Photosynthesis is a process by which plants make their own food by utilizing the Co2 from Air, light from sun & water from soil Photosynthesis can b done in 2 steps Light reaction: it takes place in thylakoid of chloroplast & in the presence of light & generate ATPs & NADPH molecules Dark reaction: it takes place in the absence of light & in stroma region of chloroplast, it is also called as Calvin Cycle here Co2 is fixed

1. {
WELCOME
TO
ALL OF YOU
FOR
TODAY’S PRESENTATION
BACHELORS OF SCEINCE 3RD YEAR
SUBJECT: BOTANY
TOPIC: LIGHT REACTION AND DARK
REACTION
CREATED AND PRESENTED BY: ATIF ALI ZAKIR

3.  THE PROCESS OF PHOTOSYNTHESIS IS COMPLICATED
,OXIDATION REDUCTION PROCESS RESULTING IN THE
OXIDATION OF WATER AND REDUCTION OF CO2
 THE MECHANISM OF PHOTOSYNTHESIS COMPLETED IN
TWO PHASE
A. LIGHT REACTION / HILL’S REACTION
B. DARK REACTION / BLACKMAN’S REACTION
 IN LIGHT REACTION ASSILIMATORY POWER IS
GENERATE i.e,( NADPH + H+ve +ATP) IS GENERATED AND
O2 IS RELEASED
 AND THE ASSILIMATORY POWER IS UTILISED IN DARK
REACTION IN REDUCING OF CO2 TO CARBOHYDRATES
 H2O IS ELECTRON DONOR IN PHOTOSYNTHESIS
MECHANISM OF PHOTOSYNTHESIS

4. ABSORPTION OF
LIGHT BY
CHLOROPLAST
PIGMENTS
TRANSFER OF
LIGHT ENERGY
FROM ACESSORY
PIGMENTS TO
CHL-A
ACTIVATION OF
CHL-A MOLECULES
BY PHOTON OF
LIGHT
PHOTOLYSIS OF
WATER AND O2
EVOLUTION
(OXIDATION OF
H2O)
ELECTRON
TRANSPORT &
PRODUCTION OF
NADPH & ATPs
LIGHT REACTION OR HILL’S REACTION
IT CAN BE COMPLETED IN FIVE STEPS

5.  DIFFERENT PIGMENTS ABSORBS DIFFERENT
WAVELENGTHS OF VISIBLE LIGHT
B. TRANSFER OF LIGHT ENERGY FROM ACESSORY
PIGMENTS TO CHL-A
A. ABSORPTION OF LIGHT BY CHLOROPLAST PIGMENT
ACCESSORY PIGMENTS
ABSORBS LIGHT &
TRANSFER TO CHL-A
THEN CHL-A TAKE PART IN
LIGHT RXN
CHL-A ABSORBS LIGHT ALSO
(PS-I 700,PSII-680)

6. PS-I & PS-II
RECEIVES LIGHT
CHL-A GET
ENERGY &
BECOME EXCITED
MOLECULE
DUE TO
EXCITATION
ENERGY
RELEASE IN THE
FORM OF
ELECTRON
C. ACTIVATION OF CHL-A MOLECULE BY
PHOTONS OF LIGHT
D. PHOTOLYSIS OF WATER AND EVOLUTION OF O2
ASSOCCIATED
WITH O2
EVOLVING
COMPLEX IN PS-II
THIS CAN BE
CATALYSED BY
MN+,CL- IONS
WHEN PS-II
RECEIVES LIGHT
IT BECOME
ACTIVE
IT SPLITS WATER
INTO OH & H IONS
(PHOTOLYSIS OF
H2O)
2H2O ---LIGHT--- 4H+ + 4OH- RECOMBINE IN THE PRESENCE OF Mn , Cl ------
---4e- + O2 + 2H2O

7. CHL-A
RECIEVES
LIGHT AND
BECOME
EXCITED
EXPELS EXTRA
ENERGY WITH
AN ELECTRON
IN (PS-II & PS-I)
THIS
ELECTRON
TRAVEL A
NUMBER OF
CARRIERS
ETIHER
CYCLED BACK
OR USE IN
REDUCE
NADPH INTO
NADP
AND ENERGY
IS USED IN
THE
FORMATION
OF ATP FROM
ADP
THIS IS KNOWN AS
PHOTOSYNTHETIC
PHOSPHORYLATION
OR PHOTO -
PHOSPHORYLATION
E. ELECTRON TRANSPORT & PRODUCTION OF
NADPH & ATPs

