Biology Now, 2e

10 ■ CHAPTER 01 The Nature of Science

SCIENCE

a single variable, known as the independent

variable. In this case, Blehert’s independent

variable was fungal exposure. Some bats were

exposed; others were not. A dependent variable

is any variable that responds, or could poten-

tially respond, to changes in the independent

variable. Blehert’s dependent variable was any

sign of WNS on the healthy bats.

If we think of the independent variable as the

cause, then the dependent variable is the effect. In

the most basic experimental design, a researcher

manipulates a single independent variable and

tracks how that manipulation changes the value

of a dependent variable. Blehert manipulated

his independent variable—exposing some bats

to the fungus but not others—and then tracked

his dependent variable, whether the bats showed

symptoms of WNS.

Blehert made sure his experiment was a

controlled experiment. A controlled exper-

iment measures the value of the dependent

variable for two groups of subjects that are

comparable in all respects, except that one

group is exposed to a change in the independent

variable and the other group is not. In this case,

healthy bats were either exposed to the fungus

Descriptive:

Looking for

physical

evidence of

WNS

Analytical:

Measuring the

weight of each

bat

Experimental:

Injecting a

fungicide to

determine

whether it will

protect a bat

from WNS

One research team; three approaches

Figure 1.5

Te s t i n g hy p o t h e s e s u s i n g m u l t i p l e a p p r o a c h e s

Scientists set up an underground laboratory in Tennessee’s New Mammoth Cave to test hypotheses

about white-nose syndrome (WNS) using descriptive, analytical, and experimental approaches.

Q1: Give a possible hypothesis that could be tested by weighing the bats.

Q2: State the hypothesis being tested in the photo on the bottom right.

Q3: Explain in your own words why an experimental study is the only way to show a

cause-effect relationship.