Note: Bean water incubation requires at least 3 days. Plan accordingly.
You will need: Table shown below to record observations, six beans, 50 mL beaker, and tap water. After
incubation, a clean slide, eye dropper from dissection kit, drop of bean water, toothpick, heat source,
crystal violet stain, staining tray, glass of water, work area protected from staining and microscope.
1. Set up the following table to record observations for Exercise 1 and Exercise 2.
Organisms in Micro communities
Motile or sessile
Producer or consumer
2. Place six beans from the experiment bag in the 50-mL beaker and half-fill it with tap
water. Allow the beaker to stand in a warm place for 3 to 4 days. Good locations
include the kitchen near the stove and a utility room near a hot water heater.
3. Prepare and stain a slide of the bean water. To do this, after the beans have been in
the water for several days, dip the clean eyedropper into the bean water and place a
small drop of bean water on a blank microscope slide. Spread the drop with the
toothpick until it is about 2 mm in diameter.
4. Light a candle or ignite a long kitchen match or lighter
to dry the bean-water slide. Use the test tube clamp to
hold the slide by one end in a horizontal position with
the spot of bean water on top. Gently pass the slide
through the flame several times. This process is called
“fixing” the specimen and sticks the cells in the bean water to the slide. Do not heat
the slide after the water has evaporated or pass it through the flame so slowly that
soot can accumulate on the bottom of the slide. But if the latter happens, you can
clean the bottom of the slide with a damp tissue.
5. Continue to hold the hot slide with the test tube clamp. Have a
glass with clean water by the sink or basin where you’re
working. Also have a clock or watch with a second hand
nearby. Hold the slide over the staining tray with the test tube
clamp. Place a few drops of crystal violet stain on the dried
bean residue on the slide. Be careful not to spill the crystal
violet outside the staining tray as it is a very strong stain. Staining the slide will make
the microorganisms from the bean water have more contrast and easier to see.
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6. After one minute, rinse the excess stain off of the slide by dipping it into the glass of
water. Gently shake excess water from the slide into a staining tray, and allow the
slide to air-dry.
7. View the dry slide directly with your microscope; no slide cover is required. Draw
what you see. Use the chart of microorganisms at the end of the experiment to
identify what you draw. List the organisms you observe in the table you've made.
Explain your reasons for each identification.
A. Next, make a wet-mount slide of the bean water. Place a tiny drop of the bean
water on a blank slide and carefully add a cover slip by touching it to the edge of
the drop and lowering the cover slip slowly. Check carefully for organisms. If
none seem visible, put a drop of crystal violet on the tip of a toothpick. Shake
most of the crystal violet off the toothpick into the staining tray. Gently lift the
cover slip and place the toothpick tip covered with crystal violet into the bean
water on the slide. Such a small amount won't color the water but it will stain the
organisms and help you see them more easily.
B. View the wet-mount slide with your microscope and draw what you see. Use the
following chart of microorganisms to identify organisms. List the organisms you
observe in the table. Explain your reasons for each identification.
C. Determine if each organism is motile or sessile.
D. Determine if each organism is a producer or a consumer.
Exercise 2: A Pond or Stream Water Micro community
You will need: Plastic funnel, disposable gloves, lab apron, coffee filter, blank microscope slides,
microscope slide covers, crystal violet stain, toothpick, pond or stream water, glass jar- pint-size or larger,
safety goggles and microscope.
1. Wear your laboratory apron and disposable rubber gloves to collect a sample of
water from a pond or slow moving stream in a pint-size or larger glass jar. The
source does not need to be of drinkable quality. In fact, a still or even stagnant
source may have a richer micro-community provided there are no contaminants in
the water such as oil or chemical pollutants that might kill the microorganisms. You
should wear your safety goggles when handling this pond water sample since you
don’t know what it contains.
2. If you cannot find any surface water, fill a quart or larger container or a bucket with
distilled water or well water, not water that contains chlorine, add a handful of rich
natural soil, some leaves or other natural materials you find in your yard, stir, let it sit
for a week, and draw your sample from that water.
LabPaq: BK-101 Page 70
3. Place a coffee filter inside the mouth of the funnel. Place the funnel in a small clean
glass that will suspend the funnel and keep it from falling over but is large enough to
hold half a cup of liquid below the funnel mouth,
4. Fill the 50-mL graduated cylinder with the collected pond water and slowly pour the
water sample through the filter. Repeat so that at least 100 mL of pond water passes
through the filter.
5. Remove the coffee filter from the funnel after all the water sample has drained
through it. Observe if there are any organisms large enough to see without
magnification on the filter paper. Quickly draw them for later identification. Turn the
coffee filter inside out and touch the moist tip area with the most collected residue
from the pond water to a clean glass slide. If the slide is dry, add a drop of pond
water. Carefully apply a cover slip.
6. Place the wet mount slide under the microscope. Draw what you see. Use the chart
of microorganisms at the end of this experiment to identify organisms; you can also
check the websites previously listed for other identification keys for the organisms.
List the organisms you observe in the table. Explain your reasoning for each
identification. If organisms are difficult to see, refer to step #6 in Exercise 1 and use
a tiny amount of crystal violet on a toothpick to stain the organisms so they’ll show
up more clearly.
7. Determine if each organism is motile or sessile, and if each organism is a producer
or a consumer.
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A. What are possible sources of the microorganisms in the bean water?
B. Explain the color differences between the producers and the consumers.
C. Are most organisms in the bean water producers or consumers? Are most
organisms in the pond water producers or consumers?
D. Are most producers motile or sessile? Are most consumers motile or sessile?
E. Explain the overall differences between the two environments.
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