Respiration in Plants Class 11 Biology Exam Questions

Please refer to Respiration in Plants Class 11 Biology Exam Questions provided below. These questions and answers for Class 11 Biology have been designed based on the past trend of questions and important topics in your class 11 Biology books. You should go through all Class 11 Biology Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 11 Biology Exam Questions Respiration in Plants

Class 11 Biology students should read and understand the important questions and answers provided below for Respiration in Plants which will help them to understand all important and difficult topics.

Very Short Answer Type Questions:

Question. Different substrates get oxidised during respiration. How does Respiratory Quotient (RQ) indicate which type of substrate, i.e., carbohydrate, fat or protein is getting oxidised?
R.Q. = A/B
What do A and B stand for?
What type of substrates have R.Q. of 1, < 1 or > 1?
Ans. The ratio of CO₂ evolved and consumption of O₂ in respiration is called the Respiratory
Quotient (RQ)or respiratory ratio.

Respiration in Plants Class 11 Biology Exam Questions

Substrates like carbohydrates have RQ =1 during, aerobic respiration.
Proteins and fats have RQ of < 1 and it occurs during germination of seeds.
Substrates like organic acids have RQ of > 1 under aerobic conditions.

Question. F₀ – F₁ particles participate in the synthesis of ……… .
Ans. F₀−F₁ particles present in the inner mitochondrial membrane are involved in the synthesis of ATP (Adenosine Triphosphate), the energy currency of the cell.

Question. Energy is released during the oxidation of compounds in respiration. How is this energy stored and released as and when it is needed?
Ans. Complex organic food molecules such as sugars, fats and proteins are rich sources of energy for cells because much of the energy used to form these molecules is stored within the chemical bonds that hold them together. The cells release the stored energy through a series of oxidation reactions.
During each oxidation reaction involved in food breakdown, the product of reaction has a lower energy content than the donor molecule. At the same time, electron acceptor molecules capture some of the energy lost during oxidation and store it for later use.
Cells convert the energy from oxidation reactions to energy-rich molecules such as ATP which can be used throught the cell to power metabolism and construct new cellular components.

Question. When does anaerobic respiration occur in man and yeast?
Ans. (a) In animals anaerobic respiration occurs in the situation of deficiency of oxygen during heavy exercise when pyruvic acid is reduced to lactic acid by the enzyme lactate dehydrogenase.
(b) In yeast, the incomplete oxidation of glucose occurs under anaerobic conditions, where pyruvic acid is converted to CO₂ and ethanol by the action of enzyme pyruvic acid decarboxylase and alcohol dehydrogenase.

Question. Which of the following will release more energy on oxidation? Arrange them in ascending order.
(a) 1 gm of fat
(b) 1 gm of protein
(c) 1 gm of glucose
(d) 0.5 gm of protein + 0.5 gm glucose
Ans. The ascending order of substrate that will release more energy on oxidation will be as follows
1 gm protein < 0.5gm In protein < 1 gm glucose < 1gm fat +0.5 gm glucose

Question. Explain the term ‘energy currency’. Which substance acts as energy currency in plants and animals?
Ans. The term energy currency refers to that molecule which provides energy for cellular activities, whenever required. ATP is termed as energy currency because the energy is present in the form of high energy bonds of ATP. Other energy yielding molecules are GTP, CTP, UTP, etc.

The conversion of ATP to ADP yields about 7.3 kcal/mol of energy. This is the energy source in a variety of biological processes occurring in both plants and animals.
Justification for the term ‘energy currency’ for ATP can be given as
(i) Store small packets of energy as soon as it is available thus, minimising its wastage.
(ii) Can make energy available to a distant location in cell away from where the site it is produced.
(iii) Can carry out heavy work/activity by continuosly supplying large amount of energy through its accumulation at one place.

