# AP Inter 2nd Year Botany Study Material Chapter 5 Respiration in Plants

Andhra Pradesh BIEAP AP Inter 2nd Year Botany Study Material 5th Lesson Respiration in Plants Textbook Questions and Answers.

## AP Inter 2nd Year Botany Study Material 5th Lesson Respiration in Plants

Question 1.
Different substrates get oxidized during respiration. How does respiratory quotient (RQ) indicate which type of substrate (i.e) carbohydrate, fat or protein is getting oxidized?
RQ = A/B. What do A & B stand for?
What type of substrates have RQ of 1, <1; > 1?

carbohydrates have RQ = 1
Fats have RQ value = < 1
Organic acids have RQ = > 1

Question 2.
What is the specific role of F0 – F1 particles in Respiration?
The F1 headpiece is a peripheral membrane protein complex and contains the site for the synthesis of ATP from ADP and inorganic phosphate. F0 is an integral membrane protein complex that forms the channel through which protons cross the inner membrane. The passage of protons through the channel is coupled to the catalytic site of the F1 component for the production of ATP

Question 3.
When does anaerobic respiration occur in man and yeast?
When oxygen is inadequate for cellular respiration, anaerobic respiration occurs.

Question 4.
What is the common pathway for aerobic and anaerobic respirations? Where does it take place?
Glycolysis. It occurs in cytoplasm of the cell.

Question 5.
What cellular organic substances are never used as respiratory substrates?
Pure proteins or fats are never used as respiratory substrates.

Question 6.
Why is the respiratory quotient (RQ) of fats less than that of carbohydrates?
During the oxidation of fats, the amount of CO2 evolved is less than the amount of O2 consumed so respiratory quotient value is less than one. Where as in oxidation of carbohydrates, the amount of CO2 evolved is equal to the amount of O2 consumed. So the respiratory quotient value is one.

Question 7.
What is meant by Amphibolic pathway?
Respiratory pathway involves both anabolism and catabolism so it is considered as amphibolic pathway. In this, the breakdown and the synthesis of fatty acids and proteins took place.

Question 8.
Name the mobile electron carriers of the respiratory electron transport chain in the inner mitochondrial membrane.
Ubiquinone and cytochrome – C.

Question 9.
What is the final acceptor of electrons in aerobic respiration? From which complex does it receive electrons?
Oxygen. It receives electrons from complex IV

Question 10.
Do you know of any step in Kreb’s cycle where there is a substrate level phosphorylation? Explain.
In Kreb’s cycle during the conversion of succinyl – CoA to succinic acid a molecule of GTP is synthesised. This step is a substrate level phosphorylation.

Question 1.
Why is the respiratory pathway referred to as amphibolic pathway? Explain.
Respiration involves the breakdown of substrates so traditionally called catabolic process and the respiratory pathway as a catabolic pathway. In respiration, different substrates enter into respiratory pathway at different points. If fatty acids were respired, j they would be degraded to acetyl CoA and enter the pathway Glycerol would enter the pathway after converted to PGAL. The proteins and the aminoacids would enter the pathway at pyruvate.

Fatty acids would be brokendown to acetyl CoA before entering into respiratory pathway. Rut when the organism needs to synthesis fatty acids, Acetyl CoA would be withdrawn from the respiratory pathway for it. Hence the respiratory pathway comes into the picture both during the breakdown and the synthesis of fatty acids. In this issue, respiratory pathway is involved in both anabolism and catabolism, it would be better to consider it as amphibolic pathway rather than as a catabolic one.

Question 2.
Write about two ATP yielding reactions of glycolysis.
1) 1, 3 BPGA (bisphosphoglyceric acid) looses phosphate group in the presence of phosphoglycerokinase to form 3-phosphoglyceric acid. ADP accepts phosphate group and gets converted to ATP.

2) Phosphoenol pyruvic acid undergoes dephosphorylation in the presence of pyruvic kinase results in the formation of pyruvic acid. ADP accepts phosphate group and gets converted to ATP.

Question 3.
The net gain of ATP for the complete aerobic oxidation of glucose is 36. Explain.
Balance sheet of ATP production in aerobic oxidation of Glucose.
1) Glycolysis :
1. ATP produced by substrate level phosphorylation
Bisphosphoglyceric acid to phosphoglyceric acid : 2 × 1 = 2ATP
phosphoenol pyruvic acid to pyruvic acid : 2 × 1 = 2ATP
ATP consumed : for the phosphorylation of glucose
and fructose-6-phosphate : -2 ATP
Net gain of ATP : +2 ATP

2. ATP from NADH generated in glycolysis :
G-3-P to BPGA (2NADH, each worth 2ATP) 2 × 2 = 4ATP
Total ATP gain from glycolysis in the presence of O2 : (a)6 ATP

