Photosynthesis in Higher Plants Practice Questions - DPP for NEET

 Page 1


Solution
1. (d)
Dark reaction is a thermochemical reaction. It
takes place in the stroma of the chloroplast. Dark
reaction, also called CO
2
 fixation or carbon
assimilation, occurs even in the presence of light
but it doesn’t require light. Dark reaction consists
of 3 phasescarboxylation, reduction and
regeneration of CO
2
 acceptor.
2. (d)
A : Light reaction occurs in the grana of the
chloroplast. It is the first stage of photosynthesis
in which plants capture and store energy from
sunlight. In this process, light energy is
converted into chemical energy, in the form of
the energy-carrying molecules ATP and
NADPH. It was observed by Arnon.
B : Dark reaction is a thermochemical reaction,
which takes place in the stroma of the
chloroplast. It is not a light driven reaction
but are dependent on the products of light
reactions (ATP and NADPH).
C : Glycolysis takes place in the cytoplasm. It is
a metabolic process that occurs in nearly all
living cells in which glucose is converted in a
series of steps to pyruvic acid and during
which energy is released in the form of ATP.
D : Krebs cycle is the sequence of reactions by
which most living cells generate energy
during the process of aerobic respiration. It
takes place in the mitochondria (matrix), using
up oxygen and producing carbon dioxide and
water as waste products, and ADP is
converted to energy-rich ATP.
3. (a)
A : Photolysis of water - oxygen evolving
complex ferric oxalate
B : ATP synthesis - Proton gradient concentration
C : Pigments - Absorbs light at specific wavelengths
D : High oxygen - Photorespiration
4. (d)
All statements are correct.
5. (d)
In the given diagram of ATP synthesis through
the chemiosmosis, the correct labelling of the A,
B, C and D are respectively F
0
, thylakoid
membrane, photosystem II and photosystem I.
The chemiosmotic theory (Mitchell 1961) explains
how ATP is generated in the chloroplast. ATP
synthesis in chloroplasts (photophosphorylation)
proceeds according to a mechanism that is
basically similar to that in mitochondria.
6. (d)
All statements are correct.
7. (d)
According to Blackmans law of limiting factor,
at any given time photosynthesis can be limited
either by light or CO
2
. Blackman proposed the
law of limiting factors in 1905 to determine the
rate of photosynthesis. According to this law,
when a process depends on a number of factors,
its rate is limited by the pace of the slowest
factor.
8. (b)
According to law of limiting factors given by
Blackman, when a process depends upon a
number of factors which are separate, the rate
of the process is limited by the pace of the
slowest factor. Rate of yield is dependent on
light as photosynthesis is dependent on light.
During monsoon, the light is dim and so this
reduces rate of photosynthesis and hence
yield.
9. (d)
As the intensity of light increases, the rate of
photosynthesis also increases. But at higher light
intensity, the rate of photosynthesis decreases,
because of the following reasons–
(i) other factors required for photosynthesis
become limiting.
(ii) destruction of chlorophyll occurs, so there will
be no carbohydrate (sugar) formation.
10. (c)
Under water stress, the rate of photosynthesis
declines because of stomatal closure leading to
decrease in CO
2
 supply and reduced water potential
that decrease leaf surface areas for photosynthesis.
11. (c)
In C
4
 (sugarcane plant) plant, 14CO
2
 is fixed in
malic acid in which the enzymes that fixes CO
2
is phosphoenol pyruvic acid carboxylase.
Phosphoenolpyruvate carboxylase catalyzes the
addition of bicarbonate (HCO
3
–
) to phosphoenol
pyruvate (PEP) to form the four-carbon
compound oxaloacetate and inorganic phosphate:
PEP + HCO
3
–
 Oxaloacetate + P
i
Page 2


Solution
1. (d)
Dark reaction is a thermochemical reaction. It
takes place in the stroma of the chloroplast. Dark
reaction, also called CO
2
 fixation or carbon
assimilation, occurs even in the presence of light
but it doesn’t require light. Dark reaction consists
of 3 phasescarboxylation, reduction and
regeneration of CO
2
 acceptor.
2. (d)
A : Light reaction occurs in the grana of the
chloroplast. It is the first stage of photosynthesis
in which plants capture and store energy from
sunlight. In this process, light energy is
converted into chemical energy, in the form of
the energy-carrying molecules ATP and
NADPH. It was observed by Arnon.
B : Dark reaction is a thermochemical reaction,
which takes place in the stroma of the
chloroplast. It is not a light driven reaction
but are dependent on the products of light
reactions (ATP and NADPH).
C : Glycolysis takes place in the cytoplasm. It is
a metabolic process that occurs in nearly all
living cells in which glucose is converted in a
series of steps to pyruvic acid and during
which energy is released in the form of ATP.
D : Krebs cycle is the sequence of reactions by
which most living cells generate energy
during the process of aerobic respiration. It
takes place in the mitochondria (matrix), using
up oxygen and producing carbon dioxide and
water as waste products, and ADP is
converted to energy-rich ATP.
3. (a)
A : Photolysis of water - oxygen evolving
complex ferric oxalate
B : ATP synthesis - Proton gradient concentration
C : Pigments - Absorbs light at specific wavelengths
D : High oxygen - Photorespiration
4. (d)
All statements are correct.
5. (d)
In the given diagram of ATP synthesis through
the chemiosmosis, the correct labelling of the A,
B, C and D are respectively F
0
, thylakoid
membrane, photosystem II and photosystem I.
The chemiosmotic theory (Mitchell 1961) explains
how ATP is generated in the chloroplast. ATP
synthesis in chloroplasts (photophosphorylation)
proceeds according to a mechanism that is
basically similar to that in mitochondria.
6. (d)
All statements are correct.
7. (d)
According to Blackmans law of limiting factor,
at any given time photosynthesis can be limited
either by light or CO
2
. Blackman proposed the
law of limiting factors in 1905 to determine the
rate of photosynthesis. According to this law,
when a process depends on a number of factors,
its rate is limited by the pace of the slowest
factor.
8. (b)
According to law of limiting factors given by
Blackman, when a process depends upon a
number of factors which are separate, the rate
of the process is limited by the pace of the
slowest factor. Rate of yield is dependent on
light as photosynthesis is dependent on light.
During monsoon, the light is dim and so this
reduces rate of photosynthesis and hence
yield.
9. (d)
As the intensity of light increases, the rate of
photosynthesis also increases. But at higher light
intensity, the rate of photosynthesis decreases,
because of the following reasons–
(i) other factors required for photosynthesis
become limiting.
(ii) destruction of chlorophyll occurs, so there will
be no carbohydrate (sugar) formation.
10. (c)
Under water stress, the rate of photosynthesis
declines because of stomatal closure leading to
decrease in CO
2
 supply and reduced water potential
that decrease leaf surface areas for photosynthesis.
