Pondscum Lab
Class Copy – Do not take!
Purpose
How can we identify living organisms from nonliving materials in a microscopic sample?
Hypothesis
Your hypothesis should begin with the word “to” and should reflect on the methodology we will use to observe and
identify living organisms in a pondscum sample.
Materials
Microscope
Microscope slides
Slide covers/Cover slips
Pipette
Plastic cup
Pondscum sample
Kimwipes
Paper towels or tissues
Procedures
1. Fill out the characteristics of life table on your lab worksheet. Keep in mind that your goal for this lab is to find
and identify potentially living organisms in your pondscum sample.
2. Prepare your lab table. The following materials will need to be set up at your table:
a. Microscope (plugged in and turned on)
b. One microscope slide (clean with a kimwipe if dirty)
c. One microscope slide cover
d. One pipette
e. One plastic cup
f. One small piece of paper towel or tissue paper
3. Retrieve your sample of pondscum from the class bottle and transfer it into your plastic cup using the pipette
provided. Solid detritus settles to the bottom, so make sure the bottle has recently received a good shake (with
the cap on) first so that the sample is evenly distributed.
4. Create your wet mount:
a. Use your pipette to place a small drop of pondscum
sample onto your clean microscope slide.
b. Hold your slide cover at a 45° angle. (See Figure 1)
c. Gently touch the edge of the drop of sample with the
edge of your slide cover.
d. Gently lower the cover slip down to allow the water to
spread under the slip before dropping the slip into place.
Avoid dropping the slip too far up, or else you will trap air bubbles between your microscope slide and cover
slip. Do not press on the cover slip to remove air bubbles; this will break the glass slip and/or damage your
specimen.
5. Set your wet mount on your microscope stage. Vary the placement of your slide and magnification of your
microscope until you can focus clearly on your specimen. Specifically look for organisms you believe are (or once
were) alive.
6. Begin filling out your lab worksheet, starting with your first observation.
a. You are filling in one organism per observation box. If you find a colony of the same organism, a single
cell from that colony (or the entire colony itself) represents one organism. If you find three different
species of microinvertebrate in your sample, each species has its own observation box.
b. Draw an approximate representation of the microinvertebrate you find in your sample.
c. Note what magnification you used to find the organism.
d. Briefly explain two reasons why you thought it was alive.
i. Use your characteristics of life as reference. For instance, you could list that you found evidence
of a cell splitting in half (or with a cleavage furrow present) for reproduction, or of an amoeba
consuming another organism for food.
ii. Keep in mind that the longer your sample is under view, the more likely the microinvertebrates
in the sample have died. The age of the sample (older = less alive), the temperature it was kept
at (room temperature is best), how aerated the sample was prior to use (some organisms are
aerobic and need oxygen to survive; some organisms are anaerobic and will die in the presence
of oxygen), and how long it was kept in the microscope’s light (longer amount of time = more
likely your microinvertebrates have been “cooked”) will affect the lifespan of your sample.
7. After completing your first observation, search for another microinvertebrate in your sample. If a second,
unique organism is not visible from your current POV, you will need to adjust your slide to find additional
organisms. Consider using different magnifications to assist you in finding smaller organisms.
8. Repeat steps 6 & 7 until all of your observation boxes are complete.
9. If your lab group does not have a sample with many active microorganisms, utilize the other lab group’s samples
(including the teacher example) to complete your worksheet.
Data/Observations
Your worksheet will serve as your observations. Fold your completed sheet in half and glue or staple it into your lab
notebook to receive credit.
Discussion Questions
Answer the following questions in complete sentences in your lab notebook:
1. What are the four characteristics of life?
2. How might a single-celled organism show signs of reproduction?
3. Why should you not press down on your microscope slide cover to remove air bubbles?
4. What are some factors that might affect the lifespan of your sample?
Conclusion
In your results, make sure you describe the following:
 Was your hypothesis supported by your observations?
 The magnification that was easiest to find a specimen in
 The characteristic of life that was consistently easiest to observe in most specimens
 Issues you had with creating your wet mount, and ideas for how you can fix them
 Issues you had with finding microinvertebrates in your sample, and ideas for how you can fix them
o Think about the magnification, the quality of the sample, and how saturated your wet mount was