Question

Types of experiments: Natural and manipulative

Experiments in environmental toxicology can sometimes be manipulative experiments in which the researcher actively chooses and manipulates the independent variable. In Hunt's study, for example, dosages of BPA were manipulated and the effects were measured. In manipulative studies, the researcher controls all the other variables in the experiment, so any health effects observed in the test subjects can be attributed to differences in the independent variable.In other cases, researchers use natural experiments in which the dependent variable (typically a measure of organism health) is measured under differing contexts that are not manipulated. Say, for example, that an accidental chemical spill contaminates five ponds. To determine the possible effects of the toxic chemical on frogs, a researcher could compare the hatching rate of frog eggs laid in those five ponds to the hatching rate of eggs laid in five uncontaminated ponds nearby. This would be an example of a natural experiment because concentrations of the toxic chemical in the ponds were not controlled by the experimenter, but rather resulted from the chemical spill.1. __________Blood concentrations of BPA in college students are compared to their recent consumption of canned food items 2. _____________the feeding behavior of fish in streams that receive acidic runoff from strip mines is compared to the feeding behavior of fish in unaffected streams. 3.___________the deformity rate in baby birds from nests in pesticide-sprayed fields is compared to the deformity rate in birds from nests in unsprayed fields 4 Tumor development is compared in mice exposed to five dosages of a known carcinogen in the laboratory 5. ____________Foraging activity levels are compared in tadpoles exposed to four concentrations of toxic metals in the laboratory. 6.__________Growth of corn plants is compared in field plots sprayed with three different dosage:s of weed killer 7.____________ BPA concentrations in the urine of people with diabetes are compared to BPA concentrations in the urine of people without diabetes

Answer 1

Answer no 1:

• Blood concentrations of BPA in college students are compared to their recent consumption of canned food items - Natural

As in this experiment we are not changing the amounts of canned food items consumed by the college students. Hence, it would be a natural experiment. IN a natural experiment the independent variable is not changed by the researcher.

Answer no 2:

• The feeding behavior of fish in streams that receive acidic runoff from strip mines is compared to the feeding behavior of fish in unaffected streams- Natural

A natural experiment can be described as an experiment in which the researcher will not control the independent variable. He only checks what effect a particular substance will have on the subject of test. As in the experiment, the acidic runoff in streams is not being fluctuated by the researcher, hence it is a natural experiment.

Answer No 3:

• The deformity rate in baby birds from nests in pesticide-sprayed fields is compared to the deformity rate in birds from nests in unsprayed fields- Natural

In this experiment, the amounts of pesticide spray are not being changed. The effects of a pesticide spray on birds is being compared with those who do not receive the pesticide spray. Hence, this experiment will be a natural experiment.

Answer No 4:

• Tumor development is compared in mice exposed to five dosages of a known carcinogen in the laboratory- Manipulative

Manipulative experiment can be described as an experiment in which the concentration or amounts of the independent variable are varied to check the results of varied concentration on the testing object. As in this experiment, Five different dosages of the carcinogen were given to check its effect on the mice hence, it is a manipulative experiment.

Answer no 5:

• Foraging activity levels are compared in tadpoles exposed to four concentrations of toxic metals in the laboratory - Manipulative

As the concentration of the toxic metals is being varied in each experiment to check the effects of each concentration on the tadpoles, hence it is a manipulative experiment.

Answer no 6:

• Growth of corn plants is compared in field plots sprayed with three different dosages of weed killer - Manipulative

As described above, a manipulative experiment is the one in which different dosages of an independent variable are given so that the effect of each dosage could be known on the testing object. Hence, as three different dosages of weed killers are being given in this experiment, it is a kind of manipulative experiment.

Answer no 7:

• BPA concentrations in the urine of people with diabetes are compared to BPA concentrations in the urine of people without diabetes - Natural

In this experiment, the amounts of BPA concentration are being compared in people with or without diabetes hence, it is a natural experiment.