C3, C4 AND CAM PATHWAYS

2. Ancient greeks- Greeks believed that plants derived their
nourishment from the soil only

3. Jan van Helmont
After careful measurements of a plant’s water intake, and
weight increase, van Helmont concludes that trees gain most of
their mass from water.

4. British Scientist Joseph Priestly (1771)
Using a bell jar, a candle, and a plant, Priestly finds that the plant
releases a substance that keeps the candle burning—a substance
that we now know is oxygen.

5. Dutch Scientist - Jan Ingenhousz – (1779)
He proved that Priestly's experiment only happened if light available.
He experimented with aquatic plants and found that they produced
oxygen bubbles only in the light, and nothing in the dark. He
concluded that plants need sunlight to produce oxygen.

6. German Scientist - Julius Robert Mayer (1845)
He concluded that plants convert light energy to chemical energy.

7. Theodor wilhelm Engelmann (1882)
Action spectrum experiment
Engelmann used micro-spectroscope to illuminate a strand
of Cladophora with light
Clumping - highest concentration of oxygen.

8. These American scientists used isotopes
Martin Kamen & Samual Ruben (1941) (Co Discoverers of Carbon-14
Isotope)These American scientists used isotopes to determine that the
oxygen that was liberated from photosynthesis comes from water.

9. American Scientist - Melvin Calvin –(1948)
He traced the chemical path that carbon follows to form glucose. The
reactions became known as the “Calvin cycle.” (i.e light independent
reactions)

10. Robert Emerson (1957)
Proved that two photosystem exists in plants
Gave emerson’s effect

11. 1992 American Scientist - Rudolph Marcus
He won the Nobel Prize in Chemistry for describing the process by
which electrons are transferred from one molecule to another in the
electron transport chain.

12. Pigments are “molecules that absorb specific wavelength of light and
reflect all others”
Pigments are coloured.
The colour we see is the net effect of all the light reflecting back at us

13. 1. Chlorophyll-
* Chl-a.b,c,d,e,f
* Bacterio chl
* Bacterio viridin
2. Carotenoids
3. Phycobilins

14. Chlorophyll- a and b
All land plants and green algae possess two forms of this pigment:
chlorophyll a and chlorophyll b.
All chlorophylls serve as the primary means plants use to intercept
light in order to fuel photosynthesis.
Has poryphyrin head
Phytol side chain

17. Carotenoid (Lipids)
A. Carotene
C40H56
Orange red
B. Xanthophyll
C40H56O2
Yellowish brown
Eg. Fucoxanthin,
lutein

18. PHYCOBILINS
Found in blue green algae
A. phycocyanin-purple color
B. phycoxanthin- red
Structure- No Mg
No phytol tail

19. Photosynthesis
Requirements of
Photosynthesis
1. Pigments
2. Light
3. H2O
4. CO2
Products of
Photosynthesis
1. Photosynthates
2. O2
3. H2O

20. 6CO2 + 12H2O
C6H12O6 + 6H2O + 6O2
Pigments Light Energy
Photosynthetic Reaction

23. Electro Magnetic radiation
10-2 10 400 700 105 107 109
10-4
10-5
UV
X
Cosmic Visible IR
V I B G Y O R
400 450 500 550 600 650 700
PAR
Micro Radio

24. PRINCIPLE OF LIGHT ABSORPTION
Absorption of radiant energy by a plant community – follows
Lambert- Beer’s Law.
Beer’s law- Absorption of light by a solution is proportional to the
concentration of solution and the distance through which light
travels

25. ABSORPTION AND ACTION SPECTRUM

26. PHOTOSYSTEMS

27. RED DROP & EMMERSON’S ENHANCEMENT
EFFECT

28. EMMERSON’S ENHANCEMENT EFFECT

29. Absorption of Light Energy
All pigments – Absorb – Light Energy – Transfer to – Chlorophyll a
Chlorophyll a – Absorb and Conversion – To Chemical Energy
PHOTOSYSTEM
Group of Pigments
PS І (P 700)
More Chlorophyll ‘a’
Less Accessory Pigments
Absorb near FR light
PS І (P 700)
Less Chlorophyll ‘a’
More Accessory Pigments
Absorb Red light
PS ІІ (P 680)

30. PHOTOSYNTHESIS
LIGHT REACTION Light Independent Reaction
DARK REACTION
Primary Photochemical Reaction Carbon Reactions in PS
HILL’S REACTION BLACK MAN’S REACTION
Thylakoid Reaction Stroma Reaction

31. LIGHT REACTION
Production of Assimilatory Powers (ATP and NADPH)
by light, water and pigments
DARK REACTION
CO2 is reduced by Carbohydrate by
Utilizing Assimilatory Powers (ATP and NADPH) produced by
Light reaction

32. LIGHT REACTION
Production of Assimilatory Powers (ATP and NADPH)
by light, water and pigments
STAGES
1. Absorption of light energy by the pigments
2. Activation of Chlorophyll molecule
3. Photolysis of water
4. Electron Transport Chain
5. Synthesis of Assimilatory Powers

34. Photophosphorylation
The transfer of electrons through a series of electron carriers is called
electron transport and the process of formation of ATP from ADP and
Pi using the energy of electron transport is called as photosynthetic
phosphorylation or photophosphorylation.

