Designing an Experiment

Asking a Question

¨ Identifying a problem to be solved.

¨ Spontaneous generation is the idea that life could arise from nonliving matter.

¨ In today’s terms, the idea of spontaneous generation can be considered a hypothesis.

¨ Testing a hypothesis involves designing an experiment.

¨ Variables are the factors in an experiment that can change.

Ex) equipment used, types of material, amount of material, temperature, light, and time

¨ A controlled experiment is a test of the effect of a single variable by changing it while keeping all other variables the same.

¨ The manipulated variable is deliberately changed (also known as the independent variable).

¨ The responding variable is what is observed and changes in response to the manipulated variable (also known as the dependent variable).

¨ In the past, data was kept by written records but today it is recorded on computers.

¨ Data is used from the experiment to evaluate the hypothesis and draw a conclusion.

¨ Scientists expect to test each other’s investigations.

¨ Publishing a description of an experiment in a scientific journal is essential.

¨ Experiments are often repeated by other scientists to make sure the data is not flawed.

¨ Ethical considerations prevent certain experiments.

Ex) determining the effects on people of a chemical suspected of causing cancer

¨ Scientists choose volunteers who may already be exposed and compare them to a group who has not.

¨ In field studies, such as animals in the wild, researchers try not to disturb natural systems that they observe.

¨ The word theory applies to a well-tested explanation that unifies a broad range of observations.

¨ Sometimes more than one theory is needed to explain a particular circumstance.

¨ A useful theory may become the dominant view among the majority of scientists, but no theory is considered absolute truth.

¨ As new evidence is uncovered, a theory may be revised or even replaced.

¨ Science is characterized by both continuity and change.