CHSE Odisha Class 11 Biology Solutions Chapter 14 Respiration

Odisha State Board CHSE Odisha Class 11 Biology Solutions Chapter 14 Respiration Textbook Questions and Answers.

CHSE Odisha 11th Class Biology Chapter 14 Question Answer Respiration

Respiration Class 11 Questions and Answers CHSE Odisha

Very Short Answer Type Questions

Multiple choice questions:

Question 1.
The first reaction step in glycolysis, that produces ATP, is catalysed by the enzyme
(a) Hexaokinase
(b) Pyruvate kinase
(c) Phosphoglycerate kinase
(d) Phosphofructokinase
Answer:
(d) Phosphofructokinase

Question 2.
The reaction which links glycolysis with Krebs cycle is catalysed by
(a) Glutamate dehydrogenase
(b) Pyruvate dehydrogenase complex
(c) Citralilyase
(d) Pyruvate kinase
Answer:
(b) Pyruvate dehydrogenase complex

Question 3.
Which of the following respiratory substrates produces per mole the highest number of ATP molecules?
(a) Glucose
(b) Sucrose
(c) Strach
(d) Fatty acid
Answer:
(a) Glucose

Question 4.
The enzyme which splits 6-C compound to 3-C compound during glucolysis is
(a) fumarase
(b) aldolase
(c) ligase
(d) carboxylase.
Answer:
(b) aldolase

Question 5.
Glycolysis takes place in
(a) nucleus
(b) vacuole
(c) cytoplasm
(d) mitochondria
Answer:
(c) cytoplasm

Question 6.
The respiratory quotient, when carbohydrates are used as respiratory substrate, is
(a) 1.0
(b) 0.7
(c) 0.9
(d) 0.3
Answer:
(a) 1.0

Fill in the blanks:

Question 1.
Anaerobic respiration is often known as ……………. .
Answer:
Fermentation

Question 2.
The synthesis of ATP involving the direct transfer of phosphate group from a substrate molecule to ADP is called as ……………. .
Answer:
Substrate level phosphorylation

Question 3.
The formation of ethanol from pyrurate is catalysed by the enzymes ………… and alcohol dehydrogenase.
Answer:
Pyruvate decarboxylase

Question 4.
The reactions of Krebs cycle takes place inside …………… .
Answer:
Mitochondrial matrix

Short Answer Type Questions

Question 1.
Alcoholic fermentation.
Answer:
It occurs in fungi and some higher plants. The incomplete oxidation of glucose is achieved under anaerobic condition by a series of reactions in which pyruvic acid is converted to CO₂ and ethonol

Question 2.
Lactic acid fermentation
Answer:
It occurs in human’s muscles, bacteria, etc. Lactic acid is produced as an end product during the reduction of pyruvate by NADH₂ is oxidised to NAD⁺. This reaction is catalysed by lactic acid dehydrogenase, FMN proteins and Zn²⁺ions.

Question 3.
Substrate level phosphorylation
Answer:
The type of ATP synthesis involving the direct transfer of phosphate group from a substrate molecule to ADP to form ATP is called substrate level phosphorylation. It takes place during the following reactions
(i) When 1,3 bisphosphoglycerate is converted to 3-phosphoglycerate.
(ii) When phosphoenol pyruvate is converted to pyruvic acid.

Question 4.
Chemiosmotic hypothesis
Answer:
It was explained by Peter Mitchell in 1961 for which he was awarded the Noble prize in chemistry in 1978. It explains the molecular mechanism of ATP synthesis by suggesting that, the action of ATP synthase is coupled with proton gradient. It is the action of proton gradient that causes a proton motive force. This force allows ATP synthase to phosphorylate ADP and inorganic phosphate to ATP.

Question 5.
Respiratorory Quotient
Answer:
During aerobic respiration, O₂ is consumed and CO₂ is released. The ratio of the amount of CO₂ evolved to the amount of O₂ consumed in respiration is called respiratory quotient (RQ)

Amount of 02 consumed
The value of RQ depends upon the type of substrate used for respiration
RQ value of different substrates is as follows:
RQ = 1 for carbohydrates
RQ < 1 for fats = 0.7
RQ < 1 for proteins = 0.8 – 0.9

Question 6.
Oxidative phosphorylation.
Answer:
The formation of ATP molecules coupled to the transfer of electrons derived from the oxidation of organic compounds through the mitochondrial electron transport chain is called oxidative phosphorylation.

Long Answer Type Questions

Question 1.
Describe the reaction steps of glycolysis
Answer:
Glycolysis:
Glycolysis (Gr. Glycos-sugar, lysis-splitting), is a stepwise process by which one molecule of glucose (6C) breaks down into two molecules of pyruvic acid (3C).

