NCERT Exemplar Class 11 Biology Solutions Respiration in Plants
Multiple Choice Questions
1. The ultimate electron acceptor of respiration in an aerobic organism is
(a) cytochrome (b) oxygen
(c) hydrogen (d) glucose.
Solution. (b): The electron transport chain catalyses an electron flow from NADH (FADH2) to oxygen, which is the final electron acceptor of the respiratory process. It accepts a pair of electron and combines with hydrogen atom to form water molecule
2.Phosphorylation of glucose during glycolysis is catalysed by
Solution.(c): During glycolysis, glucose is phosphorylated to glucose 6-phosphate by ATP in the presence of enzyme hexokinase or glucokinase and Mg2+ as follows:
3.Pyruvic acid, the key product of glycolysis can have many metabolic fates. Under aerobic condition it forms
(a) lactic acid
(b) C02+ H20
(c) acetyl CoA + C02
(d) ethanol+ C02.
4.Electron Transport System (ETS) is located in mitochondrial
(a) outer membrane
(b) inter membrane space
(c) inner membrane
Solution.(c) : An electron transport system (ETS) or electron transport chain (ETC) is a series of coenzymes and cytochromes that take part in the passage of electrons from one carrier to another and to its ultimate acceptor. The various components of ETS are arranged in five kinds of complexes, arranged in a definite sequence in the inner mitochondrial
5.Which of the following exhibits the highest rate of respiration?
(a) Growing shoot apex
(b) Germinating seed
(c) Root tip
(d) Leaf bud
Solution. (b): Different tissues and organs respire at different rates. A useful rule of thumb is that the greater the overall metabolic activity of a given tissue, the higher is its respiration rate. Germinating seeds exhibit the highest rate of respiration. Developing buds usually show very high rates of respiration and respiration rates of vegetative tissues usually decrease from the point of growth to more differentiated regions. When a plant tissue has reached maturity, its respiration rate will either remain roughly constant or decrease slowly as the tissue ages and ultimately senescences.
6.Choose the correct statement:
(a) Pyruvate is formed in the mitochondrial matrix.
(b) During the conversion of succinyl CoA to succinic acid a molecule of ATP is synthesised.
(c) Oxygen is vital in respiration for removal of hydrogen.
(d) There is complete breakdown of glucose in fermentation.
7.Mitochondria are called powerhouses of the cell. Which of the following observations support this statement?
(a) Mitochondria synthesise ATP.
(b) Mitochondria have a double membrane.
(c) The enzymes of the Krebs’ cycle and the cytochromes are found in mitochondria.
(d) Mitochondria are found in almost all plant and animal cells.
Solution.(a): Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called power houses of the cell.
8.The end product of oxidative phosphorylation is
(a) NADH (b) Oxygen
(c) ADP (d) ATP + H20.
Solution.(d) : Oxidative phosphorylation is the transfer of electrons to oxygen to form H20 in the mitochondrial electron transport chain that is coupled to ATP synthesis from ADP and inorganic phosphate by the ATP synthase.
9.Match the following and choose the correct option from those given below.
Column A Column B
A.Molecular oxygen i. a-ketoglutaric acid
B.Electron acceptor ii. hydrogen acceptor
C.Pyruvate dehydrogenase iii. cytochrome c
D.Decarboxylation iv. acetyl Co A
(a) A-ii, B-iii, C-iv, D-i
(b) A-iii, B-iv, C-ii, D-i
(c) A-ii, B-i, C-iii, D-iv
(d) A-iv, B-iii, C-i, D-ii
Short Answer Type Questions
1.Energy is released during the oxidation of compounds in respiration. How is this energy stored and released as and when it is needed?
Solution.Energy is stored as bond energy of ATP.
2.Explain the term “Energy Currency”. Which substance acts as energy currency in plants and animals?
Solution.Energy currency is a substance which can pick up, store as well as release small packets of energy for running cellular machinery. ATP is the energy currency in both plants and animals.
3.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?
What do A and B stand for?
What type of substrates have R.Q. of 1,<1 or >1 ?
