Billie Silvey
Photosynthesis
August 2014
Light from the Sun takes about eight minutes
to reach Earth, but it takes milions of years to
travel from the Sun's core to its surface.

Without the Sun's intense energy, there
would be no life on Earth.

Photosynthesis is the process by which
plants convert light into energy, or food.  It is
divided into two main groups of reactions--
the "light reactions," which require light
energy to operate, and the "Calvin Cycle"
which turns carbon dioxide into organic
molecules.  

Photosynthesis takes in the carbon dioxide
we breathe out and puts out oxygen, which
we need to breathe in.

Plants use the energy of the Sun to change
water and carbon dioxide into glucose.  

Glucose is used by plants to make cellulose,
a building material, and starch, a food.  

Chlorophyll is the green pigment found in
plants.  It is used in photosynthesis to
absorb the sun’s energy and turn it into
chemical energy
Sunlight has many different colors in it.  
Chlorophyll absorbs red and blue light from  
the sun and reflects green light.  That’s what
gives plants their color.

When you see a color, it is actually a color
that the object does NOT absorb.  Green
plants do not absorb light from the green
range.

Photosynthesis isn't very efficient.  Of the
sunlight that reaches a leaf, about half is not
the right wavelength, some is reflected,
some is transmitted through the leaf, and
some is converted into heat energy. The
result is that, in most plants, only 1% to 4% of
the energy is used in photosynthesis.

In fall, some plants stop producing
chlorophyll.  Leaves change color because
the green light is not being reflected.