The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof and J Parnas and is often referred as the EMP pathway. It is a common pathway in both aerobic and anaerobic modes of respiration. But in case of anaerobic organisms, it is the only process of respiration. Glycolysis occurs in the cytoplasm of the cell. During the process glucose gets partially oxidised. In plants, this glucose is derived from sucrose (end product of photosynthesis) or from storage carbohydrates.

During the course of process in plant sucrose is first converted into glucose and fructose by the action of invertase enzyme, after this, these two monosaccharides enter the glycolytic pathway.

Steps Involved in Glycolysis:
In glycolysis, a chain of 10 reactions, occur under the control of different enzymes. These reactions can be categorised in to preparatory (or investment) phase and pay off (energy conserving) phase.
It involves the following steps

Step I Phosphorylation of glucose occurs under the action of an enzyme hexokinase and Mg²⁺ that gives rise to glucose-6-phosphate by the utilisation of ATP.

Step II Isomerisation of this phosphorylated glucose-6-phosphate takes place to form fructose-6-phosphate with the help of an enzyme phosphohexose isomerase (reversible reaction).

Step III This fructose-6-phosphate is again phosphorylated by ATP in order to form fructose 1, 6-bisphosphate in the presence of an enzyme phosphofructokinase and Mg²⁺.
The steps of phosphorylation of glucose to fructose 1, 6-bisphosphate (i.e. from step 1 to 3) activates the sugar thus, preventing it from . getting out of the cell.

Step IV Splitting of fructose 1, 6-bisphosphate takes place into two triose phosphate molecules, i.e. dihydroxyacetone 3-phosphate and 3-phosphoglyceraldehyde (i.e. PGAL). This reaction is catalysed by an enzyme aldolase.

Step V Each molecule of PGAL removes two redox equivalents in the form of hydrogen atom and transfer them to a molecule of NAD⁺ (This NAD⁺ forms NADH + H⁺) and accepts inorganic phosphate (Pi) from phosphoric acid. This reaction in turn leads to the conversion to PGAL (which gets oxidised) to 1, 3-bisphosphoglycerate (BPGA) (reversible reaction).

Step VI 1, 3-bisphosphoglycerate is converted to 3-phosphoglycerate with the formation of ATP.
This reaction is catalysed by an enzyme phosphoglycerate kinase. It is also known as energy yielding process. The formation of ATP directly from metabolites constitutes substrate level phosphorylation (reversible reaction).

Step VII In this step, 3-phosphoglycerate is subsequendy isomerised to form 2-phosphoglycerate, catalysed by enzyme phosphoglyceromutase (reversible reaction).

Step VIII In the presence of enzyme enolase and Mg²⁺, with the loss of a water molecule, 2-phosphoglycerate is converted into Phosphoenol Pyruvate (PEP) (reversible reaction).

Step IX High energy phosphate group of Phosphoenol Pyruvate (PEP) is transferred to a molecule of ADP, by the action of enzyme pyruvate kinase in the presence of Mg²⁺ and K⁺. This in turn produces two molecules of pyruvic acid (pyruvate) and a molecule of ATP by substrate level phosphorylation. The pyruvic acid thus, produced is the key product of glycolysis.

Question 2.
Describe the metabolic fate of pyruvate.
Answer:
Metabolic Fate of Pyruvate:
Pyruvate is the end product of glycolysis. The sequence of reactions leading to the formation of pyruvate from glucose is the common pathway occurring during anaerobic and aerobic respiration. Depending upon the absence or presence of molecular oxygen and the cellular metabolic need, Pyruvate takes up different routes for its metabolism

Metabolic fate of pyruvate under aerobic and anaerobic conditions

In the absence of molecular oxygen, respiratory electron transport chain and oxidative phosphorylation can not function in the mitochondrion because molecular oxygen is the terminal electron acceptor for these two highly coordinated processes. As a result the oxidation of NADH to form NAD does not take place. NAD is available in limited amount in the cell. When whole NAD becomes reduced to NADH in the presence of NAD dependent glyceraldehyde 3-phosphate dehydrogenase, glycolysis can not continue to operate. Under the situation of unavailability of molecular oxygen,glycolysis is the main source of chemical energy (ATP) necessary for cell .survival.

Hence, NAD is required to regenerate or to proceed the glycolysis process. Different organisms and cell type can metabolise pyruvate by fermentation also.

Various microorganisms, bacteria, animals and plants are known to catabolise pyruvic acid into various organic compounds depending upon the specific enzymes they possess.

