4. The process where by light energy is
converted to chemical energy that is store
in glucose or other organic compounds.
In the presence of light, green plant
produce organic compound and oxygen
from carbon dioxide and water.
5. The overall equation for photosynthesis is:
Twelve molecules of water plus six
molecules of carbon dioxide produce one
molecule of sugar plus six molecules of
oxygen and six molecules of water.
6CO2 + 12H2O + 18ATP +
12NADPH
C6H12O6 + 18ADP + 12NADP+ +
18Pi
6.
7. Chlorophyll a
The most importance and abundance
pigments
Absorbs light mainly in the blue-violet and
red wavelength
Blue green colour
Has a methyl (-CH3) side group in
porphyrin ring
Function to initiate light dependent
reaction
8. Chlorophyll b
Yellowish green in colour
Absorbs blue and red wavelength
Has an aldehyde (-CHO) side group in
porphyrin ring
Pass the light energy to chlorophyll a in
the reaction center.
Helps to increase the range of light a
plant can utilize for photosynthesis.
Found in green plants and green algae
9. Carotenoids
Absorbs light maximally in the blue violet
region
Red, orange or yellow pigments
Functions as accessory or antenna
pigments
Assists by capturing energy from light of
wavelength that are not absorb by
chlorophyl a and b
Protects the chloropyll from oxidation
(photoprotection)
10. Photosystem
Network of chlorophyll a, b, accessory
pigments and associated protein
embedded in the thylakoid membrane
Functions to channel the excitation
energy gathered by any one of its
pigments molecule to the reaction centre
Passes the energy out of the
photosystem for ATP synthesis
Consists of :
Antenna complex
11.
12. Antenna complex
Pigments molecule that gathers photon
and channel it to the reaction centre
Reaction centre
Consists of chlorophyll a
Pass excited electron to the primary
electron acceptor
13.
14. Two types of photosystem:
Photosystem I (PSI) / P700
It is called P700 because reaction
centre chlorophyll a of a photosystem I
absorbs wavelength of 700 nm
15.
16. Two types of photosystem:
Photosystem II (PSII) / P680
It is called P680 because reaction
centre chloropyll a of a photosystem II
absorbs wavelength of 680 nm
17.
18. Photosynthesis occurs in two main stages:
the first stage being towards light
dependent reaction
the second stage being the light
independent reaction (Calvin Benson
Cycle)
In short the light reactions capture the light
energy and utilize it to make high-energy
molecule (ATP)
ATP are used by the Calvin-Benson Cycle
to capture carbon dioxide and make the
19. The light reaction convert solar energy to
chemical energy.
In the light reaction, light energy absorbed
by chlorophyll in the thylakoid drives the
transfer of electrons and hydrogen from
water to NADP+ (nicotinemide adenine
dinucleotide phosphate), forming NADPH.
The light reaction also generate ATP by
photophosphorylation for the Calvin Cycle.
20. Photophosphorylation
Photophosphorylation is the process of
creating ATP using a proton gradient
created by the energy gathered from
sunlight.
The process of creating the proton gradient
resembles that of the electron transport
chain of cellular respiration.
But since formation of this proton gradient
is light-dependent, the process is called
photophosphorylation.
Two types of photophosporylation:
21. Non-cyclic photophosphorylation
Light energy is absorbed by accessory
(antenna) pigments of PS II / P680
Then transferred to reaction centre
(chlorophyll a)
Electron is photoactivated / excited and
released
This creates an electron deficiency
P680 oxidized to P680+
Photolysis of water molecule to form 2
electrons, 2H+ and 1 oxygen atom
22. There are 2H+ released into the thylakoid
lumen
The oxygen atom immediately combined
with an oxygen atom generated by the
splitting of another water molecule
forming oxygen molecule (O2)
Electron from photolysis of water replace
the electrons released from PS II
The P680 /PS II molecule returns to its
reduced / stabilized state
23. The electrons released from PS II are
accepted by primary electron acceptor/
pheophytin
And pass along the ETC; consists of
plastoquinone/ Pq, cyctochrome
complex, plastocyanin/ Pc and then
toP700/ PS I
24. As the electron passed through the
cytochrome complex, energy is released
through redox reaction.
The energy is used to pump H+ from the
stroma (low concentration of H+ ) into the
thylakoid lumen (high concentration of H+ )
Creating a proton gradient between the
stroma and thylakoid lumen that is used in
chemiosmosis
25. At the same time, high energy electrons
in P700 / PS I are ejected and accepted by
primary electron acceptor
This creates an electron deficiency
P700 oxidized to P700+
PSI functions as electron acceptor,
accepting electron from PSII
26. The excited electron pass along
ferredoxin/ Fd
NADP+ reductase transfers the electron
to NADP+
NADP+ receives proton from photolysis of
water to form NADPH (which is released
into the stroma)
The process also produces oxygen,
water and ATP
ATP and NADPH produced will be used
in the Calvin cycle
27.
28.
29. chemiosmosis
Production of ATP is by chemiosmosis
High concentration of H+ in the thylakoid
space
Low concentration of H+ in the stroma
H+ diffuse from the thylakoid space back
into the stroma through ATP synthase
The energy release is used to
phosphorylate ADP to form ATP (in the
stroma)
ATP and NADPH produced by non-cyclic
photophosphorylation will be used in the
30. Cyclic photophosphorylation
Involves PSI only
No production of NADPH, no release of
oxygen
Produces ATP
Occurs less commonly in plants than
noncyclic photophosphorylation, most
likely occurring when there is too little
NADP+ available.
