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Respiration
Q.1. What is respiration? Give the overall
equations of aerobic and anaerobic respiration.
Ans: 1. Respiration is defined as an intra cellular
process of oxidation in which complex organic
substances are broken down in stepwise manner with
the release of energy which is immediately converted
into metabolically usable form of energy (ATP).
2. Equation of aerobic respiration is
C6 H12 O6  6O2 
 6CO2  6H2 O  38ATP
3. Equation of anaerobic respiration is
Step
Direct ATP
Indirect ATP
formation
formation Via
ETS
1.
Glycolysi
s
2 ATP
2 NADH2  3 =
6 ATP
8 ATP
2. Link
reaction
--
2 NADH2  3
= 6 ATP
6 ATP
3. Krebs
cycle
2 ATP
6 NADH2  3 =
18 ATP
24 ATP
C6 H12 O6 
 6CO2  6H2 O  38ATP
Total ATP
2 FADH2  2 =
4 ATP
Q.2. Draw a neat and labelled diagram showing
ultrastructure of mitochondrion.
Total
ATP
4 ATP
+ 34 ATP
=38 ATP
Q.4. Describe the connecting
between glycolysis and Kerbs cycle.
Link
reaction
Ans: 1. Link reaction is acet;ylation of pyruvate.
yruvate is formed by glycolysis and it underdergoes
oxidative decarboxylation
before entering
Kerbs cycle.
2. Link reaction
mitochondrion.
Fig: Ultrastructure of mitochondrion
Q.3. Give the balanced sheet of ATP formed in
aerobic respiration.
Ans:
takes
place
3. Here removal of CO2 along with
from Pyruvate occurs.
4. It is catalysed by pyruvic
5. Coenzymes like NAD and CoA are
in
matrix
hydrogen
dehydrogenase.
required.
6. End product acetyl CoA enters Kerbs cycle
7. NADH2 formed enters ETS.
of
8. Thus from one glucose there forms 2 pyruvate and
2 NADH2  3 = 6 ATP
9. Link Reaction is.
2 pyruvate + 2 NAD + 2CoA 

2 Acetyl CoA + 2 NADH2 + 2 CO2
Q.5.
Give the significance of respiration.
Ans: (i) Respiration provides energy for biosynthesis of
cellular materials such as carbohydrates, proteins,
fats, lipids, vitamins, pigments, etc.
(ii) It is also a source of energy for cell division,
growth, repairs and replacement of worn out parts,
movements, locomotion etc.
(iii) Various intermediates of Kerbs cycle are used as
building blocks for synthesis of other complex
compounds.
(iv) Coupled with photosynthesis, it helps to maintain
the balance between CO2 and O2 in the atmosphere.
(v) Anaerobic respiration (fermentation) is used in
various industries such as dairies, bakeries, distilleries,
leather industries, paper industries, alcohol, organic
acids, vitamins, antibiotics etc.
(vi) Energy of respiration is also used to convert
insoluble substances into soluble form.
6.
How much energy is released when one
molecule of ATP is hydrolysed to ADP and iP?
Ans: When ATP is hydrolysed to ADP and iP, then
7.3 Kcal of energy gets released.
Q.7.
Ans:
1.
Chemically
ATP
is
Adenosine
triphosphate, thus it is triphosphate ester
of
adenosing ribonucleoside.
2. It has 3 components- Adenine, ribose (C5H10O5) and
3 phosphate groups.
Q.8.
ATP is called energy currency of cell, Explain.
Ans: 1. When energy is released, ATP synthesis takes
place from ADP and iP.
2. When energy is required, ATP is
hydrolysed
and energy is released which is used in metabolic
activities.
3. Therefore ATP is called energy
cell.
currency of
Q.9. Differentiate between aerobic and anaerobic
respiration.
Aerobic respiration
Anaerobic respiration
1. It requires molecular 1. It occurs in absence
oxygen.
of oxygen.
2.
Here
undergoes
oxidation.
glucose 2.
Here
glucose
complete undergoes incomplete
oxidation.
3. Metabolic water is end 3. Water is not the end
product
product
4. More energy (38 ATP) 4. Less energy (2 ATP) is
is released
released per glucose.
5. Eg. Higher plants and 6. Eg. Few bacteria,
animals
yeast
Describe structure of ATP.
Q.10. What is respiratory Quotient?
Ans: 1. The ration of volume of CO2 evolved to the
volume of O2 consumed in respiration is called
respiratory ration (RQ).
2. It depends on the type of respiratory substrate
when carbohydrates are used as respiratory substrate
and oxidized completely, i.e. aerobic respiration, the
RQ is 1.
