Science Experiments With Different Kinds of Milks for Seventh Grade
Seventh-grade science curriculum standards include such topics as diffusion, cell identification and experiment design. Different kinds of milk lend themselves well to a range of science-based inquiries appropriate for the seventh-grade classroom. Projects that investigate the scientific properties of different kinds of milk engage seventh-graders by inviting them to apply a scientific eye to a common household item.
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Cellular Observation
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All matter is in a constant state of cellular motion, but not all substances move in the same way. One of the ways to observe cellular motion is under a microscope. Although it is likely students are unable to observe individual cellular motion under the type of microscopes you have in your classroom, the fat molecules in milk allow them to observe the vibrations or effects of molecular movement.
Provide students with several types of milk with different fat contents; whole, skim, 2 percent and soy milk are suitable options. Have students create slides using each milk sample, and observe and compare the motions they are able to detect. Ask them to hypothesize why more movement is visible in whole milk than skim milk.
Color Diffusion
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Understanding diffusion is a key content standard for seventh-grade science, and a color experiment using different types of milk demonstrates the types of factors that influence diffusion.
Have students fill several bowls with different kinds of milk, including whole, skim, soy and almond. When students add several drops of food coloring to the milk, nothing happens, but when they add a drop of dish soap to each bowl, the colors swirl or burst across the surface of the milk.
The bipolarity of the dish soap interacts with the fats, vitamins and minerals in the milk, causing motion that disrupts the food coloring. The fat and vitamin content of the milk affects the type of motion observed. Students should draw the swirl effects they see in each type of milk, then compare and analyze why the colors move differently in each.
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Growing Bacteria
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The specific fat content of milk is a major contributing factor to how quickly bacteria is able to grow. Students can compare the bacteria growth rates of different types of milk with an inoculation experiment.
Spread individual milk samples in petri dishes or Petrifilm plates, and add a single drop of lactobacillus from a pipette to each sample. Lactobacillus speeds up the inoculation process, but the experiment will work without it if it's unavailable. Place the dishes in a temperature-controlled environment; the warmer the space, the more effective the bacteria growth, but do not exceed 90 degrees Fahrenheit.
Have students observe the bacteria growth in each dish at one-hour intervals and determine which type of milk grows the most bacteria.
Comparing Chemical and Physical Properties
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Seventh-graders are expected to understand the different ways they can test and compare the chemical and physical properties of substances. Challenge students to develop their ability to design experiments, form hypotheses and test theories with a project that asks them to compare the properties of different types of milk.
One group might opt to compare boiling points and hypothesize what makes some types of milk boil more quickly than others. Another group might opt to test milk density using a weight experiment as well as a specific gravity experiment that identifies the ratio of densities between types of milk. Students should present their findings in a poster format.
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References
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