NEET Biology Question Bank - Photosynthesis

20 Photosynthesis
Plants use sunlight (Photon), (H2O) and (CO2) to convert light Energy into chemical Energy by
chlorophyll. This process is known as photosynthesis.

Chemical equation :

6CO2 + 12H2O o
Sunlight
Chlorophyll C6H12O6 + 6O2 + 6H2O

Necessary factors for photoynthesis :

• Light

• Chlorophyll

• Water (H2O)

• Carbon Dioxide (CO2) (0.03 % in the atmosphere)

Photosynthetic Organisms :

• Different types of algae (Blue green algae, Brown algae, Red algae, Green algae).

• Bryophytes, Pteridophytes, Gymnosperms, Angiosperms.

• Some bacteria.

(Note : Fungi is not able to perform photosynthesis due to lack of chlorophyll.)

Advantages of Photosynthesis :

• Main products of photosynthesis are starch and sucrose.

• (O2) is byproduct which is used by organisms for respiration.

(1) What is produced as byproduct of photosynthesis ?

(A) Oxygen (B) Nitrogen (C) Carbon dioxide (D) Sulphur dioxide

(2) Which type of energy can be used by all organisms ?

(A) Light energy (B) Chemical energy (C) Heat energy (D) Water potential

(3) Which of the following type of reaction photosynthesis is ?

(A) Anabolic, Endothermic, Reduction (B) Anabolic, Endothermic, Oxidation

(C) Catabolic, Exothermic, Oxidation (D) Catabolic, Endothermic, Reduction

Answers : (1-A), (2-B), (3-A)

382

History of Photosynthesis :

No. Name of Scientist Contribution

1. Joseph Priestly Plants obtain CO2 from atmosphere and release O2.

(1733-1804)

2. Ingenhouse In bright sunlight, small bubbles were formed around the

(1730-1799) green parts of the plant.

3. Julius Von Sachs Green substance (chlorophyll) in plants is located in special

(1854) bodies (chloroplast) of plant cell. This green substances produces

glucose which is usually stored in the form of starch.

4. Robert Hill O2 released into atmosphere comes from water during

photosynthesis. He gave equation :

6CO2 + 12H2O ® C6H12O6 + 6H2O + 6O2

5. Cornelius Van Niel Photosynthesis is essentially a light dependent reaction in which

(1897-1985) hydrogen from a suitable oxidisable compound reduces CO2

to carbohydrates. He gave equation as follows :

6CO2 + 12H2O ® C6H12O6 + 6H2O + 6O2

(4) Which scientist showed that plants releases O2 and obtain CO2 ?
(A) Jan Ingenhousze (B) Julius Von Sachs (C) Joseph Priestly (D) Van Niel
(5) Which modified equation is given by Hill ?
(A) 6CO2 + 10H2O ® C6H10O6 + 5H2O + 6O2
(B) 5CO2 + 12H2O ® C6H12O6 + 5H2O + 6O2
(C) 4CO2 + 12H2O ® C6H12O6 + 6H2O + 6O2
(D) 6CO2 + 12H2O ® C6H12O6 + 6H2O + 6O2
(6) Which scientist showed that Light is necessary for study of photosynthesis in blue green algae ?
(A) Cornelius Van Niel (B) Jan Ingenhousze (C) Julius Von Sach (D) Robert Hill
(7) Which scientist demonstrated that O2 is liberated only by chlorophyll containing organs of the
plant in presence of O2 ?
(A) Priestly (B) Niel (C) Ingenhousze (D) Helmont
(8) Which type of reaction photosynthesis is ?
(A) Anabolic (B) Catabolic (C) Metabolic (D) All of the above
Answers : (4-C), (5-D), (6-A), (7-C), (8-A)

383

Structure of Chloroplast : (Site for photosynthesis)
• The proces of photosynthesis takes place in green organs of the plants.

Thylakoid
(Light Reaction)
Granum (Stack pile of thylakoids)

Intergranum membrane

Outer membrane

Stroma
Lumen of thylakoid

Structure
Chloroplast has main two parts :
(A) Grana (Membranous) (B) Stroma.
Grana :
• Each Granum is made up of flat, lamellar structure called thylakoid.
• This thylakoids contain chlorophyll pigments.
These are the main pigments of chloroplast :
Chlorophyll-a (C 55H 72O 5N 4Mg) - Green coloured

Chlorophyll-b (C 55H 70O 6N 4Mg) - Green coloured

Xanthophyll (C 40 H 56 O 2) - Yellow coloured

Carotenoids - Yellow to Orange coloured

• Amount of substances is different in all plants.
Stroma (Chlorenchyma) :
• Enzymes necessary for Calvin cycle are present in Stroma.
Functions :
• Light reaction take place in Grana.
• In Light reaction ATP and NADP are produced.
• Second phase of photosynthesis is dark reaction which occurs in Stroma, Enzymes becomes
activated, So CO2 and H2O combines to form C6H12O6.
• Dark reaction is dependent on the product of light reaction.

384

Photopigment System :

• We can identify different pigments by Chromatography.

• Pigments are classified on the basis of Primary receptor unit
colour.

• These photopigments absorb light at specific
wavelength and obtain energy from them. Reaction centre
Photons
• Chlorophyll is a main reactant of this process.
Molecules
of
• Other pigments works as accessory pigment. Photopigments

• The photosynthetic pigments at reaction centre
Light Harvesting complex
are stimulated by specific wavelength. On the
basis of is they are divided into two.

• These light harvesting complexes are known as Ps-I and Ps-II. (Ps = Photopigment system)

No. Features PS-I PS-II

(1) Reaction centre PS-I is also known as PS-II is also known as

P 700. P 680.

(2) Process Participates in cyclic Participates only in

and nonacyclic photo noncyclic photophosporylation.

phosphorylation.

(3) e  gain Picks up e  released by Picks up e  obtained by

PS-II. photolysis of water.

(4) Oxygen Does not show presence of During photolysis of water O2

Oxygen. is produced.

(5) Wavelength It gets stimulated at System is stimulated at

700 nm wavelength. 680 nm wavelength.

