Biol 1009 - Lab - Rebecca Teed
Photosynthesis - Study Sheet
Remember that photosynthesis is the opposite of respiration:
6 C02 + 6 H20 -> C6H12O6 + 6 O2
Light reactions capture energy. Certain wavelengths of light
"excite" electrons into higher orbitals (with more potential energy).
Instead of letting those electrons fall back into their former orbital,
releasing the energy as fluoresced light (as happened in one of the
demonstrations), the electrons are shuffled around in the chloroplast
and their energy used to phosphorylate the low-energy molecule
ADP to form high-energy ATP. The Calvin cycle (or dark reactions)
moves the energy from unstable ATP to stable (but still high-energy)
sugar. What became of the reactants? The water was hydrolyzed
into hydrogen, which was used as an electron donor, and oxygen,
which was thrown away, ending up in the atmosphere. The carbon
dioxide was united with the hydrogen after the photosystems were
finished with it, and made into sugar.
Paper chromatography is a way to break up a mixture of
substances (in this experiment, pigments) which are of varying
solubility with respect to a potential solvent. The most soluble
components of the mixture can travel closest to the solvent front,
while the least soluble are left behind (they keep falling out of
solution, being redissolved, carried up a little farther, falling out
again, etc.). This process works against gravity and entropy because
it is fueled by heat (which gives the solvent particles the energy to
diffuse through and up the paper).
In lab, you will have discerned that plant leaves and
chloroplasts contain several pigments, not just the two major sorts of
chlorophyll, and that these pigments absorb different wavelengths of
light (which allows the plant to use more of the light its leaves
receive, rather than be forced to allow too many wavelengths to be
wasted). Each of these pigments has a certain solubility in acetone,
which can be measured by its Rf, which should be constant for a
given solvent (although hard to measure precisely).
All of the lab objectives on p. 100 are important.
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