Glencoe Photosynthesis Lab:
"Which colors of the light spectrum are most important for plant growth?"
Website: bit.ly/pholab
9. Click the Reset button. Repeat the experiment using a different color light
filter and the same type of seed. Graph the results of your experiment. (use
the website to graph and copy it to your paper).
Objectives:
 Carry out an experiment to determine which colors of the light
spectrum are used in photosynthesis as evidenced by plant growth.
 Measure plant growth under lights of different colors of the spectrum
10. After all color filters have been tested on all of the seeds, accept or
reject your hypothesis using the evidence you have collected from the
group.
Procedure:
1. Click on the “Video” button. Watch
the animation to learn about how light
affects photosynthesis.
2. On your own paper, write a
hypothesis about which wavelength
(light color) of the light spectrum causes
the least plant growth. Assume that all
conditions other than the color of the
light are the same for each seed as it
grows: the soil, moisture, viability of the
seed (they are all good seeds). Now
make another hypothesis about which light will cause the most growth.
3. In your group, decide which member will test one type of plant seeds,
and then observe how the plants grow under different colors of light.
4. Now, choose the type of seed that you have decided to test and click on
its seed packet.
5. Click on the arrows on the color display to select a color light filter for the
chosen plant.
6. Start the experiment by clicking the light switch to the “ON” position.
7. Observe the plant growth.
8. Click on the ruler and drag it to each plant to measure the height. Use the
calculator to average the heights of the three plants under each color light
filter. Record your calculations in the Data Table.
Results: Copy the chart on your paper
Table 1: Plant Growth Under Different Color Filters
Spinach Height
Average
(cm)
Filter Color
(cm)
1
2
3
Red
Orange
Green
Blue
Violet
Table 2: Plant Growth Under Different Color Filters
Radish Height (cm) Average
Filter Color
(cm)
1
2
3
Red
Orange
Green
Blue
Violet
Table 3: Plant Growth Under Different Color Filters
Lettuce Height
Average
(cm)
Filter Color
(cm)
1
2
3
Red
Orange
Green
Blue
Violet
Graph Results: Use graph paper to design your graph. Use all available
space on your graph paper!!
Title of Graph: Plant Growth Under Different Color Filters
KEY: Spinach Average Height (cm)
Radish Average Height (cm)
Lettuce Average Height (cm)
Analysis:
1. How did you test your hypothesis?
2. Which variables did you control in your experiment?
3. Which variable did you change in order to compare your growth results?
4. Analyze the results of your experiment. Did your data support your
hypothesis? Explain
5. Explain any differences or similarities you found among the types of
seeds.
6. What conclusions can you draw about which color in the visible spectrum
causes the most plant growth?
7. Given that white light contains all colors of the visible spectrum, what
growth results would you expect under white light?
Read the following: Although plants generally get the credit for producing
the oxygen we breathe, some 75% or more of the oxygen in the planet's
atmosphere is actually produced by photosynthetic algae and
cyanobacteria. Marine algae, more commonly known as seaweeds, come in
all shapes and sizes. Algae are not plants, even though they sometimes look
like them:
 Brown alga is the largest type of
algae. They are brown or yellow-brown in
color, and they are found in temperate or
arctic waters. Brown algae typically have
a root-like structure called a "holdfast" to
anchor the algae to a surface. They are
abundant along rocky coasts, although
some float in the open ocean. Brown
algae are large in size and include the
giant kelps, which are located along the
Pacific coast and form forests that provide habitat to a wide range
of marine life.
 Red algae have a brilliant color due
to the pigment called phycoerythrin. These
algae can live at greater depths than brown
and green algae because it absorbs blue
light. This adaptation allows red algae to
survive in the deepest quarters of the
oceans.
 Green algae may be found in
marine or freshwater habitats, and some
even thrive in moist soil. Green algae are
thought to be in the evolutionary line that
gave rise to the first land plants.
8. Knowing more about algae, and the effect of light on photosynthesis,
a) Explain the evolutionary adaptations that each group has develop to
survive in their individual environment.
b) Why do you think algae produce 75% or more of the oxygen in the
planet’s atmosphere?