Solution. In RQ, A denotes C02 being released while B is 02 being consumed by unit mass of substrate. The ratio or quotient indicates the type of substrate being consumed in respiration.
R.Q. of 1 indicates aerobic respiration with carbohydrate as substrate.
RQ of < 1 (less than unity) occurs when protein or fat is being oxidised aerobically. RQ of > 1 (more than unity) is found in aerobic breakdown of organic acids.
4.F0-F1 particles participate in the synthesis of
Solution. F0-F1particles participate in the synthesis of ATP.
5.When does anaerobic respiration occur in man and yeast?
Solution. In man, anaerobic respiration occurs during heavy exercise which results in oxygen deficiency. Muscles do not get sufficient oxygen supply and pyruvic acid is reduced to lactic acid by enzyme lactate dehydrogenase. In yeast, anaerobic respiration occurs when oxygen is not available. Pyruvate gets . converted into the ethanol by enzymes pyruvate decarboxylase and alcohol dehydrogenase.
6.Which of the following will release more energy on oxidation? Arrange them in ascending order,
(a) Igmoffat (b) 1 gm of protein
(c) 1 gm of glucose
(d) 0.5 g of protein + 0.5g glucose
Solution.On oxidation 1 gm of fat releases 9.45 Kcal of energy, 1 gm of protein releases 5.65 Kcal of energy, and 1 gm of glucose releases 4.1 Kcal of energy.
0.5 g of protein + 0.5g of glucose release 2.825 Kcal + 2.05 K cal = 4.875 Kcal of energy.
The arrangement of amount of energy released in ascending order is : 1 gm of glucose < 0.5 gm of protein + 0.5 gm of glucose < 1 gm of protein < 1 gm of fat.
7.The product of aerobic glycolysis in skeletal
muscle and anaerobic fermentation in yeast are respectively__________and__________
Solution. The product of aerobic glycolysis in skeletal muscle and anaerobic fermentation in yeast are respectively pyruvic acid and
C2H5OH + co2.
Short Answer Type Questions
1.If a person is feeling dizzy, glucose or fruit juice is given immediately but not a cheese sandwich, which might have more energy. Explain.
Solution. Glucose or fruit juice is an immediate source of energy as it gets absorbed quickly whereas cheese sandwich requires time for digestion and absorption. Sick person requires immediate energy supply, so glucose or fruit juices are given for instant energy instead of cheese sandwich which has more energy than glucose or fruit juice.
2.What is meant by the statement “aerobic respiration is more efficient”?
Solution. Aerobic respiration is more efficient means it produces more energy as compared to anaerobic respiration.In aerobic respiration organic food is completely oxidised with the help of oxygen (as terminal oxidant) into carbon dioxide, water and 686 Kcal of energy is liberated per gm mole of glucose.
On the other hand, anaerobic respiration is incomplete break-down of organic substrate without using oxygen as an oxidant. In anaerobic respiration 59 Kcal of energy is liberated per mole of glucose.
3.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.
4.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?
Solution. Anaerobic respiration is a survival mechanism in aerobic organisms. Aerobic respiration occurs in normal conditions in human beings. Whenever, there is deficiency of oxygen a switchover from aerobic to anaerobic respiration takes place. During strenuous or heavy exercises muscles demand too much energy (ATP) and it consume much more oxygen to produce that energy. This increased consumption leads to oxygen deficiency and the muscle cells begin to make lactic acid by anaerobic respiration to fulfill their energy needs.
plants, when if the soil gets waterlogged, then plants obtain their energy through anaerobic respiration.
5.Oxygen is an essential requirement for aerobic respiration but it enters the respiratory process at the end. Discuss.
Solution. If Aerobic respiration is stepwise catabolic process of complete oxidation of organic food into carbon dioxide and water with oxygen acting as terminal oxidant. This is possible only if respiratory substrate is degraded step ¬wise enzymatically with the help of oxygen. Aerobic respiration requires oxygen in order to generate ATP. Oxygen is employed in the end to oxidise protons and produces water. So, oxygen acts as the final acceptor.
6.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
(i) Step-wise oxidative breakdown
(ii)Organic substances (used as substrates).
