Samacheer Kalvi 11th Bio Botany Solutions Chapter 14 Respiration

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Tamilnadu Samacheer Kalvi 11th Bio Botany Solutions Chapter 14 Respiration

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Samacheer Kalvi 11th Bio Botany Respiration Text Book Back Questions and Answers

Question 1.
The number of ATP molecules forme by complete oxidation of one molecule of pyruvic acid is
a) 12
b) 13
c) 14
d) 15
Answer:
d) 15

Question 2.
During oxidation of two molecules of cytosolic NADH + H⁺, number of ATP molecules produced in plants are:
(a) 3
(b) 4
(c) 6
(d) 8
Answer:
(c) 6

Question 3.
The compound which links glycolysis and Krebs cycle is
a) succinic acid
b) pyruvic acid
c) acetyl COA
d) citric acid
Answer:
c) acetyl COA

Question 4.
Assertion (A): Oxidative phosphorylation takes place during the electron transport chain in mitochondria.
Reason (R): Succinyl CoA is phosphorylated into succinic acid by substrate phosphorylation.
(a) A and R is correct. R is correct explanation of A
(b) A and R is correct but R is not the correct explanation of A
(c) A is correct but R is wrong
(d) A and R is wrong.
Answer:
(a) A and R is correct. R is correct explanation of A

Question 5.
Which of the following reaction is not involved in krebs cycle.
a) Shifiting of phosphate from 3C to 2C
b) Splitting of Fructose 1,6 bisphosphate into two molecules 3C compounds.
c) Dephosphorylation from the substrates.
d) All of these
Answer:
d) All of these

Question 6.
What are enzymes involved in phosphorylation and dephosphorylation reactions in EMP pathway?
Answer:
(i) Enzymes involved phosphorylation in EMP pathway:

• Hexokinase
• Phospho – fructokinase
• Glyceraldehyde – 3 – phosphate dehydrogenase

(ii) Enzymes involved in dephosphorylation in EMP pathway:

• Phosphoglycerate kinase
• Pyruvate kinase

Question 7.
The respiratory quotient is zero in succulent plants. Why?
Answer:
The respiratory quotient is zero in succulent plants like Opuntia, Bryophyllum carbohydrate are partially oxidised to organic to acid, particularly malic acid without the corresponding release of CO₂ but O₂ is consumed hence the RQ value will be zero
2 C₆H_12O6 + 3O₂ → 3C₄H₆0₅ + 3H₂O+ Energy
R.Q. of glucose in succulents \(=\frac{\text { Zero molecule of } \mathrm{CO}_{2}}{3 \text { molecules of } \mathrm{O}_{2}}\)
= 0 (zero)

Question 8.
Explain the reactions taking place in the mitochondrial inner membrane.
Answer:
In plants, an additional NADH dehydrogenase (External) complex is present on the outer surface of the inner membrane of mitochondria which can oxidise cytosolic NADH + H⁺. Ubiquinone (UQ) or Coenzyme Quinone (CoQ) is a small, lipid-soluble electron, proton carrier located within the inner membrane of mitochondria.

Question 9.
What is the name of an alternate way of glucose breakdown? Explain the process involved in it?
Answer:
During respiration breakdown of glucose in cytosol occurs both by glycolysis (about 2 / 3) as well as by oxidative pentose phosphate pathway (about 1 / 3). The pentose phosphate pathway was described by Warburg, Dickens, and Lipmann (1938). Hence, it is also called Warburg – Dickens – Lipmann pathway. It takes place in the cytoplasm of mature plant cells. It is an alternate way for the breakdown of glucose.

