Answer to Question 1A control is used in an experiment to look at the normal or untreated group. The
control allows the scientist to rule out other possible explanations for the observed
effects. In the first experiment, the control soil was a commercial potting mixture. By
growing the wheat seeds in a commercial growth medium, the scientist was able to
discount any effects of seed quality on the results.
Answer to Question 2The independent variable is the variable that is manipulated (changes in value) to
produce a change or effect in the dependent variable. In each of the three problems
posed in this exercise, the independent variable(s), such as the amount of protein
consumed daily by a hog, temperature, humidity, feed quality, or the amount of
green stuff on the pond surface, produced an effect on the dependent variable (hog
body weight, chick mortality, fish mortality). Suggest to your students that they
develop a hypothesis with independent and dependent variables that they are
interested in. This hypothesis could lead to the design of an FFA project, 4-H
competition project, or a science fair project.
Genetic control of root hair development.
The Experiment by Albrecht, 1978
Pavlov’s Salivary Conditioning Experiment (1 of 2)
Control of Homeostasis
Control of Molting in Crabs
Control of flower formation, as revealed by mutations in Arabidopsis thaliana.