Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy-rich organic molecules like glucose. It occurs in the chloroplasts of plant cells and involves two stages - the light-dependent reactions where solar energy is captured to make ATP and NADPH, and the light-independent Calvin cycle where carbon is incorporated into organic compounds using the ATP and NADPH produced. The products of photosynthesis, such as glucose, are used to synthesize other organic molecules and provide energy to drive cellular processes.

2.  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.  Photoautotrophs can photosynthesize.
 Include: Green plants, algae,
cyanobacteria and green protists.
Plants
Green protists
Algae
Cyanobacteria

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

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

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

9.  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.  LIGHT REACTION PHASE
(Dependent on light)
 DARK PHASE/ CALVIN CYCLE
 (Light independent)

11.  Takes place in the thylakoids of the
chloroplasts.
 Chlorophyll absorbs solar energy from the
sun.
 When a chlorophyll pigment absorbs light
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, 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. Fig. 10-5-2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2

14.  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
H2O CO2
Light
NADP+
ADP
+ P
i
Light RuBP
Reactions: 3-Phosphoglycerate
Photosystem II Calvin
Electron transport chain Cycle
Photosystem I
Electron transport chain
ATP G3P
Starch
NADPH (storage)
Chloroplast
O2 Sucrose (export)
.

18.  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

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

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

25. 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