It is also known as Hexose monophosphate shunt (HMP Shunt) or Direct Oxidative Pathway. It consists of two phases, oxidative phase, and non – oxidative phase. The oxidative events convert six molecules of six carbon Glucose – 6 – phosphate to 6 molecules of five-carbon sugar Ribulose – 5 phosphates with loss of 6CO₂ molecules and generation of 12 NADPH + H⁺ (not NADH). The remaining reactions known as non – oxidative pathway, convert Ribulose – 5 – phosphate molecules to various intermediates such as Ribose – 5 – phosphate(5C), Xylulose – 5 – phosphate(5C), Glyceraldehyde – 3 – phosphate(3C), Sedoheptulose – 7 – Phosphate (7C), and Erythrose – 4 – phosphate (4C). Finally, five molecules of glucose – 6 – phosphate are regenerated. The overall reaction is:

The net result of complete oxidation of one glucose – 6 – phosphate yield 6CO₂ and 12 NADPH + H⁺. The oxidative pentose phosphate pathway is controlled by glucose – 6 – phosphate dehydrogenase enzyme which is inhibited by high ratio of NADPH to NADP⁺.

Question 10.
How will you calculate net products of one sucrose molecule upon complete oxidation during aerobic respiration as per recent view?
Answer:
Sucrose is a disaccharide it will convert into glucose and fructose. In glycolysis, both will give glyceraldehyde – 3 phosphates that undergo a further process of respiration to yield 36 ATP. So Net products of one sucrose molecule during aerobic respiration will yield 72 ATP.

Samacheer Kalvi 11th Bio Botany Respiration Additional Questions & Answers

I. Choose the correct answer (1 Mark)

Question 1.
Pepys (1966) coined the term ………………..
a) Glycolysis
b) Respiration
c) ATP
d) GTP
Answer:
b) Respiration

Question 2.
In floating respiration the substrates are:
(a) carbohydrate or protein
(b) carbohydrate or fat
(c) protein or fat
(d) none of the above
Answer:
(b) carbohydrate or fat

Question 3.
The amount of heat energy liberated during respiration is ……………….. KJ
a) 686
b) 2868
c) 8268
d) 8628
Answer:
b) 2868

Question 4.
The end product of glycolysis is:
(a) pyruvate
(b) ethanol
(c) malate
(d) succinate
Answer:
(a) pyruvate

Question 5.
It is a nuclear tide consist of a base adenine a pentose sugar – ribose and three phosphate groups called
a) FAD
b) NAD
c) FADH₂
d) ATP
Answer:
d) ATP

Question 6.
Which of the following is known as terminal oxidation:
(a) glycolysis
(b) electron transport chain
(c) Kreb’s cycle
(d) pyruvate oxidation
Answer:
(b) electron transport chain

Question 7.
The Reaction which is important in cellular respiration is
a) Respiration
b) Redox reaction
c) Oxidation
d) Reduction
Answer:
b) Redox reaction

Question 8.
Who was awarded the Nobel prize in 1953 for the discovery of the TCA cycle?
(a) Lipmann
(b) Hans Adolf Kreb
(c) Petermitchell
(d) Dickens
Answer:
(b) Hans Adolf Kreb

Question 9.
Which is the common stage for both aerobic and anaerobic respiration
a) preparatory phase
b) pay off phase
c) Electron transport system
d) Glycolysis
Answer:
d) Glycolysis

Question 10.
Electron transport system during aerobic respiration takes place in:
(a) cytoplasm
(b) mitochondria
(c) chloroplast
(d) Golgi apparatus
Answer:
(b) mitochondria

Question 11.
Two ATP molecules are consumed during this phase of Glycolysis
a) endergonic phase
b) Oxidative phase
c) Pay off phase
d) triose phase
Answer:
a) endergonic phase

Question 12.
In aerobic prokaryotes each molecule of glucose produces:
(a) 36 ATP
(b) 32 ATP
(c) 34 ATP
(d) 38 ATP
Answer:
(d) 38 ATP

Question 13.
Sir Hans Adolf Kreb was awarded Nobel prize in physiology in 1953 for the discovery of
a) Kreb cycle (or) TCA cycle
b) Glycolysis
c) ETC
d) Calvin Cycle
Answer:
a) Kreb cycle (or) TCA cycle

