This document provides an overview of photosynthesis presented by a group of 6 students. It describes the key processes and phases of photosynthesis including light reaction, dark reaction, photophosphorylation, photosystems, and alternative pathways such as C4 and CAM photosynthesis. The light reaction uses energy from sunlight to split water and produce ATP and NADPH. The dark reaction then uses these products to fix carbon from carbon dioxide into sugars.

1. PHOTOSYNTHESIS
group members
Maryam wahab
Hina zamir
Amna javed
Maleeha inayat
Saleha qazi
Yusra shair
7th may,2015

2. OUTLINE :
 Overview of mechanism of photosynthesis
 Pigments
 Process of photosynthesis
 Phosphorylation
 Photosystems
 Dark reaction
 C4 and CAM pathway

3. OVERVIEW OF PHOTOSYNTHESIS
 A process by which autotrophic organisms use
light energy to make sugar & oxygen gas from
carbon dioxide & water.
 Occurs in chloroplast, an organelle in mesophyll

4. MECHANISM OF
PHOTOSYNTHESIS Divided into 2 phases :
 Light reaction
 a) photolysis of water
 b)phosphorylation
 Dark reaction (carbon fixation or calvin cycle)
 Light reaction is light dependent & takes place in
grana of chloroplast & its product is NADPH & ATP.
 Dark reaction is light independent & occurs in
stroma of chloroplast.

5. FOUR PHASES OF
PHOTOSYNTHESIS 1) light absorption & energy delivery by antenna
systems
 2) primary electron transfer in reaction centers
 3) energy stabilization by secondary processes
 4)synthesis & export of stable products
 First 3 phases makeup the light reaction & fourth
encompasses the dark reaction.

6. PIGMENTS Substances that have ability to absorb specific
wavelengths of light & reflect all others.
 Pigments are colored.
 Easily excited by light energy.
 The color we see is the net effect of all the light
reflecting back at us…!
 photosynthetic pigments are of 3 types
 1)Chlorohylls (chlorophyll a & b)
 2)Accessory photosynthetic pigment or carotenoids
(carotene & xanthophyll)
 3) phycobilins

7. CHLOROPHYLL A
 Most important pigment in photosynthesis.
 Absorbs blue,red & violet wavelengths in the visible
spectrum.
 Formula is C55H72O5N4Mg
 Complex ring structure having 2 parts i.e. head & tail
 Head(porphyrin ring) : 4 complex pyrole rings of carbon
& nitrogen.
 In the centre of porphyrin ring a single magnesium atom
is attached to the nitrogen of each pyrrole ring.
 Maximum absorption by chlorophyll a occurs in blue &
red regions.
 Tail is attached to one of the pyrrole rings.
 It is a long hydrocarbon phytol (C20H39) & anchors
chlorophyll molecule in thylakoid membrane.

8. STRUCTURE OF CHLOROPHYLL A

9. CHLOROPHYLL B
 Its structure is similar to chlorophyll a but CH3 is
replaced by CHO.
 So molecular formula is C55H70O6N4Mg
 It primarily absorbs blue light .
 It is used to complement absorption spectrum of a
by extending the range of light wavelengths a
photosynthetic organism is able to absorb.

10. ACCESSORY PIGMENTS
 They are not directly involved in LDR .
 includes carotenes & xanthophylls.
 carotenes are hydrocrbons with general molecular
formula C40H56
 They absorb wavelengths that are not efficiently
absorbed by chloropyhlls .
 Carotenoid is yellow to orange in color
 Xanthophyll is yellow in color.
 Carotenoids have 2 important roles in plants
 1)transfer the light energy they capture to
chlorophyll to use in the LDR.
 2)Protect chlorophyll a from photo-oxidation

11. PROCESS OF
PHOTOSYNTHESIS

12. PROCESS :
 Photosynthesis occur in two phases :
 Phase 1 : Light reaction ( granna -thalakoid
membrane )
 Phase 2 : Dark reaction( stroma)
 Reaction
6 CO2 + 6 H2O sunlight C6 H12 O6 + 6 O2
carbon dioxide + water = glucose(sugar ) + oxygen

