Download Photosynthesis

12/22/2009
Photosynthesis
Visible light is a small band within a
very broad electromagnetic spectrum.
Chloroplasts capture sunlight energy
for photosynthesis.
In the 1600s, a Flemish scientist named
Jan Van Helmont (1580–1644)
conducted an experiment to find out.
• He grew a willow tree in a carefully
weighed amount of soil.
• He
H noticed
i d that
h the
h mass off the
h soil
il b
barely
l
changed while the mass of the tree
greatly increased.
• He concluded that the extra mass came
from water, not from the soil.
The Sun provides Earth with a steady
source of light.
How does a tiny
seed grow into a
massive tree?
Where did all of that
mass come from?
• Later experiments carried out by other
scientists showed that plants use carbon
dioxide (from the air) and water to make a
simple carbohydrate (glucose) and oxygen.
• So the tree’s mass comes from air and
water!
t !
• This chemical reaction (photosynthesis)
takes place only in the presence of light.
Visible light is part of a collection of waves
known as the electromagnetic spectrum.
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12/22/2009
Light is a wave, like a ripple on a pond.
Waves can be described by their
wavelength (the length from peak to peak),
and their energy.
Light waves have very short wavelengths.
• They range from 800 nm (red light) to 400
nm (violet light).
– One nanometer (nm) is equal to onebillionth of a meter!
How is a plant cell similar to solar cells
found in calculators?
• A solar calculator has
solar cells that convert
li h energy into
light
i
electrical energy.
• The electrical energy
powers the calculator.
Your eyes see sunlight as white light,
but it is really made up of different
colors of light.
• A clear prism can split
white light into a
rainbow of color
Color is how we experience the energy
of light.
• All of the colors of
visible light
have different
energies.
• Red light has the lowest energy and violet
light has the highest energy.
• As we move through the rainbow from red
to violet, the energy of the light increases.
A plant cell has chloroplasts that work
much like solar cells found in calculators.
• Chloroplasts also
convert energy in a
process called
photosynthesis.
• Plant cells then store
this energy from the
sun in the form of
molecules.
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12/22/2009
Photosynthesis is a chemical reaction
that takes place in the chloroplasts of
plant cells.
Photosynthesis
During photosynthesis, plants use the energy
of sunlight to produce energy
energy-rich
rich molecules
called carbohydrates (ex. glucose).
In photosynthesis, plants take in carbon
dioxide and water and release glucose
and oxygen wastes.
Why most plants are green?
Chlorophyll is found inside the
chloroplasts of plant cells.
Plants need red and blue light to grow.
• Chlorophyll is the main
pigment used in
photosynthesis.
– A pigment is a
molecule that absorbs
some colors of light
and reflects others.
• Chlorophyll absorbs
mostly blue and red
light, and reflects green
light.
• This is why most plants
look green.
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12/22/2009
Why don’t plants absorb all colors of
light?
• The reason is the same reason you wear
light-colored clothes when it’s hot outside.
• Like you, plants must reflect some light to
avoid absorbing too much energy and
overheating.
Why do leaves
change color?
In some parts of
the world, the
l
leaves
off some
plants, such as
sugar maple trees,
turn brilliant red or
gold in the autumn.
Also, certain colors of visible light have
just the right amount of energy to make
photosynthesis occur.
Infrared light has too
little energy to make
photosynthesis
occur.
Ultraviolet light has
more energy but
would cause other
chemical reactions.
Chlorophyll masks other plant pigments
during the spring and summer.
• In the autumn
photosynthesis slows
down.
down
• Chlorophyll breaks
down; and red, orange,
and yellow pigments in
the leaves are revealed!
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