Question 14.
Respiratory quotient for oleic acid is:
(a) 0.69
(b) 0.71
(c) 0.80
(d) 0.36
Answer:
(b) 0.71

Question 15.
Which is act as metabolic sink and central role in intermediary metabolism
a) Calvin cycle
b) Glycolysic
c) Kreb cycle
d) Pebntose pathway
Answer:
c) Kreb cycle

Question 16.
The end products of mixed acid fermentation in Enterobacteriaceae are:
(a) lactic acid, ethanol, formic acid, CO₂ and H₂
(b) lactic acid, formic acid and CO₂
(c) lactic acid, ethanol, CO₂ and O₂
(d) ethanol, formic acid, CO₂ and H₂
Answer:
(a) lactic acid, ethanol, formic acid, CO₂ and H₂

Question 17.
Which is final common pathway for oxidation of fuel molecule like amino acid, fatty acid and Carbohydrate.
a) Calvin cycle
b) ETS system
c) Kreb cycle
d) Glycolysis
Answer:
c) Kreb cycle

Question 18.
Pentose phosphate pathway was described by:
(a) Pepys and Black man
(b) Kreb and Embden
(c) Warburg, Dickens and Lipmann
(d) Warburg and Pamas
Answer:
(c) Warburg, Dickens and Lipmann

Question 19.
Which is small lipid-soluble, electron-proton carrier located within the inner membrane of mitochondria?
a) Cytochrome
b) Ubiquinone
c) Phytochrome
d) Mitochondria
Answer:
b) Ubiquinone

Question 20.
In pentose phosphate pathway the glucose – 6 – phosphate dehydrogenase enzyme is inhibited by high ratio of:
(a) FADH to FAD
(b) glucose to glucose – 6 – phosphate
(c) NADPH to NADP
(d) GTPH to GTP
Answer:
(c) NADPH to NADP

Question 21.
Common steps of aerobic and anaerobic respiration takes place in
a) Entirely in Cytoplasm
b) Partialy in Cytoplasm
c) Mitochondrial Matrix
d) Paitialy in mitochondria
Answer:
a) Entirely in Cytoplasm

Question 22.
As per the recent view, when a glucose molecule is completely aerobically oxidised, the net yield of ATP in plant cell is:
(a) 38
(b) 36
(c) 30
(d) 32
Answer:
(c) 30

Question 23.
Identify from the following one which does not act as a respiratory substrate
a) Carbohydrate
b) Protein
c) Glucose
d) Minerals
Answer:
d) Minerals

Question 24.
The phenomenon of climacteric is present in:
(a) banana
(b) coconut
(c) cauliflower
(d) brinjal
Answer:
(a) banana

Question 25.
Pyruvic acid produced by glycolysis is further undergoing the reaction like
a) Alcoholic fermentation
b) Lactic acid fermentation
c) Aerobic Respiration
d) Pentose phosphate pathway
Options:
a) A, B, and C
b) C and D
c) A and B
d) B C and D
Answer:
a) A, B, and C

Question 26.
Match the following:

Substrate	RQ
A. Palmitic acid	(i) 1.6
B. Oleic acid	(ii) 4.0
C. Tartaric acid	(iii) 0.36
D. Oxalic acid	(iv) 0.71

(a) A – (ii), B – (iii); C – (i); D – (iv)
(b) A – (iii), B – (iv); C – (i); D – (ii)
(c) A – (ii); B – (iv); C – (i); D – (iii)
(d) A – (iii); B – (i); C – (iv); D – (ii)
Answer:
(b) A – (iii), B – (iv); C – (i); D – (ii)

