Photosynthesis is a very crucial process in nature and I have cleared a lot of basics concepts in this presentation. Any student in grade 11 or 12 (medical sc/biology/biotech) or a college student from science field will be able to clear his/her concepts through this ppt. Plz do follow my Instagram page @biologistindia

1. PHOTOSYNTHESIS
CONVERTINGLIGHT ENERGY INTO CHEMICAL
ENERGY
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2. PHOTOSYNTHESIS IN HIGHER PLANTS
• DEFINITION: Photosynthesis is an enzyme regulated anabolic
process of manufacture of organic compounds such as
carbondioxide and water with the help of sunlight, inside the
chlorophyll containing cells. The organisms which carry out
such process are called PHOTOAUTOROPHS.
• Photosynthesis involves two types of reactions:
1. LIGHT REACTIONS
2. DARK REACTIONS
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3. HISTORY AND TIMELINE
• OXYGEN:Discovered by PRIESTLEY IN 1774
• CHLOROPHYLL: Discovered and named by PELLETIER and CAVENTOU
• CALVIN CYCLE: By MALVIN CALVIN
• Z-SCHEME: Given by HILL and BENDALL
• HILL’S REACTION/LIGHT REACTION:BY HILL
• DARK REACTION: BLACKMANN
• PHOTPHOSPHORYLATION: By ARNON et al
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4. WHY PLANTS REQUIRE PHOTOSY NTHESIS?
• Since plants are photo-autotrophs and prepare prepare food for
themselves on their own, plants require an internal mechanism
with which they can utilize and convert light energy into
chemical energy to prepare consumable forms of energy rich
food.
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5. WHY IT IS SO IMPORTANT??
• Sustains life on earth
• Plants are the producers while all other organisms are consumers. So if
there are no plantsthen all the organisms will also die
• Many useful plants products such as timber, resins, drugs, oils, food etc are
derived from the process of photosynthesis in plants
• Photosynthesis is the only known method by which oxygen is added into
the atmosphere to compensate for the oxygen losses due to respiration of
organisms and burningof fuels
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6. LOCATION AND PROCESS OF PHOTOSYNTHESIS:
• https://www.youtube.com/watch?v=PiAUPg4UrrE
• Photosynthesisoccurs in thylakoid membrane of the
chloroplast cells
• CYCLIC photophosphrylation occurs in STOMA LAMELLAE
• NON-CYCLIC photophosphorylation occurs in GRANA
LAMMELLE
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7. THYLAKOID:
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8. LIGHT REACTION:
• These are of two types
1. NONCYCLIC PHOTOPHOSPHORYLATION
2. CYCLIC PHOTOPHOSPHORYLATION
• Here ASSIMILATORY POWER (ATP and NADPH) will be
synthesized
• Both are used to carry out the metabolic activities of
the plant cell.
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9. CHLOROPHYLL PIGMENTS
• CHLOROPHYLL A and CHLOROPHYLL B have a major role to
play in the process of photosynthesis.
• When sunlight is incident on to the plant cells , a particular
wavelength of light is absorbed by the chloroplast cells.
• Light consists of photons , so indirectly photons of light of a
specific wavelength strike the chlrolophyll b molecules which
are called the ANTENNA MOLECULES.
• These antenna molecules will reach an excited state and by
resonance transfer their energy to a CORE MOLECULE which is
CHLOROPHYLL A .
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10. LIGHT HARVESTING PHOTOSYSTEMS (LHC)
• There are two LHCs or photosystems or reaction
centres or photocentres:
1. PS2
2. PS1
• Now the energy from chlorophyl A core molecule
will be supplied to photocentre ( PS2 in case of
NON-CYCLIC photophosphorylation)
• This will cause the photocentre to loose an electron
which will further be picked up by ELECTRON
TRANSPORT CHAIN followed by PS1.
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11. NON CYCLIC PHOTOPHOSPHORYLATION
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13. Quantum Requirement
• In order to release one complete molecule of oxygen
,upon absorption of one photon of light,four water
molecule undergo photolysis (water splitting) which
release :
1. One oxygen molecule
2. Four electrons
• Reactions involved are:
4H2O 4H* + 4OH-
4OH- 2H2O + O2 + 4e-
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14. PROCESS OF LIGHT REACTION OR
PHOTOCHEMICAL PHASE
• Photochemical phase involves :
1. PHOTOLYSIS OF WATER: It refers to phenomenon of
water breaking up into hydrogen and oxygen. An
OXYGEN EVOLVING COMPLEX (OEC)and electron
carrier is reqd.to carry out this process. Light causes
changes in Manganese ions attached to OEC and
removes electrons from the OH-ve component of
water thereby forming oxygen. The released
electrons are carried by electron carrier and transfer
them to PS2 or P680.
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15. CONTINUED....
2. PRODUCTION OF ASSIMILLATORY POWER: The electrons released during
photolysis of water are picked up by P680photocentre of PS2. on receing
a photon of light energy, the photocentre expels an electron with a gain
of energy (23kcal/mole). This is the PRIMARY REACTION which involves
conversion of light energy into chemical energy and is also called
QUANTUM CONVERSION.
3. Now the electron extruded by PS2 is picked by quencher PHAEOPHYTIN.
From here the electron carriers will be PLASTOQUINONE(PQ),
CYTOCHROME b-f COMPLEX and PLASTOCYANIN(PC). While passing to
cytochrome complec, the electron loses its energy for the creation of
proton gradient and synthesis of ATP from ADP and iP and the process is
called PHOTOPHOSPHORYLATION.
