Investigation 7B
Investigating Pond Water
7B Investigating Pond Water
Which microscopic organisms are found in pond water?
If you took a single drop of water from a pond
and looked at it under the microscope, you’d be
lucky to find anything. To increase the number
of organisms in your sample you can create a
hay infusion. A hay infusion is a culture that
uses water collected from a pond, stream,
creek, or puddle and dried grass. You simply
place dry grass a container of water and allow
the culture to sit for approximately one week. At
the end of the week, the culture will be teeming
with different types of small microscopic
organisms. In this investigation, you will make a
hay infusion and then using what you have
already learned, try to identify the microorganisms.
A
Materials
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Glass jar
Pond or creek water
Hay or dry grass
Milk
Yeast
Depression slides
Coverslips
Corn syrup
Light microscope
Dropper
Setting up
1. Place pond water into the glass jar until the jar is about half-filled.
2. Add several pieces of cut hay or dry grass to the jar.
3. Add a teaspoon of milk and a grain of yeast.
4. Loosely cover the jar with the lid. [Be sure not to tighten the lid of the jar completely
since the organisms need oxygen.]
5. Place the jar in a warm place, in front of a window or in an incubator.
6. Check the hay infusion periodically, although it will take about a week for the
organism growth to peak, spot checking the culture will ensure you see lots of
different organisms.
Safety tip: The hay infusion will contain a large number of bacteria. Make sure you wash your
hands completely after handling the hay infusion, samples, and depression slides.
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B
Stop and think
a.
What types of organisms do you think you will find under the microscope after a week?
b.
Why is it important not to tighten the lid of the jar completely?
C
Doing the experiment
1. Place a drop of water into your depression
slide chamber.
2. Place a single drop of corn syrup into the
well of the depression slide chamber. The
corn syrup will slow the movement of the
organisms without harming the
organisms.
3. Remove jar’s lid. Take a small drop of the
water from the top of the jar and place it
into the depression slide chamber.
4. Carefully, place a cover slip on top of the
chamber and place under the microscope.
5. Using your low-power objective, bring the
sample into focus. It is important to
remember that the organisms will be
moving quickly, so this step can be tricky.
6. Once you have found the correct plane of
focus, switch to the high-power objective.
7. Make a sketch of what you observe under the microscope. It is possible you will see a
number of organisms, and this is good. Make a careful sketch of every organism you
see.
8. Once you have completed Steps 1-7, wash and thoroughly dry the chamber of the
compression slide.
9. Repeat the procedures with drops of water taken from different areas of the jar.
10. Once you have completed your drawings, try to identify the organisms you have
observed in your hay infusion. A sheet of photos will be provided by your teacher. Use
other resources such as books or the Internet if needed.
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Investigation 7B
Investigating Pond Water
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Sample Location:
(top, middle, bottom)
D
a.
Table 1: Hay infusion observations
Sketch of the Organism
Name of organism
Thinking about what you observed
How many different types of organisms did you identify?
b. What type of information did you use to help you identify the different organisms in your
hay infusion?
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c.
Is there a difference between the types of organisms you observed at the bottom, middle,
and top of the jar?
d. What sample contained the largest number of different organisms?
e.
Which organisms belong to the Kingdom Protista? Which organisms do not?
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