Solution. (i) Stepwise oxidative breakdown means release of small amount of energy so that same can be trapped and stored for later use. Aerobic respiration consists of three steps- glvcolvsis Krebs terminal oxidation.
(ii) Organic substances means respiratory
substrates which are oxidised during
respiration to liberate energy inside the living
cells. The common respiratory substrates are carbohydrates, proteins, fats and organic
7.Comment on the statement – Respiration is an energy producing process but ATP is being used in some steps of the process.
Solution. Respiration is an energy producing process but ATP is being used in some steps of the process because respiratory substrate must be activated before it can be used in oxidative breakdown that release energy. Activation is carried out through phosphorylation of the substance with the help of ATP, viz, glucose/ fructose to fructose 1, 6 bi-phosphate.
8.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?
At step E, energy is being used up.
9. Why is respiratory pathway referred to as an amphibolic pathway? Explain.
Solution. The organic substances (i.c., carbohydrates, fats, proteins, etc) are broken down to release energy by the process of cellular respiration. The process is considered as a catabolism or a catabolic pathway. The breakdown of respiratory substrates provides carbon skeleton for the synthesis of a large number of other essential plant products, such as polysaccharides, proteins, fats, nucleic acids, pigments, cytochromes etc. Thus, the same respiratory process acts as catabolic pathway for respiratory substrates and also acts as anabolic pathway for the synthesis of various intermediary metabolic products and secondary metabolites. The respiratory pathway, therefore, acts both as catabolic as well as anabolic pathway. Thus, it is called as amphibolic pathway rather than as a catabolic pathway.
10.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.
Solution. ATP is known as energy currency of the cell. Two other energy carriers present are GTP (guanosine triphosphate) and CTP (cytidine triphosphate).
11 .ATP produced during glycolysis is a result of substrate level phosphorylation. Explain.
Solution. During glycolysis one of the two phosphates of diphosphoglycerate is linked by high energy bond. It can synthesise ATP and form 3-phosphoglycerate. The enzyme is phosphoglycerate kinase. The direct synthesis of ATP from metabolites is called substrate level phosphorylation, (i.e. instead of formation of ATP from oxidative phosphorylation via electron transport chain).
1,3- diphosphoglycerate + ADP
12. Do you know any step in theTCA cycle where there is substrate level phosphorylation. Which one?
Solution. In TCA cycle, coenzyme A split off from succinyl CoA and forms succinic acid. In this process one molecule of GTP (guanosine triphosphate) is formed which later gives one molecule of ATP. This reaction is also referred to as substrate level phosphorylation
13.ln a way green plants and cyanobacteria have synthesised all the food on the earth. Comment.
Solution. Cyanobacteria are unicellular prokaryotic organisms. They contain thylakoid (chromoplasm) and the membranes of thylakoid contains chlorophyll a, carotenes, xanthophylls, phycocyanin, allophycocyanin and phycoerythrin.
These pigments enable them to manufacture food for themselves and aquatic animals. Green plants are multicellular organisms
capable of making food by using C02 , H20 and light energy in special cell organelles called chloroplast. So, bacteria and green plants make food for living organisms on earth.
14. 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?
Solution. A single step release of large amount of energy will be harmful to the cell as most of it will remain unutilised and would cause damage to cellular organisation.
Step-wise release of small amount of energy is useful as:
1. It can be trapped and stored for later use.
2.There will be little wastage. ‘
3.Process of energy release can be controlled as per requirement.
4.It produces a number of intermediates which are used for synthesis of several types of substances.
15. Respiration requires 02. How did the first cells on the earth manage to survive in an atmosphere that lacked 02?
Solution. Anaerobic type of respiration does not require oxygen. The first cells evolved on earth in a reducing environment free of oxygen. They survived on anaerobic mode of respiration.
16.lt is known that red muscle fibres in animals can work for longer periods of time continuously. How is this possible?
