Washington College STEM Lab: Instructions
Part I: Observations of the Blackworm
COMPOUND LIGHT MICROSCOPE OBSERVATIONS OF THE BLACKWORM
You will use the compound light microscope to make observations of the
blackworm, Lumbriculus variegatus. This worm is an oligochaete, the same
group in which the common earthworm is found. Its habitat is freshwater.
That lab will focus on the effect of environmental conditions on the pulsation
rate of the worm’s dorsal blood vessel.
● Working with a partner observe a blackworm under the microscope. Do
this by placing a worm in a drop of water (enough water that the worm can
move around) onto a microscope slide using a plastic transfer pipette (DO
NOT use a coverslip).
● Scan the worm to be sure that you can distinguish its anterior (head) end
from its posterior (tail) end. (Both ends of the worm may be clear. You can
determine the anterior region by watching to see which end of the worm
is exploring its environment). Determination of the ends of the animal is
important because, when you determine pulsation rate, you will want to
note which part of the blood vessel (e.g. middle, posterior) you are
observing.
● Working with a partner, obtain a worm for viewing by sucking it and some
of the spring water in which it is living into a plastic pipette. Insert a
capillary tube into the plastic pipette and gently blow the worm into the
capillary tube. If you use a Kimwipe to suck a bit of water out of each end
of the capillary tube, the worm will be trapped in the tube by air bubbles
on each end. This will help to restrict the movements of the worm for
better observations.
● Using two small mounds of clay, one near each end of the tube, mount the
tube on a glass microscope slide so that the long axis of the tube is parallel
to the long axis of the slide. You want enough clay to adhere the tube to
the slide, but not so much that the tube hits the 4x objective of the scope
when you try to focus on it.
● Observe using the scanning objective only (4x objective) You may rotate
the capillary tube to see different aspects of the worm.
● Make observations
observations.
of the worm’s
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anatomy
and record your
● Make observations
observations.
of the worm’s
behavior and record your
Note that the worm has a circulatory system (a closed circulatory system)
thus; red blood cells circulate in this system. You should also note that it has
two blood vessels that run the length of the organism, a large dorsal blood
vessel (you must be able to determine which blood vessel is the dorsal blood
vessel), and a thinner ventral blood vessel. The larger dorsal blood vessel
pulses to move blood through the circulatory system (which we will measure).
Lateral vessels are also present.
Your instructor will project a video of pulse in dorsal blood vessel of the
blackworm: http://www.youtube.com/watch?v=SUHQ38XYKeA
● After one minute (time to allow the worm to acclimate to the tube) you can
begin to determine the number of pulsations of the dorsal blood vessel per
minute for your worm. Since the worm may not stay still for an entire
minute, do this by counting the number of pulses per 20 seconds, and
multiply your answer by three. In order to count the pulsations focus on
one area and count as the pulsations arrive at this same location. It’s best to
choose a location in the middle of the worm. Do not follow a pulsation
down the length of the worm.
You will record this data in a data collection table. Create a data collection
table: your table should include the data for the number of pulsations (heart
rate) per 20 seconds, and pulsations (heart rate) per minute for 5 different
worms. In addition you should determine the average pulsation (heart rate)
rate per minute for the blackworms.
Part II: Design an Experiment with the Blackworm
Investigating the Effects of Drugs on Pulsation Rate in Lumbriculus variegatus
Our subject of interest today is the blackworm, Lumbriculus variegatus.
When scientists are designing an experiment to test a hypothesis, they need to consider
sample size, controls and replication. Sample size is important because in order to
determine if the data supports the hypothesis, more than one sample needs to be tested.
For example, if you hypothesized that dandelions grow better in the sun versus the shade,
you would not measure just one dandelion but instead measure many in the sun and many
in the shade. In addition to sample size, a good experimental design contains a control.
A control group goes through all of the steps of an experiment but lacks, or is not
exposed to, the factor being tested. For example, if you are testing the reaction of an
organism to a particular liquid, water can be the control substance substituted for the test
liquid. If you are testing the reaction of an organism to a particular powder, you could
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substitute fine sand for the test power. Lastly, a scientist performs experiments with
replicates and averages the data. This ensures a most precise measurement of the data.
You will measure the blood vessel pulsation rate in blackworms that you expose to one or
more chemicals. Worms that have not been exposed to a chemical will serve as controls.
Blood vessel pulsation in blackworms is partially controlled by neurotransmitters that are
secreted by nerve cells (very similar to control of human heartbeats). The frequency of
the pulsations can easily be calculated by observing the pulse in the middle section of the
worm. Because the rate of pulsation is easily seen and calculated and some chemicals
can diffuse through the worm’s thin skin, it is easy to test the effects of exposure to
different chemicals on the cardiovascular system of the blackworms.
