| Preparation |
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What to do |
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Assessment |
In earlier investigations in this soil unit, students mostly focused on the inorganic parts of the soil profile. In this investigation, students will observe some of the living things in soil.
For each group of four students:
This investigation is considered generally safe to do with students, but they should wear non-latex disposable globes and must wash their hands when they finish. As always, please review the investigation for your specific setting, materials, students, and conventional safety precautions.
To set the scene, bring in a soil sample that includes several earthworms and other visible organisms (including plant material such as roots). While students look at the new sample, tell them that their task will be to find clues that there are both living things and recently living things in the sample.
After the scene is set, introduce your students to the investigation question: “What lives in the soil?”
Tell your students that they will be investigating this question and that at the end of their investigations, they will be able to provide reliable answers.
Have your students brainstorm ideas about how this investigation question could be investigated.
Have students think about the material that floated on the top of the water when they separated soil in an earlier investigation. What did they notice when they observed the floating material? [It looked like pieces of wood, leaves, etc.]
Ask students to suggest the names of organisms that live in the soil. Plants will be the most obvious. Ask them if they have ever noticed other things growing in and moving around in the soil. What do they think animals moving in the soil would find to eat? Ask them if they think that the animals and plants that live in the soil are good or bad for the soil. [Students might think that insects and worms harm the plants growing there.]
Suggest that students make a poster display showing the web of living things that they found in their soil samples and how they think these are related to one another. To do this, they will need to find more information about the various types of life found in the soil community. You might assign research topics to each group, e.g. “Find out what kinds of insects live in the soil and what they do for the soil community.”
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Complete this investigation by asking your students to reflect on the investigation question and how their answers may have changed as a result of what they have learned. Ask them why they think it’s important to know what living things are in soil. Remind the students that many different soil organisms benefit the soil by aerating it and adding nutrients.
Soil organisms come in all shapes and sizes—microscopic forms include varieties of bacteria, fungi, algae, and protozoa; macroscopic forms include insects, worms, and even burrowing mammals and reptiles. Students will be surprised to hear that there are many more living things in the soil than those they found while examining their samples. In fact, healthy soil is loaded with life. One estimate is that a hectare of soil supports about 20,000 kilograms of living things, approximately equal to the weight of 40 horses. (Non-living organic matter is present at about 20 times this amount!)
But if we can’t see these living things, how do we know they are there? In fact, their presence can be detected by many of the clues they leave behind as they go about their activities. Like nearly all living things, soil organisms provide an important chemical clue that they are alive and breathing. They exhale or simply give off the chemical carbon dioxide—a chemical that is easily detected in water by use of an indicator. The more carbon dioxide present, the more living things are present in the soil.
