Unit 10: Review
Photosynthesis Lab
Photosynthetic balanced equation
Balanced equation for photosynthesis.
6 CO2 + 12 H2O + light energy
carbon dioxide
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C6H12O6 + 6 O2 + 6 H2O
water
glucose
oxygen
water
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I. Using the spectroscope to measure the
wavelengths of transmitted light
In lab we have two types of spectroscopes, handheld and tabletop.
Using the spectroscope continued
A spectroscope is a device that shows the wavelengths of light
that enters it. Allowing white light through the prism of a
spectroscope will display all the colors of the visible light
spectrum. Using a colored filter or test tube of pigment extract
to block the entrance slit of the spectroscope will display only
some of the colors because the others, not displayed, are
absorbed by the filter.
An absorption spectrum is the range of light wavelengths
absorbed by a particular colored filter or pigment.
Colored filters used: red, green, blue
handheld spectroscope
tabletop spectroscope
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Spinach leaf
extract
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II. Determining the absorption spectrum of photosynthetic
pigments using a spectrophotometer
Determining the absorption spectrum
continued
A spectrophotometer can be used to measure
absorption and transmittance of light
through solutions.
Carotenoids
Wavelength
%transmittance data
Spectrophotometer
The solutions that will be tested are solutions of
carrot pigment extract (#1) and spinach
leaf pigment extract (#3). A blank (#2) was
prepared to calibrate the
spectrophotometer.
Carrot extract absorption spectrum is seen above in orange.
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#1
#2 #3
1
Determining the absorption spectrum
continued
Paper chromatography is used to separate
substances from one another based on their
characteristics. This exercise separates pigments
of a spinach leaf. The separation is due to the
solubility of the pigment in the chromatography
solvent (10% acetone in petroleum ether) and the
affinity of the pigment to the paper surface. The
finished product is called a chromatogram.
Chlorophyll b
Chlorophyll a
The spinach absorption spectrum is the composite of
chlorophyll a and b spectra.
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III. Pigment Chromatography
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Roll of chromatography paper
Pigment Chromatography
continued
Solvent line
Pigment Chromatography
continued
Chromatography solvent
cm
16
The chromatogram
Rf (ratio factor) value of each pigment
There are four pigments that are seen on the
chromatogram.
- Carotene (orange)
- Xanthophyll (yellow)
- Chlorophyll a (blue-green)
- Chlorophyll b (yellow-green)
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To determine the Rf value of a pigment you must measure
the distance traveled by the pigment/distance traveled
by the solvent.
-To determine distance traveled by the pigment you
must measure from the middle of the pigment band to
the baseline.
The pigment with the greatest affinity for the
solvent (is most soluble in the solvent) traveled
the farthest distance.
The pigment with the greatest affinity for the paper
traveled the least distance.
-To determine the distance traveled by the solvent you
must measure from the solvent line to the baseline.
Baseline
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IV. Starch localization in leaves
C6H12O6
carbohydrate
+
6 O2
Baseline 0
Which area contains starch?
+
6 H2O
This carbohydrate can be used to make glucose. Glucose can be used to provide
energy or can be stored. Plants store excess glucose mainly in the form of starch
(polymer of glucose).
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Starch localization in leaves continued
The formula of photosynthesis indicates a carbohydrate as an end product.
6 CO2 + 12 H2O + light energy
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Leaf pigments must be removed by
placing it in boiling 95% ethanol.
(Ethanol cannot be boiled directly on
the hotplate. A beaker
containing ethanol is placed into
a larger beaker of boiling water.)
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V. Chloroplast structure
Starch localization in leaves continued
Photosynthesis occurs in the chloroplasts of a cell. The stages of photosynthesis are
the light reactions and the Calvin cycle (also known as the dark reactions
because they are light-independent). The light reactions occur at the thylakoid
membrane. The Calvin cycle occurs in the stroma.
Leaf pigments must be removed by placing it in
boiling 95% ethanol.
Plant cells contain chloroplasts. In this cell model, chloroplasts are represented by
green structures. Below you will find enlargements of chloroplasts to show the
cross section and surface view.
Iodine is then added to the leaf. If starch is present the
area will become blue-black (review macromolecules
unit).
Before
boiling
After
staining
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Chloroplast continued
Cross section
Surface
Chloroplast continued
Cross-section view
of chloroplast
Regions of the chloroplast are
-outer membrane
-inner membrane
-intermembrane space
-stroma
-thylakoid disk
Surface view of
chloroplast
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Plant cell model
End of Lab
Review ☺
-thylakoid disk
granum (g) – one stack
grana – multiple stacks
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