11. (c)
In C
4
 (sugarcane plant) plant, 14CO
2
 is fixed in
malic acid in which the enzymes that fixes CO
2
is phosphoenol pyruvic acid carboxylase.
Phosphoenolpyruvate carboxylase catalyzes the
addition of bicarbonate (HCO
3
–
) to phosphoenol
pyruvate (PEP) to form the four-carbon
compound oxaloacetate and inorganic phosphate:
PEP + HCO
3
–
 Oxaloacetate + P
i
This reaction is used for carbon fixation in CAM
(Crassulacean acid metabolism) and C
4
organisms, as well as to regulate flux through the
citric acid cycle (also known as Krebs or TCA
cycle) in bacteria and plants.
12. (d)
If the supply of oxygen is decreased to an illuminated
wheat plant, its photosynthesis would increase.
13. (a)
Photolysis of water is a process of breakdown of
water molecules into hydrogen (H
+
) and oxygen
[O] and electrons by the influence of light during
the light reactions of photosynthesis. The
hydrogen released from the water molecule is
transferred to the hydrogen acceptor. NADP
becomes reduced to form NADPH
2
. The splitting
of water is associated with the PSII.
14. (a)
Chemiosmotic hypothesis has been put forward
by Mitchell (1961) to explain the mechanism of
ATP synthesis.
15. (a)
ATP synthesis is linked to the development of a
proton gradient across the membranes of thylakoid.
16. (a)
Both statements are correct.
17. (d)
The light driven synthesis of ATP and NADPH
provides energy and reducing power for the
conversion of inorganic carbon into organic
carbon; for the production of sugars and fixation
of CO
2
 into trioses.
18. (b)
(II) In photosynthesis, protons or hydrogen ions that
are produced by the splitting of water
accumulate within the lumen of the thylakoids.
19. (b)
The use of radioactive 
14
C by Melvin Calvin in
algal photosynthesis studieshad led to the
discovery that the first CO
2
 fixation product was
a 3-carbon organic acid.
20. (a)
In Calvin cycle, carboxylation is the most crucial
step where CO
2
 is utilised for the carboxylation
of RuBP. In this CO
2
 reacts with ribulose 1,5
biphosphate to yield two molecules of 3-
phosphoglycerate, a reaction catalyzed by the
chloroplast enzyme ribulose biphosphate
carboxylase-oxygenase, referred to as RuBisCO.
21. (d)
In C
4
 plants , the process by which C
4
 acids are
converted into C
3
 acids in the bundle sheath cell is
known as decarboxylation. Shortly after the
discovery of the C
4
 cycle the Crassulacean acid
metabolism (CAM) pathway was dissected and
elucidated as a C
4
 variant. This pathway is found
in desert succulents and epiphytes. In the typical
C
4
 cycle, the fixation reaction occurred in a
mesophyll cell and the decarboxylation reaction
occurred in a bundle sheath cell, Decarboxylation
is a chemical reaction that removes a carboxyl
group and releases carbon dioxide (CO
2
). Enzymes
that catalyze decarboxylation are called
decarboxylases.
22. (c)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only.
Photorespiration is absent in C
4
 plants and is
present in C
3
 plants. Photorespiration involves
three cell organelles–Peroxisomes, chloroplasts
and mitochondria.
23. (d)
Photorespiration is the process by which in the
presence of light plant consumes oxygen and
releases carbon dioxide (instead of fixing carbon
dioxide) during photosynthesis, resulting in a
decrease in photosynthetic output since no ATP
is produced and carbon (as well as nitrogen in
the form of ammonia) is lost inevitably. In this
pathway there is no synthesis of sugar, ATP or
NADPH, due to which photorespiration refers
to as a wasteful process. This process reduces
efficiency of photosynthesis in C
3
 plants.
24. (a)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only. It
is absent in C
4
 plants and present in C
3
 plants.
Photorespiration occurs because oxygen rather
than carbon dioxide links to the rubisco enzyme
in the Calvin cycle. It involves three cell
organelles - peroxisomes, chloroplast and
mitochondria.
25. (c)
The Calvin cycle takes place in the stroma of
chloroplasts of mesophyll cell because enzymes
and intermediates of the Calvin cycle are located
in the stroma of chloroplasts.
Page 3


Solution
1. (d)
Dark reaction is a thermochemical reaction. It
takes place in the stroma of the chloroplast. Dark
reaction, also called CO
2
 fixation or carbon
assimilation, occurs even in the presence of light
but it doesn’t require light. Dark reaction consists
of 3 phasescarboxylation, reduction and
regeneration of CO
2
 acceptor.
2. (d)
A : Light reaction occurs in the grana of the
chloroplast. It is the first stage of photosynthesis
in which plants capture and store energy from
sunlight. In this process, light energy is
converted into chemical energy, in the form of
the energy-carrying molecules ATP and
NADPH. It was observed by Arnon.
B : Dark reaction is a thermochemical reaction,
which takes place in the stroma of the
chloroplast. It is not a light driven reaction
but are dependent on the products of light
reactions (ATP and NADPH).
C : Glycolysis takes place in the cytoplasm. It is
a metabolic process that occurs in nearly all
living cells in which glucose is converted in a
series of steps to pyruvic acid and during
which energy is released in the form of ATP.
D : Krebs cycle is the sequence of reactions by
which most living cells generate energy
during the process of aerobic respiration. It
takes place in the mitochondria (matrix), using
up oxygen and producing carbon dioxide and
water as waste products, and ADP is
converted to energy-rich ATP.
3. (a)
A : Photolysis of water - oxygen evolving
complex ferric oxalate
B : ATP synthesis - Proton gradient concentration
C : Pigments - Absorbs light at specific wavelengths
D : High oxygen - Photorespiration
4. (d)
All statements are correct.
5. (d)
In the given diagram of ATP synthesis through
the chemiosmosis, the correct labelling of the A,
B, C and D are respectively F
0
, thylakoid
membrane, photosystem II and photosystem I.
The chemiosmotic theory (Mitchell 1961) explains
how ATP is generated in the chloroplast. ATP
synthesis in chloroplasts (photophosphorylation)
proceeds according to a mechanism that is
basically similar to that in mitochondria.
6. (d)
All statements are correct.
7. (d)
According to Blackmans law of limiting factor,
at any given time photosynthesis can be limited
either by light or CO
2
. Blackman proposed the
law of limiting factors in 1905 to determine the
rate of photosynthesis. According to this law,
when a process depends on a number of factors,
its rate is limited by the pace of the slowest
factor.
8. (b)
According to law of limiting factors given by
Blackman, when a process depends upon a
number of factors which are separate, the rate
of the process is limited by the pace of the
slowest factor. Rate of yield is dependent on
light as photosynthesis is dependent on light.
