PHOTOSYNTHESIS VAN HELMONT’S EXPERIMENT (1649) 5 years 2,3 kg shoot + 90,9 kg soil only water = 77 kg tree + 90,8 kg soil.
Download ReportTranscript PHOTOSYNTHESIS VAN HELMONT’S EXPERIMENT (1649) 5 years 2,3 kg shoot + 90,9 kg soil only water = 77 kg tree + 90,8 kg soil.
Slide 1
PHOTOSYNTHESIS
Slide 2
Slide 3
VAN HELMONT’S EXPERIMENT (1649)
5 years
2,3 kg shoot + 90,9 kg soil
only water
= 77 kg tree + 90,8
kg soil
Slide 4
JOSEPH PRIESTLEY’S EXPERIMENT 1771
EXP. 1
EXP. 2
What do you think happened to
the mouse in experiment 1?
What do you think happened to
the mouse in experiment 2?
Why do you think that happened?
Why do you think that happened?
Slide 5
In the early 1900`s scientists believed that
light reactions split carbon dioxide and
release oxygen.
C
Dark
CO2
reactions
+ H 2O
C H2 O
O2
In 1930 van
photosynthesis.
CO2 + 2 H2S
Neil
studied
bacterial
CH2O + H2O + 2S
Slide 6
In bacterial photosynthesis:
Oxygen is not released
This proves that light
does not split carbon
dioxide in plant
photosynthesis.
Light reactions split
water and release oxygen.
Anabaena sp.
Slide 7
WHAT IS PHOTOSYNTHESIS?
Photosynthesis is the
process which converts
light
energy
into
chemical energy.
Slide 8
WHICH ORGANISMS DO PHOTOSYNTHESIS?
• Photosynthesis occurs in some bacteria
(blue green algae), algae (green , goldenyellow, red, brown) and in plants.
• In autotrophic eukaryotes, photosynthesis
occurs inside chloroplast.
• In autotrophic prokaryotes photosynthesis
occurs in the cytoplasm.
Slide 9
Slide 10
STRUCTURE OF CHLOROPLAST
Slide 11
Slide 12
Slide 13
STRUCTURE OF CHLOROPLAST
• All chloroplasts contain the green
pigment chlorophyll which is found in
the thylakoid membranes and absorbs
the
light
energy
that
initiates
photosynthesis.
• Chloroplasts like mitochondria contain
DNA, RNA and ribosome and can
duplicate themselves
Slide 14
OVERALL EQUATION OF
PHOTOSYNTHESIS
Light energy
6CO2 + 12 H2 O
C 6 H 12 O 6 + 6 H2 O + 6 O 2
Enzymes, ETS
Slide 15
What is the source of oxygen that is released?
Slide 16
STAGES OF PHOTOSYNTHESIS
LIGHT
ENERGY
WATER
CARBON DIOXIDE
ADP + Pi
GRANA
STROMA
Light reactions
convert light energy
into chemical
energy
ATP
NADP+
Dark reactions
result in the
reduction of carbon
dioxide into glucose
NADPH2
OXYGEN
GLUCOSE
Slide 17
STAGES OF PHOTOSYNTHESIS
There are two, linked stages of photosynthesis:
1. The light reactions in the grana produce ATP
by photophosphorylation and split water,
evolving oxygen and forming NADPH2 by
transferring electrons from water to NADP+.
2. The dark reactions (Calvin Cycle) occur in the
stroma and use the energy of ATP and the
reducing power of NADPH2 to form sugar from
CO2.
Dark reactions don’t require light directly, it
usually occurs during the day, when the light
reactions are providing ATP and NADPH2.
Slide 18
Slide 19
LIGHT AND PHOTOSYNTHETIC PIGMENTS
Light falling on an object may,
pass through it (be transmitted)
be reflected (seen as colour)
be absorbed (has its energy converted into
the energy of motion)
Only absorbed light is available for
photosynthesis
Slide 20
LIGHT AND PHOTOSYNTHETIC PIGMENTS
Photosynthetic pigments are
organic molecules that
absorb light.
Main plant pigments are
chlorophyll and carotenoids
with several forms of each
type.
• The pigments absorb the
visible light wavelengths.
380nm
750nm
violet
green
red
Slide 21
Slide 22
PHOTOSYSTEMS
Chlorophyll a and one or
more types of accessory
pigments such as
chlorophyll b and various
carotenoids surround a
single molecule of
specialized chlorophyll a
(P680 and P700), forming a
“photo-system”.
Photo-system I (PSI)
contains P700 and photosystem II (PSII) contains
P680 at the reaction center.
Slide 23
Organization of Photosystems in Grana
Slide 24
PHOTOSYNTHETIC PIGMENTS
Chlorophyll contains C, H, O, N and Mg in its structure.
(Mg containing protein).
Its synthesis requires the presence of light, Fe, and K.
