Properties of Light

Property of Light WavePerceived by Humans asUnits of MeasureRange Perceived
Wavelength Color nanometers (nm) 400-700 nm
Amplitude Brightness/Intensity footcandles (fc) 0 - 10,000 fc
What is white light? All visible wavelengths of light together
In white light a leaf appears green because:
it reflects Green light
and absorbs All other wavelengths of light


Compare and contrast etiolated growth in darkness and normal growth in light (hint: your lab exercise should assist you!)

Etiolated Growth
Tall Stem
Thin Stem
White Stem
Unexpanded Leaves
Yellow Leaves
Preserving Cotyledon Reserves
Normal Growth
Short Stem
Thick Stem
Light Green Stem
Expanded Leaves
Green Leaves
Using Up Cotyledon Reserves

Phototropism in Grass Coleoptiles

Color of light perceived Blue
Where light is perceived Tip (apex)
Hormone produced at perception site IAA (auxin)
Side of plant accumulating the hormone Shaded
Side of plant with accelerated growth Shaded
Direction of curvature growth Toward Light


Provide the 4th grade (one-step) reaction diagram for photosynthesis:


  Now dissect this into the 8th grade (two-step) reaction diagrams for photosynthesis:

Light Reactions


  Light Independent Reactions

Sketch a graph of how the rate of photosynthesis relates to the color of light. Be sure to label your axes with both name and some measurement scale with units.


Sketch another graph, this time showing how the rate of photosynthesis and respiration relate to the intensity of light. Be sure to label your axes with both name and some measurement scale with units.
The intensity of light where the two curves cross is called the _____________________________.

What is happening when a plant is kept at an intensity...

higher than this point?____________________________________

lower than this point?____________________________________

This page © Ross E. Koning 1994.

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