Light as Energy: Photosynthesis

Project Description

What does the fact that spinach fluoresces have to do with photosynthesis? This simple and visually dramatic demonstration we’ll extract chlorophyll from the leaves of spinach and see that it teaches us about how plants gather and store energy from sunlight.

Grades: 1 to 12+
Duration: 1/2 Hour – 1 Hour

NGSS HS-PS4-4: Evaluate the validity and reliability of claims in published materials of the effects that different frequencies of electromagnetic radiation have when absorbed by matter

Supplies: 6-8 fresh spinach leaves, a red, green and violet laser, several table spoons ethanol, mortar and pestle

Featured Products
Laser Blox

Laser Blox

Step 1

Background

One of the most common fluorescent molecules in nature is chlorophyll, the green pigment found in plants. Leaves appear green when lit by the sun because they reflect the wavelengths of light that we perceive as green, and absorb all of the other wavelengths of light found in sunlight. Blue and red light are the wavelengths that drive photosynthesis. The energy of light is proportional to wavelength: the shorter the wavelength, the higher the energy. When illuminated by ultraviolet light (short wavelength and high energy) the plant pigment glows red, which is lower energy. the “missing energy” or the difference in energy between the high= energy of the UV light and the lower energy red light is released as heat energy.

Instructor Tip:
For a great background activity on what FLUORESCENCE is, try this!

More on Chlorophyll Fluorescence HERE

 

Step 2

Extract the chlorophyll from the spinach

Place 4-6 spinach leaves and 1-2 T of ethanol and mix/crush/grind to a thin paste.

Step 3

Observe fluorescence of Chlorophyll

Filter the mixture through a coffee filter into a test tube. Shine a violet (405nm) Laser Blox through the test tube and observe the red glow!

Step 4

Discussion

What does chlorophyll do with the light energy it has absorbed if the light energy can not be converted to chemical energy (because we’ve extracted it!)?

The intact leaves of green plants absorb photons in the blue/violet range of the visible spectrum. Electrons excited by UV light enter the electron transport chain within the membrane of the thylakoid and are used to synthesize sugar for the plant.

Crushing the spinach leaves and adding ethanol isolates the chlorophyll from the thylakoid membranes of the chloroplasts. Freed from the electron transport chain, the electrons release their energy in the form of red light.

 

 

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