', clearly distinguish between catabolic (energy release, substrate breakdown) and anabolic (synthesis of precursors) roles of the Krebs cycle, providing examples for each.

Question (N) The common pathway for both aerobic and anaerobic respiration is
(A) Krebs cycle
(B) Glycolysis
(C) ETS
(D) Terminal oxidation
Answer: (B) Glycolysis
In simple words: Glycolysis is the initial metabolic pathway that breaks down glucose, and it is common to both aerobic and anaerobic respiration.

🎯 Exam Tip: Remember that glycolysis is the universal first step for glucose breakdown in almost all organisms, regardless of oxygen availability, making it common to both respiration types.

Exercise 4. Compare

Question (A) Photosynthesis and respiration.
Answer:

🎯 Exam Tip: When comparing photosynthesis and respiration, highlight their complementary nature, contrasting their energy flow (trapping vs. releasing), cellular locations, raw materials, and end products.

Question (B) Aerobic respiration and Anaerobic respiration
Answer:

🎯 Exam Tip: Key differentiators for aerobic and anaerobic respiration include oxygen requirement, completeness of glucose oxidation, ATP yield, and specific end products (e.g., \( \text{H}_2\text{O} \) vs. ethanol/lactic acid).

Exercise 5. Differentiate Between

Question (A) Respiration and combustion.
Answer:

🎯 Exam Tip: Focus on the controlled, biological, and stepwise nature of energy release in respiration, contrasting it with the rapid, uncontrolled, and often heat/light-producing nature of combustion.

Question (B) Distinguish between Glycolysis and Krebs cycle.
Answer:

🎯 Exam Tip: When distinguishing glycolysis and Krebs cycle, focus on their cellular location, oxygen dependence, linearity versus cyclicity, major products, and relative ATP yields.

Question (C) Aerobic respiration and fermentation.
Answer:

🎯 Exam Tip: Clearly state the oxygen requirement, the extent of food oxidation, the ATP yield, and the specific end products to effectively differentiate between aerobic respiration and fermentation.

Question 6. Identify the cycle given below. Correct it and fill in the blanks and write description of it in your own

ℹ️ चित्र व्याख्या (Diagram Explanation): सिनाइल-कोएंजाइम A, अल्फा-केटोग्लूटारेट, सक्सिनेट, फ्यूमरेट, मैलेट, और ऑक्सालोएसिटेट जैसे यौगिकों के माध्यम से एसिटाइल-कोएंजाइम A के ऑक्सीकरण को दर्शाने वाला क्रेब्स चक्र (या साइट्रिक एसिड चक्र) का एक योजनाबद्ध प्रतिनिधित्व। इसमें डीहाइड्रोजेनेशन, संघनन, जलयोजन, और ऑक्सीडेटिव डीकार्बोक्सीलेशन जैसे विभिन्न चरण और \( \text{NAD}^+ \), \( \text{NADH+H}^+ \), CoQ, GTP (ATP) और \( \text{CO}_2 \) जैसे प्रमुख अणु शामिल हैं, जो कोशिकीय श्वसन में ऊर्जा उत्पादन को उजागर करते हैं।
Answer:
1. Krebs cycle or citric acid cycle is the second phase of aerobic respiration which takes place in the matrix of the mitochondria.
2. The acetyl CoA formed during the link reaction undergoes aerobic oxidation.
3. This cycle serves a common oxidative pathway for carbohydrates, fats and proteins.
4. In mitochondria pyruvic acid is decarboxylated and the remaining 2-carbon fragment is combined with a molecule of coenzyme A to form acetyl-CoA.
5. This reaction is an oxidative decarboxylation process and produces \( \text{H}^+ \) ions and electrons along with carbon dioxide. During the process \( \text{NAD}^+ \) is reduced to \( \text{NADH+H}^+ \).
In simple words: The diagram illustrates the Krebs cycle, also known as the citric acid cycle, a mitochondrial process where acetyl CoA is completely oxidized, serving as a central pathway for energy generation from carbohydrates, fats, and proteins, while also producing reducing equivalents and intermediates.

🎯 Exam Tip: When analyzing such diagrams, be able to identify the cycle, name key intermediates, explain the main reactions (e.g., oxidation, decarboxylation), and state the inputs and outputs, particularly the formation of reducing equivalents and ATP.

11th Biology Digest Chapter 13 Respiration And Energy Transfer Intext Questions And Answers

Can You Recall? (Textbook Page No. 151)

Question (i) Which nutrients are used for energy production?
Answer: Nutrients like carbohydrates, fats and proteins are used for energy production.
In simple words: Nutrients such as carbohydrates, fats, and proteins are broken down by organisms to release energy.

🎯 Exam Tip: Understanding the primary energy sources is foundational for metabolism questions.