C6 H12 O6 
 6CO2  6H2 O  Energy
6CO 2
RQ 
1
6O 2
3. For proteins and fats RQ is less than 1.
4. In case of anaerobic respiration RQ is infinity as O2
is not used.
glycolysis
Glucose 
 2 pyruvic acid+ 2 NADH2 +2ATP
reduction
2 Pyruvic acid +2NADH2 

2Lactic acid +2NAD
Q.13. Explain respiration is an Amphibolic pathway.
Ans: 1. Respiration involves breakdown of
substrates (carbohychates, fats, proteins) and hence it
is catabolic process. But some intermediates of
respiration are used in biosynthesis (Anabolism)
of
molecules, thus respiration is called Amphibolic i.e.
both catabolic and anabolic pathway.
2. Respiratory intermediates can
biosynthesis of fatly acids and glycerol.
Q.11. What is
fermentation.
fermentation?
Give
uses
of
Ans: 1. Fermentation is a chemical change brought
about in an organic substrate due to enzyme activity
of microorganisms.
beused
for
3. Many acids of Kerbs cycle are used for synthesis of
aminoacids and thus proteins.
4. Thus respiratory intermediates Link during
synthesis as well as breakdown processes.
2. There are many applications of fermentation in
industries and household products.
3. Examples- Curd is produced by lactic acid
fermentation yeast is used in Bakery and Brewery for
alcohol fermentation.
Production of various
antibiotics and vitamins is also based on fermentation.
Long Answer Questions
Q.1.
Describe various steps involved in glycolysis.
Ans: 1. Glycolysis is the first step involved in both
aerobic and anaerobic respiration.
2. It takes place in cytoplasm.
Q.12.
Explain lactic acid fermentation.
Ans: 1. Production of curd from milk is lactic acid
fermentation. It is carried out by Lactic acid bacteria.
2. First milk sugar Lactose is converted into glucose.
3. In second stem Glucose undergoes glycolysis to
form pyruvate. Then pyruvate undergoes reduction ot
form Lactic acid.
4. Lactose 
 Glucose + galactos
3. It is independent of oxygen.
4. It is ten steps process which is controlled by
different enzymes.
5. Glycolysis or EMP pathway consists of two major
phasesA) Preparatory phase and cleavage (steps 1-5)
In preparatory phase glucose is activated by
phosphorylation and converted into fructose 1,6
diphosphate. In cleavage it is converted or splitted
into two triose phosphates 3- Phosphogly ceraldehyde
(PGAL) and dihydroxy acetone phosphate (DHAP). As
they are isomers, there forms 2 molecules of PGAL. In
this phase 2 ATP are used.
B) Oxidative and payoff phase (steps 6-10)
In this phase oxidation occurs by removal of
hydrogen to form 2 NADH2 molecules. In 2 different
steps 4 ATP are formed.
6. Various steps involved in glycolysis
can
be
schematically represented as
follows.
Some
short forms used are PGA = phosphoglyceric acid
PEPA= phosphoenol pyruvic acid.
7. Significance of glycolysis :1. At the end of glycolysis, one glucose molecule is
converted into two molecules of pyruvate (3c).
2. In preparatory phase 2 ATP are used and in payoff
phase & ATP are generated. Thus there is a net gain
of 2ATP.
3. The 2 NADH2 formed during oxidative step (6), pass
via ETS to produce (2  3ATP  6ATP) total 6 ATP.
4. Thus in aerobic respiration, total gain of 8 ATP via
glycolysis is 2ATP+ 6ATP = 8ATP
5. Glycolysis reactions can be presented as
2 Glucose + 2ADP + 2 iP+ 2 NAD 
 2Pyruvate + 2
ATP +2 NADH2.
Q.2. What is TCA/Kerbs cycle ? Describe its
different steps.
Ans: 1. Second phase in aerobic respiration 0in Kerbs
cycle as various steps are described by Hons Kerbs. Its
first stable product formed is citric acid (6c), hence it is
called citric Acid cycle. In this cycle first & acids
(citrate, cis -aconitate, isocitrate,
oxalosuccinate).
contain three carboxylic acid groups, hence it is called
Tricarboxylic Acid cycle- TCA cycle.
9. Oxidation –IV _ Malate dehydrog enase
2. This cycle occurs in mitochondrial matrix only if
oxygen is available in the cell.
2) During each turn 3 molecules of water are used up
and 2 molecules of CO2 are released.
3. There are many steps each is catalysed by specific
enzyme.
3) Two turns of cycle produces 6 NADH2, 2 FADH2 and
2 ATP.
4. Acetyl CoA enters the cycle and undergoes
complete oxidation and forms reduced conenzymes
NADH2 and FADH2.
4) Total gain of ATP via Kerbs cycle as follows .
5. There are 4 oxidation (dehydrogenation) steps and
2 decarboxylation steps.
6. Initial acceptor (oxaloacetic acid) of acetyl CoA is
regenerated.
