Questions - Answers
Very 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 required?
A: Energy is released in a series of 6 biological Oxidation steps during the process of respiration. This energy can not be used directly. So it is trapped and stored in the form of biological currency called ATP. Each ATP stores 7.6 K.Cal. of energy. ATP breaks and this energy is used in various functions of the cell where and when necessary.
2. Explain the term 'Energy Currency'. Which substance acts as energy currency in plants and animals?
A: Energy released in biological Oxidation steps of respiration is not fit to be utilised directly. So it is stored in a chemical energy units called 'Energy Currency' as it can be used like cash when and where necessary. ATP acts as energy currency in plants and animals.
3. Different substrates get Oxidised during respiration. How does RQ indicate which type of substrate i.e., carbohydrate fat or protein is getting Oxidised?
RQ = A/B
What do A and B stand for?
What type of substrates have RQ of 1, < 1, > 1?
A: RQ indicates the type of substrate based on the no. of CO2 molecules released per no.of O2 molecules absorbed during the respiration RQ = A/B .
A indicates the number of CO2 (molecules) released. B indicates the number of O2 (molecules) absorbed.
If RQ = 1, the substrate is carbohydrate (Glucose).
RQ < 1, the substrate may be fats or proteins.
RQ > 1, the substrate may be organic acid like Malic acid, Tartaric acid etc.
4. What is specific role of F0 − F1 particles in respiration?
A: F0 − F1 particles are present in the inner membrane of mitochondria. They are working form of Complex − V (ATP synthase). F0 is towards perimitochondrial space. F1 is protruded into matrix. H+ pass through F0 (Proton channel) and fall into F1 (smallest rotating machine). Protons loose energy which is used in the synthesis of ATP. Thus F1 is the site of ATP synthesis.
5. When does anaerobic respiration occur in man and Yeast?
A: Anaerobic respiration occurs in Yeast and man when Oxygen is not available.
6. Distinguish between obligate anaerobes and facultative anaerobes.
A: Anaerobic organisms, when Oxygen is available continue aerobic respiration are called facultative anaerobic organisms (facultative anaerobes).
e.g.: Anaerobes which die when Oxygen is available are called obligatory anaerobes.
7. Explain the economic importance of fermentation.
A: Fermentation results in the formation of economically useful products like alcohol. Acetic acid (Vinegar), Lactic acid and Butyric acid etc.
8. What is the common pathway for aerobic and anaerobic respirations? Where does it take place?
A: Glycolysis is the common pathway for aerobic respiration and anaerobic respiration. It occurs in Cytosol.
9. Why are mitochondria called as the power houses of the cell?
A: Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP (biological energy currency). Hence mitochondria are called power houses of the cell.
10. What is the reason for describing ATP synthesis in F0 − F1 particles of mitochondria as oxidative phosphorylation?
A: The energy released during the oxidation of reduced co - enzymes (in ETS) like NADH2 and FADH2 is used in the synthesis of ATP in F0 − F1 particles. So it is called oxidative phosphorylation.
11. Which substance is known as connecting link between Glycolysis and Krebs Cycle? How many Carbons does it have?
A: Acetyl Co A is the connecting link between Glycolysis Krebs Cycle. It has 2 Carbons.
12. What cellular organic substances are never used as respiratory substrates?
A: Pure proteins and fats are never used as respiratory substrates.
13. Why is the RQ of fats is less than that of Carbohydrates?
A: When carbohydrates are used as substrate in respiration, equal amount of CO2 and O2 are evolved and consumed respectively. So RQ is 1.
When fats are used as substrate in respiration less CO2 is evolved and more O2 is absorbed. So RQ is less than that of Carbohydrates (i.e. less than 1).
14. What is meant by 'Amphibolic pathway'?
A: Basically respiration is catabolic process. The intermediate compounds formed in it are also useful in Anabolism of several products.
e.g.: Pyruvic acid is useful in the synthesis of amino acids like Alanine. Acetyl Co A is used in the synthesis of hormones like Gibberllins and ABA. α − Keto glutaric acid is useful in the synthesis of Glutamine (Amino Acid). As Respiratory pathway is involved in Anabolism and Catabolism, it is considered as Amphibolic pathway.
15. Name the mobile electron carriers of the respiratory electron transport chain in the inner mitochondrial membrane.
A: Ubiquinone (UQ) and Cyt − C are mobile electron carriers.
