Bumpy: How do Bacteria Help Some Plants Live?

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Author: Janice VanCleave


How do bacteria help some plants live?


  • Trowel
  • Clover plants
  • Quart (liter) plastic bucket
  • Tap water
  • Paper towels
  • Magnifying lens




  1. Use the trowel to dig up a clover plant. Be sure to get as much of the root as possible.
  2. Fill the bucket about halfway with water.
  3. Dip the roots of the clover plant up and down in the bucket of water until the roots are free of dirt.
  4. Lay the wet plant on a paper towel. Blot the plant with another paper towel to absorb any excess water.
  5. Close one eye and look through the magnifying lens.
  6. Move the plant back and forth in front of the magnifying lens until it is clearly visible. Slowly turn your body in different directions until the best light source is found.
  7. Study the roots of the plant carefully. Find the nodules (rounded bumps) growing on the roots.


Small nodules that look like tiny potatoes seem to be growing on the roots. Some of the nodules are separate and appear at different places along the roots; however, most of the nodules are grouped together in clumps at the top of the roots.


In order to live, plants need the nitrogen compounds that are found in soil. Nitrogen gas makes up 78 per cent of the earth's atmosphere, but plants cannot use this form of nitrogen. Bacteria called nitrogen-fixing bacteria change nitrogen gas into nitrogen compounds that plants can use. Some nitrogen-fixing bacteria live in the soil, while others live on the roots of plants such as clover. The bacteria enter the root hairs of the plant, and as they multiply a nodule forms. The bacteria and clover help each other. The bacteria "fix" nitrogen gas so that the plant can use it, and the plant provides food for the bacteria. This is an example of symbiosis: when two organisms, living together, are mutually benefited.


Try It With A Microscope

Microscope Procedure

  1. Use scissors to cut a section about ½-inch (1.3-cm) long from one of the smaller roots. The piece must contain at least one small nodule.
  2. Place the root section on a microscope slide.
  3. Position a desk lamp so that the slide is brightly lit from above.
  4. Adjust the mirror under the stage of the microscope to produce a dark background for the viewing field.
  5. Slowly move the slide around while viewing it under low power.

Microscope Results

The outside surface of the nodules looks rough and bumpy, while the root has a smoother appearance.

Let's Explore

    1. Are the nodules hollow? Ask an adult to cut a nodule in half. Use a magnifying lens to examine the content of the nodule.
    2. Place the open nodule on a microscope slide and examine it using the previous microscope procedure. Science Fair Hint: Photographs of the clover nodules, along with diagrams of images viewed through the microscope, can be used as part of a project display.

Show Time!

People are simply imitating nature when they recycle resources. Elements that are important to life, such as nitrogen, are naturally recycled. Nitrogen is found in the air, in soil, and in all living things. Use a biology text to find a diagram of the nitrogen cycle. Prepare a display chart of the nitrogen cycle. Photograph plants and animals needed for the chart, and use the photographs on the chart instead of drawings.

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