photosynthesis in higher plants

Level - I

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SECTION - A

School/Board Exam. Type Questions

Very Short Answer Type Questions :

1. Who provided evidence for production of glucose when plants grow?

Sol. Julius Von Sachs.

2. What are pigments and which is the chief pigment associated with photosynthesis?

Sol. Pigments are substances that have an ability to absorb light at specific wavelengths. The chief pigment

associated with photosynthesis is chlorophyll a.

3. Define photophosphorylation.

Sol. The process of ATP formation from ADP and Pi in presence of light in chloroplasts is called

photophosphorylation.

4. Expand RuBisCO.

Sol. RuBisCO stands for Ribulose Bisphosphate Carboxylase/Oxygenase.

5. What is photorespiration?

Sol. Photorespiration is loss of fixed carbon as CO2 in the presence of light due to oxygenase activity of RuBisCO.

6. Name the technique used to separate leaf pigments.

Sol. Paper chromatography is used to separate leaf pigments.

7. What is the first stable product of C4 cycle?

Sol. First stable product of C4 cycle is oxaloacetic acid.

8. Name two photosynthetic pigments belonging to carotenoids.

Sol. Carotenoids include carotene and xanthophyll.

9. Give the chemical equation of photosynthesis.

Sol. Overall equation for photosynthesis is :

Sunlight2 2 6 12 6 2 2Chlorophyll

6CO 12H O C H O 6O 6H O

Chapter 10

Photosynthesis in Higher Plants

Solutions (Set-1)


80 Photosynthesis in Higher Plants Solutions of Assignment (Set-1) (Level-I)

10. Who gave the law of limiting factors?

Sol. Law of limiting factors was given by Blackmann (1905).

Short Answer Type Questions :

11. Describe photosynthetic unit.

Sol. Photosynthetic unit is smallest group of pigment molecules that absorb light and promote release of electrons.

12. Describe briefly the contribution of Joseph Priestley.

Sol. Joseph Priestley in 1770 performed a series of experiments that revealed the essential role of air in the growth

of green plants. He hypothesised that plants restore to the air whatever the breathing animals and the burning

candles remove.

13. Complete the given below sequence of C4 pathway?

CO2 fixation A Transport Decarboxylation B.

Sol. CO2fixation C

4acid Transport C

3 acid + CO

2

14. Differentiate between photorespiration and aerobic respiration.

Sol. S. No. Photorespiration Aerobic respiration

1. It occurs only in the green cells. It occurs both in the green and non-green cells.

2. It occurs only in the presence of light. It occurs all the time irrespective of the presence

of light.

15. What is RuBisCO? Where is it present in C3 and C

4 plants?

Sol. RuBisCO is the most abundant enzyme. This enzyme catalyses the carboxylation reaction for the fixation of

CO2 into a stable organic intermediate. In C

3 plants, RuBisCO is present in all photosynthetic cells and in

C4 plants, this enzyme is present in bundle sheath cells.

16. Why do the leaves appear green in colour?

Sol. Chlorophyll, the chief pigment of leaves, absorbs mainly the blue and red wavelengths of visible spectrum. It

reflects the green wavelength of light and that is why the leaves appear green.

17. What are light harvesting complexes?

Sol. The light harvesting complexes are made up of hundreds of photosynthetic pigment molecules bound to

proteins. They help to make photosynthesis more efficient by absorbing different wavelengths of light.

18. What is Blackman’s law of limiting factors?

Sol. Blackman’s Law of Limiting Factors states that :

If a chemical process is affected by more than one factor, then its rate will be determined by the factor which

is nearest to its minimal value : It is the factor which directly affects the process if its quantity is changed.


81Solutions of Assignment (Set-1) (Level-I) Photosynthesis in Higher Plants

19. Give comparison between the cyclic and non-cyclic photophosphorylation.

Sol. S. No. Cyclic photophosphorylation Non-cyclic photophosphorylation

1. It is performed by photosystem I. It is performed by both photosystem I and

photosystem II.

2. It involves only the synthesis of ATP. It involves the synthesis of ATP and

NADPH.

3. No oxygen is evolved. Oxygen is liberated.

4. External source of electrons is not required External source of electrons is required

20. How many ATP and NADPH molecules will be required to make one molecule of glucose through the Calvin

pathway?

Sol. To make one molecule of glucose, 6 turns of Calvin cycle are required. It utilizes 18 ATP and 12 NADPH

molecules.

21. What is the advantage of having more than one pigment molecule in the photosynthetic unit?

Sol. Though chlorophyll-a is the major pigment responsible for trapping light, other thylakoid pigments like chlorophyll

b, xanthophylls and carotenoids which are accessory pigments also absorb light and transfer it to chlorophyll

a. They enable a wider range of wavelengths of incoming light to be utilised for photosynthesis and also protect

chlorophyll a from photo-oxidation.

22. Briefly describe the contribution of Jan Ingenhousz, which led to gradual development in our understanding of

photosynthesis.

Sol. Jan Ingenhousz (1730–1799) showed that sunlight is essential to the plant process that somehow purifies the

air fouled by the burning candles or the breathing animals. In an experiment with an aquatic plant, he showed

that in bright sunlight, small bubbles were formed around the green parts of plant, while in the dark, they did

not. Later he identified these bubbles to be of oxygen. Hence, he showed that it is only the green parts of

the plants that could release oxygen in the presence of light.

