1. Photosynthesis involves the conversion of light energy from the sun into chemical energy in the form of ATP and NADPH through a series of light-dependent and light-independent reactions. 2. The light reactions take place in the thylakoid membranes of the chloroplast and involve the absorption of light by chlorophyll and the splitting of water to produce oxygen, protons, and electrons. 3. The electrons are used to produce ATP and NADPH via a process called photophosphorylation. The light-independent reactions take place in the chloroplast stroma and use the ATP and NADPH to fix carbon from carbon dioxide into sugars like glucose.

2. INTRODUCTION
 Anabolic process
 Light energy is converted to chemical
energy (ATP)
 Redox reaction : H2O gets oxidised and CO2
gets reduced to food i.e. carbohydrate and
the chemical energy i.e ATP is stored in the
food and during this process O2 is released.
 Equation of photosynthesis :

8. The following events occur during this
process –
(i) Absorption of light energy by
chlorophyll.
(ii) Conversion of light energy to
chemical energy and splitting of water
molecules into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to
carbohydrates.

9. AUTOTROPHS
PHOTOAUTOTROPHS
e.g : all green
plants,green sulphur
bacteria,cyanobacteria
CHEMOAUTOTROPHS
e.g :Bacteria like
nitrosomonas, sulphur
bacteria

10. SITE OF PHOTOSYNTHESIS

12.  Peristromium
 Length-4-10 microns
 Breadth-2 to 3 microns
 Plastidome
 Grana- 40 to 60 in no.
 Intergrana or frets or
stroma lamellae
 Thylakoids- each granum
has 12-20 thylakoids
 Quantosomes-each have
230-300 molecules of
photosynthetic pigments.It
is a photosynthetic
unit.(Park and Biggins)

13. PHOTOSYNTHETIC PIGMENTS
 DEFTN : They are the pigments present in the chloroplasts
and capture light energy.
 These pigments absorb light of a particular wavelength and
reflect light of another wavelength. Thus the colour of the
pigment indicates the wavelength reflected by the pigment
 TYPES : 3 main types are- chlorophyll , carotenoid and
phycobilins.
a) Chlorophylls : Most imp. and active pigments in
photosynthesis. Green in colour and soluble in organic
solvents but insoluble in H2O.(chl-a,chl-b,chl-c,chl-d,chl-
e,bacteriochlorophyll,bacterioviridin).
Chla (blue green)-C55H72O5N4Mg
Chlb (yellow green)-C55H70O6N4Mg

14. STRUCTURE OF CHLOROPHYLL MOLECULE

15. b) Carotenoids- 2 types
carotenes xanthophylls
Carotenes are orange in colour-C40H56 e.g of a major
carotene is beta carotene.
Xanthophylls are yellow in colour-C40H56O2 e.g of a major
xanthophyll in plants are lutein.
c)Phycobilins- They are soluble in H2O.Present only in red
algae and blue green algae. 2 types
Phycocyanin (blue) Phycoerythrin (red)

16. ROLE OF PHOTOSYNTHETIC PIGMENTS
Chl.a –essential pigment
and is the reaction
centre.
Chl.b and carotenoids
are the accessory
pigments
Carotenoids protect
chl.a from
photooxidation

17. PHOTOSYSTEM OR PIGMENT SYSTEM (P.S)
 The reaction centre and accessory pigments together form
PS
 2 TYPES
PSI PSII
 Each PS consists of
CC LHC
(Reactn centre (few chl.b and 50 carotenoid mols)
and
electron carriers)
PSI-P700 PSII-P680

18. EXPERIMENTS DONE TO PROVE SOURCE OF O2 IS H2O AND
NOT CO2
 Van Neil (1930)- green sulphur bacteria which used H2S
instead of H2O in photosynthesis.
 Robert Hill (1937) –Isolated chloroplasts from spinach
placed it in h20 free of co2 added ferric salts and
haemoglobin and exposed to light.
Ferric Ferrous ,Haemoglobin oxyhaemoglobin
2H2O + 2A 2AH2 + O2 (Hills Reactn)
 Ruben and Kamen (1941)-isotope of oxygen
Dr.Arnon (1954)-NADP is Hydrogen acceptor
Early thinking: O2 released came from the CO2
CO2  C + O2 C + H2O  CH2O
sugar

19. NATURE OF LIGHT
 Light behaves as a wave while propagating and on
interaction with matter it behaves as small packets of
energy called as photons.
 Amount of energy in photon is called a quantum.
 Quantum is inversely proportional to wavelength of light.
 Visible light violet (390nm) to red (760nm).
 PAR Photosynthetically active radiation
 Max.absorption in red and blue region and little in orange
and yellow regn and nothing in green.

21. PHOTOLYSIS OF H2O
H2O H+ + OH-
4H2O 4H+ + 4OH-
4OH- 4OH + 4e-
4OH 2H2O2
2H202 2H2O + O2
4H20 4e- +4H+ +2H2O +O2

22.  There are 2 phases in photosynthesis :
Light reactn Dark reactn
(Site-grana (Site-stroma
Photophosphorylation) light independent reactn)

23. LIGHT REACTION OR PHOTOPHOSPHORYLATION
 Photo-light and Phosphorylation-addition of phosphate
Light
ADP+iP ATP
Chl.a
 Photophosphorylation
Cyclic Non Cyclic