2) Oxidative decarboxylation of pyruvic acid
Pyruvic acid to acetyl COA
(2 NADH, each worth 3 ATP) : (b)2 × 1 = 6 ATP

3) Krebs cycle
1. ATP produced in substrate level phosphorylation:
Succinyl CoA to succinic acid : 2 × 1 = 2 ATP
2. ATP from NADH: Isocitric acid to Oxalosuccinic acid : 2 × 3 = 6 ATP
a-Ketoglutaric acid to succinyl CoA : 2 × 3 = 6 ATP
Malic acid to Oxalocaetic acid : 2 × 3 = 6 ATP
3. ATP from FADH2 : Succinic acid to fumaric acid : 2 × 2 = 4 ATP
Total ATP value of krebs cycle : (a)24 ATP
Net gain of ATP in aerobic respiration per mole glucose
(a + b + c) : 36 ATP

Question 4.
Define RQ. Write a short note on RQ.
The ratio of the volume of CO2 evolved to the volume of O2 cosumed in respiration is called the Respiratory Quotient (RQ).

The respiratory quotient depends upon the type of respiratory substrate used during respiration.
1) When carbohydrates are used as substrate, the RQ is 1, because equal amounts of CO2 and O2 are evolved and consumed.
Ex : C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy
RQ = $$\frac{6CO_2}{6O_2}$$ = 0.1

2) When fats are used in respiration the RQ is less than 1.
Ex : 2(C51 H98 O6) + 145 O2 → 1 O2 CO2 + 98 H2O + Energy Tripalmitin
RQ = $$\frac{102CO_2}{145O_2}$$ = 0.7

3) When protein are respiratory substrates the ratio would be about 0.9

Question 5.
Describe briefly the process of fermentation.
In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by set of reactions where pyruvic acid is converted to CO2 & Ethanol. The ezymes, pyruvic acid decarboxylase, and alcohol dehydrogenase catalyse these reactions. Two types of fermetations are :

1. Alcoholic fermentation
2. Lactic acid fermentation

1) Alcoholic fermentation :
This is most common type of fermentation process. In alcoholic fermentation, pyruvic acid is broken to ethyl alcohol & CO2 in two steps.
i) The pyruvic acid is decarboxylated to acetaldehyde in the presence of enzyme pyruvic decarboxylase.

ii) Acetaldehyde is then reduced to ethyl alcohol by NADH+ + H+ produced in glycolysis acetaldehyde is final hydrogen acceptor. The reaction is catalysed by alcohol dehydrogenase.

2) Lactic acid fermentation:
Pyruvic acid formed at the end of glycolysis is converted to lactic acid by lactobacillus lactibacteria.

Question 6.
Explain various complexes involved in electron transport system of respiration.
Electron flow through the mitochondrial electron transport (Aerobic respiration) is carried out by five enzyme complexes. These complexes are the integral proteins of the inner mitochondrial membrane. They are complex I, II, III, IV & V out of these first four complexes involved in Electron transport chain.
i) Complex I :

ii) Complex II :
Succinate dehydrogenase (or) ubiquinone.This complex trasfers electrons from succinate to ubiquinone via Fe – S – centres.

iii) Complex III :
Cytochrome ‘c’ Reductase or cyt-b-c, complex. This complex contains cytochrome ‘b’ and cytochrome ’c’ cyt-c(mobile carrier). The ultimate electron acceptor of complex-III. This complex works through Q-cycle mechanism.

iv) Complex IV :
Cytochrome -c- oxidase. It contains two heme proteins called cyta and cyta3 and two copper proteins. This complex transfers electrons to oxygen.

v) Complex V :
ATP synthase or F0 – F1 complex. This complex involved for the production of ATP from ADP & inorganic phosphate.

Question 7.
Describe the structure of Complex-V and explain the process of oxidative phospho-rylation as explained by chemosmotic hypothesis.

Complex – V is an ATP synthase. This complex-V consists of two major components, F1 and F0. The F1 head piece is a peripheral membrane protein complex and contains the site for synthesis of ATP from ADP and inorganic phosphate. F0 is an integral membrane protein complex that froms the channel through which protons cross the inner membrane. The passage of protons through the channel is coupled to the catalytic site of the F1 component for the production of ATP For each ATP produced, 3H+ passes through F0 from the intermembrane space to the matrix down the electrochemical proton gradient.

In photophosphorylation light energy is utilised for the production of proton gradient required for phosphorylation, but in respiration it is the energy of oxidation reduction utilized for the proton gradient. It is for this reason that the process is called oxidative phosphorylation. Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that one molecule of FADH2 produces 2 molecules of ATP.

