Microscopes: Making a Hay Infusion

This experiment is an easy source of protozoa for your regular microscope or your laser microscope. You can even see some of them with a good magnifying glass.

It can also lead to some interesting investigations and science projects.

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To raise your own micro zoo, you will need:

  • a glass
  • water
  • dead grass
  • yeast

Fill the glass about half full of water. If you use tap water, let it sit overnight, so most of the chlorine will escape. If you are in a hurry, check your backyard for containers that have some rain water.

Add a handful of dead grass to the water. This can be old yard clippings, grass from that corner of your yard where the grass never does well, or a handful of hay or straw. Then sprinkle in a pinch of baking yeast. Place the glass in a warm place overnight.

For the next week or so, check the water every day with your microscope, looking at drops from the surface, from the grass, and from the bottom of the glass. Within a day or two, you should start to see quite a few protozoa swimming around. Make notes and drawings of the organisms you see, and notice how which are common and which are rare. You should see this change daily as the populations interact.

OK, now for the questions. First, where did the protozoa come from? Many of them were living on the grass. When the grass dies and dries up, the protozoa encyst. They dry up too, but they don't die. Instead, they form tiny cysts where they can remain dormant for a very long time, waiting for rain or other water to make them active again.

Other protozoa arrive through the air. No, they don't have wings. When they encyst, the cysts are smaller than dust, and they are easily carried by the air. Think about the dust that collects on your furniture. Part of that dust is encysted protozoa. When that dust falls into your glass, they become active again.

Next, why did we add the yeast? Yeast are tiny fungi, and they reproduce quickly, feeding on the nutrients from the dead grass. The yeast make excellent food for the protozoa.

At first, the population will be unbalanced. Depending on which protozoa start out in your water, you may have a huge number of one kind, and very few of another. Since they feed on different things, and in different ways, you will probably notice that the common kind will decrease, and the rare kind will boom. These fluctuations can continue for quite a while.

This project has great science fair potential. You might investigate different variables, such as comparing dead grass with dead leaves, live grass, dirt, etc., to see how the results vary. You might also compare the project with rain water and fresh tap water, to see how effective the chlorine really is. Or you could do the same test with a glass of chicken soup, to see how safe it is to leave food sitting out too long. Just be sure that no one eats your project!

Have a wonder-filled week.