(9) Number of piles of flat lamellar thylakoids is known as ........ .
(A) Grana (B) Stroma (C) Granum (D) Lamellae

385

(10) In the process of photosynthesis ........ .
(A) O2 is liberated and NADPH2 is formed.
(B) Production of ATP and NADPH2 occurs.
(C) Production of ATP and NADPH2 occurs and O2 is released.
(D) Fixation of CO2 occurs.
(11) Which of the following is the place for chlorophyll ?
(A) In Stroma (B) On the surface of chloroplast
(C) In Grana (D) Overall chloroplast
(12) In which part of the leaf process of photosynthesis occurs ?
(A) Vascular bundle (B) Mesophyll tissue (C) Upper epidermis (D) Lower epidermis
(13) Where does the chloroplast present in the cell ?
(A) In the centre (B) Near to nucleus (C) Scattered (D) At periphery
(14) The intense light oxidise chlorophyll and causes damage to the plant. It is known as ...........
(A) Photorespiration (B) Photooxidation (C) Photolysis (D) Photoreduction
(15) What is LHC ?
(A) Lower Hard Complex (B) Light High Complex
(C) Light Harvesting Complex (D) Light Heavy Complex
(16) Which of the following group is accessory photosynthetic pigment ?
(A) Chlorophyll-b, Xanthophyll, Chlorophylla (B) Chlorophyll-b, Xanthophyll, Carotenoides
(C) Chlorophyll-b, Carotenoids, Chlorophyll-a (D) Chlorophyll-b, Fibrin, Xanthophyll
(17) Which pigments are yellow to Orange ?
(A) Chlorophyll-a (B) Xanthophyll (C) Carotenoids (D) Chlorophyll-b
(18) How many Light Harvesting complexes are formed, by photosynthetic pigments ?
(A) Two (B) Three (C) Four (D) Five
(19) How many chlorophyll pigments are present in each pigment system ?
(A) 300 to 400 (B) 400 to 500 (C) 350 to 800 (D) 250 to 400
(20) Which system is more sensitive to intense wavelength of light in photo pigment system ?
(A) PS-I (B) PS-II
(C) Splitting of water molecule by light (D) Light harvesting system
(21) What is known as PS-II ?
(A) P 700 (B) P 680 (C) LHC-I (D) RHC-I

Answers : (9-A), (10-C), (11-C), (12-B), (13-D), (14-B), (15-C), (16-B), (17-C), (18-A), (19-D), (20-A),
(21-B)

386

Phases of Photosynthesis :
(A) Light Reaction :
• There are mainly two types : Primary
electron-
(a) Cyclic Photophosphorylation : acceptor

Cytochrome system

Photon

Reaction Where
centre
Ferredoxin

Plastoquinone

Cytochrome

Cyclic Photophosphorylation Reaction : Plastocynin

In cyclic photophosphorylation e– transporters Ferredoxin (Fd) ® Plastoquinone (PQ) ®
Cytochrome system ® Plastocyanin (Pc) sends electron to its main source of PS-I.
(b) Noncyclic Photophosphorylation :

Primary Primary
electron- acceptor
acceptor

Cytochrome
System
NADP
reductase

Photon Photon

Electron Transport
System

Photolysis of water
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From PS-II to PS-I :
Electron passes Quinone ® Plastoquinone ® Cytochrome system ® Plastocyanin ® PS-I.
Here in PS-I Ferredoxin accepts the electron and next utilized for reduction of NADP.
Summary of Cyclic and Noncyclic Photophosphorylation :

Cyclic photo
phosphorylation

Photosystem-II Noncyclic Photosystem-I
Photophosphorylation

No. Features Cyclic Photo Phosphorylation Non Cyclic Photophosphorylation

1. Production Produces ATP. Produces ATP and NADPH2.

2. Oxygen Oxygen does not Oxygen is produced by

take part. photolysis of water.

3. Photopigment system Only PS-I participates. Participation of PS-I & PS-II both.

4. e– Transportation Electrons released from PS-I Electrons released from PS-I and PS-II

goes back to the same source. does not revert to the main source.

No e– from any other molecules Outer e– released from photolysis of

enter in the system. water enter in the system.

5. Efficiency Usually occurs during Usually occurs during aerobic

anaerobic condition, less light condition, high light intensity and

intensity and less CO2 high CO2 concentration.

concentration.

6. Process Usually occurs in bacteria Usually occurs in

like organisms. CO2 fixative plants and

another photosynthetic

organisms.

388

(c) Photolysis of Water :
The splitting of water molecule using energy of light is known as photolysis of water. The entire
process can be presented as under :

Light Energy

Chlorophyll

(22) Which of the following accepts electron at last that released by photolysis of water ?
(A) PS-I (B) PS-II (C) OAA (D) NADP
(23) How many water molecules split at a time in light reaction of photosynthesis ?
(A) 1 (B) 4 (C) 2 (D) 6
(24) Which are the essential ions for photolysis of water ?
(A) Mn+2, Cu+2, C1– (B) Na+, Mg+2, C1– (C) Mn+2, Ca+2, C1– (D) Mn+2, Fe+2, C1–
(25) Which pigment is associated with oxidation of water ?
(A) PS-I (B) PS-II (C) Phycobilism (D) Carotenoids
(26) What is the product formed by 4OH at the end of photolysis of water ?
–

(A) 2H2O (B) 2NADPH 2 (C) O 2 (D) (A) and (B) both
(27) What is primary acceptor of 4e released by PS-I in cyclic photophosphorylation ?
(A) Cytochrome (B) Electron transport system
(C) Electron acceptor (D) PS-II
(28) Which of the following process occurs in cyclic photophosphorylation ?
(A) Reduction of NADP (B) Photophosphorylation
(C) Photolysis (D) Production of O2
(29) How many photons are accepted by PS-I for initiation of cyclic photophosphorylation in light
reaction of photosynthesis ?
(A) One (B) Two (C) Three (D) Four
(30) Where does photophosphorylation occur ?
(A) In PS-I (B) In PS-II (C) In (A) and (B) both (D) In thylakoid
(31) What is Phosphorylation ?
(A) Production of ATP from ADP in presence of light
(B) Production of ADP from ATP in presence of light.
(C) Oxidation of NADPH2 in presence of light.
(D) Reduction of NADPH2 in presence of light.
(32) What happens during electron transportation ?
(A) Energy is released (B) Energy is utilized
(C) Reduction (D) Energy is stored

