Photosynthesis
Making energy from the sun.
Photosynthesis
• Photosynthesis has two primary roles on
Earth:
– The first role is to capture the energy of sunlight
and convert it in to sugar.
– The second is to capture Carbon from the
atmosphere and convert it in to forms of Carbon
that other organisms can use.
A little physics:
• Photosynthesis uses light from the sun.
• Light is a form of energy, and energy comes in
different levels.
• The “white” light that we get from the sun is a
mixture of different energy wavelengths.
• Each wavelength corresponds to a different
color.
A little physics…continued.
A little more physics
• When we talk
about “color”
what we are
really talking
about is what
wavelengths are
absorbed as well
as which
wavelengths are
reflected back.
Plants
• So plants appear
green in general
because
______________
light is reflected
and ____________
light is absorbed.
Where does the energy go?
Where does the energy go?
• The primary
structures that
absorb the energy
are chloroplasts.
– Chloroplasts reflect
green light and
absorb red and blueviolet light.
– They use the energy
in these
wavelengths to
power the reaction
of photosynthesis.
The Reaction of Photosynthesis:
• Think for a minute about what plants need to
survive.
• What are some things that plants need?
The Reaction of Photosynthesis
• Plants need:
– Water
– Carbon Dioxide
– Sunlight
The Reaction of Photosynthesis
• Plants make
– Sugar
• Plants give off
– Oxygen
The Reaction of Photosynthesis
• In words,
• Plants use Carbon Dioxide and Water in the
presence of sunlight to produce sugar and
oxygen.
• http://www.youtube.com/watch?v=mYbMPw
mwx88
In Chemical Symbols:
Photosynthesis: Process
• Step 1.
– Light from the sun hits the leaf, which contains the
chloroplast.
Photosynthesis: The Process
• Step 2:
• Inside the
chloroplast, there
are stacks of
thylakoids called
grana. Each of
the thylakoids has
three types of
pigment:
Chlorophyll a and
b, and
carotenoids.
Photosynthesis: The Process
• Step 3: The Chlorophylls absorb light in the
red and blue-violet spectrum. The
carotenoids absorb light in the green
spectrum. They use this energy to give
electrons to electron carriers, chemicals that
will move the electrons outside of the
thylakoids. These steps together are called
“light dependent reactions” because they
must have light to take place.
Photosynthesis: The Process
• Step 4: Electron carrying molecules move out
of the thylakoids and in to the surrounding
space called the stroma.
• Here, they give the electrons to the Calvin
Cycle which uses carbon dioxide to make
sugar and release oxygen.
• These steps are called “light-independent
reactions” because they do not need light to
occur.
Photosynthesis: The Process
Factors that can affect Photosynthesis:
• Temperature
– Temperature can speed up or slow down chemical
reactions. Cool temperatures slow down
photosynthesis, as do very high temperatures.
• Light
– Light is critical to providing the energy for
photosynthesis to happen. Not enough light, not
enough energy.
• Water
– Another key ingredient in photosynthesis. Without
enough water, the reaction cannot occur.
Photosynthesis:
• http://vimeo.com/1616728
The Leaf in Cross Section: