Photosynthesis
►A
naturally occurring biological
process
►Very complex
►It is an endogenic, anabolic
reaction resulting in the production
of glucose and oxygen.
►Carried out by green plants, bluealgae and certain bacteria.
•Organisms (autotrophs) are able to
harness the energy contained in
sunlight through a series of
reactions.
•Resulting in the production of
oxygen and sugar and other
compounds.
Overall equation for
photosynthesis
►6
CO2 + 6 H2O
C6H12O6 + 6O2
sunlight
(radiant energy)
Reactants
Products
Leaf Structure
►Chloroplasts
are concentrated in
the mesophyll of the leaf
►Tiny pores in the lower epidermis
(stomata) allows for CO2 to enter
and O2 to exit.
►Veins carry water and nutrient
from the plants roots to the leaves
Chloroplast
►Organelle
where
photosynthesis takes place
►Contain chemical compounds
called:
Chlorophyll
Chloroplast Structure
►Has
inner and outer membranes
►Inner membrane encloses a thick
fluid called STROMA
►Floating in the stroma are diskshaped sacs called
Thylakoids.(arranged in stacks
called GRANA)
Thylakoids
►The
thylakoid is the structural
unit of photosynthesis. Both
photosynthetic prokaryotes and
eukaryotes have these flattened
sacs/vesicles containing
chlorophyll
The Light Reaction
►Take
place in the thylakoid
membranes, convert light energy
to the chemical energy of ATP and
NADPH.
►The light reactions use the
reactant water from the equation
and release the product oxygen.
Calvin Cycle
►Like
a sugar factory within a
chloroplast.
►It is called a cycle because the
starting material is regenerated
each time the process occurs.
►The starting material that gets
regenerated is a compound called
RuBP, a sugar with five carbons
The Calvin cycle
►Takes
place in the stroma
►Uses ATP and NADPH to convert
carbon dioxide to sugar
Inputs and Outputs
(Reactant and Products)
►With
each turn of the Calvin cycle,
there are chemical inputs and
outputs.
►The inputs are carbon dioxide from
the air and the ATP and NADPH
produced by the light reactions.
Calvin Cycle Inputs
►The
Calvin cycle uses carbon from
the carbon dioxide, energy from
the ATP, and high-energy electrons
and hydrogen ions from the
NADPH.
Calvin Cycle Outputs
►Is
an energy-rich sugar molecule.
That sugar is not yet glucose, but a
smaller sugar named G3P.
►The plant cell uses G3P as the raw
material to make glucose and other
organic molecules it needs.
Summary of Photosynthesis
► Recall
that the overall equation for
photosynthesis is:
►6
CO2 + 6 H2O
C6H12O6 + 6 O2
Flow of Energy
►By
converting light energy to
chemical energy, photosynthesis is
the first step in the flow of energy
through an ecosystem.
Some of that chemical energy then
passes from producers to consumers.
Even when people eat meat, you can
trace its stored energy back to
photosynthesis.
Photosynthesis is the ultimate source of
all the food you eat and all the oxygen
you breathe.
►The
nature of light
►The energy produced by the sun
reaches the earth as electromagnetic
radiation.
►Light and other forms of
electromagnetic radiation are
considered to have both a wave
nature and a particle nature.
►Particles
or packets of light (its
particle nature) are known as
photons - the smallest divisible
units of light.
 The distance moved by a photon
during one of it vibrations is
referred to as its wavelength and
is measured in nanometers (nm).
►A
Visible light
very small part of this spectrum can
be seen by the human eye i.e.
between the wavelengths 400 and
700 nm.
► This part of the electromagnetic
spectrum is called visible light.
 Almost all life depends ultimately
on this part of the spectrum for its
energy.
Why plants only use visible
light as a source of energy for
photosynthesis
►Visible
light
 Each photon of visible light
contains just enough energy to
excite the electrons of
molecules without causing
damage to the cell.
Light and photosynthesis
► Chlorophyll
absorbs blue-violet and red-
orange
Reflects green back
► Chlorophyll a, the most important lightabsorbing pigment in plants, does not
absorb light in the green part of the
spectrum. Light in this range of
wavelengths is reflected.
Light and photosynthesis
► Plants
do not depend only on chlorophyll a
but also have other pigments (accessory
pigments) which absorb light of different
wavelengths.