13. PHASE 1.LIGHT REACTION
 Also called Light Dependent Reaction which contain Photosystem I
and Photosystem II.
 Occurance: chloroplast (granna - thylakoid)
 Chlorophyll (thylakoid) traps energy from light
 Requirement light ,water
NADP + ADP + Pi
 Products O2 ATP & NADPH
 Two steps
 Energy is Capture from Sunlight.
 light energy, trapped by chlorophyll, is used
 Step 1 photolysis of water
 Water is Split into Hydrogen Ions ,electron and Oxygen (O2).
The O2 Diffuses out of the Chloroplasts (Byproduct).
 Formation of reduced NADPH ( chemical energy )
 Step 2 phosphorylation
 The Light Energy is Converted to Chemical Energy, which is Temporarily Stored
in ATP (ADP + Pi + energy )

14. PHASE 2. DARK REACTION
 Other names :
Calvin Cycle
Light Independent Reaction
Carbon Fixation or C3 Fixation
 Does not require light
 Location Occurs in stroma of chloroplast
 Requirments
ATP and NADPH as a fuel
CO2 (air )
 Product glucose sugar
 Step
CO2 fixation in glucose sugar
 The Chemical Energy Stored in
ATP and NADPH powers the
formation of Organic Compound
glucose (Sugar) using CO2

16. OVER ALL MECHANISM :

17. PHOTOPHOSPHORYLATION

18. DEFINITION
 In the process of photosynthesis, the phosphorylation
of ADP to ATP using the energy of sunlight is called
photophosphorylation.
 In photophosphorylation, light energy is used to create
a high-energy electron donor and a lower energy
electron acceptor. Electrons then move spontaneously
from donor to acceptor through an electron transport
chain.
 TYPES OF PHOTOPHOSPHORYLATION
 There are two types of photophosphorylation
 1.Cyclic photophosphorylation
 2.Non-cyclic photophosphorylation

19. CYCLIC
PHOTOPHOSPHORYLATION
 In bacterial photosynthesis, a single photosystem is
involved.
 When an electron is energized by absorption of light, it is
ejected from the photosystem reaction centre.
 The electron then passes down through an electron
transport system, and finally to the reaction centre.
 The energy released during this electron transport is used
to produce ATP.
 Since the excited electron returns to the reaction centre,
this mechanism for making ATP is called cyclic
photophosphorylation.
 No reducing power needed for biosynthesis generated in
this process

20. CYCLIC

21. NON-CYCLIC
PHOTOPHOSPHORYLATION
 Plants and cyanobacteria utilize two photosystems
which work sequentially to produce both energy and
reducing power.
 First, a photon of light ejects a high electron from
photosystem II.
 The electron lost from photosystem II does not return
to photosystem II, but is replaced by an electron
generated from the enzymatic splitting of water and
the release of oxygen.

22.  The electron then travels from the excited reaction
centre of photosystem II down an electron transport
chain and finally to the reaction centre of photosystem
I.
 This transport system generates a photon motive force
that is used to produce ATP.
 Since the excited electron does not return to
photosystem II, this mechanism for making ATP is
called non-cyclic photophosphorylation.

23. NON-CYCLIC

24. PHOTOSYSTEMS

25. INTRODUCTION
 Photosystems are involved in light reaction
 Photosystems are functional and structural units of protein complexes
involved present in thalykoid membrane of GRANUM.
 Both photosystems work together.
 Together carry out the primary photochemistry of photosynthesis: the
absorption of light and the transfer of energy and electrons.
 They are found in the thylakoid membranes of plants, algae and
cyanobacteria (in plants and algae these are located in the chloroplasts),
or in the cytoplasmic membrane of photosynthetic bacteria.
 There are two kinds of photosystems: II and I.
 The flow of electrons occurs in two ways
---Non-Cyclic Pthway: passes through both photosystems (Z-
scheme)
---Cyclic Pathway : occurs only in PSI.

26.  Each photosystem consists of
two parts:
 Antenna Complex :
Cluster of Chlorophyll
a,b and carotenoid
molecules which gather
light ad transfer it to
reaction centre.
 Reaction Centre: Has
chlorophyll "a" molecules
slightly slightly
different from other
chlorophyll molecules.

