Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of glucose. It involves two stages - the light dependent reactions where sunlight is absorbed and converted to chemical energy. And the light independent reactions where carbon dioxide is fixed into organic compounds like glucose using the energy from the light reactions. Chloroplasts are the organelles where photosynthesis takes place and contain chlorophyll and other pigments that absorb sunlight as well as membranes and proteins that facilitate the light and dark reactions.

2. Photosynthesis is defined as synthesis
of carbohydrates (glucose) from inorganic
materials like CO2, H2O with the help of solar
energy trapped by pigments like chlorophyll.
REACTION
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
P A I R E
Photochemical Anabolic Intracellular Redox
(Reduction)
Endergonic
Light
Chloroplast

3. Ultrastructure of chloroplast
Polymorphic, double membrane,
lipoproteins.
Inner, outer membrane
(peristromium), periplastidil space.
Internally filled with homogenous
proteinaceous matrix -- stroma
Network of lamellae, Grana and
stroma lamellae (IGL, fret channels)
Granum – stack of thyllakoids
Thyllakoids – membrane bound
flattenned sacs, contains
Quantasomes.(aggregation of pigment molecules)
DNA – plastidome hence it is
semiautonomous organelle

4. Thyllakoids enclose fret
channels, they also contain the
energy trapping machinery i.e. a
Chlorophyll A molecule (reaction
entre) surrounded by 230 to 300
other pigment molecules
(accessory pigments).

5. Light is the only source of energy for photosynthesis.
Role of light
It varies qualitatively and quantitatively.
For Photosynthesis Visible spectrum of light is considered because
only visible spectrum is available to the plants.
Light is made up of different wavelengths; each wavelength has a
specific amount of energy, less the wavelength more the energy.
Plants have the unique photosynthetic apparatus (chloroplast) which
traps this light energy and converts it into biologically usable form of
energy (ATP).

6. Plants absorb light primarily using the pigment chlorophyll, which is the
reason that most plants have a green color.
Besides chlorophyll plants also use pigments such as carotenes and
xanthophylls. Algae also use chlorophyll, but various other pigments are
present as phycocyanin, carotenes, and xanthophylls in green algae,
phycoerythrin in red algae (rhodophytes) and fucoxanthol in brown algae
and diatoms resulting in a wide variety of colors.
These pigments are embedded in plants and algae in special antenna-
proteins. In such proteins all the pigments are ordered to work well
together. Such a protein is also called a light-harvesting complex
Role of Pigments
Pigments form the unit which absorbs the radiant sun light. Pigments are of
two types Essential pigments (Chlorophyll A) & Accessory pigments. Chlorophyll
A is termed as essential pigment as it absorbs light as well as forms ATP
whereas accessory pigments only absorb light & transfer it to Chlorophyll A,
they cannot form ATP. The main function of the pigments is to absorb energy,
form ATP & NADPH2.

7. Formerly it was thought that Oxygen liberated during photosynthesis is from
CO2, & the reaction is as follows:
CO2 + 2 H2O → (CH2O)n + O2 H2S  H2 + S
Role of Water
But it was observed that H2S was used instead of water by Green sulphur
bacteria and sulphur deposits were obtained
Thus Van Neil suggested splitting of water.

8. Robert Hill affirmatively proved photolysis of water
He isolated chloroplast and suspended them in CO2 free medium.
He added Haemoglobin and ferric salts as oxygen & hydrogen acceptors
respectively.
He illuminated the sample and found Oxyhaemoglobin and Ferrous salts
proving lysis of water.
He added that there is an unknown Hydrogen acceptor in plants.
Ruben & Kamen confirmed splitting of water by using radioactive Oxygen.
Prof. Arnon found the unknown Hydrogen acceptor to be NADP.
(NADP -- Nicotinamide adenine dinucleotide phosphate)
Photosynthesis splits water to liberate O2 and fixes CO2 into sugar
Role of Water