During monsoon, the light is dim and so this
reduces rate of photosynthesis and hence
yield.
9. (d)
As the intensity of light increases, the rate of
photosynthesis also increases. But at higher light
intensity, the rate of photosynthesis decreases,
because of the following reasons–
(i) other factors required for photosynthesis
become limiting.
(ii) destruction of chlorophyll occurs, so there will
be no carbohydrate (sugar) formation.
10. (c)
Under water stress, the rate of photosynthesis
declines because of stomatal closure leading to
decrease in CO
2
 supply and reduced water potential
that decrease leaf surface areas for photosynthesis.
11. (c)
In C
4
 (sugarcane plant) plant, 14CO
2
 is fixed in
malic acid in which the enzymes that fixes CO
2
is phosphoenol pyruvic acid carboxylase.
Phosphoenolpyruvate carboxylase catalyzes the
addition of bicarbonate (HCO
3
–
) to phosphoenol
pyruvate (PEP) to form the four-carbon
compound oxaloacetate and inorganic phosphate:
PEP + HCO
3
–
 Oxaloacetate + P
i
This reaction is used for carbon fixation in CAM
(Crassulacean acid metabolism) and C
4
organisms, as well as to regulate flux through the
citric acid cycle (also known as Krebs or TCA
cycle) in bacteria and plants.
12. (d)
If the supply of oxygen is decreased to an illuminated
wheat plant, its photosynthesis would increase.
13. (a)
Photolysis of water is a process of breakdown of
water molecules into hydrogen (H
+
) and oxygen
[O] and electrons by the influence of light during
the light reactions of photosynthesis. The
hydrogen released from the water molecule is
transferred to the hydrogen acceptor. NADP
becomes reduced to form NADPH
2
. The splitting
of water is associated with the PSII.
14. (a)
Chemiosmotic hypothesis has been put forward
by Mitchell (1961) to explain the mechanism of
ATP synthesis.
15. (a)
ATP synthesis is linked to the development of a
proton gradient across the membranes of thylakoid.
16. (a)
Both statements are correct.
17. (d)
The light driven synthesis of ATP and NADPH
provides energy and reducing power for the
conversion of inorganic carbon into organic
carbon; for the production of sugars and fixation
of CO
2
 into trioses.
18. (b)
(II) In photosynthesis, protons or hydrogen ions that
are produced by the splitting of water
accumulate within the lumen of the thylakoids.
19. (b)
The use of radioactive 
14
C by Melvin Calvin in
algal photosynthesis studieshad led to the
discovery that the first CO
2
 fixation product was
a 3-carbon organic acid.
20. (a)
In Calvin cycle, carboxylation is the most crucial
step where CO
2
 is utilised for the carboxylation
of RuBP. In this CO
2
 reacts with ribulose 1,5
biphosphate to yield two molecules of 3-
phosphoglycerate, a reaction catalyzed by the
chloroplast enzyme ribulose biphosphate
carboxylase-oxygenase, referred to as RuBisCO.
21. (d)
In C
4
 plants , the process by which C
4
 acids are
converted into C
3
 acids in the bundle sheath cell is
known as decarboxylation. Shortly after the
discovery of the C
4
 cycle the Crassulacean acid
metabolism (CAM) pathway was dissected and
elucidated as a C
4
 variant. This pathway is found
in desert succulents and epiphytes. In the typical
C
4
 cycle, the fixation reaction occurred in a
mesophyll cell and the decarboxylation reaction
occurred in a bundle sheath cell, Decarboxylation
is a chemical reaction that removes a carboxyl
group and releases carbon dioxide (CO
2
). Enzymes
that catalyze decarboxylation are called
decarboxylases.
22. (c)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only.
Photorespiration is absent in C
4
 plants and is
present in C
3
 plants. Photorespiration involves
three cell organelles–Peroxisomes, chloroplasts
and mitochondria.
23. (d)
Photorespiration is the process by which in the
presence of light plant consumes oxygen and
releases carbon dioxide (instead of fixing carbon
dioxide) during photosynthesis, resulting in a
decrease in photosynthetic output since no ATP
is produced and carbon (as well as nitrogen in
the form of ammonia) is lost inevitably. In this
pathway there is no synthesis of sugar, ATP or
NADPH, due to which photorespiration refers
to as a wasteful process. This process reduces
efficiency of photosynthesis in C
3
 plants.
24. (a)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only. It
is absent in C
4
 plants and present in C
3
 plants.
Photorespiration occurs because oxygen rather
than carbon dioxide links to the rubisco enzyme
in the Calvin cycle. It involves three cell
organelles - peroxisomes, chloroplast and
mitochondria.
25. (c)
The Calvin cycle takes place in the stroma of
chloroplasts of mesophyll cell because enzymes
and intermediates of the Calvin cycle are located
in the stroma of chloroplasts.
26. (d)
RuBisCO is an enzyme present in chloroplasts,
involved in fixing atmospheric carbon dioxide
during photosynthesis and in oxygenation of the
resulting compound during photorespiration. It is
the most abundant enzyme on the earth and
catalyzes the carboxylation of CO
2
 to ribulose 1,
5-bisphosphate, initiates photorespiration when
the CO
2
/O
2
 ratio is low.
27. (c)
(I) Electron gradient is important because
breakdown of this gradient leads to
synthesis of ATP.
28. (c)
Light-induced CO
2
 liberation from a C
2
 compound
of dark phase is called photorespiration. This
process is considered to nullify the result of
photosynthesis as there is no synthesis of ATP or
NADPH.
29. (c)
In C
3
 plants the primary CO
2
 acceptor is RuBP
and the initial stable product is PGA. While in C
4
plants, the primary CO
2
 acceptor is PEP and the
first stable product is OAA.
30. (a)
Maize is a C
4
 plant. It possesses Kranz anatomy
which is absent in C
3
 plants.
31. (b)
Reaction center in PS - II is P
680
. PS-II is located
on the inner surface of appressed parts of grana
thylakoid. PS-II is inolved only in non-cyclic
electron transport.
32. (b)
(II) The break down of the gradient provides
enough energy to cause a conformational
change in the CF
1
  particle of the A TP synthase.
33. (a)
Both statements are correct.
34. (d)
In non-cyclic reaction of photosynthesis, electrons
from chlorophyll molecules in photosystem I are
used in the formation of NADPH. The source of
those electrons is photosystem II which splits
water molecule.
35. (d)
Calvin cycle that take place in stroma of the
chloroplasts during photosynthesis, is light in
dependent. But they usually do not occur in night
because this cycle is dependent on the products
of the light reactions. The Calvin cycle proceeds
in three stages: carboxylation [CO
2
 is covalently
linked to a carbon skeleton (RuBP)], reduction
(carbohydrate is formed at the expense of ATP
and NADPH) and regeneration (the CO
2
acceptor RuBP reforms at the expense of ATP.
