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Teacher professional development and classroom resources across the curriculum

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Life Science: TerrAqua Column

Now You See It

petri culture
Culture of waterfern (upper left) and moss
(upper right) after seven days

If you could shrink yourself to the size of a microbe, what do you think you’d see in your TerrAqua Column? “Now You See It” helps make the world of microbes observable through cultures that are visible because they’re made of millions — even billions — of individual organisms. This activity uses special materials that support microbial life — Petri plates that contain prepared media, which acts as a food source.

Your cultures will include mostly bacteria and some fungi. Bacteria will generally appear at first as small pinpoint-sized colonies that will grow to become much larger. Two types of fungi may grow. Yeast colonies resemble bacterial colonies, while molds will develop into fuzzy growths. It’s not important that you identify which is which, just that you observe and appreciate what can’t be seen in soil, air, water, and on plants and animals.

Materials Required


  1. When your Petri plates arrive, be sure not to open the lids. You’ll inadvertently introduce microbes if you do.
  2. To conserve media and make side-by-side comparisons, use a permanent marker to divide each plate into thirds on both the lid and the bottom.
  3. Select surfaces to be tested for the presence of microbes. A good variety will include soil, water, air (the surface of the bottle), plants, and animals.
  4. Write the names of the surfaces you’re testing at the outer edge of the bottom side of the Petri plate (the top may move around). Consider making one of the sections a “control,” which you do not disturb. The control can be used to make comparisons.
  5. Using a sterile swab for each surface, gently swipe the surface, taking care not to pick up debris.
  6. Open the Petri plate, and starting at the outer edge, gently make a streak in an “S” shape in the appropriate section. Don’t press hard!
  7. Replace the lid and tape it closed.
  8. Turn each plate upside-down to avoid a “rain” of condensation from the lid as the colonies grow.
  9. Incubate in a warm place.
  10. Observe microbial growth in your plates over a two-week study period.

Note: It is safe to culture microbes in this way — they grow in a closed container and are types that are already present in the environment. To dispose of the plates, spray with disinfectant solution, seal, and throw away. The only thing to be careful about is opening the plate — each time you do, you may introduce new microbes!

Activity Questions

Before you swab your plates

  1. What are the distinguishing characteristics of bacteria?
  2. What are the distinguishing characteristics of fungi?
  3. Which surfaces do you think harbor these microbes?
  4. How do you think different surfaces might compare?
  5. What do you expect to see as colonies develop on your plates?

After your study period

  1. What surfaces did you test for the presence of microbes?
  2. Describe the microbial growth that resulted from testing these surfaces.
  3. How did different surfaces compare?
  4. Were you surprised by your results? Why?
  5. What can you conclude about microbial life in your TerrAqua Column?



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