Solution. Red muscle fibres are contain a dark red and 02 storing and transporting pigment called myoglobin. Myoglobin binds and stores oxygen as oxymyoglobin in the red fibres. Oxymyoglobin releases oxygen for utilisation during muscle contraction. These fibres contain more mitochondria and less sarcoplasmic reticulum. So they work for longer periods of time.
17.The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration. Explain.
Solution. In aerobic respiration, complete oxidation of respiratory substrate produces a number of reduced coenzymes. They are used in formation of ATP (3 for each NADH2 and 2 for each FADH2.). This is in addition to substrate level ATP synthesis. In anaerobic respiration there is only substrate level ATP synthesis. Reduced coenzymes are not given out (the ones formed in glycolysis are utilised in formation of end product). Therefore, the number of ATP synthesised in aerobic respiration (38 ATP/glucose) is much higher as compared to number of ATP produced in anaerobic respiration (2 ATP/glucose).
18 .RuBP carboxylase, PEPcase, Pyruvate dehydrogenase, ATPase, Cytochrome oxidase, Hexokinase, Lactate dehydrogenase. Select/ choose enzymes from the list above which are involved in
(c) Both in photosynthesis and respiration
Solution.(a) RuBP carboxylase and PEPcase are involved in photosynthesis.
(b) Pyruvate dehydrogenase, cytochrome oxidase and hexokinase are involved in respiration.
(c) ATPase is involved both in photosyn-thesis and respiration.
19. How does a tree trunk exchange gases with the environment although it lacks stomata?
Solution. The old tree trunk is covered by dead woody tissue called cork. Lenticels are aerating pores present in the bark of the trunk, which take part in exchange of gases between the trunk and the outside air. It is filled up by loosely arranged thin walled rounded and suberised or unsuberised cells called complementary cells. They enclose intercellular spaces for gaseous exchange.
20. Write two energy yielding reactions of glycolysis.
Solution. Two energy yielding reactions of glycolysis are as follows:
(i) 1, 3-biphosphoglycerate + ADP
(ii)Phosphoenol pyruvate + ADP
21 .Name the site (s) of pyruvate synthesis. Also, write the chemical reaction wherein pyruvic acid dehydrogenase acts as a catalyst.
Solution. The site of pyruvate synthesis is cytoplasm. It is end product of the glycolysis. The reaction where pyruvic acid dehydrogenase acts as a catalyst is the link reaction or gateway step which occur inside mitochondria. Here pyruvate undergoes oxidative . decarboxylation (removal of hydrogen and C02) in the presence of CoA.
Pyruvate + CoA +NAD+
22.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.
Solution. (a) Krebs’ cycle occurs in the matrix of mitochondria. Events of aerobic respiration that occur in the matrix of the mitochondrion are as follows:
1.Oxidation of pyruvate to Acetyl-CoA:
Pyruvate + NAD+ + CoA
2.Formation of citrate:
3.Formation of isocitrate:
4.Formation of a-ketoglutarate or oxidative decarboxylation of isocitrate:
5.Oxidative decarboxylation of a-ketoglu-tarate:
6.Substrate level ATP/ GTP synthesis:
7.Hydration of fumarate:
8.Oxidation of malate:
Oxaloacetate + NAD(P)H + H+
(b) Events of aerobic respiration that occurs in the inner mitochondrial membrane are as follows:
(i) Oxidation of succinate :
(ii)Electron transport from NADH2 and FADH2 to oxygen
(iii)ATP synthesis (oxidative phosphorylation)
23.Respiratory pathway is believed to be a catabolic pathway. However, nature of TCA cycle is amphibolic. Explain.
Solution. Refer Answer 9.
Long Answer Type Questions
1.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.
a = Glyceraldehyde 3-phosphate
b = Phosphoenol pyruvic acid
c = Ethanol
d = Lactic acid
The given metabolic pathway in figure is anaerobic respiration or fermentation. Anaerobic respiration is an enzyme mediated energy liberating catabolic process of step-wise but incomplete breakdown of organic substrate without using oxygen as an oxidant. Energy is liberated during breaking of bonds between various types of atoms. The common products of anaerobic respiration are C02, ethyl alcohol and lactic acid.