23. List the processes which occur during the photochemical phase of photosynthesis.

Sol. Light reaction or photochemical phase includes :

(i) Light absorption

(ii) Water splitting

(iii) Oxygen release

(iv) Formation of high energy chemical intermediates, ATP and NADPH.

24. Briefly describe the Z-scheme and why is it called so?

Sol. The whole scheme of transfer of electrons, starting from the PS II, uphill to the acceptor, down the electron

transport chain to PS I, excitation of electrons, transfer to another acceptor, and finally down hill to NADP+

causing it to be reduced to NADPH + H+ is called the Z-scheme, due to its characteristic shape. This

characteristic shape is formed when all the carriers are placed in a sequence on a redox potential scale.

25. How does PS II supply electrons continuously in noncyclic ETS?

Sol. During the non-cyclic photophosphorylation, a continuous supply of electrons is needed, The electrons that

were moved from photosystem II must be replaced. This is achieved by electrons available due to splitting of



water. The splitting of water is associated with the PS II, water molecule is splited into hydrogen ions (H+),

[O2] and electrons. The oxygen released is one of the net products of photosynthesis. The electrons needed

to replace those removed from photosystem I are provided by photosystem II.

+ –2 22H O 4H +O +4e

26. Give the diagrammatic explanation for ATP synthesis through chemiosmosis.

Sol.

Stroma

P680PSII

Light H+

Light

NADP+ +H

+

NADPH

FNR

Fd

Plastocyanin

H O2

Oxidation of water

2

1O H

2

H+

H+

H+

H+

CF0

CF1

Lumen (high H )

+

Thylakoid membrane

Low

ATPH

+

ADP + P1

High Electrochemical

PotentialGradient

Stroma (low H )+

PQ

PQH2 P700

PS IPC

Plastoquin

one

CytochromeB f

6

H+

ATPsynthase

27. Give the significance of photosynthesis.

Sol. Photosynthesis is a vital physico-chemical process by which the green plants use light energy to drive the

synthesis of organic compounds. This process links the physical and biological world. The plants biomass (dry

matter), derived through photosynthesis, supports humans and all other organisms (hetrotrophic) living in

biosphere. During photosynthesis, O2 is released, which is helpful to living organisms for aerobic respiration

and also in making of ozone in outer layer of atmosphere.

28. Write a short note on photosynthetic pigments.

Sol. Photosynthetic pigments:

(i) Chlorophyll a – Bright or blue green

(ii) Chlorophyll b – Yellow-green

(iii) Xanthophylls – Yellow

(iv) Carotenoids – Yellow to yellow-orange

These photosynthetic pigments (chlorophyll) give green colour to the leaves. They have an ability to absorb

light at specific wavelengths necessary for photosynthesis.

29. List the various external and internal factors affecting photosynthesis.

Sol. External factors : Availability of sunlight, temperature, CO2

concentration and water.

Internal factors : Number, size, age and orientation of leaves, mesophyll cells, chloroplasts.



30. What is PEP? What is its role in the biosynthetic process?

Sol. PEP is phosphoenol pyruvate. It plays a very vital role in CO2 fixation in C

4 plants. The primary CO

2 acceptor

is PEP and the enzyme responsible for this CO2 fixation is PEP carboxylase or PEPcase. PEP is regenerated

during the Hatch and Slack pathway in the mesophyll cells.

Long Answer Type Questions :

31. Explain the significance of the three phases of Calvin cycle.

Sol. The three phases are :

Carboxylation : Calvin cycle is the only process for synthesis of photosynthate. This is the most crucial

step of the Calvin cycle where CO2 is utilized for the carboxylation of RuBP. This reaction is catalysed by

the enzyme RuBisCO which results in the formation of two molecules of 3-PGA (first stable compound).

Reduction : These are a series of reaction that lead to the formation of glucose. The steps involve utilization

of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO2 molecule fixed. Six turns

of the cycle are required for the removal of one molecule of glucose from the pathway.

Regeneration : Regeneration of the CO2 acceptor molecule RuBP is crucial if the cycle is to continue

uninterrupted. The regeneration step requires one ATP for phophorylation to form RuBP.

32. Mention the site of occurrence of following events in maize plant.

(a) Regeneration of RuBP

(b) RuBP + CO2 3PGA

(c) PEP + CO2

OAA

(d) C4 acid formation

(e) C3 acid formation

Sol. (a) Stroma – Bundle sheath cells

(b) Stroma – Bundle sheath cells

(c) Cytoplasm – Mesophyll cells

(d) Mesophyll cells

(e) Bundle sheath cells

33. (a) Mention the photosystems and other components involved in non-cyclic photophosphorylation.

(b) Name the components involved in Cyclic ETS.

(c) Which is the major limiting factor for photosynthesis.

(d) What is the CO2 saturation point for C

3 & C

4 plants.

(e) Which abiotic factor affects the photosynthesis indirectly.

Sol. (a) Water splitting complex, PS II, H-carrier, Cytochrome b - f complex, PS I, NADP reductase.

(b) PS I, cytochrome b-f complex, H-carrier.

(c) CO2 is the major limiting factor for photosynthesis.

(d) C4 – 360 ppm C

3 > 450 ppm.

(e) Water is one of the reactants in the light reaction but the effect of water as a factor is more through its

effect on the plant, rather than directly on photosynthesis.