Question 27.
Indicate the correct statement:
(a) In Bryophyllum, carbohydrates are partially oxidised to organic acid
(b) In opuntia, the Respiratory Quotient value is 0.5
(c) Alcoholic fermentation takes place in Enterobacteriaceae
(d) Muscles of vertebrate does not have lactate dehydrogenase enzyme
Answer:
(a) In Bryophyllum, carbohydrates are partially oxidised to organic acid

Question 28.
The order of aerobic respiration in plant cell is:
(a) glycolysis, Kreb’s cycle, pyruvate oxidation and electron transport chain
(b) glycolysis, pyruvate oxidate, Kreb’s cycle, electron transport chain
(c) pyruvate oxidation, glycolysis, Kreb’s cycle, electron transport chain
(d) none of the above order
Answer:
(b) glycolysis, pyruvate oxidate, Kreb’s cycle, electron transport chain

Question 29.
The complete reactions of glycolysis take place in:
(a) mitochondria
(b) cristae
(c) cytoplasm
(d) outer membrane of mitochondria
Answer:
(c) cytoplasm

Question 30.
The Coenzyme quinone is a proton carrier located within:
(a) outer membrane of mitochondria
(b) cytoplasm
(c) inner membrane of mitochondria
(d) matrix of mitochondria
Answer:
(c) inner membrane of mitochondria

Question 31.
How many molecules of CO₂ are produced during link reaction:
(a) 1
(b) 6
(c) 4
(d) 2
Answer:
(d) 2

Question 32.
In the case of groundnut, during seed germination they use:
(a) carbohydrate as a respiratory substrate
(b) fat alone as a respiratory substrate
(c) fat and protein as a respiratory substrate
(d) protein alone as a respiratory substrate
Answer:
(c) fat and protein as a respiratory substrate

Question 33.
Lactic acid fermentation takes place in:
(a) yeast
(b) bacillus
(c) Enterobacteriaceae
(d) none of the above
Answer:
(b) bacillus

Question 34.
The net result of complete oxidation of one glucose-6-phosphate in pentose phosphate pathway yield:
(a) 6 CO₂ and 12 NADPH + H⁺
(b) 6 CO₂ and 10 NADPH + H⁺
(c) 8 CO₂ and 16 NADPH + H⁺
(d) 8 CO₂ and 14 NADPH + H
Answer:
(a) 6 CO₂ and 12 NADPH + H+

Question 35.
Ribose – 5 – phosphate and its derivatives are used in the synthesis of:
(a) lignin
(b) coenzyme A
(c) anthocyanin
(d) xanthophyll
Answer:
(b) coenzyme A

II. Answer the following (2 Marks)

Question 1.
What is ATP? Why it is called universal energy currency of the cell?
Answer:

• ATP is a nucleotide consisting of a base adenine a pentose sugar – ribose and three phosphate groups.
• On hydrolysis, it release energy from three phosphate group and hence it is called universal energy currency of the cell.

Question 2.
What is meant by protoplasmic respiration?
Answer:
Respiration utilizing protein as a respiratory substrate, it is called protoplasmic respiration. Protoplasmic respiration is rare and it depletes structural and functional proteins of protoplasm and liberates toxic ammonia.

Question 3.
What is Redox reaction? Is it important?
Answer:

• The reaction in which NAD+ and FAD gain (reduction) (or) lose (oxidation) electrons are called redox reaction.
• Yes, it is important in cellular respiration.

Question 4.
Explain briefly about aerobic respiration.
Answer:
Respiration occurring in the presence of oxygen is called aerobic respiration. During aerobic respiration, food materials like carbohydrates, fats and proteins are completely oxidised into CO₂, H₂O and energy is released.