Question 1.
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.
Glucose is broken down into 2 molecules of pyruvic acid is called glycolysis. It was given by gustav embden, Otto Mayerhof and J.Parnas so called EMP pathway. It occurs in the cytoplasm of the cell and takes place in all living orgnisms. In this, 4 ATP are formed of which two are utilised and 2 NADPH+ K+ are formed. A+ the end of glycolysis, 2PA, 2ATP and 2NADPH+ H+ are formed as end products. The ATP and NADPH+ H+ are utilised for fixation of CO2.

Glycolysis occur in cytoplasm. Pyruvic acid, 2ATP, 2NADPH+H are the end products. In aerobic respiration, pyruvic acid, 2 NADPH + H+ are completely oxidised through TCA cycle, ETS pathway and produce 36 ATP molecules. In Anaerobic respiration, pyruvic acid is partially oxidised results in the formation of Ethyol alcohol and CO2.

Question 2.
Explain the reactions of Krebs cycle.

The acetyl CoA enters into the [mito chondrial matrix] a cyclic pathway tricarboxylic acid cycle, more commonly called krebs cycle after the scientist Hans Krebs who first elucidated it.

1) Condensation :
In this acetyl CoA condenses with oxaloacetic acid and water to yield citric acid in the presence of citrate synthetase and CoA is released.

2) Dehydration :
Citric acid looses water molecule to yield cisaconitic acid in the presence of aconitase.

3) Hydration :
A water molecule is added to cis aconic acid to yield isocitric acid in the presence of a conitase.

4) Oxidation I:
Isocitric acid undergoes oxidation in the presence of dehydrogenase to yield succinic acid

5) Decarboxylation :
Oxalosuccinic acid undergoes decarboxylation in the presence ofdecarboxylase to form a-keto glutaric acid.

6) Oxidation II, decarboxylation :
α – keto glutaric acid undergoes oxidation and decarboxylation in the presence of dehydrogenase and condenses with co.A to form succinyl co. A.

7) Cleavage :
Succinyl co.A splits into succinic acid and co.A in the presence of thiokinase to form succinic acid. The energy released is utilised to from ATP from ADP and PI.

8) Oxidation – III:
Succinic acid undergoes oxidation and forms Fumaric acid in the presence of succinic dehydrogenase.

9) Hydration :
A water molecule is alcohol to Fumaric acid in the presence of Fumarase to form Malic acid.

10) Oxidation IV :
Malic acid undergoes oxidation in the presence of malic dehydrogenase to form oxaloacetic acid.

In TCA cycle, for every 2 molecules of Acetyl co.A undergoing oxidation, 2 ATP, 8 NADPH+ H+, 2FADH2 molecules are formed.

Intext Questions

Question 1.
Differentiate between
a) Respiration and Combustion
b) Glycolysis and Krebs cycle
c) Aerobic respiration and Fermentation
a)

 Respiration Combustion 1) Oxygen is utilised, CO2, water and energy are released. 1) It requires oxygen.

b)

 Glycolysis Krebs cycle 1) It occurs in the cytoplasm. 1) It occurs in the mitochondrial matrix. 2) It occurs in all living organisms. 2) It occurs in higher plants onlv.

c)

Question 2.
What are respiratory substrates? Name the most common respiratory substrate.
Substances which oxidises in respiration are called respiratory substrates. Ex: Glucose, Fats, Proteins and Organic acids. Among them glucose is the common respiratory substrate.

Question 3.
Give the schematic representation of glycolysis.

Question 4.
What are the main steps in aerobic respiration? Where does it take place?
Glycolysis = Cytoplasm
PAOD = Matiix (Mitochondria)
Krebs cycle = Matrix (Mitochondria)
Electron transport system = Matrix (Mitochondria)

Question 5.
Give the schematic representation of an overall view of Krebs cycle.

Question 6.
Explain ETS
NADPH + H+ or FADH2 formed in glycolysis and Mitochondrial matrix are oxidised through the electron transport system and the electrons are passed on to O2 resulting in the formation of H2O. The metabolic pathway through which an electron passes from one carrier to another is called electron transport system.

NADPH + H+ is oxidised and releases electrons in the presence of NADH dehydrogenase (complex I), which are transferred to ubiquinone located with in the inner membrane. Ubiquinone also receives reducing equivalents via FADH2 (Complex II). The reduced ubiquinone (Ubiquinol) is oxidised and releases electrons which are accepted by cytochrome c1 Cytochromec (Complex III) cytochrome C is a small protein, acts as a mobile carrier for the transfer of electrons between complex III and TV to cytochromes a and a3, finally reaches $$\frac{1}{2}$$O2 along with 2H+, produce 1 H2O molecule.