24. CYCLIC PHOTOPHOSHORYLATION

25. NON CYCLIC PHOTOPHOSPHORYLATION
Fd-NADP
reductase

26. CHEMIOSMOTIC HYPOTHESIS
 Dr.Peter Mitchell-1961
 Chemiosmosis-Movement of ions across a selectively
permeable membrane down their electrochemical gradient
 Chemiosmosis is the source of ATP in photophosphorylation
and ATP synthase is the enz. which makes ATP by
chemiosmosis.
 Photolysis of H2O takes place in thyakoid memb. Hence more
protons in thylakoid memb.
 Stroma has the enz. required for reduction of NADP to
NADPH2 and proton is required for this reduction.
 Protons are more in lumen of thylakoid and less in stroma
hence an electrochemical gradient of proton or a proton
gradient is formed across the thyl.memb.
 Movement of protons take place to stroma and ATP synthase
uses this energy of proton diffusion to form ATP from ADP

28. DARK REACTION
 2nd phase of photosynthesis.
 Site-Stroma
 This reactn is independent of light but it requires the products
of light reactn i.e. ATP and NADPH2
 Its called the blackmans reactn (Blackman)
CO2 +2NADPH2 + 2ATP
CH2O+H20+2NADP+2ADP+2iP

29. CALVIN CYCLE OR C3 PATHWAY
 Dr. Melvin Calvin-1954 carried expt on unicellular green algae-
chlorella and scenedesmus to find out path of carbon and used
C14.
 1st stable product is a 3 C compd and hence its called a C3 cycle
or calvin cycle or calvin-benson cycle
 CO2 is fixed by a CO2 acceptor in stroma and converted to a
stable compd and this stable compd. undergoes changes and
final product glucose is produced in 90 secs.
 Initial CO2 acceptor is regenerated and cycle continues.
 3 phases in C3 cycle:
a)Carboxylation b)Reduction c)Synthesis and Regeneration.

30. A) CARBOXYLATION
 RUBP-1,5-Ribulose bisphosphate or RUDP-1,5-Ribulose
diphosphate
 RUBP carboxylase-RUBISCO
 PGA-3-Phosphoglyceric acid
2 Mol. Of
3-PGA

31. B) REDUCTION
 Utilisation of assimilatory power
 1,3-di PGA-1,3-diphosphoglyceric acid
 3PGAL-3-Phosphoglyceraldehyde
 DHAP-Dihydroxyacetonephosphate (isomer of 3PGAL)
triose phosphate isomerase
 Some 3PGAL DHAP

32. C)SYNTHESIS
 For synthesis of 1mol. of glucose 6 Turns of calvin cycle
or 6mol. Of RUBP and 6 mol. of CO2 are required.
 Thus out of 12 mol. of PGAL only 2mol. Is used in synthesis
of glucose.
1mol.of PGAL +1 mol. Of DHAP
Fructose-1,6-diphosphate
Dephosphorylation
Fructose-6-phosphate
Isomerisation
Glucose-6-phoshate
Dephosphorylation
Glucose

33. C)REGENERATION
 RUBP is regenerated in this process called sugar
phosphate interconversions where 10mol. of PGAL is used
in regeneration.
 The intermediates are sugar phoshates e.g-erythrose-4-
phosphate(4C),Xylulose-5-phosphate(5C),Ribose-5-
phosphate(5C),Sedoheptulose-7-phosphate(7C) and
6mol.of RUMP are formed and 6ATP will phosphorylate to
form 6RUBP.
 6 mol.of ATP are used in regeneration and 12 ATPs and
12NADPH2 are used in reduction.Thus,18ATP and
12NADPH2 are used in synthesis of 1 mol. of glucose.
 E.g of C3 plants – Hibiscus , sunflower, rice, potato etc.

35. PHOTORESPIRATION
 C3 plants show photorespiration.
 RUBISCO can act as carboxylase and oxygenase
because its active site can bind to both CO2 and O2
which is competitive and is seen during day time when
temp.are more or high.
 At high temp. the stomata closes and CO2 concntrtn
And O2 and instead of carboxylation,oxidation of
RUBP takes place.
 Photorespiration reduces the photosynthetic efficency of
plants by 25%
 It is the respiration initiated in chloroplast and takes place
only during day time.

36. oxidation
Phosphorylation

37. DIVERSITY IN PHOTOSYNTHETIC PATHWAY
A] C3 PATHWAY(CALVIN)
B]C4 PATHWAY(HSK)
C]CAM PATHWAY (CRASSULACEAN ACID METABOLISM)

38. C4 OR HSK PATHWAY
 1st stable product-OAA(Oxalo acetic acid) 4C
 C4 plants show Kranz anatomy.
 Kranz anatomy-mesophyll are not differentiated
 Bundle sheath cells are radially arranged around the
vascular bundle
 Dimorphic chloroplasts-bundle sheath cells have
large,less in no. agranal chloroplasts and mesophyl cells
have small,more in no. granal chloroplasts.
 Mesophyll have PEP carboxylase and bundle sheath cells
have RUBISCO.
 E.g of C4 plants-sugarcane, maize, jowar etc

40. MECHANISM OF HSK PATHWAY

41. CAM PATHWAY
 C4 and C3 pathway take place in mesophyll cells
 C4 takes place during night time and C3 during day
time.

42.  Thus during night time the cocentration of organic acid
increases and during day time it becomes zero.
 This day and night fluctuation in acid concentration is an
imp. feature of CAM plant
 E.g of CAM plants-cactus , pineapple , bryophyllum etc.

43. INTERDEPENDENCE OF LIGHT AND DARK REACTION

45. SIGNIFICANCE OF PHOTOSYNTHESIS
 Very imp. process by which food is synthesized and
heterotrophic org. depend on them for food
 Reduce air pollution by maintaining a balance of CO2 and
O2 in air
 Protects us from harmful U.V rays of sun
 Releases O2
 Plant products like timber,gums,alkaloids,rubber etc. are
products of photosynthesis and are economically imp.