Question 5.
What is Glycolysis? (or) EMP Pathway?
Answer:

• Glycolysis is the conversion of glucose into pyruvic acid in the cytoplasm of cell.
• The enzymes which are required for glycolysis are present in the cytoplasm.
• The Net gain of glycolysis is 2 ATP and 2 NADH₂
• [These reactions of glycolysis were worked out in yeast cells by three scientist Gustav Embden (German) otto Meyerhoff (German) and J Pamar (Polish) So it is called as EMP pathway)

Question 6.
What do you know about transition reaction?
Answer:
In aerobic respiration the pyruvate with coenzyme A is oxidatively decarboxylated into acetyl CoA by pyruvate dehydrogenase complex. This reaction is irreversible and produces two molecules of NADH + H⁺ and 2CO₂. It is also called transition reaction or Link reaction.

Question 7.
What is the Kreb cycle (or) Citric acid cycle (or) TCA cycle?
Answer:

• Kreb cycle is the conversion of acetyl coenzyme A into CO₂ and water in the mitochondrial matrix.
• It is named after its discoverer, German Bio Chemist Sir Hans Adolf Kreb (1937).

Question 8.
Explain briefly about the amphibolic pathway.
Answer:
Krebs cycle is primarily a catabolic pathway, but it provides precursors for various biosynthetic pathways thereby an anabolic pathway too. Hence, it is called the amphibolic pathway.

Question 9.
What is Substrate level phosphorylation?
Answer:
A molecule of ATP synthesis from substrate without entering the electron transport chain is called substrate-level phosphorylation.

Question 10.
What is oxidative phosphorylation?
Answer:
The transfer of electrons from reduced coenzyme NADH to oxygen via complexes I to IV is coupled to the synthesis of ATP from ADP and inorganic phosphate (Pi) which is called Oxidative phosphorylation.

Question 11.
What is climacteric? Give example.
Answer:
An abnormal rise in respiratory rate of ripening in fruits is called climacteric, ex. apple, banana mango, papaya. Pear.

Question 12.
Define respiratory quotient.
Answer:
The ratio of the volume of carbon dioxide given out and the volume of oxygen taken in during respiration is called Respiratory Quotient.

Question 13.
How many ATP molecules are produced in aerobic prokaryotes? Why?
Answer:
In the case of Aerobic prokaryotes due to lack of mitochondria each molecule of glucose produces 38 ATP molecules.

Question 14.
Explain the term alcoholic fermentation.
Answer:
The cells of roots in waterlogged soil respire by alcoholic fermentation because of lack of oxygen by converting pyruvic acid into ethyl alcohol and CO₂. Many species of yeast (Saccharomyces) also respire anaerobically. This process takes place in two steps:

Question 15.
Write the significance of RQ.
Answer:

• RQ value indicates which type of respiration occurs in living cells, either aerobic (or) anaerobic
• It also helps to know which type of respiratory substrate is involved.

Question 16.
What do you understand by the term mixed acid fermentation?
Answer:
This type of fermentation is a characteristic feature of Enterobacteriaceae and results in the formation of lactic acid, ethanol, formic acid, and gases like CO₂ and H₂.

Question 17.
Characteristics of Anaerobic Respiration.
Answer:

• Anaerobic respiration is less efficient than aerobic respiration.
• A limited number of ATP molecules is generated per glucose molecule.
• The formation of CO₂ and is used for carbon fixation in photosynthesis.

Question 18.
What is the control mechanism of the pentose phosphate pathway?
Answer:
The oxidative pentose phosphate pathway is controlled by the glucose-6-phosphate dehydrogenase enzyme which is inhibited by a high ratio of NADPH to NADP⁺.

Question 19.
Does anaerobic respiration take place in higher plants?
Answer:”

• Normally higher plants do not show anaerobic respiration.
• If the roots of a plant get waterlogged they use a different form of respiration called anaerobic respiration.