Using one of the three different drugs available in the lab (caffeine, nicotine, and alcohol)
you will design an investigation to see how pulsation rate changes in response to
exposing your worms to drugs. In addition to giving you different chemicals from which
to choose, we have provided you with different concentrations of each chemical. You
have several options on how to design your experiment; you can investigate the effects of
one or more drugs, investigate the effect of different concentrations of a drug, and/or
investigate the effect of the length of exposure time to the drug.
A. Designing your experiment
Your experiment MUST measure a control and two different chemical conditions. Some
suggestions are examining different concentrations or different exposure times to a
chemical. Think about (and answer) the questions below as you are designing your
experiment. Present your experimental plan to your lab instructor (or TA). Do not
proceed with your experiment until it has been approved.
1.
2.
3.
4.
What is your question (hypothesis)?
What is your dependent variable (what YOU measure)?
What is your independent variable (what YOU change)?
Describe your methods (what are you going to do?). Include the number of
replications and be specific about your control.
5. How do you think this variable will affect the pulsation rate (increase or decrease)?
EXPLAIN WHY. (what is the physiological effect of this chemical?
6. What results would support your prediction?
7. Make a data collection table using Excel to record your results.
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B. Perform your experiment
1. Fill small glass dishes half full with your chemical or control solutions.
2. Place approximately 3-5 worms in the CONTROL dish. Do not add any
worms to the chemical dish.
3. Allow the worms to acclimate in the control solution for approximately 2
minutes.
4. Using a plastic pipette obtain one worm and place it in the capillary tube.
5. Mount the capillary tube containing the worm on the stage of the
microscope using clay.
6. Observe using the scanning objective (4x) only. You may rotate the
capillary tube to see different aspects of the worm. Allow 1-2 minutes for
your worm to recover after being transferred into the capillary tube.
7. Determine the number of pulsations of the dorsal blood vessel per minute
for your worm. Do this by counting the number of pulses per 20 seconds,
and multiply your answer by three.
8. Repeat steps 4-7 for 2 different worms in the control solution. Record
your data in a data collection table. So you will measure 3 different worms
in total and record the pulse rate for each one.
Now it is time to move on to your experimental conditions
9. Using a pipette or a spoon, transfer 1 worm into one of your chemical
solution (s) and incubate for 5 minutes (or variable time depending on
your experimental question).
10. After incubation, rinse the worm briefly with water, place the worm into a
capillary tube and measure pulsation rate as you did previously. Record
your data in a table.
11. Next, repeat steps 9-11 for two additional worms. So you will measure 3
different worms in total and record the pulse rate for each one.
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Washington College STEM Lab Worksheet
LEARNING OBJECTIVES:
Content:
1. Understand the steps of the scientific method
2. Demonstrate an ability to describe the effect of different chemicals on
pulsation rate in blackworms
Part I:
1. Make observations of the worm’s anatomy and record your
observations.
2. Make observations of the worm’s behavior and record your
observations.
Data collection table:
Part II:
1. What is your hypothesis? Predict what you think will happen.
2. What is your dependent and independent variable?
3. Describe your methods (Sample Size and control).
4. Make a data collection table to record your results.
Data collection table:
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Assignment: (30 points)
1. Title and Name. Write a specific title for your lab report. You DO NOT need to
make a separate title page just include your name and title at the top of the first page
of your lab report.
2. Write a modified introduction. A modified introduction includes your question
(hypothesis) and your prediction and an explanation of your prediction (why did you
make this prediction?)
3. Using your data collection table, determine the average pulsation rate for the
control and experimental worms. Include your data collection table with your
assignment.
4. Create a data analysis table (see example below) indicating the average pulsation
rate (pulsation/min) for the control and each of the experimental worms. The table
must have a number, title and properly labeled columns and rows.
5. Generate a column graph (see example below) illustrating the mean pulsation/min
for your control and experimental conditions. Your graph must have labeled axes
with proper units and a title.
Questions:
1. According to your data what effect did the chemical treatment have on the
average pulsation rate of the blackworms? Explain the observed effect based on
the physiological role of the chemical(s) used in the experiment.
2. Was your prediction supported by the data? Explain.
Table 1: Average pulsation rate for blackworms exposed to fruit punch and sprite for 15 minutes
(N= 3).
Chemical
Control
Fruit Punch
Sprite
Ave. Pulsation
(beats/min)
21
36
44.25
Figure 1: Average pulsation rate (beats/min) of blackworms exposed to fruit punch and sprite.
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