Chlorophyll a
absorbs red and blue light
is the primary photsynthetic
pigment
is involved directly in converting of
light energy into chemical energy
presence of chlorophyll a hides the
effect of carotenes and xanthophyll
in leaves
molecular formula is
C55 H72 O5 N 4 Mg
Chlorophyll b
absorbs red and blue light,
reflects green
transfers the absorbed light to
the chlorophyll a
molecular formula is
C55 H70 O6 N 4 Mg
Slide 25
PHOTOSYNTHETIC PIGMENTS
Slide 26
ACCESSORY PHOTOSYNTHETIC
PIGMENTS
Caroten(orange)
Xantophyll (yellow)
Phycoerythrin (red)
Phycocyanin (blue)
They absorb light energy
and transfer it to the
chlorophyll.
Slide 27
REACTIONS OF PHOTOSYNTHESIS
LIGHT
REACTIONS
DARK
REACTIONS
Cyclic
Non-Cyclic
photophosphorylation photophosphorylation
Slide 28
LIGHT REACTIONS
Cyclic photophosphorylation
Various pigments in PSI
collect light, passing the
energy on to P700
An electron with raised
energy levels is
accepted by ferredoxin
and passed onto an
ETS where ATP is
produced as the energy
level falls back to the
starting point.
Slide 29
Electron Excitation
Slide 30
LIGHT REACTIONS
Cyclic photophosphorylation
è
Ferredoxine (Fd)
Plastoquinone (PQ)
ADP + Pi
è
ATP
è
Cytochrome b6
ADP + Pi
Photosystem I
è
ATP
PSI ( Chl a)
è
light
Plastocyanine
Cytochrome f
è
Slide 31
The overall equation for cyclic electron
transport
light
2ADP + 2Pi
2ATP
chlorophyll
Slide 32
Slide 33
LIGHT REACTIONS
Non-Cyclic photophosphorylation
1. When PSII absorbs light, an electron is removed from chlorophyll. This
hole in PSll must be filled.
2. Water is split by photolysis.
3. Electrons from water molecule are passed to PSII and then onto PQ
(plastoquinon).
4. As in cyclic photophosphorylation, ATP is produced via the ETS, with
the electron dropping down to PSI.
5. Light energy also causes the release of an electron from PSI which is
accepted by ferrodoxin.
6. Electrons pass from ferrodoxin to NADP leading to the production of
NADPH2, with hydrogen coming from the separation of water into ions.
7. Electrons lost by PSI are replaced with the electrons coming from the
ETS (PSII).
Slide 34
LIGHT REACTIONS
Non-Cyclic photophosphorylation
2è
Cytochrome f
Ferredoxine (Fd)
2è
ADP + Pi
2è
2NADP+
Plastocyanine
2NADPH + H2
ATP
2è
Cytochrome b6
2è
2è
Plastoquinone (PQ)
2ePSII (Chl a (P680))
è
2e-
PSI ( Chl a(P700))
source
light
H2O
½ O2
light
By product
2H+
photolysis
Slide 35
LIGHT REACTIONS
The products of the two types of light
reactions are ATP, NADPH2 and oxygen.
The first two products enter the dark reactions
of photosynthesis, where they become involved
in the Calvin Cycle and the synthesis of PGAL
and eventually of glucose.
Oxygen is diffused into the air.
Slide 36
Non-Cyclic photophosphorylation
2e-
2NADP+
4
3
2
2NADPH + H2
1
To dark reactions
Slide 37
Non-Cyclic photophosphorylation
Slide 38
Pathway of electron transport
H2O
2e-
PSII
2e-
PSI
2e-
2NADP+
2e- To dark
reactions
The overall equation for non-cyclic electron transport
2H2O + ADP+ Pi + 2NADP+
ATP + 2NADPH2 + O2
Dark
reactions
By
product
Slide 39
Slide 40
COMPARISON OF CYCLIC AND
NON-CYCLIC PHOTOPHOSPHORYLATION
CYCLIC P.
NON-CYCLIC P.
Pathway of è
CYCLIC
NON-CYCLIC
First è donor
PSI
WATER
Last è acceptor
PSI
NADP+
Products
ATP
ATP, NADPH2, O 2
PSI ONLY
PSI and PSII
Numbers of PS
involved
Slide 41
DARK REACTIONS (CALVIN CYCLE)
Dark reactions involve a series of chemical
reactions, first described by Melvin Calvin.
CO2
is
incorporated into more complex
molecules and eventually carbohydrate.
Energy for the reactions is supplied by ATP with
NADPH2 acting as a reducing agent, both coming
from the light reactions.
As long as CO2, ATP and NADPH2 are present
light is not required for the Calvin cycle to
continue. That’s why they are called dark
reactions.
Slide 42
DARK REACTIONS (CALVIN CYCLE)
Every turn of the cycle fixes one molecule of CO2
by producing two molecules of PGA and then two
molecules of PGAL.
Thus six turns produce sufficient quantities of
PGAL for the production of one molecule of
glucose.
During dark reactions, for the incorporation of one
carbon dioxide molecule into the process 3 ATP
and 2 NADPH2 are used.
Therefore, for the synthesis of a hexose (glucose)
18 ATP and 12 NADPH2 are used.
Slide 43
DARK REACTIONS (CALVIN CYCLE)
6CO2
6 RuDP
6 (6C)UNSTABLE MOLECULE
6ADP + 6Pi
6H2 O
12 PGA(3C)
12ATP
6ATP
12ADP + 12Pi
12 DPGA
6 RuMP
With series of
reactions
10 PGAL
12 NADPH2
12H2 O
12NADP+
12 PGAL
2 PGAL
2Pi
GLUCOSE(6C)
Slide 44
Slide 45
Slide 46
Slide 47
FACTORS AFFECTING THE RATE OF
PHOTOSYNTHESIS
PRINCIPLE OF LIMITING FACTOR
(1905 –Blackman)
When a chemical process is affected by
more than one factors, its rate is limited by
the factor which is nearest its minimum
value.
