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 occurs in the chloroplasts of plant cells, using chlorophyll and takes place in two stages - the light-dependent reaction which converts light energy to chemical energy in the form of ATP and NADPH, and the light-independent Calvin cycle which uses this energy to convert carbon dioxide into sugars like glucose. Photosynthesis is essential for life as it provides food and oxygen and removes carbon dioxide from the atmosphere.

2. WHAT IS PHOTOSYNTHESIS?
 The process that occurs in green plants,
whereby solar energy is converted into chemical
energy and stored as organic molecules by
making use of carbon dioxide, sunlight, and
water. Water and Oxygen are formed as
byproducts
 Photosynthesis can be summarized in the
following equation:
6 CO2 + 12 H2O + Light energy
C6H12O6 + 6 O2 + 6 H2O
(glucose)

3. WHO OR WHAT CAN PHOTOSYNTHESIZE?
Photoautotrophs can photosynthesize.
Include: Green plants, algae, cyanobacteria
and green protists.
Plants
Green protists
Cyanobacteria
Algae

4. WHY DO PLANTS PHOTOSYNTHESIZE?
To provide nutrients and oxygen for
heterotrophs.
Heterotrophs are dependent on
autotrophs, because they cannot produce
there own food.

5. WHAT PART OF THE PLANT IS
RESPONSIBLE FOR
PHOTOSYNTHESIS?
 Photosynthesis occurs in the chloroplasts
of plant cells.
 The chloroplasts are mainly concentrated
in the mesophyll cells of leaves.
 Chloroplast contain chlorophyll – green
pigment that absorbs sunlight.
 Chlorophyll fill the space in the thylakoid
membrane.

6. CHLOROPLAST MESOPHYLL CELL
(PALLISADE AND
SPONGY)

7. 1 µm
Thylakoid
space
Chloroplast
Granum
Intermembrane
space
Inner
membrane
Outer
membrane
Stroma
Thylakoid

8. RAW MATERIALS OF
PHOTOSYNTHESIS
• The raw materials of
photosynthesis are:
 water,
carbon dioxide and
sunlight.

9. HOW RAW MATERIALS
REACH THE CHLOROPLASTS
 Water is absorbed through the root hair into the
xylem of the roots, into the xylem of the stem,
through the xylem of the leaves into the mesophyll
cells and finally into the chloroplasts.
 Carbon dioxide diffuses from the atmosphere
through the stomata, into the intercellular
airspaces in the leaves, and finally into the
chloroplasts of the mesophyll cells.
 The chlorophyll and other pigments in the
thylakoid membrane absorb the solar energy to
drive photosynthesis

10. PHOTOSYNTHESIS CONSIST OF 2
STAGES:
LIGHT REACTION PHASE
(Dependent on light)
DARK PHASE/ CALVIN CYCLE
(Light independent)

11. LIGHT REACTION PHASE
Takes place in the thylakoids of the chloroplasts.
Chlorophyll absorbs solar energy from the sun.
When a chlorophyll pigment absorbs light (photon
of energy), it excites the electrons, which goes
from ground state to an excited state, which is
unstable, but can be used as potential energy.
When unused excited e- fall back to the ground
state, photons and heat are given off.

12.  The electrons are excited in the
photosystems fount in the thylakoid
membrane.
This potential energy is then used firstly to
split water – into hydrogen & oxygen.
2H2O 2H2 + O2
 Oxygen is released as a byproduct –
diffuse through stomata into atmosphere.
The hydrogen reduces NADP+ to NADPH
Some energy is then used to
photophosphorylate ADP to generate ATP.
ADP + P ATP

13. Light
Fig. 10-5-2
H2O
Chloroplast
Light
Reactions
NADP+
P
ADP
i
+
ATP
NADPH
O2

14. CALVIN CYCLE
 Carbon dioxide diffuses through the
stomata of the leave and finally into the
stroma of the chloroplast.
 The carbon dioxide is accepted by a 5C
molecule called ribulose biphosphate
(RuBP) which then forms an unstable 6C
compound.
 6C compound dissociates into 2 x 3C
compounds called phosphoglycerate
(PGA)

15.  PGA is then reduced to phosphoglyceraldehyde
(PGAL/ G3P) by accepting a phosphate from ATP
and a hydrogen electron from NADPH.
Thus changing ATP back to ADP and NADPH to
NADP.
 PGAL are now used for the following reactions:
 Some PGAL are used to make RuBP again,
so that the cycle can start over again.
 Some PGAL are used to form hexose sugars
like glucose and fructose. Which combine to
form disaccharides and polysaccharides.
* The carbohydrates can then be converted to
other biological compounds like proteins or fats
by adding mineral salts like nitrates and
phoshates.

16. CO2 +
RuBP(5C)
6C compound
2x PGA (3C)
PGAL
ATP = ADP + P
NADPH = NADP + H

17. .
Fig. 10-21
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
CO2
NADP+
ADP
Pi
+
RuBP 3-Phosphoglycerate
Calvin
Cycle
G3PATP
NADPH
Starch
(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2

18. THE NATURE OF SUNLIGHT
Light is a form of energy =
ELECTROMAGNETIC ENERGY/
ELECTROMAGNETIC RADIATION
The electromagnetic energy travel in waves.
Distance between crests of electromagnetic
waves = WAVELENGTH
Wavelength range from ≤ 1nm (gamma rays) –
≥ 1 km (radio waves)
The entire range of radiation wavelengths =
ELECTROMAGNETIC SPECTRUM

19. ELECTROMAGNETIC
SPECTRUM

20. UV
Fig. 10-6
Visible light
Infrared
Micro-
waves
Radio
wavesX-raysGamma
rays
103 m
1 m
(109 nm)106 nm103 nm1 nm10–3 nm10–5 nm
380 450 500 550 600 650 700 750 nm
Longer wavelength
Lower energyHigher energy
Shorter wavelength

21. The most important part for life is the visible
light (380nm – 750nm)
We can see this light as various colours.
Light consist of particles = PHOTONS
Photons have energy- The shorter the wave
length the greater the energy of the photon.
Therefore violet light has more energy than red
light.
Photosynthesis are driven by visible light of the
sun.

22. MAIN PIGMENTS USED DURING
PHOTOSYNTHESIS:
 Chlorophyll a – Absorb violet, blue and red
light. Reflects and transmits green light (that
is why plant leaves appear green)
 Chlorophyll b – Absorb violet, blue and red
light. Reflects and transmits green light (that
is why plant leaves appear green).
 Carotenoids – Play an accessory role in
photosynthesis. They are shades of yellow and
orange and able to absorb light in the violet-
blue-green range. These pigments become
noticeable in the fall when chlorophyll breaks
down.

23. HOW A PHOTOSYSTEM
HARVESTS LIGHT
 The thylakoid membrane of a chroloplast
contains several photosystems.
 A photosystem consist of a protein complex
called a reaction-centre complex surrounded by
several light harvesting complexes.
 Study the diagram to understand the process of
light harvesting.

24. THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
STROMA
e–
Pigment
molecules
Photon
Transfer
of energy
Special pair of
chlorophyll a
molecules
Thylakoidmembrane
Photosystem
Primary
electron
acceptor
Reaction-center
complex
Light-harvesting
complexes

25. The Importance of Photosynthesis:
A Review
Energy entering chloroplasts as sunlight gets
stored as chemical energy in organic compounds
Sugar made in the chloroplasts supplies chemical
energy and carbon skeletons to synthesize the
organic molecules of cells.
Plants store excess sugar as starch in structures
such as roots, tubers, seeds, and fruits
In addition to food production, photosynthesis
produces the O2 in our atmosphere