36. (a)
Both statements are correct.
37. (d)
According to the experiment performed by the
student, photosynthesis will not take place because
intact chloroplast is needed for the process of
photosynthesis. Photosynthesis is the process by
which green plants create energy from sunlight.
It occurs at the cellular level in the leaves of plants
and is the way in which they produce oxygen
and carbohydrates. The oxygen is released into
the atmosphere, and the carbohydrates, simple
sugars, are used by the plant for growth. In order
to carry out photosynthesis, green plants need
several ingredients. Chlorophyll, the pigment in
plants that makes them green, is essential to the
photosynthetic process. This chemical is produced
naturally by all green plants and its role in
photosynthesis is to absorb light.
38. (b)
(II) Mesophyll cells in C
3
 plants show Calvin
cycle CO
2
 fixation.
39. (b)
"ADP is phosphorylated and NADP is reduced"
occurs during light phase of the photosynthesis.
The 'light-dependent reactions' is the process by
which plants capture and store energy from
sunlight. In this process, light energy is converted
into chemical energy, in the form of the energy-
carrying molecules ATP and NADPH.
40. (a)
During light reaction, as electrons move through
the photosystems, protons are transported across
the membrane because of the primary acceptor
of e
–
 (located towards the outer surface of the
membrane) transfers its electrons not to an e–
carrier but to H carrier.
Page 4


Solution
1. (d)
Dark reaction is a thermochemical reaction. It
takes place in the stroma of the chloroplast. Dark
reaction, also called CO
2
 fixation or carbon
assimilation, occurs even in the presence of light
but it doesn’t require light. Dark reaction consists
of 3 phasescarboxylation, reduction and
regeneration of CO
2
 acceptor.
2. (d)
A : Light reaction occurs in the grana of the
chloroplast. It is the first stage of photosynthesis
in which plants capture and store energy from
sunlight. In this process, light energy is
converted into chemical energy, in the form of
the energy-carrying molecules ATP and
NADPH. It was observed by Arnon.
B : Dark reaction is a thermochemical reaction,
which takes place in the stroma of the
chloroplast. It is not a light driven reaction
but are dependent on the products of light
reactions (ATP and NADPH).
C : Glycolysis takes place in the cytoplasm. It is
a metabolic process that occurs in nearly all
living cells in which glucose is converted in a
series of steps to pyruvic acid and during
which energy is released in the form of ATP.
D : Krebs cycle is the sequence of reactions by
which most living cells generate energy
during the process of aerobic respiration. It
takes place in the mitochondria (matrix), using
up oxygen and producing carbon dioxide and
water as waste products, and ADP is
converted to energy-rich ATP.
3. (a)
A : Photolysis of water - oxygen evolving
complex ferric oxalate
B : ATP synthesis - Proton gradient concentration
C : Pigments - Absorbs light at specific wavelengths
D : High oxygen - Photorespiration
4. (d)
All statements are correct.
5. (d)
In the given diagram of ATP synthesis through
the chemiosmosis, the correct labelling of the A,
B, C and D are respectively F
0
, thylakoid
membrane, photosystem II and photosystem I.
The chemiosmotic theory (Mitchell 1961) explains
how ATP is generated in the chloroplast. ATP
synthesis in chloroplasts (photophosphorylation)
proceeds according to a mechanism that is
basically similar to that in mitochondria.
6. (d)
All statements are correct.
7. (d)
According to Blackmans law of limiting factor,
at any given time photosynthesis can be limited
either by light or CO
2
. Blackman proposed the
law of limiting factors in 1905 to determine the
rate of photosynthesis. According to this law,
when a process depends on a number of factors,
its rate is limited by the pace of the slowest
factor.
8. (b)
According to law of limiting factors given by
Blackman, when a process depends upon a
number of factors which are separate, the rate
of the process is limited by the pace of the
slowest factor. Rate of yield is dependent on
light as photosynthesis is dependent on light.
During monsoon, the light is dim and so this
reduces rate of photosynthesis and hence
yield.
9. (d)
As the intensity of light increases, the rate of
photosynthesis also increases. But at higher light
intensity, the rate of photosynthesis decreases,
because of the following reasons–
(i) other factors required for photosynthesis
become limiting.
(ii) destruction of chlorophyll occurs, so there will
be no carbohydrate (sugar) formation.
10. (c)
Under water stress, the rate of photosynthesis
declines because of stomatal closure leading to
decrease in CO
2
 supply and reduced water potential
that decrease leaf surface areas for photosynthesis.
11. (c)
In C
4
 (sugarcane plant) plant, 14CO
2
 is fixed in
malic acid in which the enzymes that fixes CO
2
is phosphoenol pyruvic acid carboxylase.
Phosphoenolpyruvate carboxylase catalyzes the
addition of bicarbonate (HCO
3
–
) to phosphoenol
pyruvate (PEP) to form the four-carbon
compound oxaloacetate and inorganic phosphate:
PEP + HCO
3
–
 Oxaloacetate + P
i
This reaction is used for carbon fixation in CAM
(Crassulacean acid metabolism) and C
4
organisms, as well as to regulate flux through the
citric acid cycle (also known as Krebs or TCA
cycle) in bacteria and plants.
12. (d)
If the supply of oxygen is decreased to an illuminated
wheat plant, its photosynthesis would increase.
13. (a)
Photolysis of water is a process of breakdown of
water molecules into hydrogen (H
+
) and oxygen
[O] and electrons by the influence of light during
the light reactions of photosynthesis. The
hydrogen released from the water molecule is
transferred to the hydrogen acceptor. NADP
becomes reduced to form NADPH
2
. The splitting
of water is associated with the PSII.
14. (a)
Chemiosmotic hypothesis has been put forward
by Mitchell (1961) to explain the mechanism of
ATP synthesis.
15. (a)
ATP synthesis is linked to the development of a
proton gradient across the membranes of thylakoid.
16. (a)
Both statements are correct.
17. (d)
The light driven synthesis of ATP and NADPH
provides energy and reducing power for the
conversion of inorganic carbon into organic
carbon; for the production of sugars and fixation
of CO
2
 into trioses.
18. (b)
(II) In photosynthesis, protons or hydrogen ions that
are produced by the splitting of water
accumulate within the lumen of the thylakoids.
19. (b)
The use of radioactive 
14
C by Melvin Calvin in
algal photosynthesis studieshad led to the
discovery that the first CO
2
 fixation product was
a 3-carbon organic acid.
20. (a)
In Calvin cycle, carboxylation is the most crucial
step where CO
2
 is utilised for the carboxylation
of RuBP. In this CO
2
 reacts with ribulose 1,5
biphosphate to yield two molecules of 3-
phosphoglycerate, a reaction catalyzed by the
chloroplast enzyme ribulose biphosphate
carboxylase-oxygenase, referred to as RuBisCO.