Some of these types are as follows
(i) During alcoholic fermentation, in fungi (e.g., yeast), and some higher plants, the incomplete oxidation of glucose is achieved under anaerobic condition-by a series of reactions in which pyruvic acid is converted to CO₂ and ethanol.
It is done under two steps
(a) Pyruvic acid is first decarboxylated to acetaldehyde formed in the presence of enzyme pyruvic acid decarboxylase.
CH₃CCOOH → CH₃CHO (Acetaldehyde) + CO₂

(b) This acetaldehyde is further reduced to ethyl alcohol or ethanol in the presence of enzyme, i.e. alcohol dehydrogenase.
CH₃CHO + NADH + H² → C₂H₅OH (Ethanol) + NAD⁺

(ii) During lactic acid fermentation occuring in muscles, organisms like some bacteria produce lactic acid as an end product from pyruvic acid.
During the reduction, the pyruvic acid produced in glycolysis is reduced by NADH₂ to form lactic acid, CO₂ is not produced and NADH₂ is oxidised to NAD⁺. This reaction is catalysed by a lactic acid dehydrogenase, FMN proteins and Zn²⁺ ions.

Major pathways of anaerobic respiration

Likewise, in case of animal cells also (such as muscles) during exercise, when there is inadequate amount of oxygen for cellular respiration, pyruvic acid is reduced to lactic acid in the presence of enzyme lactate dehydrogenase. Thus, in both the processes oxidation of reducing (NADH + H⁺) agent takes place.

Energy Yield in Fermentation:
In both alcoholic and lactic acid fermentation, the energy released is very less, i.e. not more than 7% of the energy is released from glucose and not all of it is trapped as high energy bonds of ATP.
Also, the fermentation processes are proved to be hazardous in nature because either acid or alcohol is produced on oxidation. Apart from this, yeasts may also poison themselves to death if the concentration of alcohol reaches about 13%.

Question 3.
Describe the reaction steps of Krebs cycle.
Answer:
Output of Krebs’ Cycle or Citric Acid Cycle:
During this cycle of reactions, 3 molecules of NAD⁺ are reduced to NADH + H⁺ , and one molecule of FAD⁺ is reduced to FADH₂. And also one molecule of ATP is reduced directly from GTP (by substrate level phosphorylation). For continuous oxidation of acetyl . Co-A, continued replenishment of oxaloacetic acid is necessary. In addition to this, regeneration of NAD⁺ and FAD⁺ from NADH and FADH₂, respectively are also required.
The summary equation for this phase of respiration is as follows

Till now, glucose has been broken down to release C02 and 8 molecules of NADH + H⁺, 2 FADH₂ are synthesised and just 2 molecules of ATP.

Importance of Citric Acid Cycle:
The citric acid cycle is important in the following ways
(i) This is the major pathway for the formation for ATP molecules.
(ii) Many intermediate compounds of this cycle are used in the synthesis of other biomolecules.

Question 4.
Describe the respiratory electron transport chain and explain the mechanism of ATP synthesis.
Answer:
Electron Transport System (ETS):
Electron Transport System (ETS) is the metabolic pathway through which the electron passes from one carrier to another. It occurs in the inner mitochondrial membrane.

Electron Transport System (ETS)

The electron transport system consists of four enzyme complexes, which are arranged in a series on the inner membrane of the mitochondria.
(i) Electrons from NADH produced in citric acid cycle are oxidised by NADH dehydrogenase (complex I) and are transferred to ubiquinone located within the inner membrane of the mitochondria.

(ii) Reducing equivalents are also received by ubiquinone via FADH₂ (complex II), generated during the oxidation of succinate in the citric acid cycle. This reduced ubiquinone (ubiquinol) is then oxidised with the electron transfer to cytochrome-c (small protein attached to the outer surface of the inner membrane). Now, via cytochrome-b, c₁ complex (complex III) cytochrome, acts as a mobile carrier for transfer of electrons between complex III and IV.

(iii) The (complex IV), known as cytochrome-c oxidase complex contains cytochromes-a, a₃ and two copper centres).

During the course of transfer, when’electrons pass from one carrier molecule to another (via complex I to IV) in the electron transport chain, they get coupled to ATP synthase (i.e. complex V) for the production of ATP from ADP and inorganic phosphate. The number of • ATP molecules synthesised depends on the nature of the electron donor.

One molecule of NADH on oxidation provides 3 molecules of ATP while one FADH₂ produces 2 molecules of ATP, because its redox potential is higher than NADH and thus, enters the ETS after bypassing the first site of phosphorylation. The electrons are finally accepted by oxygen having the highest redox potential in the series which along with H⁺ forms water.

Aerobic process of respiration takes place only in the presence of O₂, the role of O₂ is limited at the terminal stage of the process. Yet, the presence of oxygen is vital because it drives the whole process by removing hydrogen from the system.