III. Answer the following (3 Marks)

Question 1.
“Overall process of respiration corresponds to a reversal of photosynthesis” – State whether it is true.
Answer:

• Yes. The overall process of respiration corresponds to a reversal of photosynthesis.
• Overall equation of Respiration is C₆H_12O6 + 6O₂ → 6CO₂ + 6H₂O + Energy (686 KCal (or) 2868KJ)

Question 2.
What will happen, when you sleep under a tree during the nighttime?
Answer:
If you are sleeping under a tree during night time you will feel difficulty in breathing. During the night, plants take up oxygen and release carbon dioxide and as a result, carbon dioxide will be abundant around the tree

Question 3.
What is Compensation Point?
Answer:

• The point at which CO₂ released in respiration is exactly compensated by CO₂ fixed in photosynthesis.
• At this moment the amount of O₂ released from photosynthesis is equal to the amount of oxygen utilized in respiration.

Question 4.
Why do you call ATP as universal energy currency of cell?
Answer:
ATP is a nucleotide consisting of a base- adenine, a pentose sugar – ribose and three phosphate groups. Out of three phosphate groups the last two are attached by high energy-rich bonds. On hydrolysis, it releases energy (7.3 K cal or 30.6 KJ / ATP) and it is found in all living cells and hence it is called the universal energy currency of the cell.

Question 5.
Define Aerobic respiration.
Answer:

• Respiration occurring in the presence of oxygen is called aerobic respiration.
• It is a very complex process during which food materials like Carbohydrates, fats, and proteins are completely oxidized into CO₂, H₂O, and energy.
• It consists of four major steps.

Question 6.
Write down any three differences between aerobic and anaerobic respiration.
Answer:
Aerobic respiration:

• It occurs in all living cells of higher organisms.
• It requires oxygen for breaking the respiratory substrate.
• The end products are CO₂ and H₂O.

Anaerobic Respiration:

• It occurs in yeast and some bacteria.
• Oxygen is not required for breaking the respiratory substrate.
• The end products are alcohol and CO₂ (or) lactic acid.

Question 7.
What is gluconeogenesis?
Answer:
The synthesis of glucose from certain non – Carbohydrate Carbon Substrates such as proteins and lipids are called gluconeogenesis.

Question 8.
Derive the respiratory quotient for carbohydrates as a substrate in oxidative metabolism.
Answer:
The respiratory substrate is a carbohydrate, it will be completely oxidised in aerobic respiration and the value of the RQ will be equal to unity.

Question 9.
What is a respiratory Quotient?
Answer:
The ratio of the volume of Carbon dioxide given out and volume of Oxygen taken in during respiration is called R.Q.
\(\mathrm{RQ}=\frac{\text { VolumeofCOliberated }}{\text { VolumeofOconsumed }}\)
RQ value depends upon respiratory substrates.

Question 10.
Distinguish between glycolysis and fermentation.
Answer:
Glycolysis:

1. Glucose is converted into pyruvic acid.
2. It takes place in the presence or absence of oxygen.
3. Net gain is 2ATR
4. 2 NADH + H⁺ molecules are produced.

Fermentation:

1. Starts from pyruvic acid and is converted into alcohol or lactic acid.
2. It takes place in the absence of oxygen.
3. No net gain of ATP molecules.
4. 2 NADH + H⁺ molecules are utilised.

Question 11.
What is alcoholic fermentation?
Answer:

• The cells of roots in waterlogged soil respire by alcoholic fermentation because of lack of oxygen by converting pyruvic acid into ethyl alcohol and CO_2.
• Eg. Yeast (Saccharomyces)

Question 12.
How alcoholic beverages like beer and wine is made?
Answer:
The conversion of pyruvate to ethanol takes place in malted barley and grapes through fermentation. Yeasts carry out this process under anaerobic conditions and this Conversion increases ethanol concentration. If the concentration increases, it’s toxic effect kills yeast cells .and the left out is called beer and wine respectively.