8. { {
CYCLIC P.P.R
 IT INVOLVES ONLY PS-I (P700)
 ELECTRON EMITTED CYCLED
BACK TO PS-I
 NO NADPH FORMATION TAKES
PLACE
 ATP FORMATION FROM ADP
TAKES PLACE
 NO O2 RELEASE DUE TO NO
PHOTOLYSIS OF H20
 THIS FULFIL THE REQUIREMENT
OF NON CYCLIC PPR
NON CYCLIC P.P.R
 IT INVOLVES BOTH PS-I &
PS-II
 ELECTRON EMITTED DOSE
NOT RETURN BACK TO
SAME CHL. MOLECULE
 NADP IS FORMED & THEN
REDUCE INTO NADPH2
 ELECTRONS COME FROM
THE SOURCE OF H2O
 O 2 IS RELEASED , BOTH ATP
& NADPH2 FORMED
PHOTOPHOSPHORYLATION
 A PROCESS BY WHICH LIGHT ENERGY IS TRANSFORMED INTO
CHEMICAL ENERGY IN THE FORM OF ATP IS CALLED AS
PHOTOPHOSPHORYLATION
 IT CAN BE DONE THROUGH CYCLIC OR NON CYCLIC ELECTRON
TRANSPORT SYSTEM
 PPR IS OF TWO TYPES (CYCLIC PPR & NON CYCLIC PPR)
 IN NATURE BOTH PROCESSES OF PPR PROCEEDS
SIMULTANOUSLY

10. CYCLIC PHOTO - PHOSPHORYLATION
LIGHT FROM SUN
LIGHT ABSORBED
BY PS-I (PS700),GET
EXCITED
HIGHER ENERGY
& ELECTRON
RELEASED
ELECTRON
ACCEPT BY P.E.A
REDUCED &
TRANSFER
ELECTRON
FERODOXIN
FORWARD
ELECTRON TO
CYTOCHROME-B6
HERE ATP IS
FORMED FROM
ADP+ Pi
THEN FORWARD
TO
PLASTOQUINONE
P.Q. FORWARD TO
CYTOCHROME-F
HERE ATP IS
FORMED FROM
ADP+ Pi
CYT-F FORWARD
TO
PLASTOCYANIN
P.C. FORWARD
BACK TO PS-I
(P700)

11. NON CYCLIC PHOTO-PHOSPHORYLATION
LIGHT
FROM
SUN
ABSORBED
BY PS-II
(P680)
HIGHER
ENERGY &
ELECTRONS
RELEASED
ELECTRON
ACCEPT BY
P.E.A i.e.,
PHEOPHYTIN
FORWARD
ELECTRON
TO
CYTOCHRO-
ME-B6
HERE ATP IS
FORMED
FROM ADP+
Pi
THEN
FORWARD
TO P.Q.
P.Q. FORWARD
TO
CYTOCHROME-
F
CYT-F
FORWARD TO
PLASTOCYANI
N
P.C. FORWARD
TO PS-I (P700) &
ABSORB LIGHT
HIGHER
ENERGY &
ELECTRONS
RELEASED
ELECTRON
ACCEPTED BY
P.E.A i.e., FRS
TRANSFER
TO
FERODOXIN
FERODOXIN
REDUCE NADP
INTO NADPH2
USING
PROTON
RELEASED
DURING
PHOTOLYSIS
OF H2O
NADP GET
REDUCE INTO
NADPH2 BY
ENZYME nadp
reductase
NADP + 2ADP + 2Pi + 4H2O -----LIGHT------NADPH2 + 2ATP + O2 + 2H2O

