2. Introduction
• Single-most important biochemical process in the world on which the
existence of life on earth depends.
• It is the ability of green plants only to utilise the energy of light to produce
carbon containing compound
• The efficiency of photosynthesis has been observed between 2-2.5% for
crops
3. Photosynthesis as a process
• Photosynthesis is an oxidation reduction process in which water is oxidised
and carbon dioxide is reduced to carbohydrate
• Reduction of Co2 to carbohydrate needs assimilatory powers such as ATP
and NADPH, reduction of Co2 occurs in dark
• But the process of production of ATP and NADPH occurs in presence of
light
• Emerson and Arnold (1932) carried out the flashing light experiment and
showed existence of light and dark reactions
4. History
• Intermittent light flashes- Warburg (1920) observed that when the
intermittent flashes of light of about 1/16 seconds were given to green algae
chlorella vulgaris the photosynthetic yield per second was higher as
compared to continuous light.
• Hills reaction- in 1937, Robert Hill demonstrated that isolated chloroplast
evolve oxygen when they were illuminated in the presence of suitable
electron acceptor such as ferricyanide. Hill reaction explains that water is
used as a source of electrons for Co2 fixation and oxygen is evolved as by-
product
• Ruben, Randall and Kamen (1941) using heavy isotope (O18) in their
experiments provide the direct proof that oxygen is evolved in
photosynthesis.
5. • Red drop and Emerson effect- Photosynthesis is considered as a two
quanta process that is it takes two quanta energy to drive each electron.
Since four electrons are required for the reduction of one molecule of Co2,
eight quanta will be required to reduce it or to evolve one molecule of
oxygen.
• Quantum yield is defined as the number of O2 molecules released per light
quanta absorbed
• Emerson and Lewis (1943) worked on quantum yield of photosynthesis in
single color light of different wavelength. They observed that quantum
yield declined sharply at wavelength greater than 680nm in the red zone
this decline is called red drop
6. Two pigment system
• PS I- complex consist of 200 chlorophylls ,50 carotenoids a mol. of P 700,
one cyt f, one plastocyanin, two cyt b 563, FRS (ferridoxin reducing
substance), rich in chl-a, iron and copper . PS I controls the process of
producing a strong reductant to reduce NADH into NADPH + H+
• PS II- consists of 200 chlorophylls, 50 carotenoids a mol. Of P 680, a
primary electron acceptor Q, a plastoquinone, four plastoquinone
equivalents, four Mn molecules bound to one or more proteins, two cyt b
559, one cyt b6 and chloride.
• Salisbury and Ross (1986) proposed that grana mainly contain PS II while
stroma lamellae PS I.
• PS I light is gathered by chl a and carotenoids while in PS II light is
gathered by chl b and xanthophyll
7. Production of assimilatory power in photosynthesis
• Arnon (1956) used the term assimilatory powers to refer to ATP and
NADPH.
• The process of reduction of NADP into NADPH may be denoted as
electron transport system or reduction of NADP
• While the process of formation of ATP from ADP and inorganic phosphate
(Pi) utilising light energy is called photophosphorylation.
8. Mechanism of photosynthesis: II Dark reaction
• Dark reaction process involved in photosynthesis was established by
Blackman (1905).
• C3 Photosynthesis:
• C3 plants Called C3 because the CO2 is first incorporated into a 3-carbon
compound.
• Stomata are open during the day.
• RUBISCO, the enzyme involved in photosynthesis, is also the enzyme
involved in the uptake of CO2.
• Photosynthesis takes place throughout the leaf.
• Adaptive Value: more efficient than C4 and CAM plants under cool and
moist conditions and under normal light because requires less machinery
(fewer enzymes and no specialized anatomy).
• Most plants are C3.
9. • C4 Photosynthesis: C4 plants.
Called C4 because the CO2 is first incorporated into a 4-carbon
compound.
• Stomata are open during the day.
• Uses PEP Carboxylase for the enzyme involved in the uptake of CO2. This
enzyme allows CO2 to be taken into the plant very quickly, and then it
"delivers" the CO2 directly to RUBISCO for photosynthesis.
• Photosynthesis takes place in inner cells (requires special anatomy called
Kranz Anatomy)
10. • Adaptive Value:
– Photosynthesizes faster than C3 plants under high light intensity and
high temperatures because the CO2 is delivered directly to RUBISCO,
not allowing it to grab oxygen and undergo photorespiration.
– Has better Water Use Efficiency because PEP Carboxylase brings in
CO2 faster and so does not need to keep stomata open as much (less
water lost by transpiration) for the same amount of CO2 gain for
photosynthesis.
