Flawed Scientific Theories
• Alchemy: Pb -> Au
• Photosynthesis: Light -> Sugar
What Is Photosynthesis?
• Photosynthesis is an endergonic (∆G + 686 kcal/mol)
reaction in which carbon dioxide and
hydrogen (derived from water) are fused to
make glucose (C6H12O6).
• To power this reaction, radiant energy from the
sun excites electrons in pigments. The boost
in energy is used to recharge ATP, which is
used to “pay” for the synthesis of glucose.
• 6CO2 + 6H2O + light ---- C6H12O6 + 6O2
How Does The Form Of Autotrophs Allow For
The Function of Photosynthesis?
Wavelength and Energy
• Wavelength of electromagnetic radiation (λ) is
inversely related to the amount of energy it
possesses
Accessory Pigments
• Accessory pigments absorb the other
wavelengths of light not absorbed by
chlorophyll (GBIV)
• The excited electrons of the accessory
pigments are passed on to chlorophyll,
exciting its electrons
• Examples:
– Beta Carotene (reflects orange)
– Anthocyanin (reflects red)
– Xanthophyll (reflects yellow)
Why don’t most plants have pigments that
reflect the color blue?
BIV Absorption
• Blue, indigo and violet
have the shortest
wavelengths
• Shortest wavelengths
produce the greatest
excitation of electrons
• More excited
electrons = more ATP
• Plants can’t afford
NOT to absorb blue
If red is low energy light, why do
almost all pigments absorb it?
RED LIGHT
• If light is not immediately
absorbed by the
chloroplast, it is reflected
by other objects in the
environment
• When light “bounces
back”, it does so at a
longer wavelength (red)
• The amount of reflected
red light is plentiful
• Excessive absorption
would also cause plant to
overheat and lose water
LAB: Identification of Photosynthetic
Pigments via Paper Chromatography
• Purpose:
– To isolate and view the various photosynthetic
pigments present in several different types of
leaves.
– To determine if said photosynthetic pigments are
unique to each species or if common pigment
molecules are shared between species
• Method: Paper chromatography
Paper Chromatography
• Pigments are removed from leaf tissue using a
non-polar solvent
• Pigment extract is applied to a paper
chromatogram and a solvent is passed through
the paper
• The pigments dissolve into the solvent and move
up the chromatogram using adhesion and
capillary action
• Based upon their size, weight and polarity,
different molecules move different distances up
a paper chromatogram
Rf Values & Pigment Identification
• As each unique pigment
molecule has different size,
weight and polarity, each
pigment moves a different
% of the total distance on
the chromatogram.
• This % of the
chromatogram traveled by
the pigment is its Rate of
Flow (Rf).
• Unknown pigments can be
identified or known
pigments compared by
using this value.
Hypothesis
• How will the pigments in three species of
leaves differ (or will they)? Do all species
have their own unique pigments or are
they shared across species?
– Spinichia oleracea
– Daucus carota
– Brassica cephalacea
• Will there be a difference between the
chromatograms of pigments derived from
fresh vs. canned S. oleracea?
Steps 1-5: Isolation of Pigments
• Put on goggles and aprons
• Each member of your group
will work with a different
species/preparation
–
–
–
–
Spinichia oleracea (fresh)
Spinichia oleracea (canned)
Daucus carota
Brassica acephalea
• Obtain 0.5g of leaf tissue and
0.5g of MgSO4 and grind in
mortar & pestle (no sand)
• Add powder to small test tube
with 2mL acetone solvent
(A). Stopper, shake and let
stand for 5-10 min.
Steps 6-10: Preparation of Chromatogram
• Fill the chromatography
chamber (large tube) to
depth of 0.5cm with
chromatography solvent
(CS)
• Each member should
obtain a blank
chromatogram
• Mark a pencil line 1cm
from the bottom and cut
bottom to a point
• Dip a fresh capillary tube
into the small test tube of
pigment extract and
transfer to the 1cm line of
the chromatogram.
• Let dry and repeat.
• Using a paperclip, hang
the chromatogram in the
chamber with the tip of
the chromatogram
immersed in the solvent.
DO NOT PLACE THE
PIGMENTS DIRECTLY
IN THE SOLVENT!
• Let stand for 15-20 min
Steps 11-12: Marking the Chromatogram
• Remove the
chromatogram from the
chamber, dispose of the
solvent into the waste
container.
• Mark the furthest point
the solvent traveled
immediately (this is the
solvent front)
• Identify each of the
pigment bands and
calculate the Rf value
for each band using the
formula in your lab
Photosynthesis Is Comprised Of Two Main Metabolic Pathways
• PHOTOLYSIS
•
•
•
•
•
• THE CALVIN CYCLE
aka The Light Dependent
• aka The Light
Reactions
Independent/Dark
Occurs in grana of
Reactions
chloroplast
• Occurs in stroma
Depend upon light energy to
• Do not require light
accelerate electrons of
pigments
• Using the ATP from the
photolysis, the Calvin
ATP is produced to power 2nd
set of reactions
Cycle “fixes” Carbon
Dioxide by combining it
Water replaces electrons lost
with hydrogen to make
by chlorophyll. This causes
water to split, releasing
glucose
oxygen gas.
• Leftover hydrogen is used to
build glucose