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Photosynthesis
What is photosynthesis?
Photosynthesis
refers to the process by which light energy is harnessed and
transformed into chemical energy in the form of the
food sugar. More specifically, carbon dioxide and water are
combined and their atoms are rearranged to form a sugar molecule.
The bonds
within the sugar molecule store the energy obtained from light.
Oxygen from water is released as a by-product in this process.
The following is the chemical reaction for photosynthesis:
light
energy + CO2 + H2O -> CH2O + O2
light energy + carbon dioxide
+ water -> sugar + oxygen
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Dr. Ellison's photosynthesis
experiment |
Dr. Aaron Ellison demonstrates photosynthesis
in the video. A leaf from a pitcher plant is placed in a closed
chamber that
measures the amount of carbon dioxide in the air. As photosynthesis
occurs,
carbon dioxide is removed from the air and its level falls. As
this happens, sugar is formed and oxygen is released.
Where does
photosynthesis occur?
Photosynthesis is a process that is carried
out within the cells of plants as well as certain protists, bacteria,
and archaea.
In the eukaryotes (e.g., the plants and protists), photosynthesis
is carried
out in organelles called chloroplasts. Chloroplasts contain chlorophyll,
a lipid that gives plants their green color. Chlorophyll is
what actually captures light energy. The photons in light (i.e.,
the light
particles) “jostle” the electrons in the chlorophyll molecule,
which starts the process of energy transformation.
Interestingly,
the chloroplast is actually derived from a group of bacteria
known as cyanobacteria. This is one of the examples
of symbiosis mentioned by our host, Dr. Doug Zook. In this case,
the cyanobacteria
were taken up by eukaryotic host cells billions of years ago
and the ability to photosynthesize was eventually passed onto
upon the host
cells. In addition to being important as ancient symbionts, cyanobacteria
in the ocean are responsible for most of the photosynthesis occurring
on Earth today.
How does photosynthesis reflect the properties
of energy?
In photosynthesis, light energy is changed into chemical
energy. The first law of thermodynamics is “obeyed” in
that the amount of light that is the energy input equals the amount
of chemical
energy that is the output. However, the second law of thermodynamics
seems to be defied. Energy emerges from photosynthesis in a more organized form as chemical energy, which is a higher-quality energy
than light.
This is an example of “life battling against disorder” and
is possible only by the addition of energy.
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Photo-synthesis
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