35. NON-CYCLIC PHOTOPHOSPHORYLATION

36. CYCLIC PHOTOPHOSPHORYLATION

39. PS
II
PS I
PQ Cyt b6 f
PC
2H2O
4e-
+
4H+
O2
+
Fd
NADP+ NADPH
Stroma
Lumen
ADP ATP
Thylacoid
Membrane
ATP
Synthase
H+
CF0
CF1
H+
H+
H+
H+
H+
H+
H+
H+
ATP Synthesis
Non Cyclic
Cyclic
OEC
H+

40. Dark Reaction
Reduction of CO2 to Carbohydrate by utilizing
Assimilatory Powers (ATP and NADPH)
Produced by Light Reaction.
Light Independent Reaction (Dark Reaction)
C3 Pathway
Calvin Cycle C4 Pathway
Hatch and Slack
Cycle
CAM
Pathway

41. CO2 FIXATION
Pathway by which all photosynthetic eukaryotic organisms ultimately incorporate
CO2 into carbohydrate is known as carbon fixation
Calvin cycle- PCR cycle
Discovered by Calvin and Benson
Occur in Stroma of Chloroplast
CO2 acceptor – RuBP
First stable compound – 3 Phospho glyceric acid
Major enzyme – RuBisCO

42. 1. CARBOXYLATION
2. REDUCTION
3. REGENERATION

43. Carboxylation
RuBP + 3 - PGA
CO2
RuBisCO

44. Reduction
3 - PGA 1, 3 – Bis PGA
3 – Phospho Glyceraldehyde
ATP
NADPH
Phospho glycerate
Kinase
Glyceraldehyde
3 phosphate
Dehydrogenase

45. Regeneration of RuBP
3 - PGlyAld + F 6- PO4
Sh 1, 7- BisPO4
DHAP
+ X 5- PO4
E 4- PO4
R 5 – PO4 + X 5- PO4
Ribu 5 –PO4
TK
Al
RuBP
ATP
Epi
Iso
Kinase
Sh 1,7 bis Pase

46. Ribulose 1,5
Bis-phosphate
3 Phospho-
glycerate G3P G3P G3P G3P
G3P
G3P
Dihydroxy
acetone
phosphate
(DHAP)
Erythrose-
4-phosphate
Xylulose-5-
phosphate
Sedoheptulose-
1,7- bisphosphate
Ribose-5-
phosphate
Xylulose-5-
phosphate
Ribulose-5-
phosphate
Dihydroxy
acetone
phosphate
(DHAP)
Fructose-1,6
bisphosphate
Fructose-6-
phosphate
Starch
DHAP
EXPORT
3 CO2
3 ADP
3 ATP
Pi
6 ATP 6 ADP
+ 6 Pi
6 NADPH 6 NADP+
10
11
9
8
7
6
2
1
3
4
(6)
(3)
(3)
Glyceraldehyde-3-phosphate “pool”
5

47. 3 ATP and 2 NADPH molecules are
required to fix one molecule of CO2 in
C3 plants

48. How many molecules of CO2, ATP & NADPH
require to produce one molecule of Glucose
in C3 plants
CO2 =
ATP =
NADPH =
6
18
12

49. Different leaf anatomy – “Kranz” Anatomy
The vascular bundles are surrounded by special type of cells
Bundle sheath cells
BS cells are closely link with mesophyll cells through
Plasmodesmata
Both cells contain Chloroplast - Dimorphic Chloroplast
C4 Plants

50. ‘KRANZ’ANATOMY
Cells are radially
arranged in a ring or
wreath
Kranz = Wreath

51. C3 Leaf
C4 Leaf

52. Discovered by Hatch & Slack (1966)
CO2 Acceptor - PEP
First stable compound – Oxalo Acetic Acid
Major enzyme – PEP Carboxylase
Dark Reaction in C4 Plants
C4 Cycle – Hatch & Slack Pathway- Dicarboxylic Acid Pathway

53. Variant
name
Principal C4 acid
transported to the
bundle sheath cells
Decarboxylating enzyme Examples
NADP-ME Malate NADP- dependent malic
enzyme
Maize, Sugarcane,
Sorghum
NAD-ME Aspartate NAD- dependent Malic
enzyme
Millet, Panicum
milliaceum,
Amaranthus
PEP-CK Aspartate Phosphoenol pyruvate
carboxy kinase
Guinea grass, Chloris
gayana
Chollet and Orgen (1975) found three categories of C4 plants.