(The rate of a biochemical process is
limited by the factor which is nearest its
minimum value.)
Slide 48
INTERNAL (GENETIC) FACTORS
1. Anatomy of leaves
Surface area
Thickness of cuticle
Number of stomata
Volume of airspace
Thickness of epidermis and mesophyll
Number of chloroplasts in mesophyll
2. Amount of chlorophyll
3. Amount of enzymes
4. Accumulation of end products
Slide 49
EXTERNAL (ENVIRONMENTAL) FACTORS
1.Light intensity
Relative rate of photosynthesis
Foot candles
Slide 50
Slide 51
2. Carbon dioxide concentration
Relative rate of photosynthesis
CO2 concentration(% by volume)
Slide 52
Slide 53
* Light intensity and carbon dioxide
concentration
Relative rate of photosynthesis
High CO2 concentration
Moderate CO2 concentration
Low CO2 concentration
Light intensity
Slide 54
3. Temperature
Relative rate of photosynthesis
°C
25
30
Slide 55
*light intensity and temperature
Relative rate of photosynthesis
High intensity
Low intensity
Intensity
Slide 56
4. Light wavelength
Relative rate of photosynthesis
V
380 nm
B
G Y
O R
750nm
Slide 57
ENGELMANN`S EXPERIMENT
Engelmann exposed
Spirogyra cells to a color
spectrum produced by
passing light through a
prism. He estimated the
rate of photosynthesis
indirectly by observing the
movement of aerobic
bacteria toward the portions
of the algal filament emitting
the most oxygen.
He observed that the bacteria aggregated most densely along
the cells in the blue-violet and red portions of the spectrum.
Slide 58
5. Mineral concentration and amount of water
•
•
•
•
•
•
•
•
•
•
About 1% of water absorbed by roots is used in
photosynthesis
Mg
structure of chlorophyll
Fe
synthesis of chlorophyll, protein
synthesis (Ferredoxin and cytochromes), PQ
N
structure of chlorophyll, proteins, DNA, RNA,
ATP, NAD, NADP
K
synthesis of chlorophyll, growth
P
DNA, RNA, ATP, NADP
Ca
formation of cell membrane, cell wall
S
protein synthesis
Cu
Plastocyanin synthesis
Mn and Cl
catalysts of photolysis
Slide 59
Mineral concentration/ amount of water
Relative rate of photosynthesis
Mineral concentration/ amount of water
Slide 60
6. Oxygen concentration
•
Oxygen is a competitive inhibitor of carbon dioxide fixation
•
RuDP carboxylase acts as oxygenase and causes
breakdown of the RuDP. (Photorespiration-when the oxygen
concentration is high)
•
The output of photosynthesis is decreased by 30-40% and
even as much as 50%.
•
Affects C3 plants (ex: wheat, oat, Soya bean).
•
Some species of plants have evolved alternate modes of
carbon dioxide fixation.
Ex: C4 plants like corn, sugar cane and CAM plants
(Crassulacean Acid Metabolism like desert plants). In C4
plants synthesis of one glucose requires the use of 30 ATP
molecules (not 18 ATP), but there is no loss of RuDP due to
photorespiration.
Slide 61
*Oxygen concentration
Relative rate of photosynthesis
21
oxygen concentration (%by volume)
Slide 62
Slide 63
C3 Photosynthesis : C3 plants
Adaptive Value: more efficient than C4 and CAM plants under cool and moist
conditions and under normal light because requires less machinery (fewer
enzymes and no specialized anatomy).
Most plants are C3.
Slide 64
C4 Photosynthesis : C4 plants
Slide 65
C4 Photosynthesis : C4 plants
Adaptive Value:
Photosynthesizes faster than C3 plants under high
light intensity and high temperatures because the CO2 is
delivered directly to RUBISCO, not allowing it to grab
oxygen and undergo photorespiration.
Has better Water Use Efficiency because PEP
Carboxylase brings in CO2 faster and so does not need
to keep stomata open as much (less water lost by
transpiration) for the same amount of CO2 gain for
photosynthesis.
C4 plants include several thousand species in at
least 19 plant families. Example: fourwing saltbush
pictured here, corn, and many of our summer annual
plants.
Slide 66
C4 Photosynthesis : C4 plants
Slide 67
CAM Photosynthesis : CAM Plants
Slide 68
Slide 69
CAM Photosynthesis : CAM Plants
Adaptive Value:
Better Water Use Efficiency than C3 plants under arid
conditions due to opening stomata at night when
transpiration rates are lower (no sunlight, lower
temperatures, lower wind speeds, etc.).
When conditions are extremely arid, CAM plants can just
leave their stomata closed night and day. Oxygen given off
in photosynthesis is used for respiration and CO2 given off
in respiration is used for photosynthesis.