34. Give the schematic sketches of cyclic and non-cyclic photophosphorylation.

Sol. Photosystem I

Light

e acceptor–

Electron

transport

system

Chlorophyll P700

AD

P+iP

A

TP

Fig. : Z scheme of light reaction

Photosystem II Photosystem I

LHC

LHC

ATPADP + Pi

Electron transportsystem

Light

NADPH

NADP+

H O 2e + 2H + [O]2 – +

e acceptor–

e acceptor–

Fig. : Cyclic photophosphorylation

35. Describe the Calvin cycle diagrammatically.

Sol.

TheCalvincycle

Ribulose-1,5-bisphosphate

Atmosphere

CO + H O2 2

CarboxylationADP

Triosephosphate

Reduction

ADP+

P + NADPi

+

Sucrose, starch

ATP

Regeneration3-phosphoglycerate

ATP+

NADPH

1

2

3

Fig.: Calvin Cycle

36. Describe how the C4 pathway is an adaptive advantage to the C

4 plants like sugarcane.

Sol. � C4 plants are adapted to dry tropical regions. These have better tolerance towards high temperature

conditions (40–45°C).

� These keep their stomata partially closed during hot day and PEPcase fix whatever low amount of CO2

available.

� These have a mechanissm to increase the concentration of CO2 at enzyme (RuBisCO) site. Thus,

oxygenase activity is minimised.

� Kranz anatomy with thick-walled bundle sheath cells do not allow entry of O2 into them. Bundle sheath

cells themselve do not generate O2 (non-cyclic photophosphorylation being absent). Thus, photorespiration

is absent.



37. Distinguish between Bundle sheath and Mesophyll cells of C4

plant.

Sol.

1. carboxylation

2. Forms C acid

3. Thick walled

4. RuBisCO participates in carboxylation.

5. Possess agranal chloroplast

3

Secondary 1. Carboxylation

2. Forms C acid

3. Thin wall

4. PEPcase carryout carboxylation.

5. Granal chloroplast

4

Primary

Bundle Sheath Cells Mesophyll cells

38. How are ATP, NADPH and oxygen produced in non-cyclic photophosphorylation?

Sol. Non-cyclic Photophosphorylation involves both Photosystem I and Photosystem II. The two photosystems are

connected through an electron transport chain. Both ATP and NADPH + H+ are synthesised by this kind of

electron flow. Oxygen is released due to splitting of water molecule during the process.

First in PS II, the P680

molecule absorbs 680 nm wavelength of red light causing electrons to become excited and

jump into an orbit which is farther from the atomic nucleus. These electrons are picked up by an electron acceptor

which passes them to an electron transport system of cytochromes. This movement of electrons is downhill

on redox potential scale. The electrons are then passed onto the pigments of PS I, simultaneously, electrons

in the reaction center of PS I (P700

) are excited when they receive light of wavelength 700 nm and

these electrons are transferred to an other acceptor molecule that has a greater redox potential. These

electrons are then moved downhill again to a molecule of NADP+. The addition of these electrons reduces the

NADP+ to NADPH + H+. This whole scheme of transfer of electrons is called the Z-scheme due to its

characteristic shape. This shape is formed when all the carriers are placed in a sequence on a redox potential

scale.

39. Compare Photosystem I and Photosystem II.

Sol.

1. PS-I absorb maximally at 700 nm of

sunlight.

2. The reaction center is P .

3. PS-I is present on non-appressed side of

Grana and stroma lamellae.

4. Found in both grana and stroma lamellae.

5. Molecular oxygen is not released when this

system operates individually.

6. Participates in both cyclic as well as

non-cyclic flow of electrons.

700

1. PS-II absorb maximally at 680 nm of

sunlight.

2. The reaction center is P .

3. PS-II is present in appressed part of Grana.

4. Found in grana lamellae only.

5. Molecular oxygen is released by photolysis

of water when this system operates.

6. It is involved only in non-cyclic flow of

electrons.

680

Photosystem I / Pigment system I Photosystem II / Pigment system II

40. (a) Describe cyclic photophosphorylation.

(b) Give the following information about photorespiration.

(i) First reaction (ii) Energy requirement

(iii) In which plants does it occur (iv) Organelles involved



Sol. Cyclic Photophosphorylation

(a) The process of cyclic photophosphorylation involves only PS I and this process takes place in the stroma

lamella membrane. When only PS I is functional, the electron is circulated within the photosystem and

the phosphorylation occurs due to cyclic flow of electrons. The excited electron does not pass on to

NADP+ and is cycled back to the PS I complex through the electron transport chain. ATP is produced

by this process but NADPH + H+ is not produced. Cyclic photophosphorylation also occurs when only

light of wavelength beyond 680 nm are available for excitation.

(b) (i) RuBisCORuBP 3 PGA + Phosphoglycolate

(ii) ATP is required

(iii) C3 plants

(iv) Chloroplast, Peroxisomes Mitochondria

41. Give an account of external factors affecting photosynthesis.

Sol. External factors affecting photosynthesis

(a) Light : It is an essential factor for photosynthesis.

(i) Light intensity : There is a linear relationship between incident light and CO2 fixation at low light

intensities. At higher light intensities, gradually the rate does not show further increase as other

factors become limiting. The light saturation occurs at 10 percent of the total sunlight available to

plants. Increase in incident light beyond a point causes the breakdown of chlorophyll and thus resulting

in decrease in photosynthesis.