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(33) The process associated with cyclic photophosphorylation ........ .
(A) O2 is produced (B) Phosphorylation occurs
(C) Reduction of NADPH2 (D) Photolysis of water
(34) Sequence of electron transport released from cyclic photophosphorylation ........ .
(A) Fd ® Cyt ® Pc ® PQ (B) Fd ® PQ ® Cyt ® Pc
(C) PQ ® Q ® Cyt ® Pc (D) Q ® PQ ® Cyt ® Pc
(35) Which electron transporter is not present in cyclic photophosphorylation ?
(A) Fd (B) Q (C) PQ (D) Cyt

(36) What is photon ?
(A) Electron transporter (B) Molecules of chlorophyll
(C) Molecule form of light (D) Wave form of light
(37) Which of the following molecule works as a reaction centre in noncyclic photophosphorylation ?
(A) Chlorophyll a of PS-I (B) Chlorophyll a of PS-II
(C) LHC (D) (A) and (B) both

(38) Who accepts 4e released by PS-I at last in Noncyclic photophosphorylation ?

(A) PS-I (B) PS-II (C) NADP (D) RuBP

(39) Who accepts 4e released by PS-II at last in Noncyclic photophosphorylation ?

(A) PS-I (B) NADP (C) RuBP (D) H 2 O

(40) From which photopigment system e  is obtained for reduction of NADP during Noncyclic
photophosphorylation ?
(A) PS-I (B) PS-II
(C) From PS-I and PS-II both (D) None of the above
(41) How many ATP molecules are formed during noncyclic photophosphorylation ?
(A) 2 ATP (B) 1 ATP (C) 3 ATP (D) 6 ATP
(42) Which of the following process occurs first in photosynthesis ?
(A) Production of O2 (B) Noncyclic photophosphorylation
(C) Photolysis of water (D) Reduction of NADP

4H + 2NADP 4e 2NADPH2. From where the 4e are obtained in the given process ?
+
(43)
(A) PS-I (B) PS-II (C) Photon (D) H 2 O
(44) Which of the following electron transporters are associated with cyclic and Noncyclic
photophosphorylation ?
(A) PQ (B) PC (C) Cyt (D) All of the above

(45) Which of the following accepts e  released from PS-II ?

(A) PQ (B) Cyt (C) Q (D) Pc

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(46) After removal of thylakoid, if we put leaf in CO2 and H2O containing medium in presence of
sunlight, Hexose is not the Final product, because ........ .
(A) Molecules which obtains light are absent. (B) Photosystem PS-I and PS-II are not present.
(C) Enzymes which fixes CO2 are absent. (D) CO2 fixation does not occur in presence of light.

Answers : (22-D), (23-B), (24-C), (25 -B), (26 -D), (27-C), (28 -B), (29-D), (30 -D), (31-A), (32-A),
(33-B), (34 -B), (35 -B), (36-C), (37 -D), (38 -C), (39 -A), (40-A), (41 -B), (42 -C), (43-A), (44-D),
(45-C), (46-C)

Chemiosmosis :

Stroma
Thylakoid
membrane

Synthatase

ATP synthesis through chemiosmosis

• The chemiosmotic hypothesis has been put forward to understand synthesis of ATP in
chloroplast during photosynthesis.

• ATP synthesis is dependent on concentration gradient generated across thylakoid membrane.

• Due to splitting of water molecule protons (hydrogen ions) are liberated, which are
accumulated in lumen of thylakoid.

• Outside the thylakoid membrane that is in Stroma - Protons are used to reduce NADP. So
number of protons decreases in stroma and number increases in lumen of thylakoid.

• So, concentration gradient is created across the thylakoid membrane.

391

Function of Proton Gradient :
• Enzyme ATPase has two components : F0 and F1.
• F0 is embeded in the membrane which, works as transmembrane channel.
• F1 which protrudes on the outer surface of thylakoid membrane facing stroma.
• Abundant energy is produced due to breakage of concentration gradient.
• This conformational change in F1 particle ATPase makes the enzyme to synthesize several
molecules of energy packed ATP. ADP + Pi ® ATP.
Use of ATP :
The ATP produced will be used immediately along with NADPH in the biosynthetic phase taking
place in stroma.

(47) By splitting of which molecule H+ formation occurs in thylakoid ?
(A) CO 2 (B) NAD (C) H 2 O (D) NADP
(48) Which molecule is reduced in stroma outside the thylakoid membrane according to chemiosmotic
hypothesis ?
(A) CO 2 (B) NAD (C) H 2 O (D) NADP
(49) What we can understand by chemiosmotic hypothesis ?
(A) Splitting of H2O (B) Synthesis of ATP in chloroplast
(C) Fixation of CO2 (D) Reduction of NADP
(50) What is responsible for change in F1 component of ATPase ?
(A) Presence of proton acceptor NADP+ (B) Noncyclic transportation of electrons
(C) Energy released by proton gradient (D) Enzymes of F0 component
(51) What is the cause for creation of proton gradient across the Thylakoid membrane ?
(A) Increase in number of protons in thylakoid.
(B) Decrease in number of protons in stroma.
(C) Decrease in pH in cavity of thylakoid.
(D) All of the above

Answers : (47 - C), (48 - D), (49 - B), (50 - C), (51 - D)

(B) Biosynthetic Phase : CO2 fixation, Calvin cycle, C3 path, Dark reaction, Reduction of RuBP.

• This process occurs in stroma of thylakoid.

• Light is not necessary for this process.

• H2O and CO2 combines to form sugar.

• Malvin Calvin by using radioactive C14 in algal photosynthesis described this process.

• So, this process is known as Calvin cycle.

• They got Nobel Prize in 1961.