CAM plants include many succulents such as cactuses
and agaves.
Slide 70
FATE OF PHOTOSYNTHETIC PRODUCTS
PGAL
Vitamins
Hormones
Nucleotides
RuDP
Vitamins Fructose Glucose
PGA
Nucleic
acids
Glycerol +
Lipids
Fatty acids
Pyruvic
acid
Sucrose
Maltose
Starch
Cellulose
Amino
acids
Proteins
Cellular
respiration
Products of photosynthesis; PGAL, PGA and glucose are used in various
metabolic processes
Slide 71
PHOTOSYNTHESIS
AEROBIC
RESPIRATION
Raw materials are CO2 and Raw materials organic food
H2 O
molecules and oxygen
End products are organic End products are CO2 and
food molecules and oxygen H2 O
(results in the increase of (results in the decrease of
biomass)
biomass)
Occurs in the cells that Occurs in most of the
contain chlorophyll
actively metabolizing cells
•Certain cells of plants
(assimilation parenchyma)
•Some of the protists
(algae, euglena)
•Some the bacteria
( cyanobacteria)
Slide 72
PHOTOSYNTHESIS
AEROBIC
RESPIRATION
Takes place in chloroplast of
eukaryotic cells, in the
cytoplasm of prokaryotic
cells
Takes
place
in
the
cytoplasm and mitochondria
of
eukaryotes,
in
the
cytoplasm of prokaryotic
cells
Involves
photophosphorylation
Involves substrate level and
oxidative level
phosphorylation
Location of ETS: Thylakoid Location of ETS: cristae of
membrane of chloroplast
mitochondria
Slide 73
PHOTOSYNTHESIS
AEROBIC
RESPIRATION
Principal electron transfer Principal electron transfer
components: NADP+
components: NAD+ , FAD,
CoQ, Co-A
Source of electron for ETS:
In non-cyclic
photophosphorylation water
(undergoes photolysis to
yield electron, protons and
oxygen)
Terminal electron acceptor
for ETS: In non-cyclic
photophosphorylation:
NADP+ (becomes reduced
to form NADPH2)
Immediate source: NADH2,
FADH2
Ultimate source: glucose or
other fuel molecules
Oxygen (becomes reduced
to form water)
Slide 74
PHOTOSYNTHESIS
Process occurs
presence of light
in
AEROBIC
RESPIRATION
the Takes place all the time
(day and night)
Slide 75
BACTERIAL PHOTOSYNTHESIS
Slide 76
BACTERIAL PHOTOSYNTHESIS
light
CO2 + 2 H 2
(CH2 O )n + H 2O
bacteriochlorophyll
light
CO2 + 2 H 2 S
(CH2 O )n + H 2O+ 2S
bacteriochlorophyll
Slide 77
BACTERIAL PHOTOSYNTHESIS
• H2 or H2S are the source of electron.
• They do not release oxygen as by product
because they do not use water as electron
source.
• Bacteria do not contain chloroplasts.
• The
chlorophyll,
known
as
bacterioclorophyll is present in the
cytoplasm.
• But blue green bacteria (cyanobacteria)
contain chlorophyll a and use water so
they release oxygen.
Slide 78
CHEMOSYNTHESIS
Slide 79
Examples of chemosynthetic organisms
•
•
•
•
•
Nitrifying bacteria (Nitrosomonas,
Nitrobacter)
Sulfur bacteria
Iron bacteria
Hydrogen bacteria
Methane bacteria
Slide 80
CHEMOSYNTHESIS
• Certain bacteria carry out a process in which food is
made from carbon dioxide by using the energy of
inorganic substances.
• Like photosynthetic organisms, chemosynthetic bacteria
fix carbon dioxide through the reactions of the Calvin
Cycle.
• However, the energy to make ATP and NADPH comes
from the oxidation of organic substances, not light.
• They are important for recycling of materials in
ecosystem.
Slide 81
EXPERIMENTS ON PHOTOSYNTHESIS
1. To see if carbon dioxide is necessary for photosynthesis
KOH
NaOH
I
What can you predict
about the result of
this experiment
II
*NaOH and KOH absorb CO2
Slide 82
EXPERIMENTS ON PHOTOSYNTHESIS
2. To see if chlorophyll is necessary for photosynthesis
Predict the starch test
results for the two
areas shown on the leaf
Slide 83
EXPERIMENTS ON PHOTOSYNTHESIS
3. To see if light is necessary for photosynthesis
Slide 84
EXPERIMENTS ON PHOTOSYNTHESIS
4. To prove that organic substances are produced as a result
of photosynthesis
1. Several disks are removed from a
leaf before the sun rises.
2. Mass of the discs are measured
Will there be any difference
between the two measurements?
3. Leaf is left to do photosytnhesis
4. Several new disks are
removed from the same leaf
before the sun set
5. Mass of the discs
taken several hours
later are measured
Slide 85
EXPERIMENTS ON PHOTOSYNTHESIS
5. To show that oxygen is produced during photosynthesis
How can you prove that the gas which is produced is
oxygen?