21. (d)
In C
4
 plants , the process by which C
4
 acids are
converted into C
3
 acids in the bundle sheath cell is
known as decarboxylation. Shortly after the
discovery of the C
4
 cycle the Crassulacean acid
metabolism (CAM) pathway was dissected and
elucidated as a C
4
 variant. This pathway is found
in desert succulents and epiphytes. In the typical
C
4
 cycle, the fixation reaction occurred in a
mesophyll cell and the decarboxylation reaction
occurred in a bundle sheath cell, Decarboxylation
is a chemical reaction that removes a carboxyl
group and releases carbon dioxide (CO
2
). Enzymes
that catalyze decarboxylation are called
decarboxylases.
22. (c)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only.
Photorespiration is absent in C
4
 plants and is
present in C
3
 plants. Photorespiration involves
three cell organelles–Peroxisomes, chloroplasts
and mitochondria.
23. (d)
Photorespiration is the process by which in the
presence of light plant consumes oxygen and
releases carbon dioxide (instead of fixing carbon
dioxide) during photosynthesis, resulting in a
decrease in photosynthetic output since no ATP
is produced and carbon (as well as nitrogen in
the form of ammonia) is lost inevitably. In this
pathway there is no synthesis of sugar, ATP or
NADPH, due to which photorespiration refers
to as a wasteful process. This process reduces
efficiency of photosynthesis in C
3
 plants.
24. (a)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only. It
is absent in C
4
 plants and present in C
3
 plants.
Photorespiration occurs because oxygen rather
than carbon dioxide links to the rubisco enzyme
in the Calvin cycle. It involves three cell
organelles - peroxisomes, chloroplast and
mitochondria.
25. (c)
The Calvin cycle takes place in the stroma of
chloroplasts of mesophyll cell because enzymes
and intermediates of the Calvin cycle are located
in the stroma of chloroplasts.
26. (d)
RuBisCO is an enzyme present in chloroplasts,
involved in fixing atmospheric carbon dioxide
during photosynthesis and in oxygenation of the
resulting compound during photorespiration. It is
the most abundant enzyme on the earth and
catalyzes the carboxylation of CO
2
 to ribulose 1,
5-bisphosphate, initiates photorespiration when
the CO
2
/O
2
 ratio is low.
27. (c)
(I) Electron gradient is important because
breakdown of this gradient leads to
synthesis of ATP.
28. (c)
Light-induced CO
2
 liberation from a C
2
 compound
of dark phase is called photorespiration. This
process is considered to nullify the result of
photosynthesis as there is no synthesis of ATP or
NADPH.
29. (c)
In C
3
 plants the primary CO
2
 acceptor is RuBP
and the initial stable product is PGA. While in C
4
plants, the primary CO
2
 acceptor is PEP and the
first stable product is OAA.
30. (a)
Maize is a C
4
 plant. It possesses Kranz anatomy
which is absent in C
3
 plants.
31. (b)
Reaction center in PS - II is P
680
. PS-II is located
on the inner surface of appressed parts of grana
thylakoid. PS-II is inolved only in non-cyclic
electron transport.
32. (b)
(II) The break down of the gradient provides
enough energy to cause a conformational
change in the CF
1
  particle of the A TP synthase.
33. (a)
Both statements are correct.
34. (d)
In non-cyclic reaction of photosynthesis, electrons
from chlorophyll molecules in photosystem I are
used in the formation of NADPH. The source of
those electrons is photosystem II which splits
water molecule.
35. (d)
Calvin cycle that take place in stroma of the
chloroplasts during photosynthesis, is light in
dependent. But they usually do not occur in night
because this cycle is dependent on the products
of the light reactions. The Calvin cycle proceeds
in three stages: carboxylation [CO
2
 is covalently
linked to a carbon skeleton (RuBP)], reduction
(carbohydrate is formed at the expense of ATP
and NADPH) and regeneration (the CO
2
acceptor RuBP reforms at the expense of ATP.
36. (a)
Both statements are correct.
37. (d)
According to the experiment performed by the
student, photosynthesis will not take place because
intact chloroplast is needed for the process of
photosynthesis. Photosynthesis is the process by
which green plants create energy from sunlight.
It occurs at the cellular level in the leaves of plants
and is the way in which they produce oxygen
and carbohydrates. The oxygen is released into
the atmosphere, and the carbohydrates, simple
sugars, are used by the plant for growth. In order
to carry out photosynthesis, green plants need
several ingredients. Chlorophyll, the pigment in
plants that makes them green, is essential to the
photosynthetic process. This chemical is produced
naturally by all green plants and its role in
photosynthesis is to absorb light.
38. (b)
(II) Mesophyll cells in C
3
 plants show Calvin
cycle CO
2
 fixation.
39. (b)
"ADP is phosphorylated and NADP is reduced"
occurs during light phase of the photosynthesis.
The 'light-dependent reactions' is the process by
which plants capture and store energy from
sunlight. In this process, light energy is converted
into chemical energy, in the form of the energy-
carrying molecules ATP and NADPH.
40. (a)
During light reaction, as electrons move through
the photosystems, protons are transported across
the membrane because of the primary acceptor
of e
–
 (located towards the outer surface of the
membrane) transfers its electrons not to an e–
carrier but to H carrier.
41. (c)
The pigments are organised into two discrete
photochemical light harvesting complexes (LHC)
within the Photosystem I (PS I) and Photosystem
II (PS II). These are named in the sequence of
their discovery, and not in the sequence in which
they function during the light reaction.
42. (b)
The function of water in photosynthesis is to
supply electrons in the light dependent reaction.
The light dependent reactions take place in the
membranous sections of the chloroplast -
thylakoids (grana/lamellae) which offer a large
surface area to absorb light energy. The main
function of these reactions is to provide a source
of ATP and reduced NADP, which are used to
reduce CO
2
 in the light independent reactions.
43. (a)
Liberation of oxygen is not concerned with cyclic
photophosphorylation. This system is not concerned
with photo-oxidation of water but only concerned
with the production of ATP. Non-cyclic
photophosphorylation is the light-requiring part of
photosynthesis in higher plants, in which an electron
donor is required, and oxygen is produced as a
waste product. It consists of two photoreactions,
resulting in the synthesis of ATP and NADPH.
44. (a)
Photosynthesis is a physiochemical process by
which green plants and some other organisms use
sunlight to synthesize nutrients from carbon
dioxide and water, and generates oxygen as a
by-product.
45. (d)
Photosynthesis is the most important anabolic
process on earth. It is defined as the
transformation of photonic energy (i.e. light or
radiant energy) into chemical energy by the given
parts of the plants. In the process of
photosynthesis, light energy drives the synthesis
of carbohydrates from carbon dioxide and water
with the generation of oxygen.