• Steps necessary for this process are shown as under :

392

Main Phases of Biosynthetic Phase :
6 (Ribulose 1-5 Biphosphate) (RuBP) + 6CO2 ----® 6 (Unstable product)
Carboxy-
lation (5C) (1C) (6C)

6 (Unstable product) + 6H2O ----® 12 (PGA)
(6C) (3C)
Reduction

Phase

12 PGA + 12NADPH + 12 ATP ----–® 12 PGAL + 12NADP + 12 ADP
(3C) (3C)

12 PGAL (3C) ----–® 10 PGAL (3C) + 2 PGAL (3C)

6 ATP
Regeneration phase ¬-------------

6 ADP
¯ ¯
3 PGAL (3C) 3-PGAL (3C)
Transportation as per the requirement in ¯ ¯
different plant organs 3-PGAL (3C) 3-DHAP (3C)
­ ¯ ¯
¯
Fructose 1-6 Biphosphate (6C)
Storage in Phloem + Transportation ¯ ADP
­ (Sucrose) ¯ ATP
Fructose-6 Phosphate (6C)
Unstable storage in stroma ¯
Glucose-6-Phosphate (6C)
­ ¯ ADP
¯ ATP
Starch (n  N) ¬ ¬ Glucose (6C)
(C 6H 12O 6)

393

Ribulose 1-5
Biphosphate

Unstable Product

fkCarboxylation Enzyme
Carboxylase

Regeneration Calvin Cycle

3-C Phosphoglyceric
acid
Reduction

Sucrose, Starch 3-C Triose
Phosphate

(52) In dark reaction of photosynthesis ..........
(A) 3C compound is formed by splitting of 6C sugar.
(B) Photolysis of water occurs.
(C) Molecules of chloroplast are stimulated.
(D) Carbonic compounds are formed by reduction of CO2.
(53) Which radioactive isotope is used to explain C3 - path ?
(A) C 12 (B) C 14 (C) C 13 (D) C 16
(54) Which enzyme is responsible to join CO2 and RuBP ?
(A) NADP reductase (B) ATPase
(C) RuBP Carboxylase (D) Cytochrome Oxidase
(55) Which sugar is used in first step of Biosynthesis ?
(A) C 6 H 12 O 6 (B) RuBP (C) DHAP (D) PGAL
(56) Which type of sugar is used in Calvin cycle ?
(A) Aldotriose (B) Ketotriose (C) Aldopentose (D) Ketopentose
(57) How many ATP and NADPH2 are required for fixation of one CO2 molecule ?
(A) 3ATP + 1NADPH2 (B) 2ATP + 2NADPH2
(C) 3ATP + 2NADPH2 (D) 3ATP + 3NADPH2
(58) From which molecule 3 - Carbon of phosphoglyceric acid are obtained during carbon fixation ?
(A) PEP + CO2 (B) CO 2 (C) RuBP (D) RuBP + CO2

394

(59) Calvin cycle starts with ........ .
(A) PGA (B) RuBP (C) OAA (D) PGAL
(60) How many ATP and NADPH are necessary for production of one glucose ?
(A) 12, 20 (B) 6, 3 (C) 18, 12 (D) 10, 20
(61) What is the product of carboxylation in stroma of chloroplast ?
(A) PGA (B) PGAL (C) DHAP (D) RuBP
(62) What is the product formed by removal of ‘O’ from PGA ?
(A) PGAL (B) DHAP (C) RuBP (D) OAA
(63) How many molecules of 3-PGAL are necessary for regeneration of RubP ?
(A) 12 (B) 8 (C) 10 (D) 6
Answers : (52-D), (53-B), (54-C), (55-B), (56-D), (57-C), (58-D), (59-B), (60-C), (61-B), (62-A), (63-C)
C4 – Path (Hatch Slack Pathway)
• C4 pathway is generally observed in the monocot plants which grow in the tropical regions.
• It is very clearly observed in the leaves of sugarcane.
• Special type of Kranz anatomy is seen in C4 pathway.
According to Kranz Anatomy :
Bundle Sheath Cell Mesophyll Cell
• They do not show grana organization. • They show grana organization.
(Only thylakoids are present.) (Thylakoids are arranged in piles.)
• C3-cycle is obseved for CO2 fixation. • Light reaction occurs and OAA is produced.
• This type of arrangement prevents entry of O2, evolved during light reaction, from entering
bundle sheath cells. So, there is no possibility of photorespiration.

Mesophyll cell
Photosynthetic Mesophyll
Mesophyll cell
cell
cells of C4
plants Bundle
sheath cell
Oxeloacitic acid Air space
Vein
Vascular Melic acid
tissue

Pyruvic acid

Bundlesheath
Stomata cell
Calvin
Leaf anatomy Cycle

Sucrose

Vascular
Tissue

cycle

395

Special Characters :
• Due to release of CO2 in bundle sheath cells, the concentration of CO2 goes on increasing.
As the process of CO2 fixation occurs in these cells. Also, more food is prepared through
biosynthetic fixation.
• As there is no possibility of photorespiration, C4 is more efficient than C3.
Differences between C3 and C4 path :

No. Character C3 - Path C4 - Path

1. Type of cell One (Mesophyll) Two (Mesophyll) and bundle sheath cell

2. Kranz Anatomy Does not occur Occurs

3. Chloroplast With grana With and Without grana

4. First CO2 Acceptor RuBP PEP

5. First Product PGA (C3) Oxalo acetic acid (C4)

6. Productivity (Food) Normal High

(64) Which of the following plant shows C4 path ?

(A) Sunflower (B) Potato (C) Maize (D) Bignonia

(65) Which of the following plant utilizes maximum light ?

(A) Paddy (B) Sugarcane (C) Wheat (D) Sorghum

(66) How C4 - cycle is different from C3 - cycle ?

(A) Photosynthetic product (B) Number of ATP for production of sugar

(C) Molecule of CO2 fixation (D) Photopigments which play role in photosynthesis

(67) In which part light reaction occurs in C4 plants ?

(A) cells of Mesophyll (B) In Bundle sheath cells

(C) In epidermal cells (D) In phloem

(68) What is produced by decarboxylation of Malic acid in bundle sheath cells in C4 plants ?

(A) PGA (B) PEP (C) PEPA (D) Pyruvic Acid

(69) How many Calvin cycles are necessary for production of 1 glucose ?

(A) 2 (B) 3 (C) 4 (D) 6

(70) First and Second CO2 acceptor in C4 path are ........ .

(A) RuBP, PEP (B) PEP, RuBP (C) OAA, PEP (D) PEP, OAA

396

(71) What is the number of ATP for production of 1 glucose in C4 - pathway ?

