CHRIST SCHOOL
(Affiliated to the Council for the ICSE, New Delhi. Reg. No: KA260/2013)
ChristSchoolRoad,DharmaramCollegeP.O.,Bangalore560029,Karnataka
CLASS – X
PHOTOSYNTHESIS- KEYPOINTS
is a physiological process by which green plants prepare
organic compound – Carbohydrate – using inorganic substances – CO2, H2O
in the presence of chlorophyll and light energy.
PHOTOSYNTHESIS
SIGNIFICANCE:
 Provides food for all organisms.
 Maintain O2 level.
CONDITIONS REQUIRED:
 Light energy
 Chlorophyll pigments
RAW MATERIALS REQUIRED:
 CO2
 H2O
LIGHT ENERGY
 Sun is the main source.
 Red and blue lights are more absorbed and most effective for photosynthesis.
CHLOROPHYLL PIGMENTS
 The vital plant pigment.
 Located in the chloroplasts of plant cells.
STRUCTURE OF A LEAF
STRUCTURE OF CHLOROPLAST
 Oval shaped cell organelle
 Bounded by double membrane
 Colourless ,living ground substance (Fluid) enclosed by the double membrane –
STROMA/MATRIX

Flattened membranous sac like structure in the stroma - THYLAKOID

Pile of thylakoid – GRANUM(s)/GRANA(p)

Interconnection between thylakoids of grana – STROMA LAMELLA/ INTERGRANAL
THYLAKOID / FRET
 Chlorophyll pigments are present in the walls of thylakoid.
 Chlorophyll pigments are composed of Carbon, Hydrogen, Oxygen, Nitrogen and
Magnesium.
 Chlorophyll are of 9 types.
 Two most abundant Chlorophyll molecules are Chlorophyll a and Chlorophyll b.
 Light is essential for the formation of new chlorophyll molecule.In the absence of
light, new chlorophyll does not form, old chlorophyll get disintegrated. Hence the
leaves turn yellow.
 Too much light destroys chlorophyll pigment.
 The main element which is required for the formation of chlorophyll pigment is
magnesium.
 The accessory pigments which help in the transference of light energy to
chlorophyll a are xanthophyll and carotene.
CO2
 CO2 from the atmosphere, through stomata, by diffusion.
H2O
 H2O from soil by imbibition and osmosis.

MECHANISM OF PHOTOSYNTHESIS
 Site of photosynthesis – Chloroplast of Mesophyll cells in Plant cells.
 TWO PHASES
Light dependent phase (Photochemical phase/Hill reaction)
Light independent phase (Biosynthetic phase/ Calvin cycle)
 LIGHT DEPENDENT PHASE (PHOTOCHEMICAL PHASE/HILL REACTION)
Site – Grana of the Chloroplast (Thylakoid)
Take place only in the presence of light.
Mainly occurs in two phases
 Activation of chlorophyll
 Splitting of water
 ACTIVATION OF CHLOROPHYLL – PROCESS INVOLVED:
Activation of chlorophyll molecules by absorbing light energy as
photons(Smallest unit of light energy)
The low energy molecules move to a high energy state and emit electron
transport chain in chloroplast.
The emitted energy is used to split water molecules H2 and O2 PHOTOLYSIS
Light Energy
H2O
OH-
H+ + OH-
 OH * 4
2H2O
+
O2
OH- oxidized to O2 and H2O
O2 released during photosynthesis comes from H2O, not from CO2 .
H+ produced by the splitting of H2O molecule is used to reduce NADP –
Nicotinamide Adenine Dinucleotide Phosphate ( A low energy compound
present in the cell)
NADP + 2H+ + e-

NADPH (Reduced Nicotinamide Adenine
Dinucleotide Phosphate )
NADPH is the reducing power used in light independent phase.
The electron converts low energy compound ADP into high energy compound
ATP by adding one inorganic phosphate group PHOTOPHOSPHORYLATION
Light Energy
ADP + iP
ATP
PHOTOPHOSPHORYLATION is the production of high energy compound ATP
from low energy compound ADP using inorganic phosphate and light
energy.
End products of Light dependent phase of photosynthesis – NADPH, ATP,
O2
NADPH – Reducing agent of Light independent phase
ATP – Energy source for Light independent phase
O2 – Utilized the cells for oxidation of glucose and released into the
atmosphere as a by product
 LIGHT INDEPENDENT PHASE (BIOSYNTHETIC PHASE/ CALVIN CYCLE)
Site – Stroma of the Chloroplast
Take place without using light energy.
Major event:
 CO2 is reduced to Glucose by H+ of
NADPH using
energy from ATP(Fixation of CO2 – Glucose)
 Enzyme catalysed reaction.
 CO2 enters into a cycle of reaction with the help of a CO2 acceptor –
RuBP (Ribulose biphosphate)
 NADPH - NADP
 ATP - ADP
 RuBP - Regenerated after reaction.
 End products of Light independent phase of photosynthesis GLUCOSE
 End products of photosynthesis
 Glucose, Oxygen and Water
 Fate of the products of photosynthesis
 Glucose – Readily soluble in water
 Utilized the cells for its oxidation to release energy.
 Converted to starch for storage.(Conversion of several molecules of
glucose into one molecule of starch – POLYMERISATION)
 Convert to sucrose for translocation.
 Used to synthesize cellulose, fats and proteins.
 ADAPTATIONS IN LEAF FOR PHOTOSYNTHESIS
Large surface area – maximum absorption of light
Arrangement of leaves – At right angle to the source of light to obtain
maximum light.
Cuticle and upper epidermis – Transparent and water proof to allow light to
enter freely.
Numerous stomata – Rapid exchange of gases
Thin leaves – Reduce distance between cells to facilitate rapid transport gases
Chloroplast more on upper layer – To obtain light energy quickly
Extensive vein system – rapid transport of water, minerals and food
Loosely arranged spongy mesophyll – sufficient space for the exchange of
gases
 FACTORS AFFECTING PHOTOSYNTHESIS
Light intensity
CO2 concentration
EXTERNAL
Temperature
Water content
Chlorophyll
Protoplasm
INTERNAL
Structure of leaf
 CARBON CYCLE – Leads to the formation of fossil fuels
 CARBON CYCLE involves a series of chemical reactions in which Carbon in
CO2, from the atmosphere used by living organisms and finally returned to the air.