(ii) Light quality : Light between 400–700 nm wavelength constitute the photosynthetically active

radiation (PAR). Maximum photosynthesis takes place in red and blue light of the visible spectrum

and minimum photosynthesis takes place in green light.

(iii) Duration of light : Light duration does not affect the rate of photosynthesis, but it affects the overall

photosynthesis.

(b) Carbon dioxide concentration : It is a major limiting factor influencing the rate of photosynthesis.

The C3 and C

4 plants respond differently to CO

2 concentration. At low light intensities neither type responds

to high CO2 concentration. At high light intensities, both C

3 and C

4 plants show increase in the rate of

photosynthesis. The C4 plants show saturation at about 360 mlL–1 (ppm), while C

3 plants show saturation

only beyond 450 mlL–1 (ppm), thus, the current concentration of CO2 is limiting for C

3 plants.

(c) Temperature : Photosynthesis can take place over a wide range of temperatures. The light reactions

are temperature senstive but they are affected to a much lesser extent. The dark reaction being enzymatic

are temperature controlled. Again, the temperature optimum for photosynthesis of different plants also

depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than

the plants adapted to temperate climates.

The C4 plants respond to higher temperatures and they show higher rate of photosynthesis, while C

3 plants

have much lower temperature optimum. Optimum temperature in C3 plant is 20–25°C and for C

4 plant is

30–45°C.

(d) Water : Water is one of the raw materials utilized for the process of photosynthesis. Photosynthetic

process utilizes less than 1% of the water absorbed by a plant, hence it is rarely a limiting factor in

photosynthesis. Water stress causes the stomata to close, hence reducing the CO2 availability as

gaseous exchange could not occur. Also, water stress makes leaves wilt, thus reducing the surface area

of the leaves and the metabolic activity reduces as well.

42. (a) What are the requirements of chemiosmosis.

(b) Mention the features of bundle sheath cells associated with Kranz anatomy.

Sol. (a) Chemiosmosis process requires a membrane, a proton pump, a proton gradient and ATPase enzyme.

Energy is used to pump protons across the membrane into the lumen, which creates a proton gradient



across the membrane. ATPase enzyme has transmembrane channel that allows diffusion of protons back

across the membrane, this releases energy to activate ATPase enzyme which catalyses the formation

of ATP.

(b) 1. May form several layers around vascular bundles

2. Large size cells

3. Thick walls impervious to gases

4. No intercellular spaces

5. Have large number of chloroplasts

43. Give a diagrammatic representation of a section of chloroplast.

Sol.

Fig.: Diagrammatic representation of an electron micrograph of a section of chloroplast

Outer membrane

Inner membrane

Stromal lamella

Grana

Stroma

Ribosomes

Starch granule

Lipid droplet

DNA segments

44. (a) Give the diagrammatic representation of light-harvesting complex.

(b) Mention the experimental material used by the following

(i) Van Niel

(ii) Melvin Calvin

(iii) Englemann

(iv) Joseph Priestley

Sol. (a)

Photon Reactioncenter

Pigmentmolecules

Primary acceptor

Fig. : The light-harvesting complex



(b) (i) Purple and green bacteria

(ii) Cladophora , aerobic bacteria

(iii) Green alga – Chlorella

(iv) Mouse, Mint plant

45. Give the diagrammatic representation of Hatch and Slack pathway.

Sol.

Regeneration

Decarboxylation

Fixation byCalvin cycle

CO2

C acid3

C acid4

C acid4

C acid3

HCO3

–

Phosphoenolpyruvate

Fixation

Atmospheric CO2

Plasmamembrane

Cell wall

Mesophyllcell

Plasmodesmata

Bundle sheathcell

Transport

Transport

SECTION - B

Model Test Paper

Very Short Answer Type Questions :

1. What is first stable product of C4 pathway?

Sol. Oxaloacetic acid (OAA) is the first stable product of C4 pathway.

2. Define photorespiration.

Sol. Photorespiration is a process which involves oxidation of organic compounds in plants by oxygen in the

presence of light. No ATP is produced. It results in the release of CO2 with the utilisation of ATP.

3. Expand PEPcase.

Sol. Phosphoenol pyruvate carboxylase.

4. Name the reaction centre in PS I and PS II.

Sol. The reaction center in PS I is P700

, the reaction center in PS II is P680

.

5. What is the primary acceptor molecule of CO2 during the Calvin cycle?

Sol. The primary acceptor molecule of CO2 during the Calvin cycle is Ribulose Bisphosphate (RuBP).

6. Give two examples of C4 plants.

Sol. Maize, sorghum are C4 plants.




7. What are accessory pigments?

Sol. Thylakoid pigments like chlorophyll b, xanthophylls, carotenoids are called accessory pigments, they enable

a wider range of wavelengths of incoming light to be utilised for photosynthesis and also protect chlorophyll-a

from photooxidation.

8. How many turns of Calvin cycle are required for formation of sucrose molecule?

Sol. Sucrose is a 12C compound. For fixation of 12CO2, twelve turns of Calvin cycle are required.

9. Give the diagrammatic representation of the cyclic photophosphorylation.

Sol. Photosystem I

Light

e acceptor–

Electron

transport

system

Chlorophyll P700

AD

P+iP

A

TP

Fig. : Cyclic photophosphorylation


10. Explain Moll’s half leaf experiment.

Sol. Moll’s half leaf experiment : This experiment was done to demonstrate necessity of CO2 for photosynthesis.