Question. The product of aerobic glycolysis in skeletal muscle and anaerobic fermentation in yeast are respectively ……… and ……… .
Ans. The product of aerobic glycolysis in skeletal muscles is pyruvic acid while in anaerobic fermentation in yeast ethanol and CO₂ are produced.

Short Answer Type Questions:

Question. Pyruvic acid is the end product of glycolysis. What are the three metabolic fates of pyruvic acid under aerobic and anaerobic conditions? Write in the space provided in the diagram.

Ans. The three metabolic products formed under aerobic and anaerobic conditions are (i) Lactic acid (ii) Ethanol (iii) Acetyl Co -A
Lactic acid is formed by the oxidation of pyruvic acid in under anaerobic condition in skeletal muscles.
Ethanol is formed by the oxidation of pyruvic acid in yeast under anaerobic condition.
Acetyl Co-A is formed by the oxidation of pyruvic acid that take place within the mitochondria under aerobic condition.

Question. The figure given below shows the steps in glycolysis. Fill in the missing steps A, B, C, D and also indicate whether ATP is being used up or released at step E?

Ans. Process of glycolysis is summarised as follow

Question. What is meant by the statement ‘aerobic respiration is more efficient’?
Ans. In the process of aerobic respiration, a single molecule of glucose can yield up to 36 ATP molecules. However, in fermentation or anaerobic respiration there is net gain of only 2 molecules of ATP from each glucose molecule, which is comparatively much less than that of aerobic respiration.
Hence, aerobic respiration is more efficient process.

Question. Oxygen is an essential requirement for aerobic respiration but it enters the respiratory process at the end? Discuss.
Ans. Aerobic respiration requires oxygen in order to generate ATP. Oxygen is strongly electronegative element and acts as final acceptor in respiratory process.
It pulls e⁻ (electrons) that energy from the electron transport chain ETC and take up protons from medium to form water.
O₂ enters in the respiratory process at the end, though it’s presence is vital. It drives the process of aerobic respiration by removing hydrogen from the system. Thus, acting as final hydrogen acceptor.
The energy is produced by the process of oxidative phosphorylation, utilising the energy of exidation reduction reactions.

Question. We commonly call ATP as the energy currency of the cell. Can you think of some other energy carriers present in a cell? Name any two.
Ans. An energy carrier is a highly specialised molecule that transfers, recieves and stores energy within the cell. This energy is then used to facilitate the chemical reactions within the cell. The three major types of energy carriers are ATP, NADPH and NADH.

Question. Respiratory pathway is believed to be a catabolic pathway. However, nature of TCA cycle is amphibolic. Explain.
Ans. Living cells obtain energy through respiration. It is the process of generating energy in the form of ATP molecules by breaking down food molecules like glucose, fats, etc.
The process starts with glycolysis which occurs in cytoplasm producing pyruvic acid. It is then converted to acetyl Co-A, which enters mitochondrial matrix. This initiates the tricarboxylic acid cycle.

This cycle is said to be amphibolic because many intermediate compounds formed in this cycle act as precursors for biosynthesis of many important biological molecules, i.e., co-enzymes, vitamins, hormones. Besides this, many molecules, i.e., fatty acids, aminoacids, co-enzymes etc, can enter this cycle directly.
Acetyl Co-A is related to synthesis and breakdown of fatty acids, steroids, carotenoids terpenes and aromatic compounds. a- ketoglutarate and oxaloacetate are row materials for synthesis of amino acids like glutamate and aspartate and also pyrimidines and alkaloids.
Succinyl forms pyrroole compunds like cytochrome and chlorophyll.
So, it is the cycle where both breakdown and synthesis reactions keep on going simultaneously. the following figure shows interrelationship among netabolic pathway showing respiration mediated break down of different organic molecule.