54. Carboxylation in Mesophyll
 Reduction in Mesophyll
 Decarboxylation in BS cell
 Refixation of CO2 in BS cell
 Regeneration of PEP
Steps in C4 Cycle

55. CO2 + H2O
CA
HCO3
-
OAA
PEP
PEPCo
OAA
NADPH2 NADP
MALIC
ACID
MALIC ACID
------------------NADPH2
NADP
PYRUVIC ACID
CO2
CALVIN
CYCLE
PA
PEP
ATP AMP
MESOPHYLL CELL BUNDLE SHEATH CELL
Cytoplasm Cytoplasm
Chloroplast
Chloroplast

56. NADP-ME

57. 5 ATP and 2 NADPH molecules are required to
fix one molecule of CO2 in C4 plants

58. How many molecules of CO2, ATP & NADPH
require to produce one molecule of Glucose
in C4 plants
CO2 =
ATP =
NADPH =
6
30
12

59. NAD-ME

60. PEP-CK

61. They possess higher rates of photosynthesis due to
higher affinity of PEP carboxylase to CO2.
They can carry on photosynthesis even under low
CO2 concentrations (10ppm).
Even under almost closed conditions of stomata C4
plants can continue to photosynthesize.
There is almost negligible photorespiration.
Significance of C4 Photosynthesis

62. CAM PLANTS
CAM – Crassulacean acid metabolism
Eg. Succulent xerophytes.
Some euphorbiaceae family members.
Stomata open – night
Stomata close – day

63. Cytoplasm
CO2
HCO3
H2O
CA
PEP
PEP
Case
OAA
OAA
Malic acid
NADPH
PEP
MA
DH
Chloroplast
Night – Stomata Open
Malic acid
Vacuole
Starch
Glycolysis
Nocturnal Acidification
Nocturnal Starch Breakdown

64. Malic acid
CO2
Pyruvic Acid
Calvin
Cycle
NADPH
DC
Day – Stomata Closed
Malic acid
Vacuole
Starch
Cytoplasm
Chloroplast

65. S.No. Character C3 C4 CAM
1 First CO2 acceptor
Ribulose -1,5 Bis
Phosphate
Phospho Enol
Pyruvate
Phospho Enol
Pyruvate
2 First stable compound 3- phosphoglycerate
Oxaloacetate/Malic
acid
Oxaloacetate/Malic
acid
3
First carboxylating
enzyme
RUBISCO PEPCO PEPCO
4 Type of chloroplast
Monomorphic - only
one type of chloroplast
Dimorphic
Chloroplast -Two
types of chloroplast
Monomorphic - only
one type of
chloroplast
5 Kranz anatomy Absent Present Absent
6 Site of C3 cycle
Stroma of chloroplast
(mesophyll)
Bundle sheath cell
chloroplasts
Mesophyll cell
chloroplasts
7
Site of primary
carboxylating enzyme
Stroma of Chloroplasts
Cytosol of
mesophyll
Cytosol of mesophyll
Differences between C3, C4 and CAM plants

66. S.No. Character C3 C4 CAM
8 Carbon pathway
Calvin cycle in
mesophyll
cells
Both Calvin cycle
(bundle sheath) and
Hatch – Slack cycle
(mesophyll) seen
separated in space.
Both Calvin cycle
(bundle sheath) and
Hatch – Slack cycle
(mesophyll) seen
separated in time.
9 C2 cycle Present Absent Present but in low rates
10 CO2 compensation point 25-100 ppm 0-10 ppm 0-5 ppm
11
Temperature optimum
for Photosynthesis and
growth
10 to 250C 30 to 450C 35-450C
12 WUE Low High Extremely high
13 Crops
Wheat, barley,
rice etc
Corn, Sorghum,
Sugarcane
Agave, Cactus, orchids,
succulent plants.
Pineapple is highly
productive.

67. MEASUREMENT OF PHOTOSYNTHESIS
A. Assay of Chloroplast activity
DCPIP reduced by electrons released by photosynthesis.
Convenient – to identify photosynthetic inhibitors
B. Gas exchange Measurement (Infra - red Gas Analysis IRGA)
C. Monitoring with 14CO2
a) Exposing Photosynthetic tissue to 14CO2
b) Exposing leaf to a gas mixture in a closed space