7. Major reactions of Kerbs cycle - Enzymes
involved
1. Condensation -
Citrate
synthetase
2. Isomerisation – Aconitase (Dehydration, Hydration)
3. Oxidation (Dehydrogenation)-I
dehydrogenase
4. Decarboxylation
dehydrogenase
–
I
5. Oxidative decarboxylation – II -dehydrogenase
--
–
Isocitrate
Oxalosuccinate
-
ketoglutarate
6. Hydration and phosphorylation – Succinate
Thiokinase
7.Oxidation – III ---
succinate dehydrogenase
(dehydrogenation – III)
8. Hydration --- Fumarase
(dehydrogenation-IV)
9. Significance of Krebs cycle.
1) Two molecules of pyruvate forms via glycolysis thus
Kerbs cycle occurs twice for oxidation of one glucose
molecule.
Direct ATP formed
= 2 ATP
Indirect ATP via ETS :
= 18 ATP
i.e. 6 NADH2 2 ATP
= 4 ATP
______
24 ATP
ii) Coenzyme and electron carrier (CoQ or
Ubiquinone )
iii) electron carriers = Cytochromes
(Fe-proteins) b, c1, c, a, a3
4. Complete oxidation of glucose via glycolysis, Link
reaction and TCA cycle produces reduced coenzymes
as l0 NADH2 and 2 FADH2.
5. From NADH2 hydrogens are accepted by FMN. Then
hydrogen splits into protons and electrons,
H2 
 2H  2e.
Protons are released in matrix and electrons pass to
CoQ. Electrons then pass through cytochromes b, c,
c1, a and a3. Finally electrons are accepted oxygen to
form ionic oxygenic which combines with 2H+ from
matrix to form metabolic water.
This is called terminal oxidation.
6. During electron transport energy is released which
is used for biosynthesis of ATP Via oxysomes/F1
particles. This ATP synthesis is called oxidative
phosphorylation.
Q.3. Illustrate the mechanism of Electron transport
system or Terminal oxidation.
7. From one NADH2, 3 ATP molecules form at 3 steps
as
Ans: 1. The metabolic pathway through which the
electrons pass from one carrier to another is called
electron transport system (ETS) and it is present on
inner mitochondrial membrane.
1. between NADH2 and FMN
2. It involves release of energy from NADH2 and
FADH2 and utilize it for the synthesis of ATP.
This is accomplished when they are oxidised through
ETS and electrons are passed on to O2 resulting in the
formation of H2O.
3. Members of ETS are
i)hydrogen carriers or coenzymes (NAD, FMN)
2. at cytochrome b and C1 complex
3. at cytochrome a and a3 complex.
8. From one FADH2 2ATP molecules form as electrons
from it enters directly at CoQ level and thus first ATP
step is omitted.
9. Diagrammatic presentation of ETS.
The mechanism of anaerobic respiration involves
glycolysis, decarboxylation and reduction.
10.
Significance of ETS :
1) It generates major amount of energy in form of
ATP. i.e. 34 ATP out of total 38 ATP per glucose.
2) It releases energy in stepwise manner to prevent
damage of cells.
3) It regenerates oxidised coenzymes
FAD.
NAD,
4) It provides water necessary for Krebs cycle.
(i) Glycolysis : Glycolysis or EMP Pathway is an
anaerobic process and occurs in cytoplasm. It is
similar to that of aerobic respiration. During
glycolysis, each glucose molecule is broken down into
two molecules of pyruvate with the formation of two
molecules each of NADH2 and ATP. It may be
represented as follows :
C6 H12 O6  2NAD  2ADP  2ip 
2CH3CO  COOH  2NADH2  2ADP
2CH3  CO  COOH
pyruvate
Decarboxylase
 2CH3  CHO  2CO 2
TPP  Zn 
Q.4.
Describe the mechanism of anaerobic
respiration.
Ans: Anareobic Respiration :
Incomplete oxidation of the respiratory
substrate in the absence of oxygen to yield CO2 and
ethyl alcohol is called anaerobic respiration. It give
relatively less amount of energy.
A number of bacteria and some fungi such as
yeasts show anaerobic respiration. It occurs in
cytoplasm onkly and gives net gain of 2 ATP per
glucose molecule.
(ii)
Decarboxylation:
Pyruvate
undergoes
decarboxylation by removal of a CO2 molecule. It
occurs in presence of the enzyme pyruvate
decarboxylase to give acetaldehyde.
Coenzyme
thiamine pyrophosphate (TPP) and the cofactor Zn++
is necessary for this reaction.
(ii) Reduction: Acetaldehyde is reduced to ethyl
alcohol by the reduced coenzyme NADH2. The reaction
occurs in presence of the enzyme dehydrogenase.
NADH2 is oxidized to NAD.
Dehydrogenase
2CH3  CHO  2 NADH2 

2CH3CHOH  COOH  2NAD