(A) 10 (B) 20 (C) 16 (D) 30
(72) How many times biochemical reactions occurs for production of one glucose molecule in C4 - path ?
(A) 2 (B) 4 (C) 6 (D) 8
(73) By which process Malate is formed from PEP ?
(A) Carboxylation, Dehydrogenation
(B) Carboxylation, Hydrogenation
(C) Decarboxylation, Hydrogenation
(D) Decarboxylation, Dehydrogenation

Answers : (64-C) (65-B), (66-C), (67-A), (68-D), (69-D), (70-B), (71-D), (72-C), (73-A)

Photorespiration :

• Definition : The respiration which occurs in chloroplast in presence of light is known as
photorespiration.

• Location : Chloroplast, Peroxisome and Mitochondria.

• Enzyme : RuBisCo.

Oxygenation
Carboxylasion
(Calvin cycle)

3-Phosphoglycerate
Phosphoglycocholate

Photorespiration

• CO2 and RuBP combines to form 2 PGA in biosynthetic phase which is known as
carboxylation.

• Enzyme RuBisCo (Ribulose Biphosphate Carboxylase) is resonsible for this process which is
in abundant amount.

• It can bind with O2 and CO2.

• In photorespiration it is oxygenase means behaves as enzyme for O2.

397

Chart explaining photorespiration

Chlorophyll
Phosphoglycocholate

Glycerate Glycocholate

Glycerate Glycocholate
Perixosome

Hydroxy pyruvate Glyoxylate

Serine Glycine

Serine Glycine
Mitochondria

Importance :
• RuBP is oxygenated in presence of O2 forming one molecule of 2C phosphoglycolate and
next 1 glycine is formed. Such two glycine × 2 = 4C, 3C serine is formed and 1C is removed
as release of CO2.
• So, Total 4 carbon(100%)


o 
o
3 carbon (75%) 1 CO2 (25%) is wasted

• Under condition of intense light and poor availability of CO2 photorespiration plays defensive role.

• With insufficient availability of CO2 and light energy cannot be fully utilized and excess light can
cause photooxidation and damage the plant. Photorespiration provides protection against this.
• In C3 plants some O2 binds to RuBisco and so CO2 fixation is decreased.

• In C4 plants photorespiration does not occur. This is because they have a mechanism that
increases the concentration of CO2 at the enzyme site.

• This ensures that RuBisco functions as Carboxylase minimizing Oxygenase activity.
• So productivity is C4 is more.

398

(74) What decreases photorespiration ?
+2 +2
(A) Fe (B) Mg (C) H 2 O (D) CO 2
(75) Photorespiration is harmful to plants ? Why ?
(A) ATP production does not occur. (B) RuBP is decomposed.
(C) CO2 is synthesized. (D) Amino acid is decomposed.
(76) Photorespiration occurs......
(A) At low temperature (B) More O2 and less CO2
(C) Low intensity of light (D) Less O2 and more CO2
(77) What is produced by dephosphorylation of phosphoglycolate during photorespiration ?
(A) Glycerate (B) Glycine (C) Glycolate (D) Glyoxylate
(78) In which orgenelle CO2 is released in photorespiration ?
(A) Mitochondria (B) Chloroplast (C) Peroxisome (D) Lysosome
(79) Which is the substrate for photorespiration ?
(A) Glycine (B) Serine (C) Glycolate (D) RuBP
(80) By which process Glycolate is formed from phosphoglycolate ?
(A) Reduction (B) Decarboxylation (C) Phosphorylation (D) Dephosphorylation
(81) In photorespiration, Glycolate is produced in ........ .
(A) Chloroplast (B) In mitochondria (C) In cytoplasm (D) In peroxisome
(82) Which product is formed when RuBP is oxygenated ?
(A) Phosphoglycolate, PGA (B) PGA, DHA
(C) Phosphoglycolate, Serine (D) Glyceric Acid, PGA
(83) Which of following is not true for photorespiration ?
(A) It occurs in presence of light (B) It occur in chloroplast
(C) Speciality of C3 plants (D) Speciality of C4 plants

Answers : (74 - D), (75 - B), (76 - B), (77 - C), (78 - A), (79 - C), (80 - D), (81 - A), (82 - A), (83 - D)

Factors affecting photosynthesis :
The rate of photosynthesis is very important in determining the yields of plants including crop
plants. Photosynthesis is under the influence of several factors, both internal and external. When several
factors affect any (bio) chemical process.
(1) Chemical process :
• Blackman’s (1905) law of limiting factors comes into effect. This states the following :
• “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 it its quantity is changed.”
• For example, despite of presence of green leaf, optimal light and CO2 conditions,
photosynthesis may not occur, it temperature is very low. This leaf, if given the optimal,
temperature, will start photosynthesizing.

399

(2) Light :
• Both, the intensity and quality of light influence photosynthesis : Normally as intensity of light
increases, the rate of photosynthesis increases. However, at higher intensity it is not so. At
high intensity of light, oxidation of chlorophyll, occurs and it is decomposed. This is called
photooxidation. Because of this the rate of the process drops.
• The visible spectrum of light ranges from 400 nm to 700 nm plants can absorb light from this range
only. The rate increases in orange and red light. It decreases in green light.
(3) CO2 Concentration :
The concentration of CO2 is very low in the atmosphere i.e. 0.036%. Increase in the
concentration upto 0.05% can cause an increase in CO2 fixation rates. Beyond this the levels
for can become damaging over longer periods.
• At high light intensity both, C3 and C4 plants show increase in the rates of photosynthesis.
• C3 plants responds to increased CO2 concentration and saturation is seen only beyond 450 m1 L–1.
• C4 plants show saturation at about 360 m1 L–1.
(4) Temperature :
(a) There is no notable effect of temperature in the photochemical phase but as dark reaction or
biosynthetic phase being enzymatic, temperature has a remarkable effect on it.
(b) The C4 plants respond to higher temperatures and show higher rate of photosynthesis while
C3 plants have a much lower temperature optimum.
(5) Water :
• When availability of water is reduced, the plant experiences water stress.
• One is that the stomata are closed, as a result the amount of available CO2 is reduced.
• Secondly, as water potential in leaves is lowered, they curl. Thus available leaf area is
reduced for photosynthesis.

