Symbiosis: Plants, Nitrogen, and Bacteria

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Updated on Oct 29, 2013

Grade Level: Middle School; Type: Biochemistry and Botany


Learn about why nitrogen fixing bacteria are important to plant growth.

Research Questions:

  • What are nitrogen-fixing bacteria?
  • What is a symbiotic relationship?
  • Do plants have a symbiotic relationship with bacteria?
  • What happens when there are no nitrogen fixing bacteria in a growth medium?


  • Six identical clay pots
  • Sphagnum moss or potty soil
  • Pea seeds
  • Rhizobium leguminosarum culture
  • Sterile inoculating loop
  • Magnifying lens
  • Drawing pens and paper
  • Marker
  • Camera

Experimental Procedure

  1. Label three pots “control” and 3 pots “bacteria.”
  2. Fill all pots with the same amount of moss or potting soil.
  3. Plant three seeds in each pot.
  4. Set post in the sun and water appropriately.
  5. On the fifth day after planting, sterilize your inoculating loop. Use the loop to add Rhizobium Leguminosarum culture into the three pots labeled “bacteria.” If you are using the powdered kind of bacteria, carefully sprinkle ½ teaspoon over the soil in each of the three pots.
  6. Let the peas grow undisturbed for at least nine weeks. During this time, measure the growth of each plant, the number of leaves and the size of the largest leaves. Note when new leaves formed. Take pictures regularly
  7. At the end of nine weeks, pull your plants out of the soil and examine their roots, using a magnifying lens. Draw what you observe.

Terms/Concepts: nitrogen-fixing bacteria


  • Nitrogen Cycle, Texas A & M University
  • Symbiotic Nitrogen Fixation
  • Science of Plant Life: A High School Botany Treating of the Plant and Its Relation to the Environment, by Edgar Nelson Transeau (Nabu Press, 2010)

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