A part of leaf was enclosed in a test tube containing some KOH soaked cotton (which absorbs CO2), while

the other half of leaf is exposed to air. When the two halves of leaf were tested for starch, it was found that

only the exposed part of leaf tested positive for starch.

11. Draw the graph showing action spectrum of photosynthesis superimposed on absorption spectrum of chlorophyll ‘a’.

Sol. Rate of photosynthesisAbsorption

Lig

ht absorb

ed

400 500 600 700

Wavelength of light in nanometres (nm)

Fig. : Graph showing action spectrum of photosynthesis superimposedon absorption spectrum of chlorophyll a

12. (a) What is absorption spectrum?

(b) Which pigment forms reaction centre?

Sol. (a) The graphic curve showing the amount of energy of different wavelengths of light absorbed by a substance

is absorption spectrum.

(b) The single chlorophyll molecule forms the reaction centre.



13. Where does carboxylation take place in C3 plants? Explain the process.

Sol. Carboxylation is the first stage of Calvin cycle. It is the fixation of CO2 into a stable organic intermediate. It

occurs mainly in the mesophyll cells in C3 plants. In this process, the CO

2 is utilised for the carboxylation

of RuBP. This reaction is catalysed by the enzyme RuBP carboxylase which results in the formation of two

molecules of 3-PGA.

Long Answer Type Questions :

14. Give diagrammatic representation of the Hatch and Slack pathway.

Sol.

Regeneration

Decarboxylation

Fixation byCalvin cycle

CO2

C acid3

C acid4

C acid4

C acid3

HCO3

–

Phosphoenolpyruvate

Fixation

Atmospheric CO2

Plasmamembrane

Cell wall

Mesophyllcell

Plasmodesmata

Bundle sheathcell

Transport

Transport

Fig. : Diagrammatic representation of the Hatch and Slack Pathway

15. Why productivity and yields are better in C4 plants as compared to the C

3 plants?

Sol. In C3 plants, a process called photorespiration occurs which leads to a 25 per cent loss of the fixed CO

2.

However, in case of C4 plants, they have evolved a mechanism to avoid occurence of photorespiration, This

is because they have a mechanism that increases the concentration of CO2 at the enzyme site (in bundle

sheath cells). This takes place when the C4 acid from the mesophyll is broken down in the bundle sheath cells

to release CO2, this results in increasing the intracellular concentration of CO

2. In turn, this ensures that the

RuBisCO functions as a carboxylase minimizing the oxygenase activity. Thus, C4 plants lack photorespiration,

and yields are better.

16. Briefly explain the photochemical phase of photosynthesis. Where does it take place?

Sol. Light reaction or the photochemical phase of photosynthesis includes light absorption, water splitting, oxygen

release and the formation of high energy chemical intermediates, ATP and NADPH.

It takes place in the thylakoids of chloroplast in green parts of the plant.

17. Explain the various external factors affecting photosynthesis.

Sol. External factors affecting photosynthesis

(a) Light : It is an essential factor for photosynthesis.

(i) Light intensity : There is a linear relationship between incident light and CO2 fixation at low light

intensities. At higher light intensities, gradually the rate does not show further increase as other



factors become limiting. The light saturation occurs at 10 percent of the total sunlight available to

plants. Increase in incident light beyond a point causes the breakdown of chlorophyll and thus resulting

in decrease in photosynthesis.

(ii) Light quality : Light between 400–700 nm wavelength constitute the photosynthetically active

radiation (PAR). Maximum photosynthesis takes place in red and blue light of the visible spectrum

and minimum photosynthesis takes place in green light.

(iii) Duration of light : Light duration does not affect the rate of photosynthesis, but it affects the overall

photosynthesis.

(b) Carbon dioxide concentration : It is a major limiting factor influencing the rate of photosynthesis.

The C3 and C

4 plants respond differently to CO

2 concentration. At low light intensities neither type responds

to high CO2 concentration. At high light intensities, both C

3 and C

4 plants show increase in the rate of

photosynthesis. The C4 plants show saturation at about 360 mlL–1 (ppm), while C

3 plants show saturation

only beyond 450 mlL–1 (ppm), thus, the current concentration of CO2 is limiting for C

3 plants.

(c) Temperature : Photosynthesis can take place over a wide range of temperatures. The light reactions

are temperature senstive but they are affected to a much lesser extent. The dark reaction being enzymatic

are temperature controlled. Again, the temperature optimum for photosynthesis of different plants also

depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than

the plants adapted to temperate climates.

The C4 plants respond to higher temperatures and they show higher rate of photosynthesis, while C

3 plants

have much lower temperature optimum. Optimum temperature in C3 plant in 20–25°C and for C

4 plant is

30–45°C.

(d) Water : Water is one of the raw materials utilized for the process of photosynthesis. Photosynthetic

process utilizes less than 1% of the water absorbed by a plant, hence it is rarely a limiting factor in

photosynthesis. Water stress causes the stomata to close, hence reducing the CO2 availability as

gaseous exchange could not occur. Also, water stress makes leaves wilt, thus reducing the surface area

of the leaves and the metabolic activity reduces as well.

18. Explain the Z-scheme of light reaction with diagram only.

Sol.

