Photosynthesis
6H2O + 6CO2 ---------->
C6H12O6+ 6O2
"putting together with light."
What is photosynthesis?
Photosynthesis is arguably the most
important biological process on earth. By
liberating oxygen and consuming carbon
dioxide, it has transformed the world into
the hospitable environment we know
today.
Importance of Photosynthesis
• If we can understand and control the
intricacies of the photosynthetic process, we
can learn how to increase crop yields of food,
fiber, wood, and fuel, and how to better use our
lands. The energy-harvesting secrets of plants
can be adapted to man-made systems which
provide new, efficient ways to collect and use
solar energy.
Photosynthesis takes
place in three stages:
1. Energy is captured
from sunlight
2. Light energy is
converted to chemical
energy(ATP/NADPH)
3. ATP and NADPH
power the formation of
glucose using carbon
from CO2
Molecules in Photosynthesis
Chlorophyll a
Chlorophyll b
Green pigments that absorb
light energy
Carbon Dioxide - CO2, source of carbon
for sugar formation
Water - H2O, source of hydrogen for sugar
formation and important for moving energy
during photosynthesis
Oxygen - O2, by-product of photosynthesis
Molecules in Photosynthesis, continued
ATP(A DP+P) - Energy carrying
molecule
NADPH(NADP+H) - Energy carrying molecule
Electron Acceptors - proteins that move
electrons during photosynthesis
Proton Pump - protein that moves protons
(H+) during photosynthesis
Molecules in Photosynthesis, continued
Enzymes (e.g. ATP synthetase) - proteins
that speed up the chemical reactions
RBP - 5 carbon molecule used to build glucose
PGAL - 3 carbon molecule used to build
glucose
Glucose - C6H12O6, Food product of
photosynthesis
Photosynthesis takes place in the chloroplast
Inside the Cholorplast
Thylakoid - membrane “sac” holds the
chlorophyll molecules
*photosynthesis takes place here
Grana - column of thylakoids
Stroma - liquid that fills the chloroplast
Energy is captured from sunlight
Light is a form of radiant energy - emitted in
waves that can travel through a vacuum
The complete range of radiant energy is called
the electromagnetic spectrum
Electromagnetic spectrum
Units: nm = nanometer (10-9 m or one-millionth of
a millimeter)
Km = kilometer (103 m or one-thousand meters)
Radiant Energy travels in tiny “packets”
called photons
Back it up
Chlorophyll Absorbs Photons
There are 2 types of chlorophyll molecules in the
thylakoid membrane
Chlorophyll a
Chlorophyll b
They both produce a green colorbut absorb slightly different wavelengths of
light energy
Processing :Based on
Absorption Spectra
What colors of light are best absorbed by the
chlorophyll molecules?
Chlorophyll a - Indigo and Orange
Chlorophyll b - Indigo/Blue and Orange/Red
What colors of light are least absorbed by the
chlorophyll molecules?
Green and Yellow
Back it up
How does this data
support the fact that
the chlorophyll
molecules give plants
their green color?
Because green and yellow are NOT
absorbed, they are reflected to your eye
giving chlorophyll the green color.
Photosystems-are clusters of Chlorophyll
molecules in the thylakoid membrane.
There are two clusters called:
photosystem I and photosystem II
These Photosystems start the process of
photosynthesis by absorbing photon energy
•This energy is captured by electrons in the
cholorphyll molecules.
Light Energy is Converted into Chemical Energy
This stage of photosynthesis is also called the
“Light Reaction”because light energy is
required.
1. Photons reach the chlorophyll molecules
in the photosystems found on the thylakoid
membrane and are absorbed by these
molecules.
2. Electrons in the chlorophyll become
“energized” from these photons and are
passed from Photosystem II to Photosystem I.
3. In the process of “passing” electrons
-energy is stored in ATP and NADPH
molecules
-H2O molecules are split into:
O2 - released as a by-product into
the atmosphere
H+ - used to form NADPH
Chemical Energy is Stored in Glucose
The other stage of photosynthesis is also called
the “Dark Reaction” or the Calvin Cycle
-no light
energy is
required
-occurs in the
stroma of a
chloroplast
Molecules Important to the Calvin Cycle
ATP - releases energy to keep cycle going
NADPH - releases energy to keep cycle going
-provides the hydrogen for the glucose
molecule
RuBP -5 carbon molecule used over and over
in the cycle to form glucose
PGAL - 3 carbon molecule used over and over
in cycle to form glucose
CO2 - carbon source for cycle
What affects the rate of
photosynthesis?
Light intensity - as light intensity increases the
initial rate will increase and eventually level off as all of
the electrons in the photosystems are “excited.”
Carbon dioxide - increasing levels of CO2
will increases the rate initially. So, talking to
your plants is a good thing.
:)
Temperature - increasing temperature increases all
chemical reactions, including those in photosynthesis.