Summer Research Program for Science Teachers

H. Alexandria Bodha

Demonstrating That Light is Dissipated as Chlorophyll a Fluoresces

Summary
    When a molecule of chlorophyll a absorbs a photon of light, an electron is excited from the ground state to a higher energy state.[9-12 Content Standard B- Interactions of matter and energy] In an acetone extract, the light energy is not used in the photochemical processes of photosynthesis.  Therefore, electrons are returned to the ground state and results in energy being re-emitted as fluorescent light.  This light can be seen in the red region of the spectrum and is generally at a higher wavelengths than the absorption maximum of chlorophyll a. [9-12 Content Standard B- Conservation of energy]

    In this activity the concentration of chlorophyll a is often measured fluorometrically.  A fluorometer is often used by scientists to measure the chlorophyll a fluorescence. This teacher lead activity will aid the students in creating their own chlorophyll sample and observing the chlorophyll a fluorescence by simply using a flash light.



Objectives

To demonstrate that light is dissipated as chlorophyll a fluorescences.  This is depicted as a red ring on the very top of the test tube.


Key Concept
 
Fluorescence represents a means by which a molecule dissipates excess energy.  It represents excess energy in a molecule releasing light.

SKILLS:          Observing, investigating
TIME:              30 minutes
AUDIENCE:    Teachers, middle school and high school students



Advance Preparation 

1. Put together a test tube as shown in Figure 1. (to follow)
2.  The solution should be stored in a tightly capped bottle.
3.  To prepare a saturated solution of spinach, add 50 ml acetone or nail polish remover in a fairly large test tube to 5 leaves of spinach (as needed) and 1 tablespoon of sand (if available).  Mix well and allow the solution to chill in the freezer overnight.
4.  A dark free liquid on the top of the test tube indicates that the chlorophyll is successfully extracted from the membrane of the chloroplast. [9-12 Content Standard B- Properties of matter]

 Materials & Equipment Needed

acetone or nail polish remover

spinach

test tube with cap/cover

flashlight

gloves

sand

[Teaching Standard D- Make accessible science tools]


Procedure

Remove test tube of solution from the refrigerator ( very carefully).

Turn the lights off.  Room should be dark to get the full effect!!!

While one student is holding the test tube of saturated spinach another should turn the flashlight on directly towards the test tube.

Observe.  The spinach/acetone solution will have a red ring on the top of the solution, indicating that the molecule of chlorophyll absorbs light and then sends the ray of light seen as the red ring.  Fluorescent light is not used in the process of photosynthesis and therefore to prevent it from accumulating, a photon is emitted (not absorbed).


Suggested Follow-Up


Students can also try using different filters to test for fluorescence. Filters should be placed over the light source.



 
 

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