Biology (Holt)

Stages of Scientific Investigations

Although there is no single “scientific method,” scientific investiga-
tions tend to have common stages: collecting observations, asking
questions, forming hypotheses and making predictions, confirming
predictions (with controlled experiments when appropriate), and
drawing conclusions. These stages are summarized in Figure 15.

Collecting Observations

The core of scientific investigation is careful observation. Harte had
studied the Colorado salamander population for years. He had
learned what they eat, how they behave, when they reproduce, and
what conditions they thrive in. His students had helped him collect
water samples from the ponds, as shown in Figure 15. Frequent
visits to the ponds helped him realize the salamander population
was decreasing in number. Keeping careful records of the lakes’ con-
ditions helped him find an explanation.

Asking Questions

Observations of the natural world often raise questions. Harte ques-
tioned why the number of salamanders was dropping. He talked to
other scientists, carefully observed the organisms and environment
in the Rocky Mountains of Colorado, and read scientific reports. He
answered many of his questions through his observations, but some
key questions remained unanswered.
In the natural world, the moisture that falls as rain and snow is
very slightly acidic. In the Rocky Mountains of Colorado, however,
the moisture is high in sulfuric acid from power plants that burn
high-sulfur coal. This acidic moisture, called acid precipitation, is
released into mountain ponds each spring when the snow melts,
causing the water in the ponds to become more acidic in late May.
Most of the mountains’ annual moisture falls as snow. Harte
thought acid precipitation was important in the puzzle of the declin-
ing salamander population, but he needed evidence.

SECTION 3Scientific Processes 15

http://www.scilinks.org

Topic:Biology Careers

Keyword:HX4022

Scientific Processes

Asa Bradman, a student of

John Harte, helps in Harte’s

scientific investigation by col-

lecting water samples from a

Colorado pond.

Figure 15 Testing the

acidity of water

• Collecting observations


• Asking questions


• Forming hypotheses and
  making predictions


• Confirming predictions
  (with experiments when
  needed)


• Drawing conclusions