Materials:
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Petri dishes
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Media
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inoculating loop or needle
Procedure:
1. Pouring media:
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Pour prepared media into petri
dishes. Fill each dish to about half full.
-
Pour the media into the dishes while the media is still a hot liquid.
-
Uncover each dish only when pouring and cover immediately after pouring.
Any micro-organisms in the air, on your hands, on non sterile tools or
from your breath
can land in your petri dish and grow. These uninvited cultures are
called contamination.
2. Follow the directions below to
avoid contamination:
-
Keep the lid on your petri dish as much as possible.
-
Work in a dust free area away from drafts and breezes.
Avoid working near open doors and windows or furnace ducts.
-
Seal the dish around the perimeter with either a thin strip of parafilm
or plastic wrap.
3. Seed (inoculate)
the petri dishes with micro-organisms.
The most common method of inoculation is to streak the plates with
a inoculating loop or needle.
4. Grow( incubate) the micro-organisms.
Most micro organisms grow best at around 90 degrees Fahrenheit.
In some homes a warm area can be found perhaps on top of a bookcase,
where this temperature occurs. Room temperature will often work if
you have more time.
Otherwise, you can improvise a warm area with a homemade incubator.
5. Check on the growth on your cultures
at least once a day.
When the colonies have grown sufficiently, photograph the plates if
at all possible for your report.
You can slow the growth by placing the dishes in a cool place. (The
refrigerator works
but many parents have understandable objections to putting “that stuff”
near their food.)
Many experiments will be finished at this point.
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