IV. Answer the following (5 Marks)

Question 1.
Give the schematic representation of glycolysis or EMP pathway.
Answer:
The schematic representation of glycolysis or EMP pathway:

Question 2.
Write down the biochemical events in Kreb’s cycle.
Answer:
The biochemical events in Kreb’s cycle:

Question 3.
Mention the schematic diagram of the various steps involved in the pentose phosphate pathway.
Answer:
The schematic diagram of the various steps involved in the pentose phosphate pathway:

Question 4.
Describe the events in electron transport chain in plant cell.
Answer:
During glycolysis, link reaction and Krebs cycle the respiratory substrates are oxidised at several steps and as a result many reduced coenzymes NADH + H⁺ and FADH₂ are produced. These reduced coenzymes are transported to inner membrane of mitochondria and are converted back to their oxidised forms produce electrons and protons. In mitochondria, the inner membrane is folded in the form of finger projections towards the matrix called cristae.

In cristae many oxysomes (F₁ particles) are present which have election transport carriers are present. According to Peter Mitchell’s Chemiosmotic theory this electron transport is coupled to ATP synthesis. Electron and hydrogen (proton) transport takes place across four multiprotein complexes (I – IV). They are

(i) Complex – I (NADH dehydrogenase: It contains a flavoprotein (FMN) and associated with non – heme iron Sulphur protein (Fe – S). This complex is responsible for passing electrons and protons from mitochondrial NADH (Internal) to Ubiquinone (UQ).
NADH + H⁺ + UQ ⇌ NAD⁺ + UQH₂
In plants, an additional NADH dehydrogenase (External) complex is present on the outer surface of inner membrane of mitochondria which can oxidise cytosolic NADH + H⁺ Ubiquinone (UQ) or Coenzyme Quinone (Co Q) is a small, lipid-soluble electron, proton carrier located within the inner membrane of mitochondria.

(ii) Complex – II (Succinic dehydrogenase): It contains FAD flavoprotein is associated with non – heme iron Sulphur (Fe – S) protein. This complex receives electrons and protons from succinate in Krebs cycle and is converted into fumarate and passes to ubiquinone.
Succinate + UQ → Fumarate + UQH₂

(iii) Complex – III (Cytochrome bc₁ complex): This complex oxidises reduced ubiquinone (ubiquinol) and transfers the electrons through Cytochrome bc₁ Complex (Iron Sulphur center bc₁ complex) to cytochrome c. Cytochrome c is a small protein attached to the outer surface of inner membrane and act as a. mobile carrier to transfer electrons between complex III to complex IV.
UQH₂ + 2Cyt c_oxidised  ⇌  UQ + 2Cyt c_reduced  + 2H⁺

(iv) Complex IV (Cytochrome c oxidase): This complex contains two copper centers (A and B) and cytochromes a and as. Complex IV is the terminal oxidase and brings about the reduction of 1/2 O₂ to H₂O. Two protons are needed to form a molecule of H₂O (terminal oxidation).
2Cyt c_oxidised + 2H⁺ + 1/2 O₂  ⇌  2Cyt c_reduced + H₂O

The transfer of electrons from reduced coenzyme NADH to oxygen via complexes I to IV is coupled to the synthesis of ATP from ADP and inorganic phosphate (Pi) which is called Oxidative phosphorylation. The F₀F₁ – ATP synthase (also called complex V) consists of F₀ and F₁. F₁ converts ADP and Pi to ATP and is attached to the matrix side of the inner membrane. F₀ is present in inner membrane and acts as a channel through which protons come into matrix.

Oxidation of one molecule of NADH + H⁺ gives rise to 3 molecules of ATP and oxidation of one molecule FADH₂ produces 2 molecules of ATP within a mitochondrion. But cytoplasmic NADH + H⁺ yields only two ATPs through external NADH dehydrogenase. Therefore, two reduced coenzymes (NADH + H⁺) molecules from glycolysis being extramitochondrial will yield 2 × 2 = 4 ATP molecules instead of 6 ATPs. The Mechanism of mitochondrial ATP synthesis is based on the Chemiosmotic hypothesis.