46. (b)
Half leaf experiment proves that CO
2
 is essential
for photosynthesis.
47. (c)
Joseph Priestley (in 1970) performed a series of
experiments that revealed the essential role of
air in the growth of green plants.
48. (a)
Jan Ingenhousz showed that sunlight is essential
to the plant process that somehow purifies the
air fouled by burning candles or breathing animals.
Ingenhousz in an experiment with an aquatic plant
showed that in bright sunlight, small bubbles were
formed around the green parts while in the dark
they did not form any bubbles. Later he identified
the bubbles as oxygen.
Hence, he showed that it is only the green parts
of the plants that could release oxygen.
49. (b)
Cyclic pathway of photosynthesis first appeared
in some eubacterial species. It is supposed to be
the first evidence of production of ATP in the
presence of light. However oxygen started
accumulating in the atmosphere after the evolution
of non-cyclic pathway of photosynthesis in
cyanobacteria.
50. (b)
The first step in the photosynthesis is the light-
driven oxidation (splitting or photolysis) of water.
It provides electrons for the photosynthetic electron
transport chains as well as protons for the
establishment of a proton gradient. It occurs on
the lumenal side of the thylakoid membrane. During
photolysis, water is oxidised to oxygen, protons and
electrons. Protons accumulate in the lumen.
51. (b)
Paper chromatography is an analytical method
that is used to separate coloured chemicals or
substances, especially pigments. This can also be
used in secondary or primary colours in ink
experiments. Leaf pigments of any green plants
can be separated by using paper chromatography.
A chromatographic separation of the leaf pigments
shows that the colour we see in leaves is due to a
single pigment but due to four pigments: chlorophyll
a (bright or blue green in the chromatogram),
chlorophyll b (yellow green), xanthophylls (yellow)
and carotenoids (yellow to yellow orange).
52. (a)
Proton gradient is important because the
breakdown of this gradient leads to the release of
energy. This gradient which is created by the
accumulation of H
+
 ion inside the luman. is broken
down due to the movement of protons across the
membrane to the stroma through ATP synthase.
53. (b)
Page 5


Solution
1. (d)
Dark reaction is a thermochemical reaction. It
takes place in the stroma of the chloroplast. Dark
reaction, also called CO
2
 fixation or carbon
assimilation, occurs even in the presence of light
but it doesn’t require light. Dark reaction consists
of 3 phasescarboxylation, reduction and
regeneration of CO
2
 acceptor.
2. (d)
A : Light reaction occurs in the grana of the
chloroplast. It is the first stage of photosynthesis
in which plants capture and store energy from
sunlight. In this process, light energy is
converted into chemical energy, in the form of
the energy-carrying molecules ATP and
NADPH. It was observed by Arnon.
B : Dark reaction is a thermochemical reaction,
which takes place in the stroma of the
chloroplast. It is not a light driven reaction
but are dependent on the products of light
reactions (ATP and NADPH).
C : Glycolysis takes place in the cytoplasm. It is
a metabolic process that occurs in nearly all
living cells in which glucose is converted in a
series of steps to pyruvic acid and during
which energy is released in the form of ATP.
D : Krebs cycle is the sequence of reactions by
which most living cells generate energy
during the process of aerobic respiration. It
takes place in the mitochondria (matrix), using
up oxygen and producing carbon dioxide and
water as waste products, and ADP is
converted to energy-rich ATP.
3. (a)
A : Photolysis of water - oxygen evolving
complex ferric oxalate
B : ATP synthesis - Proton gradient concentration
C : Pigments - Absorbs light at specific wavelengths
D : High oxygen - Photorespiration
4. (d)
All statements are correct.
5. (d)
In the given diagram of ATP synthesis through
the chemiosmosis, the correct labelling of the A,
B, C and D are respectively F
0
, thylakoid
membrane, photosystem II and photosystem I.
The chemiosmotic theory (Mitchell 1961) explains
how ATP is generated in the chloroplast. ATP
synthesis in chloroplasts (photophosphorylation)
proceeds according to a mechanism that is
basically similar to that in mitochondria.
6. (d)
All statements are correct.
7. (d)
According to Blackmans law of limiting factor,
at any given time photosynthesis can be limited
either by light or CO
2
. Blackman proposed the
law of limiting factors in 1905 to determine the
rate of photosynthesis. According to this law,
when a process depends on a number of factors,
its rate is limited by the pace of the slowest
factor.
8. (b)
According to law of limiting factors given by
Blackman, when a process depends upon a
number of factors which are separate, the rate
of the process is limited by the pace of the
slowest factor. Rate of yield is dependent on
light as photosynthesis is dependent on light.
During monsoon, the light is dim and so this
reduces rate of photosynthesis and hence
yield.
9. (d)
As the intensity of light increases, the rate of
photosynthesis also increases. But at higher light
intensity, the rate of photosynthesis decreases,
because of the following reasons–
(i) other factors required for photosynthesis
become limiting.
(ii) destruction of chlorophyll occurs, so there will
be no carbohydrate (sugar) formation.
10. (c)
Under water stress, the rate of photosynthesis
declines because of stomatal closure leading to
decrease in CO
2
 supply and reduced water potential
that decrease leaf surface areas for photosynthesis.
11. (c)
In C
4
 (sugarcane plant) plant, 14CO
2
 is fixed in
malic acid in which the enzymes that fixes CO
2
is phosphoenol pyruvic acid carboxylase.
Phosphoenolpyruvate carboxylase catalyzes the
addition of bicarbonate (HCO
3
–
) to phosphoenol
pyruvate (PEP) to form the four-carbon
compound oxaloacetate and inorganic phosphate:
PEP + HCO
3
–
 Oxaloacetate + P
i
This reaction is used for carbon fixation in CAM
(Crassulacean acid metabolism) and C
4
organisms, as well as to regulate flux through the
citric acid cycle (also known as Krebs or TCA
cycle) in bacteria and plants.
12. (d)
If the supply of oxygen is decreased to an illuminated
wheat plant, its photosynthesis would increase.
13. (a)
Photolysis of water is a process of breakdown of
water molecules into hydrogen (H
+
) and oxygen
[O] and electrons by the influence of light during
the light reactions of photosynthesis. The
hydrogen released from the water molecule is
transferred to the hydrogen acceptor. NADP
becomes reduced to form NADPH
2
. The splitting
of water is associated with the PSII.
14. (a)
Chemiosmotic hypothesis has been put forward
by Mitchell (1961) to explain the mechanism of
ATP synthesis.
15. (a)
ATP synthesis is linked to the development of a
proton gradient across the membranes of thylakoid.
16. (a)
Both statements are correct.
17. (d)
The light driven synthesis of ATP and NADPH
provides energy and reducing power for the
conversion of inorganic carbon into organic
carbon; for the production of sugars and fixation
of CO
2
 into trioses.