Question (ii) Why do organisms take up oxygen and release carbon dioxide?
Answer:
a. At cellular level, organisms require energy to carry out different metabolic activities.
b. The energy is made available by oxidizing/breaking the food.
Therefore, oxygen is required for aerobic organisms for breaking the food and carbon dioxide is released as a byproduct of oxidation.
In simple words: Organisms use oxygen to break down food and get energy for their life processes, releasing carbon dioxide as a waste product.

🎯 Exam Tip: Focus on the 'why' behind gas exchange, linking it directly to energy production and waste removal in cellular respiration.

Use Your Brainpower (Textbook Page No. 152)

Question. Why is glycolysis considered as biochemical proof of evolution?
Answer:
1. Glycolysis does not require oxygen. Hence it might have been used by earlier organisms for energy production, as there was no free oxygen in atmosphere of primitive earth.
2. Glycolysis is the first metabolic pathway, an ancient pathway which is common to both aerobic and anaerobic organisms.
3. All cells have glycolysis in their metabolic pathway.
4. Upto pyruvate the pathway is similar to all aerobic and anaerobic organisms. Later, the fate of pyruvic acid can be either CO2 or ethanol or lactic acid depending upon the type of organism.
5. Hence it is considered as a biochemical proof of evolution.
In simple words: Glycolysis is seen as evidence for evolution because it's a primitive, oxygen-independent pathway common to almost all life forms, suggesting it developed early in Earth's history before oxygen was abundant.

🎯 Exam Tip: Highlight the universality and oxygen-independent nature of glycolysis as key points for its evolutionary significance.

Use Your Brainpower (Textbook Page No. 152)

Question (i) What is role of Mg++, Zn++ in various steps of glycolysis?
Answer:
a. Mg++ and Zn++ are the cofactors that are tightly bound to enzymes and helps the enzymes to perform their functions.
b. They regulate the activity of the most important enzymes like Hexokinase, Phosphoffuctokinase, Triose phosphate dehydrogenase, Phosphoglycerate kinase, Enolase, Pyruvate kinase.
In simple words: Magnesium (Mg++) and Zinc (Zn++) act as cofactors, helping key enzymes in glycolysis function correctly and regulate the pathway.

🎯 Exam Tip: Remember that cofactors like metal ions are essential for enzyme activity in many metabolic pathways.

Question (ii) Why some reactions of glycolysis are reversible and some irreversible?
Answer:
Irreversible chemical reactions:
Some chemical reactions can occur in only one direction i.e. these reactions are irreversible reactions. The reactants can change to the products, but the products cannot change back to the reactants.
Reversible chemical reactions:
1. Some chemical reactions can occur in both directions i.e. these reactions are reversible reactions. In this case the reactants change to the products and the products can change back to the reactants, atleast under specific conditions.
2. Out of ten, four are irreversible reactions which involves the enzyme kinase that is required for phosphorylation reactions, these reactions involve large negative energy AG, hence the reactions are irreversible.
3. Other reversible reactions do not involve high negative energy hence are reversible.
In simple words: In glycolysis, some reactions are irreversible because they release a lot of energy, driven by enzymes like kinase, ensuring the pathway proceeds in one direction, while others are reversible with smaller energy changes.

🎯 Exam Tip: Focus on the role of enzymes and the energy change (large negative ΔG) as determinants for irreversibility in metabolic pathways.

Use Your Brainpower (Textbook Page No. 152)

Question. Why do athletes like sprinters have higher proportion of white muscle fibers?
Answer:
1. The white muscle fibres produce energy in a very short period of time that is required for fast and severe work. Thus, the energy becomes immediately available to the athletes.
2. On the other hand, the red muscle produce energy over a prolonged period of time, hence athletes have higher proportion of white muscle fibers.
In simple words: Sprinters have more white muscle fibers because these fibers provide quick bursts of energy for intense, short-duration activities, unlike red muscle fibers which are suited for endurance.

🎯 Exam Tip: Distinguish between white (fast-twitch) and red (slow-twitch) muscle fibers based on their energy production rates and suitability for different types of athletic performance.

Can You Recall? (Textbook Page No. 151)

Question. Which steps are involved in aerobic respiration?
Answer: It involves glycolysis, acetyl CoA formation (connecting link reaction), Krebs cycle, electron transfer chain reaction and terminal oxidation.
In simple words: Aerobic respiration includes glycolysis, the formation of acetyl CoA, the Krebs cycle, and the electron transport chain leading to terminal oxidation.

🎯 Exam Tip: Remember the sequence of events: Glycolysis - Link Reaction (Acetyl CoA) - Krebs Cycle - ETS - Terminal Oxidation.

Can You Recall? (Textbook Page No. 151)

Question. What is aerobic and anaerobic respiration?
Answer:
For anaerobic respiration: Anaerobic respiration is the cellular respiration that does not involve the atmospheric oxygen. It is also called as fermentation. It involves glycolysis where the product of glycolysis i.e. pyruvate is converted to either lactic acid or ethanol and for aerobic respiration.
1. Aerobic respiration occurs in the presence of free molecular oxygen during oxidation of glucose.
2. In this type of respiration, the glucose is completely oxidized to CO2 and H20 with release of large amount of energy. It involves glycolysis, acetyl CoA formation (connecting link reaction), Krebs cycle, electron transfer chain reaction and terminal oxidation.
In simple words: Aerobic respiration uses oxygen to fully break down glucose for a lot of energy, while anaerobic respiration occurs without oxygen, incompletely breaking down glucose and yielding less energy.