Fig. : Z scheme of light reaction

Photosystem II Photosystem I

LHC

LHC

ATPADP + Pi

Electron transportsystem

Light

NADPH

NADP+

H O 2e + 2H + [O]2

– +

e acceptor–

e acceptor–

19. Briefly describe the process of photorespiration.

Sol. Photorespiration : Photorespiration is a process which involves oxidation of organic compounds in plants by

oxygen in the presence of light. It is initiated in chloroplasts. This process does not produce ATP or NADPH

and is a wasteful process.



Photorespiration occurs usually when there is high concentration of oxygen. Under such circumstances,

RuBisCO, the enzyme that catalyses the carboxylation of RuBP during the first step of Calvin cycle, functions

as an oxygenase. In C3 plants, as both light and dark reactions occur in mesophyll cells, it becomes essential

for RuBisCO to catalyse both oxygenation and carboxylation reactions of RuBP, simultaneously. In C3 plants,

some O2 (released from photolysis of water), does bind to RuBisCO and hence CO

2 fixation is decreased. The

RuBP binds with O2 to form one molecule of PGA and phosphoglycolate in the pathway of photorespiration.

There is neither the synthesis of sugar, nor of ATP. Rather, it results in the release of CO2 with the utilisation

of ATP. It leads to a 25 percent loss of the fixed CO2.

20. (a) Differentiate between C3 & C

4 plants w.r.t. energy requirement for one glucose molecule formation

(b) Choose the correct labelling for given below figures

AB

Lig

ht absorb

ed

400 500 600 700

Wavelength of light in nanometres (nm)

Photon

A

B

C

(i) (ii)

Sol. (a)C Plant

3C Plant

4

18 ATP

12 NADPH

30 ATP

12 NADPH

(b) (i) A – Rate of photosynthesis

B – Absorption spectrum

(ii) A – Primary acceptor

B – Reaction centre

C – Accessory pigments

� � �



Objective Type Questions

(Introduction)

1. Which equation represents the process of photosynthesis most adequately?

(1) Sunlight6 12 6 2 2 2Chlorophyll

C H O 6O 6CO 6H O (2) Sunlight2 2 6 12 6 2Chlorophyll

6CO 6H O C H O 6O

(3) Sunlight2 2 2 2Chlorophyll

CO H O CH O O (4)Sunlight

2 2 6 12 6 2 2Chlorophyll6CO 12H O C H O 6O 6H O

Sol. Answer (4)

During photosynthesis, green plants synthesized glucose from CO2 and H

2O, in this process oxygen evolved

as by-product.

(Importance of Photosynthesis)

2. Choose incorrect w.r.t. photosynthesis

(1) It is a physico-chemical process

(2) Oxygen is evolved as a by-product in all photosynthetic organisms

(3) Occurs in unicellular and multicellular photoautotrophs

(4) Anabolic and reductive process

Sol. Answer (2)

In some bacteria, H2S is used instead of H

2O. So O

2 is not released.

(What do we know?)

3. Moll’s half leaf experiment was done to show _____ was required for photosynthesis.

(1) H2O (2) Chlorophyll (3) Light (4) CO

2

Sol. Answer (4)

In this experiment, half leaf was enclosed in a test tube containing KOH (which absorbs CO2), half leaf was

in air. When two halves were tested for starch, leaf in air showed the +ve test not other part, which shows

CO2 is required for photosynthesis.

(Historical account – Early experiments)

4. A milestone contribution to the understanding of photosynthesis was made by Cornelius van Niel, which was

based on the studies of

(1) Bacteria (2) Alga (3) Angiospermic plant (4) Lower plant

Sol. Answer (1)

Van Niel studied purple and green sulphur bacteria and showed, O2 evolved from H

2O and not from CO

2.

2 2 6 12 6 2 212H O 6CO C H O 6H O 6O

5. The essential role of air in the growth of green plants was revealed by

(1) Priestley (2) Van Niel

(3) Blackmann (4) Emerson

Sol. Answer (1)

Role of air in the growth of green plants is experimently proved by Priestley.

Solutions (Set-2)



6. Curve showing the effectiveness of different wavelength of light in photosynthesis was first given by Engelmann

using all, except

(1) Filamentous green alga Cladophora

(2) Unicellular green alga Chlorella

(3) Suspension of aerobic bacteria

(4) Prism to split the light in its components

Sol. Answer (2)

Hill used Chlorella for proving that photosynthesis completed in two phase i.e., light and dark phase.

(Where does photosynthesis take place?)

7. Grana present in chloroplast refers to

(1) Stroma lamellae (2) Stacks of quantasomes

(3) Stacks of thylakoids (4) Double membranous envelope

Sol. Answer (3)

Grana Stacks of thylakoids

(Photosynthetic units/Pigment systems)

8. Photosystem is composed of

(1) Light harvesting complex (2) Reaction centre

(3) Accessory pigments (4) More than one is correct

Sol. Answer (4)

PS has LHC I or II, Reaction Centre, Accessory pigments.

9. In the chloroplast, the stroma lamellae lack the

(1) PS I, NADP reductase (2) PS II, PS I

(3) NADP reductase enzyme, P700

(4) NADP reductase, PS II

Sol. Answer (4)

PS II and NADP reductase absent in the stroma lamellae of the chloroplast.

(The Electron Transport)

10. The movement of electrons as per Z-scheme in light reaction is

(1) From low to high energy level (2) Uphill in redox potential scale

(3) Downhill in redox potential scale (4) Both (2) & (3)

Sol. Answer (4)

It can occur uphill / downhill in redox potential scale.