18. (b)
(II) In photosynthesis, protons or hydrogen ions that
are produced by the splitting of water
accumulate within the lumen of the thylakoids.
19. (b)
The use of radioactive 
14
C by Melvin Calvin in
algal photosynthesis studieshad led to the
discovery that the first CO
2
 fixation product was
a 3-carbon organic acid.
20. (a)
In Calvin cycle, carboxylation is the most crucial
step where CO
2
 is utilised for the carboxylation
of RuBP. In this CO
2
 reacts with ribulose 1,5
biphosphate to yield two molecules of 3-
phosphoglycerate, a reaction catalyzed by the
chloroplast enzyme ribulose biphosphate
carboxylase-oxygenase, referred to as RuBisCO.
21. (d)
In C
4
 plants , the process by which C
4
 acids are
converted into C
3
 acids in the bundle sheath cell is
known as decarboxylation. Shortly after the
discovery of the C
4
 cycle the Crassulacean acid
metabolism (CAM) pathway was dissected and
elucidated as a C
4
 variant. This pathway is found
in desert succulents and epiphytes. In the typical
C
4
 cycle, the fixation reaction occurred in a
mesophyll cell and the decarboxylation reaction
occurred in a bundle sheath cell, Decarboxylation
is a chemical reaction that removes a carboxyl
group and releases carbon dioxide (CO
2
). Enzymes
that catalyze decarboxylation are called
decarboxylases.
22. (c)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only.
Photorespiration is absent in C
4
 plants and is
present in C
3
 plants. Photorespiration involves
three cell organelles–Peroxisomes, chloroplasts
and mitochondria.
23. (d)
Photorespiration is the process by which in the
presence of light plant consumes oxygen and
releases carbon dioxide (instead of fixing carbon
dioxide) during photosynthesis, resulting in a
decrease in photosynthetic output since no ATP
is produced and carbon (as well as nitrogen in
the form of ammonia) is lost inevitably. In this
pathway there is no synthesis of sugar, ATP or
NADPH, due to which photorespiration refers
to as a wasteful process. This process reduces
efficiency of photosynthesis in C
3
 plants.
24. (a)
Light induced CO
2
 liberation from a C
2
 compound
(glycolic acid) of dark phase is called
photorespiration. It occurs in green cells only. It
is absent in C
4
 plants and present in C
3
 plants.
Photorespiration occurs because oxygen rather
than carbon dioxide links to the rubisco enzyme
in the Calvin cycle. It involves three cell
organelles - peroxisomes, chloroplast and
mitochondria.
25. (c)
The Calvin cycle takes place in the stroma of
chloroplasts of mesophyll cell because enzymes
and intermediates of the Calvin cycle are located
in the stroma of chloroplasts.
26. (d)
RuBisCO is an enzyme present in chloroplasts,
involved in fixing atmospheric carbon dioxide
during photosynthesis and in oxygenation of the
resulting compound during photorespiration. It is
the most abundant enzyme on the earth and
catalyzes the carboxylation of CO
2
 to ribulose 1,
5-bisphosphate, initiates photorespiration when
the CO
2
/O
2
 ratio is low.
27. (c)
(I) Electron gradient is important because
breakdown of this gradient leads to
synthesis of ATP.
28. (c)
Light-induced CO
2
 liberation from a C
2
 compound
of dark phase is called photorespiration. This
process is considered to nullify the result of
photosynthesis as there is no synthesis of ATP or
NADPH.
29. (c)
In C
3
 plants the primary CO
2
 acceptor is RuBP
and the initial stable product is PGA. While in C
4
plants, the primary CO
2
 acceptor is PEP and the
first stable product is OAA.
30. (a)
Maize is a C
4
 plant. It possesses Kranz anatomy
which is absent in C
3
 plants.
31. (b)
Reaction center in PS - II is P
680
. PS-II is located
on the inner surface of appressed parts of grana
thylakoid. PS-II is inolved only in non-cyclic
electron transport.
32. (b)
(II) The break down of the gradient provides
enough energy to cause a conformational
change in the CF
1
  particle of the A TP synthase.
33. (a)
Both statements are correct.
34. (d)
In non-cyclic reaction of photosynthesis, electrons
from chlorophyll molecules in photosystem I are
used in the formation of NADPH. The source of
those electrons is photosystem II which splits
water molecule.
35. (d)
Calvin cycle that take place in stroma of the
chloroplasts during photosynthesis, is light in
dependent. But they usually do not occur in night
because this cycle is dependent on the products
of the light reactions. The Calvin cycle proceeds
in three stages: carboxylation [CO
2
 is covalently
linked to a carbon skeleton (RuBP)], reduction
(carbohydrate is formed at the expense of ATP
and NADPH) and regeneration (the CO
2
acceptor RuBP reforms at the expense of ATP.
36. (a)
Both statements are correct.
37. (d)
According to the experiment performed by the
student, photosynthesis will not take place because
intact chloroplast is needed for the process of
photosynthesis. Photosynthesis is the process by
which green plants create energy from sunlight.
It occurs at the cellular level in the leaves of plants
and is the way in which they produce oxygen
and carbohydrates. The oxygen is released into
the atmosphere, and the carbohydrates, simple
sugars, are used by the plant for growth. In order
to carry out photosynthesis, green plants need
several ingredients. Chlorophyll, the pigment in
plants that makes them green, is essential to the
photosynthetic process. This chemical is produced
naturally by all green plants and its role in
photosynthesis is to absorb light.
38. (b)
(II) Mesophyll cells in C
3
 plants show Calvin
cycle CO
2
 fixation.
39. (b)
"ADP is phosphorylated and NADP is reduced"
occurs during light phase of the photosynthesis.
The 'light-dependent reactions' is the process by
which plants capture and store energy from
sunlight. In this process, light energy is converted
into chemical energy, in the form of the energy-
carrying molecules ATP and NADPH.
40. (a)
During light reaction, as electrons move through
the photosystems, protons are transported across
the membrane because of the primary acceptor
of e
–
 (located towards the outer surface of the
membrane) transfers its electrons not to an e–
carrier but to H carrier.
41. (c)
The pigments are organised into two discrete
photochemical light harvesting complexes (LHC)
within the Photosystem I (PS I) and Photosystem
II (PS II). These are named in the sequence of
their discovery, and not in the sequence in which
they function during the light reaction.
42. (b)
The function of water in photosynthesis is to
supply electrons in the light dependent reaction.
The light dependent reactions take place in the
membranous sections of the chloroplast -
thylakoids (grana/lamellae) which offer a large
surface area to absorb light energy. The main
function of these reactions is to provide a source
of ATP and reduced NADP, which are used to
reduce CO
2
 in the light independent reactions.