(i) Alcoholic fermentation : It takes place in two steps:
It produces alcohol from pyruvic acid and releases carbon dioxide.
(ii) Lactic acid fermentation : It takes place in a single step
Pyruvic acid + NADH
It produces lactic acid from pyruvate and does not release carbon dioxide. Application of anaerobic respiration are as follows:
(i) It has important role in brewing (Saccharomyces cerevisiae), baking, vinegar and milk industries (Streptococcus lactis). Vinegar is produced by fermentation of sugars in the presence of acetic acid bacteria (Acetobacter aceti).
(ii) Production of industrial alcohols and organic acids like citric acid and malic acid.
2.Given below is a diagram showing ATP synthesis during aerobic respiration, replace the symbols A, B, C, D and E by appropriate terms given in the box.
F1, particle. Pi, 2H+, Inner mitochondrial membrane, ATP, F0 particle, ADP
A = ATP
B = Fi particle
C = Pi
D = 2H+
E = Inner mitochondrial membrane
3.Oxygen is critical for aerobic respiration. Explain its role with respect to ETS.
Solution. The oxidation of glucose starts with glycolysis in cytoplasm, then followed by Krebs’ cycle in matrix of mitochondria and finally electron transport chain (ETC) in inner mitochondrial membrane. The requirement of oxygen is at the end of ETC. An electron transport chain or system is a series of coenzymes arid cytochromes that take part in passage of electrons from a chemical to its ultimate acceptor. At the end of electron transport chain the electrons are given to oxygen. At the same time
oxygen accepts hydrogen ions to form water. This happens in the matrix, on the surface of the inner membrane. This is the only stage at which oxygen is used in cell respiration. If oxygen is not available, electron flow along the electron transport chain stops and NADH + H+ cannot be reconverted to NAD+. Supplies of NAD+ in the mitochondrion run out and the link reaction and Krebs’ cycle cannot continue. Glycolysis can continue because conversion of pyruvate into lactate or ethanol and carbon dioxide produces as much NAD+ as is used in glycolysis. Whereas aerobic respiration gives a yield of about 38 ATP molecules per glucose, glycolysis produces only two. Oxygen thus greatly increases the ATP yield. The figure (below) shows the electron transport chain and the role of oxygen as terminal electron acceptor.
4.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.
Solution. The assumption that we undertake in making the respiratory balance sheet are as follows:
(i) Respiratory substrate is glucose
(ii)There is sequential pathway i.e. glycolysis, in cytoplasm, TCA cycle in mitochondrial matrix- and ETS in inner mitochondrial membrane.
(iii)NADH synthesised in glycolysis enters into ETC for phosphorylation.
(iv)None of the intermediates in the pathway are utilised to synthesise any other compound.
These assumptions are not valid for a living system because of the following reasons:
(i) Glycolysis, TCA and ETC work simultaneously and do not take place one after the other.
(ii)ATP is utilised when needed.
(iii)Rate of enzyme actions are controlled by multiple means.
Comparison between fermentation and aerobic respiration in this context is as follows:
(i) Fermentation is partial breakdown of glucose whereas aerobic respiration is complete breakdown of glucose.
(ii)Net gain of only 2 ATP in fermentation whereas in aerobic respiration 38 ATP is produced.
5.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.
Solution. Glycolysis (Gk. Glycos-sugar, lysis-breaking) is the sequence of reactions or pathway by which glucose is degraded anaerobically to form pyruvic acid. Glycolysis was discovered by three German scientists Embden, Meyerhof and Parnas, so also called EMP pathway. It is divided into two phases-preparatory phase and an pay off phase. In the preparatory phase, breakdown of glucose and low energy phosphorylation occurs, and energy is expended. In the oxidative phase high energy phosphate bonds are formed and energy is released. Glycolysis occur in the cytoplasm of
the cell and is present in all living organisms. End product of glycolysis is two molecules of pyruvic acid. During aerobic respiration, the pyruvic acid enters Kerbs’ cycle and finally electron transport chain. So it produces 38 ATP molecules. During anaerobic respiration, it produces lactic acid or ethyl alcohol and produces 2ATP molecules.