Science Bus Lesson

Author: Britter Gundersen, Ross Venook

Unit: Home Science, Fall 2004

Lesson: Germs

Objectives:

-Introduce students to some specific ideas about germs

  • Germs are living organisms that come in different shapes and sizes
  • Germs are too small to see, are easily spread, and require effort to wash

Introduction:

Why do we need to clean our house?

-When you clean your room, what different things do you do? (pick stuff up, maybe vacuum)

-When you clean the kitchen, what do you do that’s the same? What different things do you do to clean the kitchen? Why? (use soap, or other cleaning solutions, and water—to clean away germs)

-Why do we work so hard to clean away germs? (when they get inside us, some germs make us sick)

What different kinds of germs exist?

-Demonstration: different types of ‘germs’

  • Bread/fruit mold
  • Petri dishes with different colonies of bacteria
  • Pictures of viruses (?)

-Discussion of good germs. (on board under ‘Good’)

  • Certain mold is used as a medicine called penicillin.
  • Bacteria live on your skin and in your stomach to help protect your skin and digest the foods that you eat and produce nutrients.
  • No good viruses (that we know of).

-Discussion of bad germs. (on board under ‘Bad’)

  • Breathe in mold—grows in your lungs
  • Tuberculosis
  • Bronchitis
  • Strep throat (streptococcus-little balls as you will see under the microscope)
  • Infections in a cut – red and swollen and puss-filled.
  • Bad viruses – HIV, flu (influenza virus), chicken pox.

Small Group Activities

1 – Handwashing

Materials – Paint (water soluble), blindfolds, liquid soap, sink, paper towels, paper and pencil.

Activity

-The idea is to show that washing hands well is hard to do when you can’t see what you’re trying to clean (just like germs, which are too small to see).

-The students will each take a role in performing an experiment in which one student gets his/her hand dirty with paint, and then tries to wash it off in the sink while blindfolded. The experiment happens once without soap, and once with soap. The student will get three tries to get it all off with just water (30 seconds each try), and three tries on the repeat experiment with soap. One student and the tutor assist the washer (turns on water, makes sure paint doesn’t get on floor, gives soap, etc…). The rest of the students time the washing intervals, judge how clean the hands are, and record the results—perhaps in a table.

  • Tasks for individual students (2-5 per tutor):
  • Wash dirty hands while blindfolded
  • Assist handwasher
  • Judge hand cleanliness against predetermined scale
  • Timer/judge

-Notes:

  • The paint should be allowed to dry before washing begins—1 minute or so. Really cover the hands with paint.
  • Determine judging criteria ahead of time with the students.
  • Depending on the student, the washing may take longer or shorter. Perhaps the tutor should do the timing.
  • Students should be instructed to wash the same way each time. This can be done by asking them to wash very vigorously for shorter periods of time, or to wash slowly.

Questions:

-What are some variables (things) that affect how quickly the paint comes off? (water temp, type of soap, method for washing, etc…)

- What happens if we don’t wash our hands completely before leaving the sink (get paint everywhere)? So, what happens if we have bacteria on our hands instead of paint?

-What is a major difference between the paint in our experiment and the bacteria/germs we have on our hands when we wash them? (you can see one, one makes you sick) How are they similar? (both will get all over whatever you touch)

2 – Viewing bacteria with microscopes—different shapes of bacteria

Materials – 4 microscopes (at least 1000x magnification), bacteria slides with three different shapes of bacteria (round, rod, spiral), paper (with three large circles) and pencils for drawing. Tutors must ensure that the microscopes are set up, and students are not to adjust the scope.

Activity –

-Main exercise is to observe different shapes of bacteria through the microscope (each microscope having one of the three shapes), and to draw the different bacteria on a sheet of paper.

-Break students into groups of two, one group per tutor. Each student should have a piece of paper and a pencil.

-At each station (different microscope with different type of bacteria), the students take turns looking through the scope and describing what they see to their partner. When one student is looking through the scope, the other could be either drawing what is being described, or drawing what they have witnessed.

-Each group will be at each microscope (taking turns) for 2-3 minutes, during which time they should produce a picture of what shape of bacteria is in that microscope. Eventually, each student should have three circles on their paper with different shapes of bacteria in each circle.

-Notes:

  • Tutors will need to periodically ensure that the scope is in focus and on the correct shape.
  • Students should be encouraged, once done with the drawing, to either investigate the microscope or to ask other questions about the bacteria. Examples of each shape of bacteria (both good and bad) could be furnished.

Questions:

-How many bacteria can you see in each slide? (counting takes up good time. The other student could count for verification) How many would fit on the head of a pin (use the magnification idea). Perhaps the tutor could let them view a human hair a one of the stations (toward the end) to provide an idea of scale.

-Why are the bacteria red? Are they all normally red? Didn’t we see them in different colors on the plates? (This red color is a stain used to allow them to be seen more easily under the scope. Bacteria come in all different colors, but each one will be mostly clear and hard to see under a microscope. The colonies only start to look a certain color when there are thousands of them piled on top of one another.)

3—(Backup) Scale/size of bacteria

Materials – sidewalk chalk, either meter-sticks of tape measures, pictures of bacteria with size scale (for reference, one fore each group)

Activity –

-Give students a sense of the size and shapes of bacteria (and viruses?) by letting them draw them to scale against a human hair that is 1-5 meters wide. This will be done on the playground outside.

-Break students into groups of four(ish). Each group will have chalk for each student, as well as at least one measuring device, and at least one picture of the different shapes of bacteria. There will also be more detailed pictures/diagrams of bacteria for the motivated students.

-Each group will need to work together to draw their scale model. They may divide the labor as they like, but there should be an example of each shape of bacteria for each student, and there should be some way to show how big they actually are. This can be as open or as closed-ended as the tutor feels up to doing.

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-Notes:

  • option: have three scale models of hair-widths, different or similar sizes, and have the students draw different types of bacteria at each station.
  • Also: have the students draw a virus on the same scale. How can they use the tools to make it the right size?