🎯 Exam Tip: The key difference is the presence (aerobic) or absence (anaerobic) of oxygen, affecting energy yield and end products.

Use Your Brainpower (Textbook Page No. 157)

Question. Do the plants breath like animals? If yes, how and why?
Answer:
1. Yes, plants breath like animals because they also require energy to carry out different metabolic activities. Hence, plants take up oxygen required for respiration and they also give out CO2.
2. Plants take care of their gas exchange needs. The stomata and lenticels are important for this purpose.
3. Leaves are well adapted for gaseous exchange during photosynthesis.
4. Large amount of gases is exchanged. In plants, each living cell is located quite close to the surface of the plants.
In simple words: Yes, plants breathe like animals, taking in oxygen and releasing carbon dioxide, because they also need energy for metabolic activities, using stomata and lenticels for gas exchange.

🎯 Exam Tip: Highlight that respiration is a universal process for energy in living cells, even in plants, though their mechanisms for gas exchange differ from animals.

Internet My Friend (Textbook Page No. 155)

Question. What is effect of carbon monoxide poisoning on cytochromes?
Answer:
1. At sub-cellular level, carbon monoxide is toxic for mitochondria.
2. It alters the mitochondrial respiratory chain at the cytochrome c oxidase level (complex IV of the mitochondrial respiratory chain) and causes inhibition of ETS.
3. This inhibition leads to the development of symptoms observed in acute CO poisoning, and in some diseases related to smoking.
4. These symptoms include headache, nausea, vomiting, dizziness, weakness, difficulty in concentration or confusion, visual changes, syncope, seizures, abdominal pain and muscle cramping.
In simple words: Carbon monoxide poisoning is toxic to mitochondria, specifically inhibiting cytochrome c oxidase (Complex IV) in the electron transport chain, which blocks cellular respiration and leads to various severe symptoms.

🎯 Exam Tip: Understand that CO directly interferes with the final step of the electron transport chain, preventing oxygen utilization and ATP production.

Can You Recall? (Textbook Page No. 151)

Question. Which is most preferred nutrient among carbohydrate, protein and fat for energy production? Why?
Answer:
1. The preferred nutrient is carbohydrate because it quickly supplies energy as compared to other nutrients.
2. Carbohydrates are easy to digest as compared to fats.
3. The RQ of carbohydrate is 1. Hence allows complete oxidation of food.
Thus, the preferred nutrient is carbohydrate.
In simple words: Carbohydrates are the preferred nutrient for energy because they provide quick energy, are easily digestible, and undergo complete oxidation (RQ = 1).

🎯 Exam Tip: Emphasize the speed of energy release and complete oxidation as key reasons for carbohydrates being the primary energy source.

Internet My Friend (Textbook Page No. 158)

Question. Calculate the RQ for different respiratory substrates using appropriate formula.
Answer:
The RQ for different respiratory substrates are:
1. Carbohydrates (R.Q. is 1)
When carbohydrates are used as substrate, equal volumes of CO2 and 02 are released and consumed respectively, thus its R.Q. is 1.
\( \text{C6 H12 O6} + \text{6O2} \implies \text{6 CO2} + \text{6H20} \)
\( \text{R.Q.} = \text{6C02} / \text{602} = \text{1.0} \)
2. Fats (R.Q. is less than 1)
Substrates like fats are poorer in oxygen than carbohydrates. Thus, more oxygen is utilized for its complete oxidation.
\( \text{2(C51 H98 06)} + \text{14502} \implies \text{102CO2} + \text{98H2O} + \text{Energy} \)
\( \text{R.Q.} = \text{C02/02} = \text{102} / \text{145} = \text{0.7} \)
3. Protein respiration (R.Q. is less than 1)
1. When proteins serve as respiratory substrate, they are first degraded to amino acids.
2. Then, amino acids are converted into various intermediates of carbohydrates.
3. However, amino acids have low proportion of O2 as compared to carbohydrates.
4. Thus, they require more O2 during their complete oxidation and value of R.Q. becomes less than 1.
5. In case of proteins, the R.Q. is approximately 0.9.
In simple words: The Respiratory Quotient (RQ) is calculated as the ratio of CO2 released to O2 consumed; for carbohydrates it's 1.0, for fats it's typically 0.7 (less than 1) due to higher oxygen demand, and for proteins it's approximately 0.9 (also less than 1).

🎯 Exam Tip: Remember the RQ values for the main substrate groups (carbohydrates=1, fats<1, proteins<1) and understand *why* they differ based on oxygen content.