• C4 plants include several thousand species in at least 19 plant families.
Example: , corn, and many of our summer annual plants
11. • CAM Photosynthesis:
• CAM plants. CAM stands for Crassulacean Acid Metabolism
• Called CAM after the plant family in which it was first found
(Crassulaceae) and because the CO2 is stored in the form of an acid before
use in photosynthesis.
• Stomata open at night (when evaporation rates are usually lower) and are
usually closed during the day. The CO2 is converted to an acid and stored
during the night. During the day, the acid is broken down and the CO2 is
released to RUBISCO for photosynthesis
12. • Adaptive Value:
•
– Better Water Use Efficiency than C3 plants under arid conditions due to
opening stomata at night when transpiration rates are lower (no
sunlight, lower temperatures, lower wind speeds, etc.).
– When conditions are extremely arid, CAM plants can just leave their
stomata closed night and day. Oxygen given off in photosynthesis is
used for respiration and CO2 given off in respiration is used for
photosynthesis.
– CAM plants include many succulents such as cactuses and agaves and
also some orchids and bromeliads
13. 1. Which among the following element is
essential for photolysis of water
(a) Nitrogen (b) Chlorine
(c) Carbon (d) Oxygen
(e) Magnesium
14. 2. Plants are known as purifiers of air due to
the process of
(a) Respiration (b) Photosynthesis
(c) Transpiration (d) Dessication
(e) Guttation
15. 4. When the CO2 uptake cannot be increased
by increasing the light, it is referred to as:
(a) Extinction point
(b) CO2 saturation point
(c) Light saturation point
(d) Light compensation point
(e) None
16. 8. Which among the following plant is used in
the study of photosynthesis?
(a) Chlorella (b) Asparagus
(c) Garden Pea (d) Acetabularia
(e) Hydrilla
17. 10. During the dark reaction of photosynthesis
(a) Water is split
(b) CO2 is reduced to organic compounds
(c) Chlorophyll is activated
(d) 6 carbon sugar is broken into 3 carbon sugar
(e) None
18. 11. The enzyme that fixes atmospheric CO2 in
C4 plant is
(a) PEP carboxylase (b) RUBISCO
(c) RUBP carboxylase (d) Hydrogenase
(e) Aldolase
20. • For every glucose molecule synthesized how
many ATPs are required?
• A) 18 ATP in C3 plant and 30 ATP in C4 plant
• B) 30 ATP in C3 plant and 30 ATP in C4 plant
• C) 30 ATP in C3 plant and 18 ATP in C4 plant
• D) 18 ATP in C3 plant and 18 ATP in C4 plant
21. • 16. Formation of energy currency of cell
during photosynthesis is called as
(a) Substrate level phosphorylation
(b) Phosphorylation
(c) Photophosphorylation
(d) Oxidative phosphorylation
(e) None of these
22. • 17. The red drop phenomenon is due to the
disruption of the photochemical activity of
(a) Pigment system I
(b) Pigment system II
(c) Carotenoids
(d) PSI and PS II
(e) Any of these
23. 18. In photosynthesis hydrogen is transferred
from the light reaction to the dark reaction by
(a) DPN (b) DNA
(c) ATP (d) NADP
(e) NAD
24. 19. The first step in photosynthesis is the
(a) Formation of ATP
(b) Ionisation of water
(c) Excitement of an electron of chlorophyll
by light
(d) Joining of two 3-carbon compound to
form glucose
(e) Formation of NADH2
25. • 21. Who among the following stated for the
first time that electron donor in
photosynthesis is water?