16. What is the final acceptor of electrons in aerobic respiration? From which complex does it receive electrons?
A: Oxygen is the final acceptor of electrons in aerobic respiration. It receives electrons from Complex - IV.
17. Name the products respectively in aerobic glycolysis in skeletal muscle and anaerobic fermentation in Yeast.
A: Lactic acid, Ethanol.
Short Answer Type Questions
1. What is meant by the statement 'Aerobic respiration is more efficient'?
A: One molecule of Glucose produces 36 ATP in aerobic respiration. But it produces 2 ATP only in anaerobic respiration. So Aerobic respiration is more efficient.
2. Why is the respiratory pathway referred to as an amphibolic pathway.
A: Respiration is a catabolic process. Many of the intermediate compounds of it are diverted in the synthesis of other substances useful in growth.
For Example
1) Pyruvic acid is used in the synthesis of Lactic acid, Ethanol (through fermentation), Alanine (Amino acid).
2) Pyruvic acid shows phosphoroclastic cleavage to supply H+ and e− required in N2 fixation.
3) Acetyl Co A is used in the synthesis of hormones like Gibberellins, ABA, Carotenoids and Phytol of Chlorophyll.
4) α − Ketoglutaric acid is used in the synthesis of Glutamine and other amino acids. This is anabolic part of Respiration. So Respiration is also referred to as Amphibolic pathway.
3. The net gain of ATP for complete aerobic respiration of Glucose is 36. Explain.
A: The details of 36 net ATP produced in aerobic respiration are as follows
I Glycolysis (Cytosol)
Direct ATP formed in SLP = 2
ATP from 2 Cytosolic NADH2 through ETS = 4
II Oxidative decarboxylation (Mitochondrial matrix)
ATP from 2 NADH2 through ETS = 6
III Krebs Cycle (Mitochondrial matrix)
ATP from 6 NADH2 through ETS = 18
ATP from 2 FADH2 through ETS = 4
Direct ATP from SLP = 2
Total 
4. ATP produced during Glycolysis is a result of substrate level phosphorylation. Explain.
A: Substrate level Phosphorylation
It occurs in Pay off phase of Glycolysis as follows
The high energy phosphate on 1st Carbon is donated to ADP to produce ATP. It is called SLP because phosphorylation is coupled with the exergonic break down of high energy bond.
In the same way 2 more ATP are formed as follows
5. Do you know any step in Krebs Cycle where there is a substrate level phosphorylation? Explain.
A: Substrate level Phosphorylation occurs once during Krebs Cycle as follows
It is a step of Cleavage.
The Cleavage of thioester bond of Succinyl Co A (exergonic) is coupled with phosphorylation of an ADP or a GDP.
In animal cells GDP is converted to GTP. It is used to make ATP
GTP + ADP 
ATP + GDP
In plants ATP is directly formed.
6. When a substrate is being metabolised, why does not all the energy that is produced get released in one step? Instead it is released in multiple steps. What is the advantage of stepwise release of energy?
A: Respiration is an oxidative, catabolic process. The organic compounds which participate in it are called substrate. The substrate is a complex, macromolecule. The energy contained in them is released C - C bonds are broken. The energy is not released in a single step. Free Energy is released in multiple steps in a controlled manner and used in the synthesis of ATP.
The advantage of stepwise release of energy
As and when NADH2 or FADH2 (reduced co enzymes) are formed in a series of oxidation steps, they participate in ETS and produce ATP simultaneously.
7. Respiration requires O2. How did the first cells on the earth manage to servive in an atmosphere that lacked Oxygen?
A: The first cells on the earth had undergone anaerobic respiration because Oxygen was lacking in the atmosphere.
In anaerobic respiration 1 molecule of Glucose produces 2 ATP only. With this meagre amount they survived. So they showed poor growth.
8. The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration. Explain.
A. During aerobic respiration
Glucose undergoes 6 biological oxidations and produces 12 reduced co enzymes (2 Cytosolic NADH2 + 8 mitochondrial NADH2 + 2 FADH2). All of them participate in ETS as mitochondria are seen in aerobic conditions. They produce a total of 32 ATP. In addition to that 4 ATP are produced as a result of substrate level phosphorylation (2 in Glycolysis and 2 in Krebs Cycle). Thus a molecule of Glucose produces 36 ATP in aerobic respiration.
