Grade Level: 6th – 8th grade
Subject Matter: Life Science, Nanotechnology
The following materials can be purchased at any science supply store or online at Carolina Biological Supply Co., http://www.carolina.com:
At least one microscope
Medicine droppers or plastic disposable pipettes – one for each student
Euglena culture (small jar that contains enough for 30 students)
Paramecium culture (small jar that contains enough for 30 students)
Deep well slides – one for each student
Protoslo quieting solution – one small bottle. This solution slows the rapid movement of microorganisms without interfering with them, to help keep them in focus under a microscope.
Toothpicks – one for each student
Roll of paper towels
Permanent markers – one for each pair of students
Paper – enough sheets for all students
Pencils- one for each student
Cilia: a group of hair-like structures that assist organisms with locomotion.
Ciliate: an organism that uses cilia for locomotion.
Flagellum: a single hair-like structure that assists an organism with locomotion.
Flagellate: an organism that uses a flagellum for locomotion.
Microorganism: a tiny organism, often made of a single cell, that can be seen only under a microscope.
Paramecium: a group of protozoa, or single-celled organisms. Paramecium move with cilia, so they are called ciliates.
Euglena: a genus of diverse unicellular organisms, some of which have both animal and plant characteristics. (They eat food the way animals do, and can photosynthesize, like plants.) Euglena move with a single flagellum, so they are called flagellates.
Note: While all the microorganisms used in this activity are safe for classroom use, be sure to read all safety and care information that comes with your cultures. If students are unfamiliar with using a microscope, plan to introduce basic microscopy and laboratory protocol before teaching this lesson.
Begin the lesson by having the students watch the SciFri Video, “Engineering Artificial Cilia.” What type of microorganisms were the researchers studying? What type of science tools did they use to observe microorganisms?
Tell students that they are going to observe the same types of microorganisms (ciliates and flagellates) discussed in the video, and that they will compare the differences and similarities between each microorganism.
Inform students that it is important to follow proper procedure for preparing a slide. Demonstrate proper slide preparation procedure for them, as outlined below:
a. Hold up the deep well slide and take the cover slip off.
b. Use the dropper or pipette to place five drops of culture in the well of the slide. If there is still space, continue to add culture until the well is almost full.
c. Inform students that the next step is to add two drops of Protoslo to the culture. Ask students to guess what they think Protoslo will do to the microorganisms. What does the name indicate? (Protoslo is a harmless chemical that will slow down microbes without interfering with their characteristic movements, so that the students will be able to observe them through the microscope.)
d. Use a toothpick to gently mix the culture and Protoslo together. (When students begin to look through the microscope, they may find that microorganisms are still moving too quickly to make observations. If so, they should add one or two more drops of Protoslo.)
e. Carefully, replace the cover slip so that there is almost no air trapped in the slide. One technique is to place the cover slip on the edge of the well, and gently slide it completely into place over the well. This might take a few attempts.
Once you have reviewed and demonstrated proper procedure for slide preparation, hand out to students the droppers/pipettes, deep well slides, toothpicks and Protoslo. Depending on class size, you may pass around the jars of cultures, or you may set up them up on a table in a separate area. Have paper towels on hand and keep some culture in reserve in case of spills.
Divide students into pairs, with one student preparing the Euglena slide and the other preparing the Paramecium slide. Students should use a permanent marker to label the Euglena slide with a small “E” on the edge of the slide, and the Paramecium slide with a small “P.” Inform students that these are the names of two different types of microorganisms.
Once the slides are prepared, have students use paper and pencils to create a chart with two columns. They should label the first column “Euglena,” and the second column “Paramecium.”
Have students place the Euglena slide on the microscope stage. Center the slide so that the culture is under the light path.
Using the low power objective (4x), have students take turns looking through the eyepiece. Students may need assistance in focusing the image.
Ask the students to record their observations (color, shape, method of locomotion, etc.) under the Euglena column, and to include a sketch of the microorganism.
To observe the microbes in more detail, have students switch to a higher power objective (10x) and adjust the sharpness of the image with the fine adjustment knob. Have students record any additional observations that they were not able to see at the lower magnification. Warning: If you are using a standard microscope, do not use the 40x objective with the deep well slide. At this point, the objective might be too close to the slide.
Repeat steps 7-10 for the Paramecium slide.
Have students compare and contrast their observations. Review the definitions for a flagellate and a ciliate. Can they identify which microorganism is the flagellate and which microorganism is the ciliate? What characteristics do both microorganisms share? What characteristics are different in each? What are some of the advantages to each type of locomotion?
Ciliates are microorganisms with small, hair-like projections on their surface called cilia. The cilia can be very numerous, covering the entire surface of many microbes, or several can be fused together to form a bundle. Cilia beat in a coordinated fashion to propel the organism through the water. Flagellates move by beating or twirl single whip-like flagella (longer hair-like appendages, compared to cilia) that extend from their bodies.
What do Euglena and/or Paramecium need in order to survive? How would you maintain the lives of these microorganisms as classroom pets?
Why did we use a deep well slide for this investigation and not a flat microscope slide and slip cover?
Compare the movements of ciliates and flagellates to the movement of humans in water. How are they different or similar? Which form of locomotion provides better maneuverability and speed?
Extend the activity by collecting samples from a local pond or lake. Make comparisons between the microorganism from a laboratory and those collected in the field.