Glencoe Photosynthesis Lab:

"Which colors of the light spectrum are most important for plant growth?"

Website: bit.ly/pholab

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

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.

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).

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.

Results: Copy the chart on your paper

Table 1: Plant Growth Under Different Color Filters

Filter Color / Spinach Height(cm) / Average
(cm)
1 / 2 / 3
Red
Orange
Green
Blue
Violet

Table 2: Plant Growth Under Different Color Filters

Filter Color / Radish Height(cm) / Average
(cm)
1 / 2 / 3
Red
Orange
Green
Blue
Violet

Table 3: Plant Growth Under Different Color Filters

Filter Color / Lettuce Height(cm) / Average
(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?