Lumbriculus variegatus Pulse Rate Lab: Stimulant Analysis
Introduction: The Lumbriculus variegatus, or blackworm, possesses great
scientific value consequent of its unique biological characteristics. Residing in
major parts of both North America and Europe, the blackworm can most
frequently be observed in marshy areas, or similar places with shallow water,
near its favored microhabitats: decomposing foliage, rotting logs, or vegetation
near water. The real scholastic significance of the blackworm can be found by
observing its closed-circulatory system, made observable by the worm’s
transparent skin. Through regular pulsations, the blackworm’s dorsal blood
vessel circulates blood and oxygen, via erythrocruorin, the worm’s equivalent to
hemoglobin, from the posterior end towards the anterior end. Study of L.
variegatus’ pulse rate allows scientists to determine the potential effects a
chemical might have on the phylum annelida and humans.
Hypothesis: If a blackworm is given stimulant, the pulse rate will be elevated.
Independent Variable: exposure to stimulant
Materials: 4 Petri dishes, 2
Dependent Variable: pulse rate
Plastic pipettes, Microscope,
Control: blackworms exposed to spring water
Cover Slip, Well Slide,
Controlled Variables: ambient temperature,
Stopwatch, 10 Blackworms,
light level of microscope, feeding frequency,
Stimulant Solution Spring
relative size of blackworms, worm-handling time Water, Paper Towels
Procedure:
1.Collect two groups of five worms in separate containers using two pipettes, one
per container. Introduce stimulant to one container and spring water to another.
2.Collect a single stimulant worm into the ‘stimulant’ pipette. Deposit the worm
onto a well slide, absorb excess water using paper towel, and cover with a
cover slip. Place this setup under a microscope.
3.Turn the microscope’s lamp on to the lowest necessary level. Using the lowpower objective, locate the dorsal blood vessel of the blackworm around the
middle third of its body length.
4.Start a stopwatch, and count the frequency of dorsal vessel pulsations for thirty
seconds. Double this number, and record in a data table.
5.Using the ‘stimulant’ pipette, collect the worm and place in a new container.
6.Repeat steps 2 through 5 for the other stimulant-exposed worms.
Allen Sanford and Michael Patterson
6.Collect a single spring-water worm using the ‘spring-water’ pipette. Deposit on
the worm on a new well slide, absorb excess water with a new piece of paper
towel, and cover with a new cover slip.
7.Repeat steps 3 and 4 for the spring-water worm.
8.Collect the worm off the well slide, and place the worm in a new spring-water
container; use the ‘spring-water’ pipette for handling.
9.Repeat steps 7 through 9 for other spring-water worms.
Results: The stimulant group demonstrated a mean pulse rate of 9.2 min-1
higher than the spring water group.
Conclusion: Our results display a statistically significant pulse rate increase in
the stimulant-exposed worms compared to the spring-water worms.
Conventional laboratory practice requires a p-value of less than .05 for a
statistical test to be considered “significant”; in a 2-sample t test, our results
demonstrated a p-value of .00554, much smaller than necessary. However, this
significance is blind to such possible inaccuracies as the doubling of our thirtysecond data and the fact that our control data was collected on a different day
than our stimulant data. While not quantitatively affecting the significance, the
lab’s results in general are qualitatively weakened by these two impediments.
Repeating the experiment with sixty-second trials, more trials per worm, and
completion of the procedure unitedly would produce more scientifically viable
results.
Reference: http://www.eeob.iastate.edu/faculty/DrewesC/htdocs