11. The assimilatory power produced during light reaction in green algae is

(1) ATP, NADPH + H+ (2) NAD+

(3) NADP (4) ATP & NADH



Sol. Answer (1)

Light reaction gives two assimilatory product.

(i) ATP (ii) NADPH + H+

12. The protons formed by splitting of water are released in the

(1) Lumen of the thylakoids (2) Outer side of the membrane

(3) Both (1) & (2) (4) Stroma of chloroplast

Sol. Answer (1)

When a photon of light strikes the reaction centre of PS II, it emites an electron. Two H2O molecules bind

to an enzyme at reaction centre and enzyme splits the water and H+ are released in the lumen and also O2

is produced.

13. The oxygen liberated during the photosynthesis comes from

(1) CO2

(2) Water

(3) Photosynthetic enzymes (4) Carbohydrates

Sol. Answer (2)

Water

2 22H O 2H O

14. Chemiosmotic hypothesis for generation of ATP during light reaction was first explained by

(1) Hill (2) Arnold (3) P. Mitchell (4) Van Niel

Sol. Answer (3)

Chemiosmotic theory for ATP synthesis was proposed by P.Mitchell.

15. The photosystem connected with splitting of water is

(1) PS II (2) PS I (3) Carotenoid (4) P700

Sol. Answer (1)

Photolysis of H2O is connected to PS II.

16. NADPH is generated through

(1) Anaerobic respiration (2) Cyclic photophosphorylation

(3) Non-cyclic photophosphorylation (4) Glycolysis

Sol. Answer (3)

PS I reduces NADP+ to NADPH in the stroma by the action of enzyme NADP reductase.

17. Read the following statements:

(a) CF0 part of ATPase is associated with breakdown of proton gradient.

(b) A H-carrier contributes in creation of proton gradient.

(c) Movement of electrons in ETS is coupled to pumping of protons into the lumen.

(d) Formation of NADPH + H+ is related with the creation of proton gradient.

How many of the above statements are correct?

(1) Two (2) One (3) Four (4) Three



Sol. Answer (3)

Cytb & f

H+

H+

F0

Lumen

ATP synthesis Storma

ADP ATP

Thylakoidmembrane

NADP+

NADPHPSII

PSI

H+

F1

18. How many components listed below are part of cyclic ETS?

700 680P , P , NADP reductase, Hydrogen carrier,

PS I, Water Splitting Complex, PS II

(1) Two (2) Three

(3) Five (4) Four

Sol. Answer (2)

P700

, PSI, Hydrogen carrier.

(Where are ATP and NADPH used?)

19. The CO2 acceptor in C

3 plants is

(1) RuBP (2) PGA (3) PEP (4) OAA

Sol. Answer (1)

In C3 plants, CO

2 acceptor is Ribulose 1-5 bi-phosphate.

20. In C3 plants, first stable product of CO2 fixation is

(1) 3-PGA (2) Starch

(3) OAA (4) Pyruvate

Sol. Answer (1)

2 × 3 PGA

2 × 3 PGAL

DHAP

RUBP 6 C RuBisCo

CO + H O2 2

C Cycle 3 (Ist stable product)

Primary acceptor

Carboxylation

ADP

ATP

Glucose

1 2

3

2ATP

2NADPH4

5

REDUCTION

Dismutase

21. Which among the following is not a step in Calvin cycle?

(1) Carboxylation (2) Reduction

(3) Photophosphorylation (4) Regeneration

Sol. Answer (3)

Photophosphorylation is the step of light reaction.



22. The enzyme responsible for carboxylation reaction (CO2

fixation) in C3 plants is

(1) RuBP oxygenase (2) Pyruvate decarboxylase

(3) RuBP carboxylase (4) PEP carboxylase

Sol. Answer (3)

In C3 plant carboxylation reaction is catalysed by enzyme RuBP carboxylase.

23. Regeneration of four molecules of RuBP in C3 cycle requires the expenditure of _____ ATP.

(1) 1 (2) 4

(3) 3 (4) 2

Sol. Answer (2)

For 1 molecule of RUBP 1ATP

For 4 molecule of RUBP 4ATP

24. The enzyme RuBP carboxylase

(1) Activity occurs in C3 and C

4 plants (2) It present in inner thylakoid membrane

(3) Is low temperature sensitive enzyme (4) Shows greater affinity for O2 than for CO

2

Sol. Answer (1)

RUBP carboxylase is used in both C3 & C

4 plants.

(The C4 Pathway)

25. Which of the following statements is not true regarding the C4 plants?

(1) They show kranz anatomy

(2) Decarboxylation process occurs in bundle sheath cells

(3) Granal chloroplast is present in bundle sheath cells.

(4) PEPcase enzyme activity occurs in mesophyll cells

Sol. Answer (3)

In Bundle sheath cells agranal chloroplasts remain present.

26. In C4 plants, first stable product of CO

2 fixation is

(1) OAA (2) RuBP (3) 3-PGA (4) Malic Acid

Sol. Answer (1)

Oxalo acetic acid is first stable product in C4 plants.

27. In C4 plants, sugar is produced in

(1) Bundle sheath cells (2) Mesophyll cells

(3) Palisade leaf cells (4) Spongy mesophyll

Sol. Answer (1)

In C4 plants sugar is synthesized in bundle sheath cells.