27. PHOTOSYSTEM II
 Absorbs light of 700nm
 Water splits, electrons enter PSII reaction centre.
 When P700 gains energy, 2 electrons become excited and
leave the molecule.
 The electrons are readily captured by primary electron
acceptor
 Primary electron acceptor>> Plastoquinone>>Cyt b>>Cyt f>>
Plastocyanine
 PHOTOPHOSPHORYLATION:
 As the electron pass through the electron trasport chain its
energy is released and is used by thylakoid membrane to
synthesize ATP.

28. PHOTOSYSTEM I (P680)
 Absorbs light of 680nm
 The electrons from photosystem II finally
reaches the reaction centre of photosystem I.
 Then electrons move to the primary electron
acceptor.
 From here they pass to Ferrodoxin (Fd).
 The elctrons then passes from Ferrodoxin to
NADP,taking H+ and form NADPH2.

29. SCHEMATIC DIAGRAM.

30. OVERALL RESULT OF Z-SCHEME.
 The result of the non-cyclic electron flow is that water is oxidzed
yielding H+,e- and O2.
 ATP is produced.
 NADP+ becomes NADPH2.
 The hydrogen and Energy of NADPH2 and ATP produced in the light
reaction are used in dark reaction.

31. DARK REACTION OF
PHOTOSYNTHESIS
The Calvin Cycle

32.  the free energy of cleavage of ~P bonds of ATP,
and reducing power of NADPH, are used to fix
and reduce CO2 to form carbohydrate.
 Carbon atoms from CO2 are bonded, or fixed,
into organic compounds = carbon fixation.
 THIS OCCURS IN THE STROMA

34.  An enzyme (rubisco),
combines CO2 with a 5-
carbon sugar RuBP
 The product, 6-C
sugar, immediately
splits into
2, -3C molecules
(PGA)
PGA–
Phosphoglyceric
Acid

35. PGA is converted to
another 3- Carbon
molecule PGAL in a 2
part process:
 Each PGA receives a
P group from ATP
 The resulting
compound receives a
proton from
NADPH and
releases the P,
producing PGAL
( ADP & NADP+
return to light rxn., to
make ATP and
NADPH)

36.  Most of the PGAL
is converted back to
RuBP
 Requires a P
from another
ATP
 Some PGAL leave
and used by plants
create organic
compounds

37. BALANCE SHEET FOR PHOTOSYNTHESIS
 How much ATP & NADH are required to make 1 molecule
of PGA from carbon dioxide?
 Each turn fixes one CO2
 PGAL is a 3-C molecule (takes 3 turns to make each
molecule)
 Each turn of the cycle:
 3 ATP ( 2 in step 2 & 1 in step 3)
 2 NADPH (step 3)

38. C4 and CAM pathway

39. C4 PLANT OR PHOTOSYNTHESIS
 What is C4 plant or photosynthesis ?
 Present particularly in monocot
 Presence of Kranz anatomy
 PEP is the initial acceptor
 First product is OAA ( 4 carbon compound /
acid)
 Oxygen does not inhibit this process

40. C4 (CONT.)
 Photorespiration is low
 Rate of transpiration is low
 No wastage of carbon dioxide
 Well adapted in xeric condition
 Distinct division of labour
 Requires more ATP than C3

41. CAM PATHWAY
 It is an adaptation of plants in arid condition
 CAM plants use both C3 and C4 pathways
 CAM plants use only mesophyll cells
 Stomata are close during the day
 Prevents carbon dioxide entrance as well while
preventing water loss
 Stomata opens at night in cooler temprature

42. CAM PATHWAY (CONT.)
 Carbon dioxide diffuses
 Carbon dioxide combines with PEP forming OAA
 OAA reduce to form Malate
 Malate stored in vacuoles
 Photosynthesis commences during the day
 Transport of malate to cytoplasm

43. CAM PATHWAY(CONT.)
 Formation of pyruvate
 Entrance of carbon dioxide to chloroplast
 Formation of starch
 Example :
 Fleshy succulants (stone crops )
 ferns

44. PHOTOSYNTHESIS
group members
Maryam wahab
Hina zamir
Amna javed
Maleeha inayat
Saleha qazi
Yusra shair
7th may,2015