Question. Why is respiratory pathway referred to as an amphibolic pathway?
Ans. Glucose is the favourite sulphate for respiration as carbohydrates are first converted into glucose. Prior to used for respiration. Fats are acetyl CO-A are broken down into glycerol and fatty acid which is further degraded into acetyl Co-A, while protein is degraded into, smaller units anino acids.
Respiratory process involves the breaking down of substrate is catabolic proceses.
Sometime the fatty acid is required them synthesis of it occurs by withdrawing acetly Co-A.
This synthesising phase is the anabolic process.
Thus, respiratory pathway involves the catabolic process (break down) and anabolic pathway synthesis of molecules using respiratory intermediates frant link, it is called as an amphibolic pathway.

Question. In a way green plants and cyanobacteria have synthesised all the food on the earth. Comment.
Ans. Cyanobacteria are unicellular prokaryotic organisms. Besides, some primitive cellular cell organelles, they have photosynthetic lamellae where photosynthetic pigments are present. There are chlorophyll-a c, phycocyanin and phycoerythrin.
These coloured pigments impart typical blue green colour to the bacteria and enable them to manufacture food for themselves and aquatic animals. Green plants are multicellular organisms capable of making food by using CO₂ , H₂O and light energy in special cell organelles called chloroplast.
So, bacteria and green plants make food for living organisms on earth.

Question. RuBP carboxylase, PEPcase, pyruvate dehydrogenase, ATPase, cytochrome oxidase, hexokinase, lactate dehydrogenase. Select/choose enzymes from the list above which are involved in
(a) Photosynthesis (b) Respiration
(c) Both in photosynthesis and respiration
Ans. RuBP Carboxylase This is a part of dark reaction of photosynthesis. It catalyses the fixing of CO₂ in C₃ cycle.
PEPcase This is a part of photosynthesis of C4 plants. It catalyses the reaction of fixing of C₂O to form first stable product oxaloacetate. 4 carbon compound.
Pyruvate dehydrogenase It is involved in aerobic respiration and catalyses the reaction of formation of acetylCo-A from pyruvic acid. It requires the participation of NAD and Co-enzyme-A.

ATPase It is a part of both respiration and photosynthesis. Both these processes uses electron transport chain and associated proton pump and ATP synthase as a key part of process. ETC uses the energy to pump hydrogen ions across a membrane.
The protons flows back through ATP synthase, driving the production of ATP.
Cytochrome Oxidase This is involved in both respiration and photosynthesis. It is an electron carrier in the electron transport chain.
Hexokinase This enzyme is also involved in, respiration. In glycolysis, it catalyses the first reaction, i.e., formation of glucose -6- phosphate from glucose molecule. It uses one ATP molecule which transfers PO4 group to glucose molecules.

Lactate Dehydrogenase
This enzyme is involved in anaerobic respiration in bacteria Lactobacillus.
Pyruvic acid formed at the end of glycolysis is converted to lactic acid by homo-fermentative lactic acid bacteria. Hydrogen from NADH molecule is transferred to pyruvate is transferred to pyruvate molecule lactic acid molecule leading formation of acid.

Question. When a substrate is being metabolised, why does not all the energy that is produced get released in one step. It is released in multiple steps.
What is the advantage of step-wise release?
Ans. The process of aerobic respiration is divided into four phases-glycolysis, TCA cycle, ETS and oxidative phosphorylation. The process of respiration and production of ATP in each phase takes place in a step-wise manner.
The product of one pathway forms the substrate of the other pathway and these substrates enter or withdrawn from the pathway according to the necessity ATP gets utilised wherever required and enzymatic rates are generally controlled. Thus, the step-wise released of energy makes the system more efficient is extracting and storing energy.