(a) Van Neil (b) Blakslee
(c) Melvin Calvin (d) Van Helmont
(e) Robert Hill
26. • 2 2. C4 pathway for CO2 fixation was first
studied
• (a) Emerson & Arnold (b) Krotkov et al
• (c) Hatch & Slack (d) Blackman
• (e) Melvin Calvin
27. • 24. Dark CO2 fixation is present in the
following plant:
(a) Bryophyllum (b) Sugarcane
(c) Maize (d) Pea
(e) Rice
28. • 25. Starch and Cellulose are compounds
consisting of many units of
(a) Amino acids (b) Fatty acids
(c) Simple sugars (d) Glycerol
(e) Glycollic acid
29. 26. Calvin cycle occurs in
(a) Cytoplasm (b) Peroxisome
(c) Chloroplast (d) Mitochondria
(e) Golgi body
30. • 27. In photosynthesis in chloroplast, dark
reactions occur in
(a) Grana lamellae (b) Stroma
(c) Thylakoids (d) Stroma lamellae
(e) Matrix
31. 28. The number of oxygen molecules released
per light quanta during light reaction is
(a) Quantum yield
(b) Quantum requirement
(c) Quantasome
(d) Photosynthetic yield
(e) RQ
32. • 29. The colour of rose petal is due to water
soluble pigment present in the
• (a) Cytoplasm (b) Intercellular space
• (c) Nucleus (d) Vacuoles
• (e) Golgi body
33. 30. NADP is
(a) An enzyme (b) A part of s-RNA
(c) A co-enzyme (d) A part of t-RNA
(e) None
34. • 31. For the synthesis of organic matter the
green plants need only
(a) Chlorophyll (b) CO2 and H2O
(c) Light (d) All of these
(e) None of these
35. • 32. In CAM plants the initial carbon dioxide
acceptor is
(a) Phosphoglyceric acid
(b) Phosphoenol pyruvic acid
(c) Ribulose 1,5 biphosphate
(d) Oxaloacetic acid
(e) Malic acid
36. • 34. Which among the following sentence is
wrong about C4 plants
(a) Leaves posses Kranz anatomy
(b) RUBISCO is present in mesophyll cells
(c) PEPCO is present in mesophyll
(d) CO2 acceptor PEP
(e) None
37. 36. Number of ATP and NADPH2 required for the
formation of one molecule of carbohydrate in C3
plant is:
(a) 3 and 2 (b) 30 and 18
(c) 18 and 12 (d) 12 and 18
(e) 18 and 30
38. • 37. During photorespiration reaction
between oxygen and substrate is happening
within
(a) Mitochondria (b) Chloroplast
(c) Peroxisome (d) Nuclues
(e) Lysosome
39. • 38. In CAM plants, reduction of CO2 to
carbohydrate takes place within
• (a) Mesophyll cell (b) Bundle sheath cells
• (c) Epidermal cells (d) Xylem cell
• (e) Phloem cells
40. • 40. Where does the light reaction of
photosynthesis takes place?
(a) Quantasomes in thylakoid
(b) Outer membrane of chloroplast
(c) Inner membrane of chloroplast
(d) Stroma
(e) Matrix
41. • 41. Solar energy brings which of the following
functions at PS-II
(a) Photolysis of Water
(b) Reduction of CO2
(c) Reduction of O2
(d) Activation of chlorophyll molecule
(e) All of these
42. • 43. In the following photosynthesising
organism chlorophyll - a is absent
(a) Bacteria (b) Flowering plants
(c) Cryptogams (d) Ferns
(e) Algae
43. • 45. Light energy is converted into chemical
energy in the presence of
(a) Pyrenoid (b) Chloroplast
(c) Ribosomes (d) Mesosomes
(e) Mitochondria
44. • 46. The concept of quantosome and
photosynthetic unit was given by
(a) Emerson (b) Warburg
(c) Arnold (d) Priestly
(e) None
45. • 47. Which among the following pigment is
called as accessory pigments?
(a) Carotene (b) Xanthophyll
(c) Phycobilins (d) All the above
(e) None of these
46. • 49. Photosynthesis is
(a) Oxidative, anabolic, endergonic process
(b) Reductive, anabolic, exergonic process
(c) Reductive, ababolic, endergonic process
(d) Oxidative catabolic exergonic process
(e) None of these
47. • 51. Ribulose 1,5 biphosphate is found in
(a) Stroma of chloroplast
(b) Grana of chloroplast
(c) Matrix of mitochondria
(d) Cristae of mitochondria
(e) None of these
48. • 52. P 700 is a special form of the following
pigment
(a) Chlorophyll -a (b) Carotene
(c) Xanthophyll (d) Chlorophyll-b
(e) Phycobilins
49. • 53. The first stable product of dark reaction
in C4 plants
(a) Phosphoglycolic acid
(b) Glycolic acid
(c) Oxaloacetic acid
(d) Phosphoglyceric acid
(e) Malic acid
50. • 54. The scientist who discovered that the site
of photosynthesis is chloroplast
•
(a) Arnon (b) Joseph Priestly
(c) Julius Sachs (d) Robert Mayer
(e) Senebier
51. 58. Which among the following sentence is TRUE
about C3 plants?
(a) Photosynthetically more efficient
(b) More efficient in CO2 fixation than C4 plants
(c) PEPCO is present in mesophyll
(d) Kranz anatomy is present
(e) First stable product is phosphoglyceric acid
52. 59. C4 pathway is shown by
(a) Sugar cane (b) Sunflower
(c) Pea (d) Rice
(e) Rhizopus
53. • 60. Carbon becomes available to crop plants
in the form of
(a) Amino acids (b) Carbonates
(c) CO2 (d) Elemental C
(e) All of these