Slide 86
EXPERIMENTS ON PHOTOSYNTHESIS
6. To find out the source of oxygen that is produced during
photosynthesis
Labeled CO2 (CO218)
Unlabeled O2
Labeled glucose
(C6H12O618)
Unlabeled H2O
Labeled O2
(O218)
Unlabeled CO2
Unlabeled glucose
(C6H12O6)
Labeled water
(H2O18)
PHOTOSYNTHESIS
Slide 2
Slide 3
VAN HELMONT’S EXPERIMENT (1649)
5 years
2,3 kg shoot + 90,9 kg soil
only water
= 77 kg tree + 90,8
kg soil
Slide 4
JOSEPH PRIESTLEY’S EXPERIMENT 1771
EXP. 1
EXP. 2
What do you think happened to
the mouse in experiment 1?
What do you think happened to
the mouse in experiment 2?
Why do you think that happened?
Why do you think that happened?
Slide 5
In the early 1900`s scientists believed that
light reactions split carbon dioxide and
release oxygen.
C
Dark
CO2
reactions
+ H 2O
C H2 O
O2
In 1930 van
photosynthesis.
CO2 + 2 H2S
Neil
studied
bacterial
CH2O + H2O + 2S
Slide 6
In bacterial photosynthesis:
Oxygen is not released
This proves that light
does not split carbon
dioxide in plant
photosynthesis.
Light reactions split
water and release oxygen.
Anabaena sp.
Slide 7
WHAT IS PHOTOSYNTHESIS?
Photosynthesis is the
process which converts
light
energy
into
chemical energy.
Slide 8
WHICH ORGANISMS DO PHOTOSYNTHESIS?
• Photosynthesis occurs in some bacteria
(blue green algae), algae (green , goldenyellow, red, brown) and in plants.
• In autotrophic eukaryotes, photosynthesis
occurs inside chloroplast.
• In autotrophic prokaryotes photosynthesis
occurs in the cytoplasm.
Slide 9
Slide 10
STRUCTURE OF CHLOROPLAST
Slide 11
Slide 12
Slide 13
STRUCTURE OF CHLOROPLAST
• All chloroplasts contain the green
pigment chlorophyll which is found in
the thylakoid membranes and absorbs
the
light
energy
that
initiates
photosynthesis.
• Chloroplasts like mitochondria contain
DNA, RNA and ribosome and can
duplicate themselves
Slide 14
OVERALL EQUATION OF
PHOTOSYNTHESIS
Light energy
6CO2 + 12 H2 O
C 6 H 12 O 6 + 6 H2 O + 6 O 2
Enzymes, ETS
Slide 15
What is the source of oxygen that is released?
Slide 16
STAGES OF PHOTOSYNTHESIS
LIGHT
ENERGY
WATER
CARBON DIOXIDE
ADP + Pi
GRANA
STROMA
Light reactions
convert light energy
into chemical
energy
ATP
NADP+
Dark reactions
result in the
reduction of carbon
dioxide into glucose
NADPH2
OXYGEN
GLUCOSE
Slide 17
STAGES OF PHOTOSYNTHESIS
There are two, linked stages of photosynthesis:
1. The light reactions in the grana produce ATP
by photophosphorylation and split water,
evolving oxygen and forming NADPH2 by
transferring electrons from water to NADP+.
2. The dark reactions (Calvin Cycle) occur in the
stroma and use the energy of ATP and the
reducing power of NADPH2 to form sugar from
CO2.
Dark reactions don’t require light directly, it
usually occurs during the day, when the light
reactions are providing ATP and NADPH2.
Slide 18
Slide 19
LIGHT AND PHOTOSYNTHETIC PIGMENTS
Light falling on an object may,
pass through it (be transmitted)
be reflected (seen as colour)
be absorbed (has its energy converted into
the energy of motion)
Only absorbed light is available for
photosynthesis
Slide 20
LIGHT AND PHOTOSYNTHETIC PIGMENTS
Photosynthetic pigments are
organic molecules that
absorb light.
Main plant pigments are
chlorophyll and carotenoids
with several forms of each
type.
• The pigments absorb the
visible light wavelengths.
380nm
750nm
violet
green
red
Slide 21
Slide 22
PHOTOSYSTEMS
Chlorophyll a and one or
more types of accessory
pigments such as
chlorophyll b and various
carotenoids surround a
single molecule of
specialized chlorophyll a
(P680 and P700), forming a
“photo-system”.
Photo-system I (PSI)
contains P700 and photosystem II (PSII) contains
P680 at the reaction center.
Slide 23
Organization of Photosystems in Grana
Slide 24
PHOTOSYNTHETIC PIGMENTS
Chlorophyll contains C, H, O, N and Mg in its structure.
(Mg containing protein).
Its synthesis requires the presence of light, Fe, and K.
Chlorophyll a
absorbs red and blue light
is the primary photsynthetic
pigment
is involved directly in converting of
light energy into chemical energy
presence of chlorophyll a hides the
effect of carotenes and xanthophyll
in leaves
molecular formula is
C55 H72 O5 N 4 Mg
Chlorophyll b
absorbs red and blue light,
reflects green
transfers the absorbed light to
the chlorophyll a
molecular formula is
C55 H70 O6 N 4 Mg
Slide 25
PHOTOSYNTHETIC PIGMENTS
Slide 26
ACCESSORY PHOTOSYNTHETIC
PIGMENTS
Caroten(orange)
Xantophyll (yellow)
Phycoerythrin (red)
Phycocyanin (blue)
They absorb light energy
and transfer it to the
chlorophyll.