Question. Name the site(s) of pyruvate synthesis. Also, write the chemical reaction wherein pyruvic acid dehydrogenase acts as a catalyst.
Ans. Pyruvate is synthesised in cytoplasm of the cell by the process of glycolysis. 1 molecule of glucose forms 2 molecules of pyruvate through a series of reactions.
Pyruvic acid dehydrogenase catalyses the reaction in which pyruvate forms acetyl Co-A. It requires NAD+, Co-enzyme A and Mg²⁺ ions for its activity. The reaction is as follows

Question. ATP produced during glycolysis is a result of substrate level phosphorylation. Explain.
Ans. Substrate-level phosphorylation is a type of metabolic reaction that results in the formation of Adenosine Triphosphate (ATP) or Guanosine Triphosphate (GTP) by the direct transfer and donation of a phosphoryl (PO ) 3 group to Adenosine Diphosphate (ADP) or Guanosine Diphosphate (GDP) from a phosphorylated reactive intermediate.

In glycolysis substrate level phosphorylation occurs in following two reactions (i) 2 molecules of 1, 3-diphosphoglyceric acid react with 2 molecules of ADP to form 2 molecules of 3-phosphoglyceric acid and 2 molecules of ATP .

Question. 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?
Ans. Aerobic respiration occurs in normal conditions in human beings. Under intense conditions such as excercises heavy, muscles demand too much energy (ATP) and consume much more oxygen to produce that energy.
This high consumption leads to oxygen scarcity and the muscle cells begin to make lactic acid by anaerobic respiration to fulfill their energetic needs. Similarly, yeast cells under deficient conditions of oxygen carry out anaerobic respiration, forming ethyl alcohol and CO₂.

Question. If a person is feeling dizzy, glucose or fruit juice is given immediately but not a cheese sandwich, which might have more energy. Explain.
Ans. The glucose as absorbed and reaches blood, giving instant energy. Whereas, cheese sandwich will require time for digestion, and absorption. Sick person requires immediate energy supply, so glucose or fruit juices contains glucose are given to them.

Question. The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration. Explain.
Ans. The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration is as given

Question. How does a tree trunk exchange gases with the environment although it lacks stomata?
Ans. The old tree trunk is covered by dead woody tissue called cork. The epidermal layers of such tree get ruptured and outer cortical cells are loosely arranged. These structures are called as lenticels.

Question. Respiration is an energy releasing and enzymatically controlled catabolic process which involves a step-wise oxidative breakdown of organic substances inside living cells. In this statement about respiration explain the meaning of
(a) Step-wise oxidative breakdown
(b) Organic substances (used as substrates).
Ans. (a) Respiration is a stepwise oxidation of organic molecules in a cell involving main three steps.
(i) Glycolysis (ii) Krebs’ cycle (iii) Electron transport chain Glucose passes through series of enzymatically controlled reactions and is finally converted into H₂O + ATP CO₂.
(b) Organic substances are the molecules normally found in living systems. They are usually composed of carbon atoms in rings or long chains to which other atoms such as hydrogen, oxygen and nitrogen are attached. e.g., glucose, fatty acids, amino acids etc.
These molecules burnt as substrate to produce energy. Respiration of glucose and fatty acids is called floating respiration and respiration of protein and amino acids are called protoplasmic respiration.

Question. Respiration requires O₂. How did the first cells on the earth manage to survive in an atmosphere that lacked O₂?
Ans. Respiration always does not require O₂. There are organisms which respire even in absence of O₂ through anaerobic respiration.
The first cells of earth i.e., chemosynthetic bacteria are the primitive organisms of early life on earth. Obtained energy by breaking down inorganic molecules like H₂S, NO^–₂, etc.
e.g., chemosynthesis occured in sulphur bacteria in the following way
12H₂S + 6 CO₂ → C₆H₁₂O₆ + 6H₂O + 12S↓

Question. Mention the important series of events of aerobic respiration that occur in the matrix of the mitochondrion as well as one that take place in inner membrane of the mitochondrion.
Ans. Krebs’ cycle occurs in the matrix of mitochondria. It is depicted in the following series of reactions

