Question

The active ingredients in many pesticides are chemical compounds that kill organisms such as insects, molds,
and weeds. Proponents claim that the use of pesticides improves crop yields and thus protects land and soil
by reducing the conversion of forests and wetlands to cropland. Opponents of pesticide use claim that
pesticides degrade water and soil quality and that other modern agricultural techniques and practices are
responsible for the improved crop yields in recent years.
(a) Design a laboratory experiment to determine whether or not a new pesticide (product X) is toxic to
minnows, a type of small fish. For the experiment you design, be sure to do all of the following.
(i) State the hypothesis.
(ii) Describe the method you would use to test your hypothesis.
(iii) Identify the control.
(iv) Identify the dependent variable.
(b) Describe experimental results that would lead you to reject your hypothesis in part (a)(i). (Be
specific.)

Answer 1

Placing minnows in two different tanks and exposing one of them to the chemical, made possible to observe the effect of the product X on small fishes. The hypothesis of low chemical concentrations lethality was rejected.

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We want to perform a simple lab experiment to determine whether Product X is toxic or not for minnows. We are opponents of pesticide use, so we believe it is toxic.

Hypothesis → The hypothesis is a conjecture or an assumption of what the

                        the researcher thinks is going to happen.

Product X in low concentrations is lethal to small fishes like minnows that are exposed to it.

Methodology

A group of twenty subadults, male minnows were used to perform this experiment. All of them were the same age and were grown under the same environmental conditions.

Half of these animals were placed on one tank, and the other half were placed on another tank.

Environmental conditions in both tanks were exactly the same. Both were exposed to the same temperature, water pH, light exposure, oxygen concentration, etc. All animals were equally fed with the same type and amount of food.

Tanks were labeled as tank A and tank B.

• Tank A received a low concentration of product X every two days.
• Tank B did not receive any chemical product.

The experiment lasted ten days. After that period of time, dead animals were counted.

• Treatment → Application of a minimal concentration of the product X.
• Independent variable → Product X → It influences the dependent

                                                                        variable.

• Dependent variable → Fishes' mortality rate → It changes according to

                                                             the presence/absence of the chemical

• Controlled variables → The tanks' environmental conditions, food

                                                supply, biological characteristics of the fishes.

        These are the variables that minght influence the results, so the    

         researcher has to keep them constant.

Results

After ten days of the experiment and using a minimal concentration of Product X, no dead animals were registrated in the tanks.

Discussion/Conclusion

• The results lead us to reject the proposed hypothesis.
• It seems that low concentrations of the product do not provoke small fishes' death.
• However, a new experiment can be proposed using different concentrations of Product X to evaluate the concentrations at which the chemical might cause a negative effect.

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