A Plant's Favorite Color

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Updated on May 20, 2013

Grade Level: 7th; Type: Biology


To determine which color of the visible spectrum is best for photosynthesis.

Research Questions:

  • What makes green plants green?
  • What is photosynthesis?
  • What is plant respiration?
  • What is a pigment?
  • What is chlorophyll?
  • Where is chlorophyll found?
  • What is glucose?
  • What is starch?
  • How can we differentiate between starch and glucose in the laboratory?
  • What constitutes the visible spectrum of light?
  • How do wavelengths influence the color of light?
  • What gives an object its color?
  • What do light filters do?
  • What does research tell us about the kind of light green plants prefer?
  • What is a hypothesis?
  • In this case, what is your hypothesis? Which wavelength will be best for photosynthesis?

On the informational level, the student will become acquainted with the process of photosynthesis: a process occurring in green plants which produces food for the organism. During photosynthesis, chlorophyll (a green pigment which gives plants their color) will, in the presence of sunlight, produce glucose (a simple sugar) which is then transformed into and stored as starch. This project leads students to delve deeper into the photosynthesis process by attempting to isolate the wavelength of light most crucial to photosynthesis

The visible spectrum of light is made up of a variety of colors. Red, yellow, orange, green, blue and violet each represent a different wavelength of light, and different wavelengths are indicative of different energy levels.The significance of this project is evident in that it fosters the opportunity to maximize the genetic growth potential of green plants.

  • 5 cardboard boxes
  • Five light filters: red, blue, green, yellow and violet
  • Package of radish seeds
  • 6 flower pots
  • Potting soil
  • Water
  • Watering can
  • Tape
  • Labels
  • Scissors
  • Box cutter
  • Paper towels
  • Light source
  • Camera (optional)

Experimental Procedure

  1. Gather all the materials you will need for this project: five cardboard boxes, five light filters, a package of radish seeds, 6 flower pots, potting soil, water, a watering can, tape, labels, scissors, a box cutter, paper towels, and a light source. A camera is optional .You may wish to take photos of the procedure and the results.
  2. Copy the Data Chart provided below so that you can readily record your observations.
  3. Cut one side out of each of the five cardboard boxes and tape a filter into that side. This will enable you to control the specific wavelength of light that reaches the plant placed inside.
  4. Get your plants started. Fill the 6 flower pots with the potting soil. Follow the directions on the radish seed package and plant the seeds. Water as directed. Radish seeds germinate rapidly and in two weeks you will have your 6 plants.
  5. Label the plants. The first is the control and the others will be labeled based on the color of the light they are receiving: red, yellow, green, blue and violet.Note that when we place a colored filter in front of a direct source of white light, only that color will pass through the filter. All the other colors of the spectrum will get absorbed by the filter.
  6. Place the plants in ther corresponding boxes. The control is not placed in a box: it is exposed to white light. Arrange all of the boxes and your control plant so that they are all equidistant from the light source. Water them daily, using the same amount of water each time.
  7. Record your observations every 3 days for the next 9 days.Is there visible growth? You may wish to take photos of the growth or lack of growth. Which color is most effective in promoting growth? What is happening with the control?
  8. What did you conclude? How did the conclusion match with your hypothesis? Which color was most effective in the process of photosynthesis?
  9. Write up your report. Include your research in your bibliography and any photographs you took.

The Data Chart

Specimens +Light Filter

Observations: Day 3

Observations: Day 6

Observations: Day 9

Plant +red filter

Plant +yellow filter

Plant +green filter

Plant +blue filter

Plant +violet filter

Control : no filter

Terms/Concepts:Green plants; Photosynthesis; Chlorophyll; Visible spectrum; Wavelength of light; Glucose; Sugar; Starch; Plant respiration; Filters


Dr. Muriel Gerhard (Ed.D.) is a retired educator with fifty seven years of experience in all aspects of public education. She has been a teacher, principal, administrator, college professor, researcher, grants writer, change agent and science editor. She is the author of several books on education used as college texts. These include the best selling Effective Teaching Strategies with the Behavioral Outcomes Approach and The Behavioral Outcomes Handbook for Teachers and Administrators. Presently she is a consultant in science education and curriculum development, a marriage and family therapist, a newspaper columnist and an author. Her latest book, recently published, is a memoir of sixty vignettes entitled "Now That I`m Dead, I Decided to Write this Book".