Electron transport chain is carried out in the inner mitochondria membrane
The inner mitochondrial membrane is specific about possessing proton (H⁺) and electron (e⁻) acceptors in a particular sequence called electron transport chain. It has four enzyme complexes.
The electrons either follow the pathway of complexes I, III and IV or II, III and IV depending upon the substrates from Krebs’ cycle.
The transfer of electrons and hydrogen atoms takes place in the following way Complex I Consists of flavoproteins of NADH dehydrogenase (FP_N) of which FMN is the prosthetic group. Combined with the flavoprotein is non-heme iron of NADH dehydrogenase.
This complex spans inner mitochondrial membrane and is able to translocate protons across it from matrix side to outer side.
Complex II Consists of flavoprotein of succinate dehydrogenase, of which FAD is the prosthetic group. Combined with the flavoprotein is non-heme iron of succinate dehydrogenase.
Between complexes II and III is the mobile carrier coenzyme-Q (Co-Q) or ubiquinone (UQ).
Complex III Consists of cytochrome-b and cytochrome- c₁. Associated with cytochrome- b is non-heme iron of complex III. Between complexes III and IV is the mobile carrier cytochrome-c.
Complex IV Consists of cytochrome-a and cytochrome- a₃, and bound copper that are required for this complex reaction to occur. This cytochrome also called cytochrome oxidase, is the only electron carrier in which the heme iron has a free ligand that can react directly with molecular oxygen.

Thus, hydride ions are transferred from the substance to be oxidised to NAD+ . From NAD+ the hydrogen atoms are transferred to FMN of flavoprotein 1 (Fp’N). After FMN the hydrogen atom undergoes ionisation, i.e., it splits into an electron and a proton.
In further stages there is no longer a transfer of hydrogens but of electrons. The electron passes to co-enzyme- Q, and from co-enzyme Q to cytochromes- b, c₁,ca , and a₃. The proton is released free.
As the hydrogen atom or electron passes down by F₀-F₁ particle the chain, there is simultaneous oxidation of one coenzyme and reduction at another steps. Oxygen is able to diffuse indside the mitochondria.
It is converted to anionic form O₂⁻, combines with 2H⁺ and forms metabolic water reduced co-enzyme NADH+H+ helps in pushing out three pairs of H⁺ to outer chamber while FADH₂ sends two pairs of H+ to outer chamber.
Oxidative phosphorylation is the synthesis of energy rich ATP molecules, with the help of energy liberated during oxidation of reduced co-enzyme (NADH₂, FADH₂) produced in respiration. The enzyme required for this synthesis is called ATP synthase present in inner mitochondria membrane.
The following figures shows this process

Question. Comment on the statement respiration is an energy producing process but ATP is being used in some steps of the process.
Ans. Respiration is necessary catabolic process which occurs in stepwise to produce energy.
Whenever biological system requires energy it is provided by hydrolysis of ATP molecule.
When one ATP is hydrolysed to ADP + Pi, i.e., one phosphate bond is broken down, thus producing 73 kcal energy.
Thus, ATP is utilised only when it is required so as to maintain the respiratory balance sheet.

Question. Do you know any step in the TCA cycle where there is substrate level phosphorylation. Which one?
Ans. In an intermediate reaction of TCA cycle, succinyl Co-A is converted to succinic acid and one GTP molecule is synthesised through substrate level phosphorylation.

Question. It is known that red muscle fibres in animals can work for longer periods of time continuously. How is this possible?
Ans. There are basically two kinds of muscle fibers
(i) Red muscles (ii) White muscles
Red muscles work for a longer time continuously because
(i) These muscle fibres are dark red which is due to the presence of red haemoprotein called myoglobin. Myoglobin binds and stores oxygen as oxymyoglobin in the red fibres. Oxymyoglobin releases oxygen for utilisation during muscle contraction.
(ii) Mitochondria are more in number, hence they work for long periods of time.
(iii) Red muscles have less sarcoplasmic reticulum.
(iv) They carry out considerable aerobic oxidation without accumulating much lactic acid.
Thus, red muscle fibres can contract for a longer period without fatigue.
(v) These muscle fibres have slow rate of contraction for long periods.
e.g., extensor muscles of the human back.