According to this theory electron carriers present in the inner mitochondrial membrane allow for the transfer of protons (H⁺). For the production of single ATP, 3 protons (H⁺) are needed. The terminal oxidation of external NADH bypasses the first phosphorylation site and hence only two ATP molecules are produced per external NADH oxidized through However, in those animal tissues in which malate shuttle mechanism is present, the oxidation of external NADH will yield almost 3 ATP molecules.

Complete oxidation of a glucose molecule in aerobic respiration results in the net gain of 36 ATP molecules in plants. Since huge amount of energy is generated in mitochondria in the form of ATP molecules they are called ‘powerhouse of the cell’. In the case of aerobic prokaryotes due to lack of mitochondria, each molecule of glucose produces 38 ATP molecules.

Question 5.
Define respiratory quotient. Explain the derivation of respiratory quotient for various substrates oxidised :
Answer:
The ratio of the volume of carbon dioxide given out and volume of oxygen taken in during respiration is called Respiratory Quotient or Respiratory ratio. RQ value depends, upon respiratory substrates and their oxidation.

(i) The respiratory substrate is a carbohydrate, it will be completely oxidised in aerobic respiration and the value of the RQ will be equal to unity.

(ii) If the respiratory substrate is a carbohydrate it will be incompletely oxidised when it goes through anaerobic respiration and the RQ value will be infinity.

(iii) In some succulent plants like Opuntia, Bryophyllum carbohydrates are partially oxidised to organic acid, particularly malic acid without the corresponding release of CO₂ but O₂ is consumed hence the RQ value will be zero.

(iv) When the respiratory substrate is protein or fat, then RQ will be less than unity.

(v) When the respiratory substrate is an organic acid the value of RQ will be more than unity.

Question 6.
Describe an experiment to demonstrate the production of CO₂ in aerobic respiration.
Answer:
Take a small quantity of any seed (groundnut or bean seeds) and allow them to germinate by imbibing them. While they are germinating place them in a conical flask. A small glass tube containing 4 ml of freshly prepared Potassium hydroxide (KOH) solution is hung into the conical flask with the help of a thread and tightly close the one holed cork. Take a bent glass tube, the shorter end of which is inserted into the conical flask through the hole in the cork, while the longer end is dipped in a beaker containing water.

Observe the position of the initial water level in a bent glass tube. This experimental setup is kept for two hours and the seeds were allowed to germinate. After two hours, the level of water rises in the glass tube. It is because the CO₂ evolved during aerobic respiration by germinating seeds will be absorbed by KOH solution and the level of water will rise in the glass tube.
CO₂ + 2KOH → K₂CO₃ + H₂O
In the case of groundnut or bean seeds, the rise of water is relatively lesser because these seeds use fat and proteins as respiratory substrate and release a very small amount of CO₂. But in the case of wheat grains, the rise in water level is greater because they use carbohydrates as a respiratory substrate. When carbohydrates are used as a substrate, equal amounts of CO₂ and O₂ are evolved and consumed.

Textbook Page No. 145

Question 1.
How many ATP molecules are produced from one sucrose molecule?
Answer:
One sucrose molecule gives rise to two glucose molecules. The net production of ATP during complete oxidation of one glucose molecule in plant cell is 36 ATP. Therefore one sucrose molecule yields 36 x 2 = 72 ATP molecules.
As per recent view in plants cells, one molecule of glucose, after complete aerobic oxidation yields only 30 ATP molecules, and hence one sucrose molecule yield only 30 x 2 = 60 ATP molecules.

Textbook Page No. 156

Question 1.
Why Microorganisms respire anaerobically?
Answer:
Some of the microorganisms live in environments devoid of oxygen and they have to adapt themselves in anoxic condition. Hence they respire anaerobically and they are called anaerobic microbes.

Question 2.
Does anaerobic respiration take place in higher plants?
Answer:
Anaerobic respiration sometimes occurs in the root of some water-logged plants.

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