(84) In which temperature range rate of photosynthesis is maximum ?
0 0 0 0 0 0 0 0
(A) 10 C to 20 C (B) 5 C to 10 C (C) 10 C to 25 C (D) 10 C to 15 C
(85) Which plants shows decreasing rate of photosynthesis in CO2 concentration ?
(A) C3 plants (B) C4 plants (C) Aquatic plants (D) CAM plants
(86) Maximum absorption of light occurs at ........ wavelength.
(A) 400 nm 700 nm (B) 600 nm 1200 nm (C) 600 nm 700 nm (D) 500 nm 900 nm
(87) At high intensity of light ........ .
(A) Rate of photosynthesis increases (B) Rate of photosynthesis decreases
(C) Oxidation of chloroplast occur (D) Reduction of chloroplast occur
(88) What happens when the amount of water decreases in plants ?
(A) Closing of stomata (B) Decrease in CO2 concentration
(C) Rolling of leaves as water potential decrease (D) All of the above
400

(89) What happens when the temperature increases in the atmosphere ?
(A) Rate of photosynthesis decreases in C4 plants.
(B) Rate of photosynthesis decrease in C3 plants.
(C) Rate of photosynthesis increases in C4 plants.
(D) Rate of photosynthesis becomes minimum in C3 plants.
(90) When does C4 plant show saturation ?
–1 –1 –1 –1
(A) 360 ml of CO2 (B) C 350 ml of CO2 (C) 400 ml of CO2 (D) 436 ml of CO2
(91) ........ is the important for structure of chlorophyll.
(A) Magnesium (B) Nitrogen (C) Phosphorus (D) Iron
(92) Which process of photosynthesis show effect of temperature ?
(A) Light reaction (B) Dark reaction
(C) Cyclic photophosphorylation (D) Photorespiration

Answers : (84-C), (85-B), (86-A), (87-C), (88-D), (89-C), (90-A), (91-B), (92-B)

A - Assertion, R - Reason.
Choose the correct option :
(A) A and R both are true and R is the correct explanation of A.
(B) A and R both are correct, R is not correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.
(93) Assertion A : ATPase present in thylakoid membrane in chloroplast possess two component.
Reason R : F0 is embedded in the membrane and F1 protudes on the outer surface of
thylakoid membrane.
(A) (B) (C) (D)
(94) Assertion A : During photorespiration NAD is reduced in peroxisome and NADH is
dehydrogenated in mitochondria.
Reason R : During photorespiration ATP is dephosphorylated to form PGA from glycerine.
(A) (B) (C) (D)
(95) Assertion : O2 is released from 4OH– produced from photolysis of water.
Reason R : NADP are reduced by 4OH+ of photolysis of water.
(A) (B) (C) (D)
(96) Assertion A : 6 times kelvin cycle occur for formation of 1 glucose.
Reason R : 18 ATP and 12 NADPH2 are utilised for formation of 1 glucose.
(A) (B) (C) (D)
(97) Assertion A : Rubisco is more active as carboxylase and less active as oxigenase.
Reason R : Productivity is more in C4 pathway.
(A) (B) (C) (D)
(98) Assertion A : There is no possibility of photosynthesis if termperature is less though amount of
CO2 and light is minimum.
Reason R : Plants follow blackman’s law of limiting factor.
(A) (B) (C) (D)

401

(99) Assertion A : If one molecule of RuBP and oxygen occurs the last product is glycine and PGA.

Reason R : If one molecule of RuBP and O2 the last product is PGA and phosphoglycolate.

(A) (B) (C) (D)

(100) Assertion A : In C4 plants PEP is the first CO2 acceptor and RuBP is last acceptor.

Reason R : In C3 plants RuBP is first CO2 acceptor.

(A) (B) (C) (D)

(101) Assertion A : The rate of photosynthesis is less at high intensity of light.

Reason R : At high intensity of light chloroplast oxidation occur.

(A) (B) (C) (D)

(102) Assertion A : In light reaction absorption of light, photolysis, release of oxygen, formation of
ATP and NADP occurs.

Reason R : LHC creates PS-I and PS-II
(A) (B) (C) (D)

Answers : (93-A), (94-D), (95-B), (96-A), (97-A), (98-B), (99-A), (100-C), (101-D), (102-B)

True - False (T - F) type questions :
Choose the correct True and False :
(103) (1) Kranz anatomy is seen in C4-plants.

(2) Melvin-Kelvin found C4-path.

(3) Photorespiration can be seen in C3-plants.

(4) 6 ATP and 4 NADPH2 are necessary for fixation of 2CO2 in C3 cycle.

(A) F T T F (B) T F T T (C) T T F T (D) F T F T

(104) (1) Photolysis occur in stroma of chloroplast.

(2) NADPH2 produced by photolysis are used in light reaction.

(3) Electron and NADP are produce from PS-I are utilise in photolysis.

(4) Mn+2, Ca+2 and Cl– are necessary for photolysis of water.

(A) F T F T (B) T T T F (C) F F T T (D) F T T F

(105) (1) The first stable product of bio synthetic is PGA.

(2) Non cyclic photophosphorylation occurs in stroma of chloroplast.

(3) Rate of photosynthesis is more in red light.

(4) Light energy is converted into chemical energy during photosynthesis.
(A) T F T T (B) T F F T (C) F F T F (D) F T F T 111
402