Slide 27
REACTIONS OF PHOTOSYNTHESIS
LIGHT
REACTIONS
DARK
REACTIONS
Cyclic
Non-Cyclic
photophosphorylation photophosphorylation
Slide 28
LIGHT REACTIONS
Cyclic photophosphorylation
Various pigments in PSI
collect light, passing the
energy on to P700
An electron with raised
energy levels is
accepted by ferredoxin
and passed onto an
ETS where ATP is
produced as the energy
level falls back to the
starting point.
Slide 29
Electron Excitation
Slide 30
LIGHT REACTIONS
Cyclic photophosphorylation
è
Ferredoxine (Fd)
Plastoquinone (PQ)
ADP + Pi
è
ATP
è
Cytochrome b6
ADP + Pi
Photosystem I
è
ATP
PSI ( Chl a)
è
light
Plastocyanine
Cytochrome f
è
Slide 31
The overall equation for cyclic electron
transport
light
2ADP + 2Pi
2ATP
chlorophyll
Slide 32
Slide 33
LIGHT REACTIONS
Non-Cyclic photophosphorylation
1. When PSII absorbs light, an electron is removed from chlorophyll. This
hole in PSll must be filled.
2. Water is split by photolysis.
3. Electrons from water molecule are passed to PSII and then onto PQ
(plastoquinon).
4. As in cyclic photophosphorylation, ATP is produced via the ETS, with
the electron dropping down to PSI.
5. Light energy also causes the release of an electron from PSI which is
accepted by ferrodoxin.
6. Electrons pass from ferrodoxin to NADP leading to the production of
NADPH2, with hydrogen coming from the separation of water into ions.
7. Electrons lost by PSI are replaced with the electrons coming from the
ETS (PSII).
Slide 34
LIGHT REACTIONS
Non-Cyclic photophosphorylation
2è
Cytochrome f
Ferredoxine (Fd)
2è
ADP + Pi
2è
2NADP+
Plastocyanine
2NADPH + H2
ATP
2è
Cytochrome b6
2è
2è
Plastoquinone (PQ)
2ePSII (Chl a (P680))
è
2e-
PSI ( Chl a(P700))
source
light
H2O
½ O2
light
By product
2H+
photolysis
Slide 35
LIGHT REACTIONS
The products of the two types of light
reactions are ATP, NADPH2 and oxygen.
The first two products enter the dark reactions
of photosynthesis, where they become involved
in the Calvin Cycle and the synthesis of PGAL
and eventually of glucose.
Oxygen is diffused into the air.
Slide 36
Non-Cyclic photophosphorylation
2e-
2NADP+
4
3
2
2NADPH + H2
1
To dark reactions
Slide 37
Non-Cyclic photophosphorylation
Slide 38
Pathway of electron transport
H2O
2e-
PSII
2e-
PSI
2e-
2NADP+
2e- To dark
reactions
The overall equation for non-cyclic electron transport
2H2O + ADP+ Pi + 2NADP+
ATP + 2NADPH2 + O2
Dark
reactions
By
product
Slide 39
Slide 40
COMPARISON OF CYCLIC AND
NON-CYCLIC PHOTOPHOSPHORYLATION
CYCLIC P.
NON-CYCLIC P.
Pathway of è
CYCLIC
NON-CYCLIC
First è donor
PSI
WATER
Last è acceptor
PSI
NADP+
Products
ATP
ATP, NADPH2, O 2
PSI ONLY
PSI and PSII
Numbers of PS
involved
Slide 41
DARK REACTIONS (CALVIN CYCLE)
Dark reactions involve a series of chemical
reactions, first described by Melvin Calvin.
CO2
is
incorporated into more complex
molecules and eventually carbohydrate.
Energy for the reactions is supplied by ATP with
NADPH2 acting as a reducing agent, both coming
from the light reactions.
As long as CO2, ATP and NADPH2 are present
light is not required for the Calvin cycle to
continue. That’s why they are called dark
reactions.
Slide 42
DARK REACTIONS (CALVIN CYCLE)
Every turn of the cycle fixes one molecule of CO2
by producing two molecules of PGA and then two
molecules of PGAL.
Thus six turns produce sufficient quantities of
PGAL for the production of one molecule of
glucose.
During dark reactions, for the incorporation of one
carbon dioxide molecule into the process 3 ATP
and 2 NADPH2 are used.
Therefore, for the synthesis of a hexose (glucose)
18 ATP and 12 NADPH2 are used.
Slide 43
DARK REACTIONS (CALVIN CYCLE)
6CO2
6 RuDP
6 (6C)UNSTABLE MOLECULE
6ADP + 6Pi
6H2 O
12 PGA(3C)
12ATP
6ATP
12ADP + 12Pi
12 DPGA
6 RuMP
With series of
reactions
10 PGAL
12 NADPH2
12H2 O
12NADP+
12 PGAL
2 PGAL
2Pi
GLUCOSE(6C)
Slide 44
Slide 45
Slide 46
Slide 47
FACTORS AFFECTING THE RATE OF
PHOTOSYNTHESIS
PRINCIPLE OF LIMITING FACTOR
(1905 –Blackman)
When a chemical process is affected by
more than one factors, its rate is limited by
the factor which is nearest its minimum
value.
