SCIENTIFIC THINKING In a study to examine the effectiveness of a new acne cream, participants were assigned to one of two groups: those who would be asked to use the cream for three months and those who would not use any treatment. Participants would be asked to keep a journal rating how bad they think their acne is on a scale of 1–10 each week. What are the well-designed aspects of this study? What are the limitations? How would you improve the design of this study to address these limitations?

A controlled experiment is one thata. proceeds slowly enough that a scientist can make careful records of the results.b. keeps all variables constant.c. is repeated many times to make sure the results are accurate.d. tests experimental and control groups in parallel.

Control subjects in an experiment .a. should be similar in most ways to the experimental subjects;b. should not know whether they are in the control or experimental group;c. should have essentially the same interactions with the researchers as the experimental subjects;d. help eliminate alternative hypotheses that could explain experimental results;e. all of the above

An experiment in which neither the participants in the experiment nor the technicians collecting the data know which individuals are in the experimental group and which ones are in the control group is known as .a. controlled;b. biased;c. double-blind;d. falsifiable;e. unpredictable

A relationship between two factors, for instance, between outside temperature and the number of people with active colds in a population, is known as a(n) a. a. significant result;b. correlation;c. hypothesis;d. alternative hypothesis;e. experimental test

In April 1986, an accident at a nuclear power plant in Chernobyl, Ukraine, scattered radioactive fallout for hundreds of miles. In assessing the biological effects of the radiation, researchers found mosses to be especially valuable as organisms for monitoring the damage. Radiation damages organisms by causing mutations. Explain why it is faster to observe the genetic effects of radiation on mosses than on plants from other groups. Imagine that you are conducting tests shortly after a nuclear accident. Using potted moss plants as your experimental organisms, design an experiment to test the hypothesis that the frequency of mutations decreases with the organism's distance from the source of radiation.

The graph below shows the results of an experiment in which mice learned to run through a maze. (c) List some variables that must have been controlled so as not to affect the results.

The graph below shows the results of an experiment in which mice learned to run through a maze. (b) Which was the control group and which the experimental? Why was a control group needed?

Suppose that in an experiment similar to the camouflage experiment described in Module 1.5, a researcher observed and recorded more total predator attacks on dark-model mice in the inland habitat than on dark models in the beach habitat. From comparing these two pieces of data, the researcher concluded that the camouflage hypothesis is false. Do you think this conclusion is justified? Why or why not?