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POPCORN PACKETS

16. CONTINUED...
• From plastocyanin the electron is picked up by the
trap centre P700 of PS1. On absorbing a photon of
light energy, P700 pushes out the electron with a
gain of energy. The electron then passes over to
carrier X, FeS, ferrodoxin and NADP-reductase
enzyme. These carriers give electrons to NADP+ for
combining to H+ ions to produce NADPH
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17. CYCLIC- PHOTOPHOSRYLATION
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19. CHEMIOSMOTIC HYPOTHESIS:
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20. CHEMIOSMOTIC HYPOTHESIS IN NON-CYCLIC
PHOTOPHOSPHORYLATION
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21. PHOSPHORYLATION
• SYNTHESIS OF ATP from ADP and inorganic
phosphate in chloroplast or mitochondria is termed
as PHOSPHORYLATION.
• In plants it is of 2 types:
1. CYCLIC PHOTOPHOSPHORYLATION
2. NONCYCLIC PHOTOPHOSPHORYLATION
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22. CYCLIC PHOTOPHOSPHORYLATION
• ONLY PS1 works to generate ATP in the presence of sunlight .
• Occurs in STROMA LAMELLAE because stroma lamellae lacks
NADP+ REDUCTASE ENZYME
• The excited electron is cycled back to PS complex through ETC.
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23. DARK REACTION:
• This is the BIOSYNTHETIC hase involving use of
ASSIMILATORY power to generate food for the plant
by fixing CO2 from the atmosphere into GLUCOSE.
• Since glucose is C6H12O6 that is it has 6 carbon
molecules therefore 6 CO2 molecules needs to be
fixed using the ASSIMILATORY POWER which is ATP
and NADPH (Nicotinamide Adenine Dinucleotide
Phosphate).
• Two cycles depending upon the plant type will be
studied here:
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24. CALVIN CYCLE for C3 PLANTS and C4 PLANTS:
• ALL photosynthetic plants undergo CALVIN CYCLE
• Enzyme used is RuBisCO (RIBULOSE BISPHOSPHATE
CARBOXYLASE OXYGENASE)
• Primary CO2 acceptor is 5-carbon compound called
RuBP
• After carboxylation first stable CO2 fixation product
are 2 molecules of 3-PGA (3-PHOSPHOGLYCERATE)
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25. Steps involved in CALVIN CYCLE
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27. 6CO2+6RuBP+18ATP+12NADPH 6RuBP+C6H12O6+18ADP+18P+12NADP+
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28. CALVIN CYCLE IN C3 PLANTS
• Occurs in mesophyll cells of plants eg RICE
• Enzyme used is RuBisCO (RIBULOSE BISPHOSPHATE
CARBOXYLASE OXYGENASE)
• Primary CO2 acceptor is 5-carbon compound called
RuBP
• After carboxylation first stable CO2 fixation product
are 2 molecules of 3-PGA (3-PHOSPHOGLYCERATE)
or C3 acid
• Optimum temp reqd. : 20 to 25 degree celsius
• Problem of photorespiration
• CO2 fixation is low under high light intensities
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29. CALVIN CYCLE in C4 PLANTS:
• C4 plants have a unique type of ANATOMY called KRANZ
ANATOMY. The vascular bundles are surrounded by
layers of large cells called BUNDLE SHEATH CELLS eg in
MAIZE, SUGARCANEand SORGHUM.
• Here the primary CO2 acceptor is a 3-carbon compound
called PEP (PHOSPHOENOLPYRUVATE)
• Enzyme involved in CO2 fixation is PEPcarboxylase or
PEPcase
• Optimum temp reqd. Is 30-40 degree celsius
• Primary stable CO2 fixation product is OAA (OXALO
ACETIC ACID) or C4 acid
• CO2 fixation more under high light intensities.
• No photorespiration
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30. Continued......
• In C4 plants, the mesophyll cells lack RuBisCO enzyme
• Also here PEP which is the primary CO2 acceptor is
present in mesophyll cells.
• So PEPcase converts CO2 into 4-crbon compound OAA
(1st stable CO2 fixation product) in mesophyll cells.
• OAA further gets converted to MALIC ACID or ASPARTIC
ACID in the mesophyll cells and are then transported to
BUNDLE SHEATH CELLS where RuBisCO enzyme is in
abundance
• These C4 acids are then further broken into C3 acids or a
3-Crbon molecule calledPYRUVATE which is transported
back to the MESOPHYLL CELLS . This pyruvate is coverted
back again to PEP in mesophyll cells and the cycle is
completed
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33. PHOTORESPIRATION:
• In C4 plants due to KRANZ ANATOMY i.e due to presence
of bundle sheath cells , such plants have thick walls and
less exposure to gaseous exchange (impervious). So
• In case of C3 plants , although RuBisCO has greater
affinityfor CO2 , but if the relative conc. Of CO2 is lower
that O2 in surrounding environment then , RuBisCO
enzyme binds to O2 and RuBP gets coverted to 1
molecule of 3-PGA and 1 molecule of
PHOSPHOGLYCOLATE
• It is a wastefulprocess as it niether forms any sugars nor
any ATP. Rather it results in release of CO2 with the
utilization of ATP
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35. CAM PLANTS
• CAM or CRASSULACEAN ACID METABOLISM was first
discovered in Bryophyllum calycinum.
• In this phenomenon the acidity of green shoots increases
at night as stomataare open and decreases during the
following day as stomataare closed.
• This occurs in mesophyll cells. During nights when
stomataare open, CO2 is fixed in the same way as in case
of C4 plants and the 4-carbon compound OAA is formed .
This further gets converted to malic acid and is stored in
the VACUOLE of the plant cell (ACIDIFICATION)
• During the following day , DEACIDIFICATION takes place
as the stomataare closed and the stored MALIC ACID is
converted to PEP and undergoes the CALVIN CYCLE to
form sugars.
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37. THANKYOU
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