conducts simple activities to observe organisms
Answers
Answer:
Overview
Students use a light microscope to examine three different microbes: bacteria in yogurt, Baker's yeast, and paramecia in pond water.
This activity is from The Science of Microbes Teacher's Guide, and is most appropriate for use with students in grades 6-8. Lessons from the guide may be used with other grade levels as deemed appropriate.
The guide is available in print format.
Procedure and Extensions
Ask students, Have you ever seen a microbe? What do you think different kinds of microbes might look like? Tell students that they will have opportunities to observe and compare different kinds of microbes: bacteria in yogurt, yeast cultures, and paramecia (or other pond organisms).
First, students will prepare and examine a slide to observe bacteria in yogurt. If necessary, demonstrate how to make a slide before having groups of students make their own. Students should follow the instructions on the Bacteria card to prepare and observe their slides. Have students draw what they observe. (Students will not be able to see any parts inside the bacterial cells, which will appear as tiny rods.) Be sure students record on their drawings the magnification at which they made their observations.
Ask, Were you able to see cells or groups of cells? Explain that students observed tiny rod-shaped bacteria, called Lactobacillus, that live on milk sugar (lactose).
Have students follow the procedures on the Yeast card to observe and draw yeast cells. Students will be able to observe many round yeast cells, some of which may be reproducing by budding. Ask, Were the yeast cells larger or smaller than the bacteria? (larger) What other differences did you notice?
Finally, have students observe the paramecium culture (or pond water, which may or may not contain paramecia).
If you are using pond water that includes a variety of organisms, you may want students to examine the water with a hand lens before using a microscope. Students should follow the directions on the Paramecia card to prepare their slides.
Have students draw one paramecium (or other pond organism). These organisms may be large enough for students to observe and label the cell nucleus and cell membrane. Students also may be able to see the cilia around the edge of each paramecium.
Tip: A tiny drop of glycerin on slides with pond water will slow the movement of microorganisms so that they are easier to observe.
Conduct a class discussion or have each student group create a table that summarizes the similarities and differences observed among the three kinds of microorganisms. Allow time for groups to add new information to their concept maps.
Have students research or discuss other types of bacteria, fungi, and protists.
Extension
It’s easy to make yogurt using the following ingredients.
2 quarts of whole milk
1 cup of plain yogurt
1 cup of half-and-half
Bring milk to a boil in a very clean pot. (Greasy or dirty pots and utensils won’t produce the desired results.) Remove from heat and let stand until cool. Pour the cooled milk into a glass or pottery jar, bowl or other glass container. Measure one cup of the milk and pour it into a medium-sized bowl. Mix in the yogurt and half-and-half. Slowly add the remaining milk, stirring gently. Place a lid on the container or cover it with plastic wrap.
Wrap the container in a blanket or heavy towel. Place it in a corner of the room where it will stay warm and undisturbed for about six hours. Then refrigerate for 10 hours.
If you prefer a more tart flavor, leave the container wrapped for eight or nine hours. For a sweeter, softer yogurt, leave the container out for about four hours. Always keep one cup of yogurt from the previous batch to use as a starter for the next batch.