Nitrogen is an important nutrient to most plants. However, this element is mostly found in the form of gas in the atmosphere. Plants can not absorb atmospheric nitrogen, but some bacteria living in the soil can convert gaseous nitrogen into fixed nitrogen, which plants can absorb with their roots. Demonstrate the importance of nitrogen-fixing bacteria by growing bean plants using soils with, and without, these microorganisms. Take some fertile soil from a garden and make two portions. Bake one of them in an oven at 400 degrees Fahrenheit for 10 minutes, to kill the bacteria. Plant three seeds in each soil sample and observe the difference during their development.
Three slices of bread, an eyedropper, water and transparent plastic bags are the materials for this experiment. Using the eyedropper, create three different moisture levels for the bread slices. For instance, two drops for one slice, seven drops for another and 15 drops for the last one. Put them in separate plastic or sandwich bags, seal and label, indicating the moisture level. Leave them in the same place and observe the distinct mold growth over time. Alternatively, use the same level of moisture in all samples, but place them in environments with different light levels, such as direct sunlight, complete darkness and shade, to observe how light affects the growth of molds.
Microorganisms living in the soil are also important to recycle dead organic matter, accelerating the decomposition process. Although more abundant in the soil, decomposing microorganisms are found everywhere, from the guts of animals to the the air. You can test the rates of decomposition in different conditions. Place three apples or other fruit in distinct environments: in the refrigerator, on the garden's soil and in a plate at room temperature. During two to four weeks, observe how temperature, humidity and a greater contact with microorganisms interfere in the decomposition process.
Dry yeasts used to make bread are microorganisms in a latent state, which become active in the presence of water and carbohydrate sources, such as flour and sugar. As the yeasts use the carbohydrates present in the dough, they produce carbon dioxide as a waste material, which creates bubbles that make the dough rise. To observe the yeast's carbon dioxide production, first mix 16 oz of white flour, 4 tsp. of oil and 1 cup of water. Separate the dough into two samples. Add 3 tsp. of dry yeast in one sample and only 1 tsp. in the other. Put the samples in labeled plastic bags and observe the difference during the fermentation.