31.
32. Light energy is absorbed by accessory
(antenna) pigments of PS I / P700
Then transferred to reaction centre
(chlorophyll a)
Electron is photoactivated / excited and
released
Accepted by primary electron acceptor
The electron pass to ferredoxin (Fd),
cytochrome complex, plastocyanin (Pc)
and back to chlorophyll a at the reaction
centre PS I / P
33.
34. 17.3 LIGHT INDEPENDENT
REACTION/CALVIN CYCLE
A series of reaction lead to the production
of NADP+ and ADP and sugar.
Occur in stroma of the chloroplast.
Input are NADPH, ATP and CO2.
First step in carbon fixation which is
catalyzed by an enzyme name RuBP
carboxylase
35. Carbohydrate produced directly from the
Calvin cycle is actually not glucose but a
three carbon sugar named glyceraldehyde-
3-phosphate (G3P).
The Calvin cycle involves three phases :
Carbon fixation
Reduction of PGAL/G3P
Regeneration of the CO2 acceptor
Ribulose bisphosphate (RuBP)
36.
37.
38. I) CARBON FIXATION
The Calvin cycle incorporates each CO2
molecule one at the time by attaching it to
a five carbon sugar named ribulose
biphosphate (RuBP).
The enzyme that catalyze this first step is
RuBP carboxylase
The product of the reaction is a six-carbon
intermediately split in half forming two
molecules of 3-phosphoglycerate (for each
39. II) REDUCTION
Each molecules of 3-phosphoglycerate
receives an additional phosphate from ATP
becoming 1,3-biphosphoglycerate
A pair of electron donated from NADPH
reduces 1,3-biphosphoglycerate to G3P ,
which store more potential energy.
G3P is a sugar ,the same three carbon
sugar formed by splitting of glucose
(glycolysis)
40. Every 3 molecules of CO2 that enter the
cycle, there are six molecules of G3P
formed.
But only one molecule of G3P will exit the
cycle become the starting material for
metabolic pathway that synthesize other
organic compound (lipid , amino acid)
including glucose and other carbohydrate.
41. III) REGENERATION OF THE CARBON
DIOXIDE ACCEPTOR (RuBP)
In the complex series of reaction, the
carbon skeletons of five molecules of G3P
are rearranged by the last step of the
Calvin cycle into three molecules of RuBP.
To accomplish this, the cycle spend three
more molecules of ATP.
The RuBP is now prepared to receive CO2
again and the cycle continues.
For the net synthesis of one G3P
molecule, the Calvin cycle requires a total
of nine molecules of ATP, and six molecule
42. Plants which use only the Calvin cycle for
fixing the carbon dioxide from the air are
known as C3 plants.
About 85% of plant species are C3 plants.
They include the cereal grains: wheat, rice,
barley, oats. Peanuts, cotton, sugar beets,
tobacco, spinach, soybeans, and most
trees are C3 plants.
C3 plants have the disadvantage that in
17.5 Alternative Mechanism Of Carbon Fixation:
Hatch-Slack(C4) And Crassulacean Acid
Metabolism (CAM) Pathways
43. PHOTORESPIRATION
Photorespiration occurs when the CO2
levels inside a leaf become low.
This happens on hot dry days when a plant
is forced to close its stomata to prevent
excess water loss.
If the plant continues to attempt to fix CO2
when its stomata are closed, the CO2 will
get used up and the O2 ratio in the leaf will
increase relative to CO concentrations.
46. When the CO2 levels inside the leaf drop to
around 50 ppm(part per million), RuBP
carboxylase starts to combine O2 with
RuBP instead of CO2.
Photorespiration uses the ATP and NADPH
produced in the light reaction.
The process result in the loss of fixed
carbon dioxide from the plant, reducing
photosynthetic efficiency and plant growth.
47. Hatch-Slack(C4) pathway
C4 plant such as sugarcane ,maize and
other tropical grasses have evolved a
special metabolic adaptation which reduce
photorespiration.
The metabolic adaptation to reduce
photorespiration is Hatch-Slack pathway.
49. C4 plants have Krantz anatomy //
mesophyll cells are arranged concentrically
around the bundle sheath cells
Plants conduct C4 pathway in the
mesophyll cell and Calvin cycle in the
bundle sheath cells
Use PEP carboxylase to fix CO2 in the
mesophyll cells
With phosphoenolpyruvate (PEP) forming
oxaloacetate (OAA)
PEP carboxylase has very a high affinity
50.
51. OAA will be converted to malate
Transported to bundle sheath cells
Malate converted to pyruvate
Releasing CO2 for normal CO2 fixation
using Calvin cycle
Ensure RuBP carboxylase will be exposed
to high CO2 level (reduce photorespiration)
Pyruvate transported back to mesophyll
cell
Converted to PEP (using energy from ATP)
52. Crassulacean Acid Metabolism (CAM)
Pathway
A second strategy to minimize
photorespiration is found in succulent
plants, cacti, pineapples and several other
plant families.
Open stomata during the night and close
them during the day.
53. During the night, stomata are open.
CO2 enters the leaf tissue.
CO2 combine with PEP to form
oxaloacetate.
Oxaloacetate converted into malate.
Malate is transported into the vacuole for
storage.
During the day, stomata are close.
Malate is moved into the chloroplasts.
Malate converted into pyruvate and
