Pre-Lab Activity 4: Identifying Experimental Variables and Controls Blackworms,

Question

Pre-Lab Activity 4: Identifying Experimental Variables and Controls Blackworms, Lumbriculus variegatus, is a group of freshwater oligochaete worms (related to earthworms and leeches). Blackworms have a large dorsal blood vessel that is easy to observe under a microscope. Design and conduct an experiment that tests the effect of chemical exposure the cardiovascular system of the blackworms. Using the scenario above, identify the following important experimental components: A. Independent Variable B. Dependent Variable C. Control Variables D. Control Group

Explanation / Answer

The experiment can be set up as follows:

1) Divide the blackworms in two groups: test group and control group.

2) Now identify the frequency and duration of exposure. Let's say exposure frequency to be one and duration to be 10 minutes. Now identify the concentration of chemical exposure that needs to be tested and make observations.

3) Note the effect of different concentrations of chemical to which blackworms are exposed.

4) Test for acute toxicity where high single exposure is done for a small duration and for chronic toxicity where lower concentration exposure is done for longer duration.

5) Observe the exposure pathway as to how chemicals enter the body.

6) Make observations of the cardiovascular activity of blackworms after exposure.

7) Once the observations are made give blackworms recovery period where the test group is not exposed to chemicals for some duration.

8) After recovery period observe the changes in the cardiovascular activity of blackworms and how the activity changed at each concentration level of exposure,

9) Finally compare results of carddiovascular activity of test group to those in control group.

A) Independent variable- Exposure concentration i.e. the concentration of chemical can be changed from low to medium or high.

B) Dependent Variable- Cardiovascular activity

C) Controlled variable- Exposure duration to chemical and exposure frequency of chenical

D) Control Group- Blackworms which are not given chemical exposure.

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