(The rate of a biochemical process is
limited by the factor which is nearest its
minimum value.)
Slide 48
INTERNAL (GENETIC) FACTORS
1. Anatomy of leaves
Surface area
Thickness of cuticle
Number of stomata
Volume of airspace
Thickness of epidermis and mesophyll
Number of chloroplasts in mesophyll
2. Amount of chlorophyll
3. Amount of enzymes
4. Accumulation of end products
Slide 49
EXTERNAL (ENVIRONMENTAL) FACTORS
1.Light intensity
Relative rate of photosynthesis
Foot candles
Slide 50
Slide 51
2. Carbon dioxide concentration
Relative rate of photosynthesis
CO2 concentration(% by volume)
Slide 52
Slide 53
* Light intensity and carbon dioxide
concentration
Relative rate of photosynthesis
High CO2 concentration
Moderate CO2 concentration
Low CO2 concentration
Light intensity
Slide 54
3. Temperature
Relative rate of photosynthesis
°C
25
30
Slide 55
*light intensity and temperature
Relative rate of photosynthesis
High intensity
Low intensity
Intensity
Slide 56
4. Light wavelength
Relative rate of photosynthesis
V
380 nm
B
G Y
O R
750nm
Slide 57
ENGELMANN`S EXPERIMENT
Engelmann exposed
Spirogyra cells to a color
spectrum produced by
passing light through a
prism. He estimated the
rate of photosynthesis
indirectly by observing the
movement of aerobic
bacteria toward the portions
of the algal filament emitting
the most oxygen.
He observed that the bacteria aggregated most densely along
the cells in the blue-violet and red portions of the spectrum.
Slide 58
5. Mineral concentration and amount of water
•
•
•
•
•
•
•
•
•
•
About 1% of water absorbed by roots is used in
photosynthesis
Mg
structure of chlorophyll
Fe
synthesis of chlorophyll, protein
synthesis (Ferredoxin and cytochromes), PQ
N
structure of chlorophyll, proteins, DNA, RNA,
ATP, NAD, NADP
K
synthesis of chlorophyll, growth
P
DNA, RNA, ATP, NADP
Ca
formation of cell membrane, cell wall
S
protein synthesis
Cu
Plastocyanin synthesis
Mn and Cl
catalysts of photolysis
Slide 59
Mineral concentration/ amount of water
Relative rate of photosynthesis
Mineral concentration/ amount of water
Slide 60
6. Oxygen concentration
•
Oxygen is a competitive inhibitor of carbon dioxide fixation
•
RuDP carboxylase acts as oxygenase and causes
breakdown of the RuDP. (Photorespiration-when the oxygen
concentration is high)
•
The output of photosynthesis is decreased by 30-40% and
even as much as 50%.
•
Affects C3 plants (ex: wheat, oat, Soya bean).
•
Some species of plants have evolved alternate modes of
carbon dioxide fixation.
Ex: C4 plants like corn, sugar cane and CAM plants
(Crassulacean Acid Metabolism like desert plants). In C4
plants synthesis of one glucose requires the use of 30 ATP
molecules (not 18 ATP), but there is no loss of RuDP due to
photorespiration.
Slide 61
*Oxygen concentration
Relative rate of photosynthesis
21
oxygen concentration (%by volume)
Slide 62
Slide 63
C3 Photosynthesis : C3 plants
Adaptive Value: more efficient than C4 and CAM plants under cool and moist
conditions and under normal light because requires less machinery (fewer
enzymes and no specialized anatomy).
Most plants are C3.
Slide 64
C4 Photosynthesis : C4 plants
Slide 65
C4 Photosynthesis : C4 plants
Adaptive Value:
Photosynthesizes faster than C3 plants under high
light intensity and high temperatures because the CO2 is
delivered directly to RUBISCO, not allowing it to grab
oxygen and undergo photorespiration.
Has better Water Use Efficiency because PEP
Carboxylase brings in CO2 faster and so does not need
to keep stomata open as much (less water lost by
transpiration) for the same amount of CO2 gain for
photosynthesis.
C4 plants include several thousand species in at
least 19 plant families. Example: fourwing saltbush
pictured here, corn, and many of our summer annual
plants.
Slide 66
C4 Photosynthesis : C4 plants
Slide 67
CAM Photosynthesis : CAM Plants
Slide 68
Slide 69
CAM Photosynthesis : CAM Plants
Adaptive Value:
Better Water Use Efficiency than C3 plants under arid
conditions due to opening stomata at night when
transpiration rates are lower (no sunlight, lower
temperatures, lower wind speeds, etc.).
When conditions are extremely arid, CAM plants can just
leave their stomata closed night and day. Oxygen given off
in photosynthesis is used for respiration and CO2 given off
in respiration is used for photosynthesis.
CAM plants include many succulents such as cactuses
and agaves.
