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Bacteria in Humans and Dogs

In this experiment, you will get to observe single-celled organisms (bacteria,
actually) that live in the mouths of both humans and dogs.

1. You’ll need to get your materials together. Be sure to label the Petri
dishes and have your other equipment out: the cotton swabs, the
canine volunteers and the human volunteers.
2. First, scrape the inside of a volunteer’s cheek use the cotton tip to
swab. Swirl the cotton swab onto a Petri dish.
3. Repeat this for the rest of your human and dog volunteers.
4. Find a dark, warm spot for your Petri dishes to live in that won’t be
disturbed for at least 24 hours.
5. After a day, remove the Petri dishes and place it next to your
compound microscope.
6. Use a fresh swab to move the bacteria from the Petri dish to the slide
and use a staining technique (covered in the Microscope Lab).

7. View each of your specimens, recording everything as you go along.
8. So what do you think? Whose mouth is cleaner – dogs or people?

Celery Stalk Water Race

If you think of celery as being a bundle of thin straws, then it’s easy to see
how this experiment works. In this activity, you will get water to creep up

through the plant tissue (the celery stalk) and find out how to make it go
faster and slower.

1. First, find four celery stalks about the same size with leaves still
attached.
2. Mix up a four-cup batch of colored water (try purple).
3. Place your celery stalks in the water, leaf-end up. After an hour or
two, take it out and place it on the paper towel. Label your celery
stalk with the each time length it was in the water.
4. Repeat this for different increments of time. Try one overnight!
5. Use a ruler and measure how high the water went. Record this in your
science journal.
6. Now make a graph that compares the time to distance traveled by
placing the time on the horizontal axis and the distance traveled on

the vertical.

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