12.  IT IS THE SECOND PHASE OF PHOTOSYNTHESIS
 IT TAKES PLACE IN STROMA REGION OF CHLOROPLAST
 LIGHT IS NOT NECESSARY FOR THIS PROCESS,HENCE CALLED
AS LIGHT INDEPENDENT REACTION
 HERE THE REDUCTION OF CO2 INTO CARBOHYDRATES TAKES
PLACE BY USING ASSILIMATORY POWERS ATP & NADPH2
GENERATED DURING LIGHT RXN
 IT INVOLVES SERIES OF ENZYMATIC REACTION WHICH
OCCURS IN CYCLE & IS ALSO CALLED AS CALVIN CYCLE
AFTER THE NAME OF SCIENTIST CALVIN MELVIN
THIS CYCLE CAN BE COMPLETED IN THREE PHASES
A. CARBOXYLATION PHASE
B. REDUCTION PHASE
C. REGENRATION PHASE
DARK REACTION/CALVIN CYCLE OR C3 CYCLE
/PHOTOSYNTHETIC CARBON REDUCTION CYCLE

13. DARK REACTION/ CALVIN CYCLE

14.  IN CARBOXYLATION PHASE ,ADDITION OF CO2 TO FIVE
CARBON COMPOUND i.e., RIBULOSE 1,5-BISPHOSPHATE ( RUBP
,PRIMARY ACCEPTOR) IN THE PRESENCE OF ENZYME RUBISCO
 THIS RESULT IN THE FORMATION OF TWO MOLECULES OF
3-PHOSPHOGLYCERATE (3-PGA & 3 Carbon Compound)
CO2 + RUBP -----RUBISCO----- 3-PHOSPHOGLYCERATE (2 mol.)
 RUBISCO IS THE PACEMAKER ENZYME OF THE CALVIN CYCLE
& IS MOST ABUNDANT IN CHLOROPLAST
 3-PHOSPHOGLYCERATE IS THE FIRST STABLE PRODUCT OF
DARK RXN HENCE CALLED AS C3 -CYCLE
 IT DOSE NOT REQUIRE ANY ATP & NADPH MOLECULE
 IN ALL MOLECULES OF CO2 REACT WITH 6 RUBP FORMING 12
MOLECULES OF 3-PHOSPHOGLYCERATE (3-PGA)
A. CARBOXYALTION PHASE

15.  THIS STEP INVOLVES THE REDUCTION OF 2 mol. OF 3PGA TO 3-
PHOSPHOGLYCERICERATE TO GLYCERALDEHYDE -3-PHOSPHATE
IN THE PRESENCE OF ENZYME PGA KINASE
 HERE ONE MOLECULE OF G3P GOES TO MAKE GLUCOSE
 AND THE REMAINING 5C- COMPOUND ENTERS IN THE
REGENERATION PHASE
 HERE TWO MOLECULES OF ATPs AND NADPH2
B. REDUCTION PHASE

16.  IN THIS PHASE THE REGENERATION OF RUBP TAKES
PLACE
 AFTER REPIDLY SIX CYCLES SIX MOLECULES OF
GLYCERALDEHYDE -3-PHOSPHATE FORMED IN 6 CALVIN
CYCLES
 FOR REGENERATION OF ONE 5C COMPOUND OF RUBP
MOLECULE ,ONE MOLECULE OF ATP IS USED
 HENCE ,THE TOTAL 18 ATPs & 12 NADPH2 MOLECULES
ARE REQUIRED FOR SYNTHESIS OF ONE GLUCOSE
MOLECULE
C. REGENERATION PHASE

17.  CO2+H2O+ LIGHT---- GIVES---- C6 H12 O6+O2
 THE FIXATION AND REDUCTION OF ONE MOLECULE OF
CO2 REQUIRES THREE MOLECULES OF ATPS
 TWO MOLECULES OF NADPH2 COMING FROM THE
LIGHT RXN
 FOR EVERY SIX MOLECULES OF 3PGA PRODUCED AT
THE EXPENSE OF 18 ATPS, 12NADPH2 AND 6 CO2
 ONLY ONE MOLECULE OF CARBON ENTERS THE
METABOLIC POOL AS A NET GAIN IN ENERGY AND THE
FIVE REMAINING MOLECULES FORMS RUBP WHICH
ACCEPT AGAIN CO2 TO INITIATE C3 CYCLE
BALANCE SHEET

18. THANK YOU SO MUCH
FOR
ATTENDING TODAY’S PRESENTATION
CREATED AND PRESENTED BY
ATIF ALI ZAKIR
STUDENT OF MSC BOTANY II YEAR
SAIFIA SCIENCE COLLEGE BHOPAL