During Anaerobic respiration
Glucose undergoes one biological oxidation.
As it occurs in Cytosol completely, 2 NADH2 formed in this biological oxidation are wasted as there are no mitochondria. Thus a total of 2 ATP are only formed in anaerobic respiration (as a result of SLP).
9. RUBP Carboxylase, PEP case, Pyruvate dehydrogenase, ATP ase, Cytochrome oxidase, Hexokinase, Lactic dehydrogenase.
Select the enzymes from the above which are involved in
a) Photosynthesis
b) Respiration
c) Both photosynthesis and respiration
A: a) Photosynthesis
1) RuBP Carboxylase
It participates in Carboxylation of C3 Pathway.
2) PEP Case
It participates in Carboxylation of C4 Pathway.
b) Respiration
1) Pyruvate dehydrogenase
It participates in the oxidative decarboxylation of Pyruvic Acid.
2) Cytochrome oxidase
It participates in ETS as Complex - IV.
3) Hexokinase
It participates in Glycolysis during the conversion of Glucose to Glucose - 6 - Phosphate.
4) Lactic Dehydrogenase
It participates in Lactic acid fermentation.
c) Both in Photosynthesis and Respiration
1) ATPase
It is ATP synthase.
It acts as coupling factor in photosynthesis.
It acts as F0 − F1 particles in ETS of respiration.
10. How does a tree trunk exchange gases with environment although it lacks stomata?
A: The tree trunk exchanges gases with environment through lenticels. These are naked openings in the bark. They consist loosely packed, paired parenchymatous cells called complimentary cells. They have inter connections through intercellular spaces which provide network.
11. Write about 2 energy yielding reactions of Glycolysis.
A: The 2 energy yielding reactions of Glycolysis are
1) Dephosphorylation or substrate level phosphorylation.
This kind of ATP formation where a phosphate group is directly transferred from the substrate to ADP to form ATP is called substrate level phosphosphorylation.
12. Name the sites of Pyruvate synthesis. Also write the chemical reaction where in Pyruvate dehydrogenase acts as a catalyst.
A: Pyruvic acid is synthesised in 2 sites as follows
1) Glucose is converted to 2 molecules of Pyruvic acid in Cytosol during Glycolysis.
2) Malic acid is converted to Pyruvic acid in bundle sheath cells of C4 Plants by a process called oxidative decarboxylation.
3) Pyruvic acid is also formed from Amino acids when proteins are used as substrate in respiration. Pyruvic dehydrogenase acts as a catalyst during oxidative decarboxylation of Pyruvic acid. It occurs in mitochondrial matrix.
13. Mention the important series of events of aerobic respiration that occur in the matrix of mitochondrion as well as in the inner membrane of the mitochondrion.
A: 1) Pyruvic acid undergoes oxidative decarboxylation
2) Acetyl Co A participates in Krebs Cycle.
It undergoes 4 biological oxidations and 2 decarboxylations and forms
3 NADH2, 1 FADH2. One ATP is also formed in substrate level Phosphorylation.
The reduced Co enzymes formed in Cytosol and mitochondrial matrix participate in ETS which occurs inner mitochondrial membrane. They pass through a series of complex enzymes (I,
II, III, IV, V) and produce ATP. O2 is required in it.
14. The respiratory pathway is believed to be a catabolic pathway. However, the nature of TCA Cycle is amphibolic. Explain.
A: The intermediate compounds formed in Krebs Cycle (TCA Cycle) are diverted to anabolic phase also for synthesising Amino acids, proteins, pigments, hormones etc.
1) Acetyl Co A is used in the synthesis of Gibberellins, ABA (hormones).
2) Acetyl Co A is used in the synthesis of Carotenoids and Phytol of Chlorophyll pigment.
3) Acetyl Co A is also vitamin source (Pantothenic Acid).
4) Acetyl Co A is also used to synthesise fatty acids.
5) α − Ketoglutaric acid is the substrate in the synthesis of Glutamic acid and other amino acids.
6) Oxalo Acetic acid forms Aspartic acid (amino acid) by transamination.
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 2 applications of it.
A: a = 1, 3 − Bisphosphoglyceric acid
b = Phosphoenol pyruvic acid
c = Acetaldehyde
d = Ethyl alcohol
Brief explanation for the above process (Anaerobic respiration)
It occurs completely in Cytosol as follows
II Decarboxylation
II Reduction (Fermentation)
The above process is also applied in
1) Alcohol fermentation.