(106) (1) Light reaction occurs in grana of chloroplast.
(2) Temperature factor affects biosynthetic phase.
(3) Chlorophyll-b works as reaction centre.
(4) Productivity of C4 is less comparatively to C3 plants.
(A) F T T F (B) T T F T (C) F T F T (D) T T F F
(107) (1) Hatch-Slack found C3 plants.
(2) Photorespiration does not occur in C4 cycle.
(3) Law of limiting factor is found by blackman.
(4) The plants which use PEP during CO2 fixation are called C4 plants.
(A) F T T F (B) T F T F (C) F T T T (D) T F F T
(108) Choose Correct pair :
Column - I Column - II
P. Grana region of Chloroplast (i) Kreb’s cycle (A) P - ii, Q - iii, R - iv, S - i
Q. Stroma region of Chloroplast (ii) Light reaction (B) P - i, Q - ii, R - iii, S - iv
R. Cytoplasm (iii) Dark reaction (C) P - ii, Q - i, R - iv, S - iii
S. Mitochondrial cytoplasm (iv) Glycolysis (D) P - iii, Q - iv, R - i, S - ii
(109) Choose Correct pair :
Column - I Column - II
P. Carboxylation (i) Production of O2 (A) P - ii, Q - ii, R - iii, S - iv, T - v
Q. Photophosphorylation (ii) Photorespiration (B) P - iii, Q - v, R - i, S - ii, T - iv
R. Photolysis (iii) RuBiSCo (C) P - i, Q - iii, R - iii, S - iv, T - ii
S. Phosphoglycolate (iv) Chemosynthesis (D) P - i, Q - iii, R - iv, S - ii, T - v
T. Nitrosomonas (v) ATP
(110) Choose Correct pair :
Column - I Column - II
1. PS-I P. Chemiosmotic hypothesis (A) 1 - Q, 2 - R, 3 - P, 4 - S
2. PS-II Q. Cyclic photophosphorylation (B) 1 - Q, 2 - S, 3 - P, 4 - R
3. Cytochrome-b R. Present in thylakoid (C) 1 - Q, 2 - R, 3 - S, 4 - P
4. ATPase S. Photolysis of water (D) 1 - R, 2 - S, 3 - Q, 4 - P
(111) Choose Correct pair :
Column - I Column - II
1. Cyclic photophosphorylation P. O2 is released and NADP is reduced
2. Biosynthetic phase Q. Depends on concentration of O2 and CO2
3. Non cyclic photophosphorylation R. Formation of 2ATP
4. Photorespiration S. Photorespiration phase occurs in stroma
(A) (1-R), (2-P), (3-Q), (4-S) (B) (1-r), (2-S), (3-Q), (4-P)
(C) (1-R), (2-S), (3-P), (4-Q) (D) (1-P), (2-R), (3-Q), (4-S)

403

(112) Choose Correct pair :
Column - I Column - II
1. C 6H 12 O 6 P. Regenerated during process of C3 cycle
2. OAA Q. Amino acid produced in peroxisome
3. RuBP R. Product of photosynthesis
4. Glycin S. First stable product of C4 path
(A) (1-R), (2-S), (3-Q), (4-P) (B) (1-R), (2-S), (3-P), (4-Q)
(C) (1-S), (2-R), (3-P), (4-Q) (D) (1-R), (2-P), (3-DS), (4-Q)
(113) Choose Correct pair :
Column - I Column - II
P. C4 Chloroplast p. RuBP
Q. First acceptor of C3 q. With Grana and without grana
R. First acceptor of C4 r. Possess Grana
S. C3 Chloroplast s.. PEP
(A) P - s, Q - r, R - p, S - q (B) P - r), Q - s, R - p, S - q
(C) P - q), Q - p, R - s, S - r (D) A - q), Q - p, R - r, S - s
(114) Choose Correct pair :
Column - I Column - II
1. 1733-1804 p. Time period of priestly
2. 1897-1985 q. Time period of Ingenhousz
3. 1854 r. Time period of Julius Von Sachs
4. 1730-1799 s. Time period of Cornelius Van Niel
t. Time period of Robert Hill
(A) (1-p), (2-s), (3-r), (4-q) (B) (1-p), (2-q), (3-r), (4-s)
(C) (1-p), (2-s), (3-t), (4-q) (D) (1-p), (2-r), (3-s), (4-q)
(115) Choose Correct pair :
Column - I Column - II
1. Photolysis of water ® p. Non cyclic photophosphorylation
2. ATP ase ® q. Peroxisome
3. RuBisCo ® r. Mitochondria
+
4. NAD reduction ® s. Thylakoid membrane
t. Stroma
(A) 1 - t, 2 - p, 3 - q, 4 - p (B) 1 - t, 2 - r, 3 - s, 4 - p
(C) 1 - p, 2 - s, 3 - t, 4 - r (D) 1 - p, 2 - s, 3 - t, 4 - q
(A) T. P, Q, R (B) T, R, S, P (C) P, S, T, R (D) P, S, T, Q

Answers : (103-B), (104-C), (105-A), (106-D), (107-C), (108-A), (109-B), (110-B), (111-C), (112-
B), (113-C), (114-A), (115-D)

404

Ribulose 1-5
biphosphate

3 - Regeneration

Triosephosphate

(116) What is shown in the chart-1 ? Chart-1
(A) Reduction (B) Oxidation (C) Carboxylation (D) Decarboxylation
(117) Which process is indicated by Z in chart-1 ?
(A) Reduction (B) Carboxylation (C) Oxidation (D) Decarboxylation
(118) Which process is indicated by Y in chart-1 ?
(A) 3-Phosphoglycerate (B) 2-Phosphoglycolate (C) Triosphosphate (D) Decarboxylation
(119) Name chart-1
(A) C4 path (B) Kreb’s cycle (C) CAM pathway (D) Calvin cycle
(120) What is indicated as P in chart-1 ?
(A) Sucrose, Starch (B) Fructose, Starch (C) Maltose, Starch (D) Glucose, Starch

Electron
Receptor

Electron
Receptor

R

Chart-2

405

(121) Name chart-2
(A) Cyclic photophosphorylation (B) Photorespiration
(C) Non-cyclic photophosphorylation (D) Photolysis
(122) What is indicated by P in chart-2 ?
(A) P 700 (B) P 680 (C) P 670 (D) P 750
(123) What is indicated as Q in chart-2 ?
(A) P 700 (B) P 750 (C) P 680 (D) P 580
(124) What is indicated by R in chart-2 ?
(A) Thylakoid membrane (B) Cytoplasmic stroma
(C) Electron transport system (D) Mitochondria
(125) Which process is indicated by S in chart-2 ?
(A) ATP + ADP + Pi (B) ADP + Pi ® ATP
(C) 2H2O2 ® 2H2O + O2 (D) CO2 + H2O ® CH2O + O2

(126) What is indicated by P and Q in the chart ?

(A) P – Cytochrome A & A, Q – Thylakoid membrane

(B) P – Thylakoid membrane, Q – Cytochrome A & A
Q Stroma
(C) P – Cytochrome b & f, Q – Cytochrome a & a

(D) P – Stroma, Q – Thylakoid membrane
Synthatase
(127) Which process is indicated by this figure ?