Question. Write two energy yielding reactions of glycolysis.
Ans. The following figure shows the process of glycolysis, and sites for yielding energy during glycolysis

Thus, ATP is produced during degradation of 1,3 biphosphoglyceric acid into 3-phosphoglyceric acid and during degradation of 2-phosphoenol pyruvate into pyruvic acid.

Long Answer Type Questions:

Question. Oxygen is critical for aerobic respiration. Explain its role with respect to ETS.
Ans. Role of O₂ in Aerobic Respiration
The respiration of glucose starts with glycolysis in cytoplasm, followed by in Krebs’ cycle and finally Electron Transport Chain (ETC) in inner mitochondrial membrane. The requirement of O₂ is at the end of ETC.
Where, it acts as final hydrogen acceptor. O₂ is responsible for removing electrons from the system. If oxygen is not available, electrons could not be passed through the co-enzymes,
inturn proton pump will not be established and ATP will not be produced via oxidative phosphorylation. Thus Oxygen play a critical role in aerobic respiration in mitochondrial matrix.

Question. In the following flow chart, replace the symbols a, b, c and d with appropriate terms. Briefly explain the process and give any two application of it.

Ans. The metabolic pathway given in the figure is fermentation. The products marked as a, b, c and d represents
a—Glyceraldehyde 3 phosphate, b—Phosphoenol pyruvic acid c—Ethanol, d—Lactic acid

The fermentation is of two types
(i) Alcohol Fermentation in Yeast Fermentation is an incomplete oxidation of glucose under anaerobic condition. Alcohol fermentation in yeast occurs in 2 sets of reaction thus, converting pyruvic acid into ethanol and CO₂.
A. In the first step, pyruvic acid is decarboxylated (equation I), resulting in the formation of acetaldehyde and CO₂.

(ii) Lactic Acid Fermentation in Muscles
In animal tissue like muscles, during exercise, when oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is NADH+H+ which is reoxidised to NAD+ in the subsequent processes.
Two applications of fermentation process are (i) It helps in manufacture of ethyl alcohol.
(ii) It also helps in curdling of milk to make curd aided by bacteria Lactobacillus.

Question. Enumerate the assumptions that we undertake in making the respiratory balance sheet. Are these assumptions valid for a living system? Compare fermentation and aerobic respiration in this context.
Ans. The calculations of the net gain of ATP for every glucose molecule oxidised can be made on the following assumptions
(i) There is sequential pathway that follows, i.e., glycolysis, TCA cycle and ETS in cytoplasm, mitochondrial matrix and inner mitochondrial membrane respectively.
(ii) NADH, synthesised in glycolysis enters in to ETC for phosphorylation.
(iii) None of the intermediates in the pathway are utilised to synthesise any other compound.
(iv) Glucose forms respiratory substrate.
These assumptions are not valid for a living system because of following reasons
(i) These all pathways work simultaneously and do not take place one after the other.
(ii) ATP is utilised when needed.
(iii) Rate of enzyme actions is controlled by multiple means.
Comparisan between fermentation and aerobic respiration are as follows

Question. Give an account of glycolysis. Where does it occur? What are the end products? Trace the fate of these products in both aerobic and anaerobic respiration.
Ans. Glycolysis occurs in cytoplasm. One glucose molecule forms 2 pyruvic acid molecules.
In anaerobic conditions it forms 2 ATP and ethanol + water.
In aerobic conditions it form 36 ATP + water + CO₂. The steps of glycolysis are as follows

Question. Given below is a diagram showing ATP synthesis during aerobic respiration, replace the symbols A, B, C, D and E by appropriate terms as given below.
F₁, particle, formation of Pi, 2H+ , inner mitochondrial membrane, ATP, Fo particle, ADP.