Answer to Question 1
D
Answer to Question 2
It is possible to demonstrate a relationship between two variables by simply observing them. However, simple observation cannot establish the direction of the relationship. For example, you may observe that two variables change together consistently: as variable A increases, variable B also increases. However, you cannot determine whether changes in A are causing changes in B, or whether changes in B are causing changes in A. To avoid this problem in an experiment, the researcher takes charge and manipulates one of the variables. For example, the researcher increases the value of variable A and then observes variable B to see if it is affected by the increase. If B also increases, then the researcher can conclude that changing variable A has caused changes in variable B.
Chuckwalla body lengths at the end of a laboratory rearing experiment
Aerial and close-up views of a large biodiversity experiment in Cedar Creek, Minnesota. Each of the
Hormonally controlled cycles
Variable penetrance of mitochondrial mutations
Polygenic inheritance of wheat kernel color controlled by two additive genes
The Hershey-Chase experiment