9. Light Reaction
PrimaryProcess
Photochemical
Phase

10. Cyclic Photophosphorylation
Photons
Sun’s
energy
FRS
Ferredoxin
Cytochrome b6
Cytochrome f
Plastocyanin
PS I
Photoexcitation e-
e-
e-
e-
e-
e-
ATP
ADP
ATP
ADP

11. Non Cyclic Photophosphorylation
Photons
Sun’s
energy
PQRS
Plastoquinone
Cytochrome b6
Cytochrome f
Plastocyanin
PS II
Photo
excitation
4e-
4e-
4e-
4e-
4e-
4e-
ATP
ADP
PS I
FRS
4e-
4e-
Ferredoxin
2NADP
2NADPH2
Photo
excitation
4e-
4H2O
4H+ 4OH-
4e-
2H2O
+ O2
Photons
Sun’s
energy
4e-
4e-

12. Dark Reaction
Biochemical Phase
Secondary Process
Blackman Reaction
Calvin Cycle
C3 Pathway

13. Co2
Dihydroxyacetone
phosphate
Fructose-1,6-diphosphate
Fructose-6-phosphate
Glucose-6-phosphate
Glucose
Rubisco
RuMp
Additive -6c- Compound
Phosphoglyceric acid
Sedoheptulose
Erythrose
Phosphoglyceraldehyde
RuDp
ADP
ATP
NADPH2
NADP
iP
iP
ADP
ATP

14. LIGHT
REACTION
NADPH2 & ATP
NADP & ADP
Light Water
O2 Water
Carbondioxide
Carbohydrates
Dark
REACTION
Interdependance of light & dark reaction

15. Diversities
in Co2
fixation

16. C4 pathway
Mesophyll
Phosphoenol pyruvic acid
CO2
Oxaloacetic acid
Bundlesheath
Pyruvic acid
Pyruvic acid
Malic acid
Co2
PEP
Carboxylase
ADP
ATP
NADPH2
NADP
Sugars
Calvin Cycle

17. Phosphoenol pyruvic
acid
Oxaloacetic
acid
Malic acid
starch
pyruvic acid
Phosphoenol pyruvic
acid starch
Night time
Day time
Co2
PEP
Carboxylase
Glycolysis
Co2
Calvin Cycle
Crassulacean acid metabolism

18. Photorespiration

19. Respiration initiated in chloroplast in presence of
intense light is called photorespiration.
RuDp carboxylase(RUBISCO) has the ability to
combine with Oxygen & Carbondioxide both.
In case of low CO2 concentration & high O2
concentration with intense light, RuDp combines
with O2 forming Phosphoglycolate and PGA
PGA is used in Calvin Cycle but Phosphoglycolate
undergoes dephosphorylation & oxidation to form
Glyoxylate.

20. Glyoxylate forms amino acid Glycine(2 mol) which
enters Mitochondria, forms Serine & CO2
Serine gets converted to Glycerate, enters chloroplast
& forms PGA but one molecule of CO2 is lost in
mitochondria thus reducing the efficiency of
photosynthesis (25%).

21. Chemiosmotic
theory

22. Dr. Peter Mitchell proposed the chemiosmotic theory
(nobel 1978) . Movement of ions across a selectively
permeable membrane down the electrochemical
gradient is called as chemiosmosis.
It relates to the ATP generation by movement of
Hydrogen ions.
Protons accumulate in the lumen and diffuse from
area of higher concentration to an area of lower
concentration developing an electrochemical
gradient.
This is harnessed to make ATP. ATP synthetase makes
ATP by chemiosmosis.
It allows protons to pass and uses kinetic energy for
phosphorylation.

23. Due to photolysis on the inner side of membrane
Hydrogen ions accumulate in the lumen (thyllakoids)
NADP reductase is on the stroma side.
NADP reductase decreases the number of protons by
using them for formation of NADPH2 thereby causing
a concentration gradient.
Protons hence move spontaneously generating
energy which is used for ATP synthesis.

24. If a chemical/biochemical process is affected by more
than one factor, then the rate will be determined by
the factor which is nearest to its minimal value.
Law of limiting factors