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 two phases - the light-dependent reactions where sunlight is captured and its energy is used to produce ATP and NADPH, and the light-independent reactions where carbon dioxide is incorporated into organic compounds to produce carbohydrates like glucose. It is a critical process that supports life on Earth by producing food and oxygen and removing carbon dioxide from the atmosphere.

1. PHOTOSYNTHESIS
The Most Important Chemical Process on Earth

2. “light” “to make or
compose”

3. • food-making process in plants
• process by which green plants convert
light energy into chemical energy
• complex chemical reaction or process by
which plants put together carbohydrates
• also called photophosphorylation and
carbon fixation

4. Nature of Light

5. The Leaf

8. Process Location Reactants Products
Light Dependent
Reactions
(Photosystems)
Thylakoid
membranes
• sunlight
• H2O
• ATP
• NADPH
• O2
Light Independent
Reactions
(Calvin Cycle)
Stroma • ATP
• NADPH
• CO2
sugar

9. Aristotle Jan Baptista van Helmont Stephen Hales Joseph Priestly
Jan IngenhouszJean SenebierNicolas de SaussureRuben and Kamen

10. • since plants grew from the
soil, it seemed evident to
Aristotle that their substance
must come from the soil
• regarded the soil as
equivalent to a vast stomach
that prepares and supplies the
food of plants

11. • considered water to be the
source of life and the basic
nutrient for plants
• demonstrated that soil
contributes very little to the
increase in weight of plants
and it must be water

13. • recognized the importance
of light and air in plant
nourishment
• described the leaves as
organs of transpiration and
he postulated that plants
exchange gases with their
surrounding air

14. • unknowingly
discovered
oxygen and
demonstrated
that plants
produce the
gas
• was the first
to prove the
different
qualities of the
gases released
by plants and
the ones
exhaled by
animals

16. • demonstrated the
importance of light in the
production of oxygen by
green plants
• systematically investigated
the release of air from green
parts of plants during day
time especially from the
lower side of leaves

17. Device used by Ingenhousz to
investigate photosynthesis

18. • showed the importance of
a “fixed air” (carbon dioxide)
in the process
• showed that plants absorb
carbon dioxide and release
oxygen (dephlogisticated air)

19. • showed the importance of
water for the production of
organic materials by the
plants
• verified Ingenhousz´s
hypothesis that plants
assimilate carbon dioxide
from the air while nitrogen
and other nutrients are
derived from the soil

20. • revised the basic equation into 2 types of
reactions as:
Light reaction:
2H2O + light → 4H + O2
Dark reaction:
4H + CO2 → CH2O + H2O

21. During 1900s – extensive studies on
photosynthesis arise and equation of photosynthesis
had been formulated as:
6CO2 + 6H2O C6H12O6 + 6O2
light
chlorophyll
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
light
chlorophyll
Revised (by Ruben and Kamen):

22. The Nature of Light
Light – considered to have both particle and wave nature
Photons
 particles or packets of light
 smallest divisible units of light
 move in wave-like behavior
 carry a fixed amount of energy
Wave
 characterized by
 wavelength
 frequency
c = 299,792,458 m/s
or 3 x 108 m/s

23.  distance between two light waves
 distance moved by a photon during one of its vibrations
 distance from peak to peak (or trough to trough)

24.  the shorter the wavelength, the more energy each
photon contains
 arranged from shorter to longer wavelengths
known as electromagnetic spectrum
 measured in nanometers (nm)

25.  sunlight is composed of different
colors (ROYGBIV)
 leaves absorb all colors except green
 pigments in leaves absorb those
wavelengths within the visible light
portion with a wavelength of 400-700
nm
 theoretically, photosynthesis requires
approximately 12 photons to convert
one mole of CO2 to carbohydrates

27. 52%44%
4%
Composition of Sunlight
Infrared Visible Light Ultraviolet
Back to Overview

28.  main photosynthetic organ of
the plant
 usually broad, flat and thin to
ensure the exposure of all cells
to light
 usually green in color

29. Carbon dioxide enters, while
oxygen exits through a leaf’s
stomata
 contains large number of
stomata

30.  contains numerous
chloroplasts containing the
green pigment chlorophyll

32. Back to Overview

33. Power plants: Researchers explore how to harvest
electricity directly from plants
•Ramaraja
Ramasamy
(right) and
•Yogeswaran
Umansakar
developed a
way to interrupt
photosynthesis
modified
thylakoids