43. (a)
Liberation of oxygen is not concerned with cyclic
photophosphorylation. This system is not concerned
with photo-oxidation of water but only concerned
with the production of ATP. Non-cyclic
photophosphorylation is the light-requiring part of
photosynthesis in higher plants, in which an electron
donor is required, and oxygen is produced as a
waste product. It consists of two photoreactions,
resulting in the synthesis of ATP and NADPH.
44. (a)
Photosynthesis is a physiochemical process by
which green plants and some other organisms use
sunlight to synthesize nutrients from carbon
dioxide and water, and generates oxygen as a
by-product.
45. (d)
Photosynthesis is the most important anabolic
process on earth. It is defined as the
transformation of photonic energy (i.e. light or
radiant energy) into chemical energy by the given
parts of the plants. In the process of
photosynthesis, light energy drives the synthesis
of carbohydrates from carbon dioxide and water
with the generation of oxygen.
46. (b)
Half leaf experiment proves that CO
2
 is essential
for photosynthesis.
47. (c)
Joseph Priestley (in 1970) performed a series of
experiments that revealed the essential role of
air in the growth of green plants.
48. (a)
Jan Ingenhousz showed that sunlight is essential
to the plant process that somehow purifies the
air fouled by burning candles or breathing animals.
Ingenhousz in an experiment with an aquatic plant
showed that in bright sunlight, small bubbles were
formed around the green parts while in the dark
they did not form any bubbles. Later he identified
the bubbles as oxygen.
Hence, he showed that it is only the green parts
of the plants that could release oxygen.
49. (b)
Cyclic pathway of photosynthesis first appeared
in some eubacterial species. It is supposed to be
the first evidence of production of ATP in the
presence of light. However oxygen started
accumulating in the atmosphere after the evolution
of non-cyclic pathway of photosynthesis in
cyanobacteria.
50. (b)
The first step in the photosynthesis is the light-
driven oxidation (splitting or photolysis) of water.
It provides electrons for the photosynthetic electron
transport chains as well as protons for the
establishment of a proton gradient. It occurs on
the lumenal side of the thylakoid membrane. During
photolysis, water is oxidised to oxygen, protons and
electrons. Protons accumulate in the lumen.
51. (b)
Paper chromatography is an analytical method
that is used to separate coloured chemicals or
substances, especially pigments. This can also be
used in secondary or primary colours in ink
experiments. Leaf pigments of any green plants
can be separated by using paper chromatography.
A chromatographic separation of the leaf pigments
shows that the colour we see in leaves is due to a
single pigment but due to four pigments: chlorophyll
a (bright or blue green in the chromatogram),
chlorophyll b (yellow green), xanthophylls (yellow)
and carotenoids (yellow to yellow orange).
52. (a)
Proton gradient is important because the
breakdown of this gradient leads to the release of
energy. This gradient which is created by the
accumulation of H
+
 ion inside the luman. is broken
down due to the movement of protons across the
membrane to the stroma through ATP synthase.
53. (b)
In C
4
 plants, a 4 - C compound oxaloacetic acid
(OAA) is the first stable product, and phosphoenol
pyruvate (PEP) is the CO
2
 acceptor. This reaction
is catalyzed by the enzyme PEP carboxylase or
PEPcase in mesophyll cells of the leaf.
54. (c)
In C
4
 plants, photosynthesis occurs in chloroplast
of mesophyll and bundle sheath cells. While in C
3
plants photosynthesis occurs only in mesophyll cells.
55. (a)
ATP synthase has a channel that allows diffusion
of protons back across the membrane that is from
lumen to stroma. This releases enough energy to
activate ATPase enzyme that catalyses the
formation of ATP from ADP.
56. (d)
Assertion : When the two photosystems work in
a series, first PS II and then the PS I, a process
called non-cyclic photo-phosphorylation occurs.
Reason : In cyclic phosphorylation the electron
moves from PS I to ETS and than back to PS I.
57. (d)
Photosystem (PS) - I and II are two pigments
system of light reaction. Non-cyclic
photophosphorylation is the light-requiring part of
photosynthesis in higher plants, in which an
electron donor is required, and oxygen is produced
as a waste product. It consists of two
photoreactions, resulting in the synthesis of ATP
and NADPH
2
. The hydrogen needed for the
reduction of NADP (nicotinamide adenine
dinucleotide phosphate) is made available from
the breakdown of water.
58. (b)
In Z-scheme, the movement of electrons is
downhill in terms of an oxidation reduction or redox
potential scale.
59. (b)
Chlorophyll a is the chief pigment associated with
photosynthesis.
60. (d)
Photorespiration (C
2
 cycle) is enhanced by bright
light, high temperature, high oxygen and low CO
2
concentration. In C
3
 plants, RuBisCO, acts as
ribulose biphosphate oxygenase under low
atmospheric concentration of C2 and increased
concentration of O
2
. Thus, photorespiration is
favoured by C
3
 plants.
61. (d)
All the statements regarding splitting of water is
correct. In photosynthesis, water splitting donates
electrons to power the electron transport chain
in photosystem II.
62. (a)
Protons or hydrogen ions produced by photolysis
of water accumulates in the lumen of thylakoids,
because photolysis of water takes place on the
inner side of the membrane.
63. (b)
64. (b)
The C
4
 plants show kranz anatomy, with their
vascular bundles, being surrounded by two cellular
rings i.e., bundle sheath cells (inner) and mesophyll
cells (outer). The main function of this anatomy is to
provide a site in which CO
2
  can be concentrated
around RuBisCO, that is to maintain a higher
concentration of CO
2
  in the bundle sheath compared
to the mesophyll. This happens as the boundary layer
of the kranz has a low conductance to CO
2
, thereby
avoiding photorespiration. Therefore, C
4
 plants are
able to more efficiently fix carbon in drought, high
temperatures, and limitations of nitrogen or CO
2
.
65. (a)
Tomatoes and bell pepper are allowed to grow in
carbon dioxide enriched atmosphere that leads to
higher yields this is done because C
3
 plants respond
to higher CO
2
 concentration (beyond 450 ?l L
–1
)
by showing increased rates of photosynthesis
leading to higher productivity.
66. (c)
In the given diagrammatic representation of
Hatch and Slack pathway (also known as C
4
pathway), the steps marked as P, Q and R are
respectively C
4
 acids, decarboxylation and C
3
acids. It is a metabolic cycle involved in the non-
light-requiring phase of photosynthesis in certain
plants having specific metabolic and anatomical
modifications in their mesophyll and bundle sheath
cells which facilitate the temporary fixation of
carbon dioxide (CO
2
) into four-carbon organic acid.
These acids are then broken down to three-carbon
organic acids along with CO
2
 in bundle sheath cells,
where this freed CO
2
 is then fixed into
carbohydrates in a normal Calvin cycle pathway.
67. (d)
Given graph shows the action spectrum of
photosynthesis superimposed on absorption
spectrum of chlorophyll a.