2) Lactic acid fermentation.
3) Acetic acid fermentation.
2. Explain Mitchel's Chemiosmosis in relation to Oxidative Phosphorylation.
A: 12 reduced co - enzymes formed in Cytol and mitochondrial matrix undergo oxidation in the inner membrane.
Each reduced co - enzyme releases one pair of energetic e-. Thus 12 pairs of energetic e- are released. These e- were acquired by NAD+ and FAD in biological oxidation have great mobility potential. The energy of e- is used to transport H+ from mitochondrial matrix to perimitochondrial space (PMS). Pair of e- from each mitochondrial NADH2 can shift 10+ from matrix to perimitochondrial space.
So 8 mitochondrial NADH2 can shift a total of 80 H+ Pair of e− from each FADH2 can shift 6+ only. So 2 FADH2 can shift 12 H+ Pair of e− from Cytosolic NADH2 can also shift 6 H+ only. So 2 Cytosolic NADH2 can shift 12 H+. As a result 104 H+ are shifted from mitochondrial matrix to PMS. H+ concentration gradient is established between PMS and matrix. H+ concentration is more in PMS and less in matrix. Inner membrane is impermeable to protons. So return of H+ is prevented. Acc. to Peter Mitchel's Chemiosmotic model, the energy present with H+ is used to synthesise ATP when they return from PMS to matrix through F0 − F1 particles.
F0 − F1 particles connect PMS and matrix. F0 acts as H+ channel and present towards PMS. F1 protrudes into matrix.
When H+ moves through F0 energy is released. This energy rotates the F1 particle (smallest rotatory machine). Some of this energy is used in ATP synthesis. As ATP formation is linked with oxidation of reduced co enzymes. It is also called Oxidative Phosphorylation.
Each Mit − NADH2 can produce 3 ATP (1 H+ is wasted) as energy of 3 H+ is required to produce 1 ATP. Cyt NADH2 and FADH2 can produce 2 ATP each.
3. Give the schematic representation of Glycolysis.
A: Glycolysis is common to Aerobic and Anaerobic respiration. It occurs in Cytosol. All the enzymes required for Glycolysis are present in Cytosol. It is also called Embden, Meyerhof and Paranas pathway or Hexose diphosphate pathway or Core respiration.
One Glucose produces 2 Pyruvic Acids (end products). 2 NADH2 and 2 ATP are also formed. Glucose undergoes 1 biological oxidation. Neither Oxygen is taken nor CO2 is released. It occurs as follows
4. What are the main steps in aerobic respiration? Where does it take place?
A: Aerobic respiration has 4 main steps.
1) Glycolysis - It occurs in Cytosol.
2) Oxidative decarboxylation.
3) Krebs Cycle.
4) Electron Transport System -It takes place in mitochondria.
5. Give the schematic representation of an overall view of Krebs Cycle.
A: It occurs in mitochondrial matrix. Complete oxidation of the substrate occurs in it. Oxygen is not taken but CO2 is released. As complete oxidation involves several chemical reactions which occur in a cyclic form and it was discovered by Krebs, it is called Krebs Cycle. It is also called as Tricarboxylic Acid Cycle or Citric Acid Cycle or Organic Acid Cycle or Central metabolic pathway and some times as even Amphibolic pathway. All the enzymes required for Krebs
Cycle are present in mitochondrial matrix except succinate dehydrogenase
which is present in the inner membrane.
The following are formed in Krebs Cycle for 1 Glucose
NADH2 = 6
FADH2 = 2
Direct ATP = 2
6 H2O are required
7. a) Distinguish Aerobic respiration and Anaerobic respiration.
8. Name the products respectively in aerobic glycolysis in skeletal muscle and anaerobic fermentation in Yeast.
A: Lactic acid, Ethanol.
9. If a person is feeling dizzy, glucose or fruit juice is given immediately but not a cheese sandwich, which might have more energy. Why?
A: Glucose gives energy in less time. Cheese sandwich has more energy but it takes more time.
10. In a way green plants and Cyanobacteria have synthesised all the food on earth. Comment.
A: The phototrophic, green, autotrophs are green plants and Cyanobacteria. They prepare carbohydrates (Glucose). All the other organisms (animals including man) depend on the plants either directly and indirectly. Thus they prepare the food for all on the earth.