During this electron flow, 10H+ moves from matrix to inner mitochondrial membrane [4 H+ at complex I, 4H+ at complex III, 2 at complex IV]. As a result H+ concentration increases towards the inner membrane of mitochondria. So the H+ comes back to the matrix side through ATPage [F0, F1], involves in the synthesis ATP.

Question 7.
Distinguish between the following
a) Aerobic respiration and Anaerobic respiration
b) Glycolysis and Fermentation
c) Glycolysis and Citric acid cycle
a)

 Aerobic respiration Anaerobic respiration 1. It occurs in the presence of O2. 1. It occurs in the absence of O2. 2. It occurs in four steps. a) Glycolysis b) PAOD c) Krebs cycle d) ETS pathway 2. It occurs in two steps. a) Glycolysis b) Fermentation 3. End products are CO2 and H2O. 3. End products are CO2 and Ethyl alcohol. 4. 686 K.Cal of energy is released. 4. 56 K.Cal of energy is released. 5. 36 ATP are formed. 5. 2 ATP are formed.

b)

 Glycolysis Fermentation 1. It is the 1st step in both aerobic anaerobic respiration. 1. It is the 2nd step of anaerobic repsiration. 2. End products are PA, ATP, NADPH+ H+ 2. End products are CO2 and C2H5OH

c)

 Glycolysis Citric acid cycle 1. It occurs in the cytoplasm. 1. It occurs in the mitochondrial matrix. 2. It occurs in all living organisms. 2. It occurs in higher plants only.

Question 8.
What are the assumptions made during the calculations of net gain of ATP?
It is possible to make calculations of the net gain of ATP for every glucose is oxidised.
These calculations can be made only on certain assumptions that:

1. There is a sequential, orderly pathway functioning with one substrate forming the next and with glycolysis, TCA cycle, ETS pathway following one after another.
2. The NADH synthesised in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.
3. None of the intermediates in the pathway are utilised to synthesize any other compound.
4. Only glucose is being transferred – no other alternative substrates are entering in the pathway at any of the intermediary stages.

But these kind of assumption are not really valid in a living system all pathways work simultaneously and do not take place one after another.

Differences

 Fermentation Aerobic respiration 1) Partial breakdown of glucose. 1) Complete oxidation of glucose. 2) End products are CO2 and Ethyl alcohol. 2) End products are CO2 and H2O. 3) 2 ATP molecules are formed. 3) 36 ATP are formed.

Question 9.
Discuss “The respiratory pathway is an amplibolic pathway”.
Respiration involves the breakdown of substrates so traditionally called catabolic process and the respiratory pathway as a catabolic pathway. In respiration, different substrates enter into respiratory pathway at different points. If fatty acids were respired, they would be degraded to acetyl CoA and enter the pathway Glycerol would enter the 1 pathway after converted to PGAL. The proteins and the aminoacids would enter the pathway at pyruvate.

Fatty acids would be brokendown to acetyl CoA before entering into respiratory pathway. Rut when the organism needs to synthesis fatty acids, Acetyl CoA would be withdrawn from the respiratory pathway for it. Hence the respiratory pathway comes into the picture both during the breakdown and the synthesis of fatty acids. In this issue, respiratory pathway is involved in both anabolism and catabolism, it would be better to consider it as amphibolic pathway rather than as a catabolic one.

Question 10.
Define respiratory quotient (RQ). What is its value for fats?
The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called respiratory quotient.
Respiratory quotient value of fats is less than one
2C51 H98 O6 + 145 O2 → 1 02 CO2 + 98 H2O + energy
(Tripalmitin) Respiratory quotient = $$\frac{102}{145}$$ = 0.7.

Question 11.
What is oxidative phosphorylation?
Synthesis of ATP from ADP and Pi coupled to electron transport from substrate to molecular oxygen is called oxidative phosphorylation.

Question 12.
What is the significance of step-wise release of energy in respiration?
The key is to oxidise glucose not in one step but in several small steps enabling some steps to be just large enough such that the energy is released can be coupled to ATP synthesis. All the energy entained in a substrate is not released free into the cell or in a single step. It is release in a series of slow step wise reactions controlled by enzymes, and it is trapped as chemical energy in the form of ATP.

13. Find the correct ascending sequence of the following, on the basis of energy released in respiratory oxidation.
a) 1 gm pf fat
b) 1 gm of protein
c) 1 gm of glucose
d) 0.5 gm of protein + 0.5 gm of glucose
c → b → d → a

Question 14.
Name the products, respectively in aerobic glycolysis in skeletal muscle and anaerobic fermentation in yeast.
In aerobic glycolysis :
Pyruvic acid, ATP, NADPH + H+

In skeletal muscle :
Lactic acid

In anaerobic fermentation :
CO2 and Ethanol

Question 15.
If a person is feeling dizzy, glucose or fruit juice is given immediately but not a cheese sandwich, which might have more energy. Why?