(A) ATP synthesis by chemiosmosis (B) Food synthesis by chemiosmosis

(C) Photolysis by chemiosmosis (D) Electron transport by chemiosmosis

Answers : (116-C), (117-A), (118-A), (119-D), (120-A), (121-C), (122-B), (123-A), (124-C), (125-
B), (126-C), (127-A)

Questions for NEET :
(128) Which of the following step is necessary for photosynthesis ?
(A) ATP formation
(B) Photolysis of water
(C) Production of chlorophyll with the help of photon
(D) Production of C6H12O6
(129) Who found the laws of limiting factors of photorespiration ?
(A) Hill (B) Blackman (C) Niel (D) Calvin
+
(130) How many H ions are formed by photolysis of 12H2O during Non-cyclic photophosphorylation ?
+ + + +
(A) 24H (B) 12H (C) 36H (D) 32H
406

(131) In which light the rate of photosynthesis is more ?
(A) Blue (B) Green (C) Orange or Red (D) Blue or Green
(132) What happens due to absorption of light ?
(A) Release of O2 (B) Absorption of CO2
(C) Oxidation of chlorophyll (D) Reduction of chlorophyll
(133) What is correct for C4 plant ?
(A) CO2 combines with PEP (B) CO2 combines with PGA
(C) CO2 combines with PGAL (D) CO2 combines with RuBP
(134) How many glycine molecules are necessary to release CO2 during photorespiration ?
(A) 1 (B) 3 (C) 2 (D) 4
(135) Where does the process of Reduction of NAD occurs during photorespiration ?
(A) Chloroplast and Peroxisome (B) Chloroplast and Mitochondria
(C) Mitochondria and Peroxisome (D) Mitochondria
(136) What happens when we put plants in lower intensity of light ?
(A) Photosynthetic unit becomes more active because of light.
(B) More CO2 fixation occurs in presence of light in plants.
(C) Root system develops more.
(D) Leaves are converted into thorns.
(137) Where we find Hill-reaction ?
(A) Higher level of plants (B) In complete darkness
(C) During waterstress (D) In presence of fatty cyanide
(138) Which of the following is incorrect for photorespiration ?
(A) Associated with chloroplast (B) Occurs during daytime
(C) Speciality of C4 plants (D) Speciality of C3 plants
(139) In which organism chlorophyll is absent during photosynthesis ?
(A) Bacteria (B) Cyanobacteria (C) Red algae (D) Brown algae
(140) Which minerals are necessary for the formation of chlorophyll ?
(A) Fe, Mg (B) Ca, K (C) Fe, Ca (D) Ca, Cu
(141) What is true for puruvic acid in CAM plants ?
(A) Increases during day time (B) Decreases during night
(C) Decreases during day time (D) Increases during night
(142) How many e– are utilise for formation of 1 mole glucose and 6O2 molecule ?
(A) 6 (B) 12 (C) 18 (D) 24
(143) What is present in blue algae ?
(A) Chlorophyll (B) Xanthophyll (C) Phycocyanin (D) Fucoxanthnin

407

(144) Choose the correct sequence for Kelvin cycle :

(1) ATP and NADPH formed during photosynthesis are utilised and forms carbohydrate.

(2) It is the process in which Ribulose 1, 5 biphosphate except CO2 and RuBP is regenerated.

(3) It is the process in which ribulose 1, 5 biphosphate bind with CO2 or carboxylation occur.

(A) 3 – 1 – 2 (B) 3 - 2 - 1 (C) 1 - 2 - 3 (D) 2 - 1 - 3

(145) Which of the following statement is appropriate for light and process of photosynthesis ?

(A) Cytochrome a stimulates 680 nm, PS-I stimulates 700 nm, PS-II absorb move photons.

(B) Na+ and Mg ions are necessary for photolysis of water.

(C) O2 participates in photophosphorylation.

(D) PS-I and PS-II both participate in iron cyclic photophosphorylation.

(146) Productivity of C3 plant are more because ..............

(A) Photorespiration is less in it (B) Leaf area is more

(C) More amount of chloroplast occur in leaves (D) Thin cuticle layer is present

(147) Which enzyme is responsible for fixation of CO2 with PEP in mesophyll of C4 plants ?

(A) Pyruvate dehydrogenase (B) PEP Carboxylase

(C) Pyruvate decarboxylase (D) RuBisco

Answers : (128-C), (129-B), (130-C), (131-C), (132-C), (133-A), (134-C), (135-B), (136-A), (137-
A), (138-C), (139-B), (140-A), (141-A), (142-B), (143-A), (144-A), (145-D), (146-C), (147-D)

408

Photosynthesis
® External Factors
Light, Co2 conc, temperature,
Formation of glucose from Co2 and Factors affecting
water in the presence of sunlight and ® ® Water, O2 etc.
Photosynthetisis
chlorophyll ® Internal Factors
® Site of photosynthesis Chlorophyll conc, leaf age,
Chloroplasts that consists of Stroma, Grana stacks, Thylakoids phytohormones, etc.,
and stroma lamellae.
Thylakoids contain Photosynthetic pigments. Includes P700 as
photocentre and light
® Photosynthetic Pigments ® PS-I harvesting complex
Photosynthetic pigments include Chlorophylls, Carotenes and (LHC) with electron
carriers
phycobilins. These pigments are packed in two major
pigment system.
Includes P as
® PS-II photocentre and 680
LHC
® Photosynthetic Mechanism
® Photolysis
An enzymatic anabolic reaction
Water molecule is broken ® Cyclic photophosphorylation
involving many intermediates down into H+ and OH– Only PS-I involves in
ions by absorbing light electron transport and
energy. It produces e– producs only ATP
® Photochemical Phase ® Non-cyclic photophos
Light dependent phase phorylation
occuring in Thylakoids
® Photophosphorylation
Both PS-I and PS-II
Electons released in involve and produce both
photolysis of water are ATP and NADPH
® Biosynthetic Phase used for production of
ATP CAM Cycle
Light independent reaction that ®
occurs in Stroma In xerophytes, CO2 is
fixed at night. It helps in
reducing transpiration.
C3 Cycle C4 Cycle

Also called Calvin cycle. Glucose is formed by Co2 fixation but
Co2 combines with RuBP initial acceptor is PEP in mesophyll calls
and produces glucose. 3C and first stable product is 4C Oxaloacetic
phosphorlyceric acid is acid. C4 plants have Kranz Anatomy and
first stable product are more efficient than C3 plants.

¯
Photorespiration
Light dependent oxygenation of RuBP and releases CO2 in photosynthetic cells of C3 plants.

•
409