Slide 70
FATE OF PHOTOSYNTHETIC PRODUCTS
PGAL
Vitamins
Hormones
Nucleotides
RuDP
Vitamins Fructose Glucose
PGA
Nucleic
acids
Glycerol +
Lipids
Fatty acids
Pyruvic
acid
Sucrose
Maltose
Starch
Cellulose
Amino
acids
Proteins
Cellular
respiration
Products of photosynthesis; PGAL, PGA and glucose are used in various
metabolic processes
Slide 71
PHOTOSYNTHESIS
AEROBIC
RESPIRATION
Raw materials are CO2 and Raw materials organic food
H2 O
molecules and oxygen
End products are organic End products are CO2 and
food molecules and oxygen H2 O
(results in the increase of (results in the decrease of
biomass)
biomass)
Occurs in the cells that Occurs in most of the
contain chlorophyll
actively metabolizing cells
•Certain cells of plants
(assimilation parenchyma)
•Some of the protists
(algae, euglena)
•Some the bacteria
( cyanobacteria)
Slide 72
PHOTOSYNTHESIS
AEROBIC
RESPIRATION
Takes place in chloroplast of
eukaryotic cells, in the
cytoplasm of prokaryotic
cells
Takes
place
in
the
cytoplasm and mitochondria
of
eukaryotes,
in
the
cytoplasm of prokaryotic
cells
Involves
photophosphorylation
Involves substrate level and
oxidative level
phosphorylation
Location of ETS: Thylakoid Location of ETS: cristae of
membrane of chloroplast
mitochondria
Slide 73
PHOTOSYNTHESIS
AEROBIC
RESPIRATION
Principal electron transfer Principal electron transfer
components: NADP+
components: NAD+ , FAD,
CoQ, Co-A
Source of electron for ETS:
In non-cyclic
photophosphorylation water
(undergoes photolysis to
yield electron, protons and
oxygen)
Terminal electron acceptor
for ETS: In non-cyclic
photophosphorylation:
NADP+ (becomes reduced
to form NADPH2)
Immediate source: NADH2,
FADH2
Ultimate source: glucose or
other fuel molecules
Oxygen (becomes reduced
to form water)
Slide 74
PHOTOSYNTHESIS
Process occurs
presence of light
in
AEROBIC
RESPIRATION
the Takes place all the time
(day and night)
Slide 75
BACTERIAL PHOTOSYNTHESIS
Slide 76
BACTERIAL PHOTOSYNTHESIS
light
CO2 + 2 H 2
(CH2 O )n + H 2O
bacteriochlorophyll
light
CO2 + 2 H 2 S
(CH2 O )n + H 2O+ 2S
bacteriochlorophyll
Slide 77
BACTERIAL PHOTOSYNTHESIS
• H2 or H2S are the source of electron.
• They do not release oxygen as by product
because they do not use water as electron
source.
• Bacteria do not contain chloroplasts.
• The
chlorophyll,
known
as
bacterioclorophyll is present in the
cytoplasm.
• But blue green bacteria (cyanobacteria)
contain chlorophyll a and use water so
they release oxygen.
Slide 78
CHEMOSYNTHESIS
Slide 79
Examples of chemosynthetic organisms
•
•
•
•
•
Nitrifying bacteria (Nitrosomonas,
Nitrobacter)
Sulfur bacteria
Iron bacteria
Hydrogen bacteria
Methane bacteria
Slide 80
CHEMOSYNTHESIS
• Certain bacteria carry out a process in which food is
made from carbon dioxide by using the energy of
inorganic substances.
• Like photosynthetic organisms, chemosynthetic bacteria
fix carbon dioxide through the reactions of the Calvin
Cycle.
• However, the energy to make ATP and NADPH comes
from the oxidation of organic substances, not light.
• They are important for recycling of materials in
ecosystem.
Slide 81
EXPERIMENTS ON PHOTOSYNTHESIS
1. To see if carbon dioxide is necessary for photosynthesis
KOH
NaOH
I
What can you predict
about the result of
this experiment
II
*NaOH and KOH absorb CO2
Slide 82
EXPERIMENTS ON PHOTOSYNTHESIS
2. To see if chlorophyll is necessary for photosynthesis
Predict the starch test
results for the two
areas shown on the leaf
Slide 83
EXPERIMENTS ON PHOTOSYNTHESIS
3. To see if light is necessary for photosynthesis
Slide 84
EXPERIMENTS ON PHOTOSYNTHESIS
4. To prove that organic substances are produced as a result
of photosynthesis
1. Several disks are removed from a
leaf before the sun rises.
2. Mass of the discs are measured
Will there be any difference
between the two measurements?
3. Leaf is left to do photosytnhesis
4. Several new disks are
removed from the same leaf
before the sun set
5. Mass of the discs
taken several hours
later are measured
Slide 85
EXPERIMENTS ON PHOTOSYNTHESIS
5. To show that oxygen is produced during photosynthesis
How can you prove that the gas which is produced is
oxygen?
Slide 86
EXPERIMENTS ON PHOTOSYNTHESIS
6. To find out the source of oxygen that is produced during
photosynthesis
Labeled CO2 (CO218)
Unlabeled O2
Labeled glucose
(C6H12O618)
Unlabeled H2O
Labeled O2
(O218)
Unlabeled CO2
Unlabeled glucose
(C6H12O6)
Labeled water
(H2O18)