28. The C4 and C

3 plants differ from each other in

(1) Type of pigments involved in photosynthesis

(2) The primary acceptor of CO2 during carbon fixation

(3) Type of end products of photosynthesis

(4) Number of NADPH that are consumed during the starch synthesis process

Sol. Answer (2)

In C3

plant primary CO2 accepter is RUBP white in C

4 plant it is PEP.



29. Which one of the following is a C4 plant?

(1) Papaya (2) Potato (3) Maize (4) Pea

Sol. Answer (3)

Maize is a C4 plant.

30. The CO2 fixation during the Hatch and Slack pathway occurs in

(1) Large thick walled cells (2) Mesophyll cells

(3) Vascular bundles (4) Bundle sheath cell cytoplasm

Sol. Answer (2)

C4 pathway occurs in mesophyll cells.

31. ‘Kranz’ anatomy of leaves is found in

(1) C4 plants (2) C

3 plants

(3) CAM plants (4) All plants

Sol. Answer (1)

Kranz anatomy is shown by C4

plants.

32. The enzyme required for the CO2 fixation in the C

4 cycle is

(1) PEP carboxylase (2) RuBP oxygenase

(3) RuBP carboxylase (4) PGA dehydrogenase

Sol. Answer (1)

In mesophyll cell, PEP carboxylase is required for CO2 fixation.

33. Which of the following statement is correct regarding the C4 plants?

(1) The carbon fixation is catalysed by PEP carboxylase

(2) Mesophyll cells lack the RuBisCO enzyme

(3) Photorespiration is absent

(4) More than one option is correct

Sol. Answer (4)

In C4 plants, RuBisCO enzyme is absent in mesophyll cell. PEP carboxylase present in mesophyll cell.

34. RuBisCO in C4 plants shows minimum oxygenase activity due to

(1) Abundance of RuBisCO (2) Formation of C4 acid

(3) Decarboxylation of C4 acid (4) Cyclic photophosphorylation

Sol. Answer (3)

Due to decarboxylation of C4 acid, CO

2 evolve in bundle sheath cell.

35. The primary acceptor of CO2 in C

4 plants is

(1) RuBP (2) Phosphoenol pyruvic acid

(3) OAA (4) Malic acid

Sol. Answer (2)

In mesophyll cell of C4 plant primary acceptor of CO

2 is PEP.



36. PEPcase and RuBisCO in C4 plants are present respectively in

(1) Cytoplasm and thylakoids (2) Stroma and cytoplasm

(3) Stroma and thylakoids (4) Cytoplasm and stroma

Sol. Answer (4)

PEPcase in cytoplasm and RuBisCO in the stroma.

37. Plants like sugarcane show high productivity and high efficiency of CO2 fixation, because of

(1) Absence of photorespiration (2) EMP pathway

(3) Calvin cycle (4) TCA cycle

Sol. Answer (1)

Photorespiration is a wasteful process that decreases efficiency of C3 plants but absent in C

4 plants.

38. Choose the correct sequence of steps involved in C4 cycle.

(1) CO2 fixation Regeneration Transport

(2) CO2

fixation Recarboxylation Decarboxylation

(3) Transport Regeneration CO2 fixation

(4) CO2 fixation Transport Decarboxylation

Sol. Answer (4)

CO2 fixation occurs first of in mesophyll cells than transported into bundle sheath cells, where decarboxylation

takes place.

(Photorespiration)

39. A wasteful process which involves oxidation of organic compounds in plants in presence of light is called

(1) Photorespiration (2) PCR Cycle (3) Hill’s reaction (4) Bioluminiscence

Sol. Answer (1)

Photorespiration reduces the rate of photosynthesis.

40. Identify the incorrect match.

(1) Regeneration of PEP – Mesophyll cells

(2) RuBP oxygenase activity – Chloroplast

(3) Photorespiratory loss of CO2

– Cytoplasm

(4) Decarboxylation in C4 pathway – Bundle sheath cell

Sol. Answer (3)

CO2 releases in mitochondria during photorespiration.

(Factors affecting Photosynthesis)

41. Law of limiting factor was given in

(1) 1950 (2) 1905 (3) 1920 (4) 1915

Sol. Answer (2)

Given by Blackman in 1905.

42. Which of the following would rarely be a limiting factor for photosynthesis?

(1) Chlorophyll (2) Light (3) Carbon dioxide (4) Temperature

Sol. Answer (2)



Light is limiting for plants growing in shade.

43. The CO2 concentration at which C4 plants show saturation is about

(1) 360 ppm (2) 380 ppm (3) 450 ppm (4) 500 ppm

Sol. Answer (1)

In C4

plants CO2 compensation point is at 360 ppm.

44. Linear relationship exists between incident light and rate of CO2 fixation at/in

(1) High light intensity (2) Low light intensity

(3) Dense forests (4) More than one option is correct

Sol. Answer (4)

Rate of photosynthesis increases at high CO2 concentration and high light intensities.

45. Choose the correct labelling for given figure

C

Ra

te o

f p

ho

tosyn

the

sis

Light Intensity

(1) D-Saturation point, E-Maximum photosynthesis (2) A-Achieved at high light intensity

(3) D-10% of total sunlight, E-Compensation point (4) A-Light saturation at 10% of total sunlight

Sol. Answer (1)

D-Saturation point Because after this point there is no increase.

E-Maximum photosynthesis

C

Ra

te o

f p

ho

tosyn

the

sis

h

� � �

photosynthesis in higher plants

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