Chapter 1.3Scientific Processes

Objectives

• Describe the stages common to scientific investigations.

• Distinguish between forming a hypothesis and making a prediction.

• Define the word theory as used by a scientist.

Scientific Processes

• • Collecting observations• • Asking questions• • Forming hypotheses and making

predictions• • Confirming predictions

(with experiments when needed)• • Drawing conclusions

A Case Study in Science

• Observations Suggest Questions

1897 Dr. Ronald Ross was working in Secunderabad, India.

• Wanted to determine cause of Malaria

• Was a leading cause of death

Doctors knew the disease was caused by a microscopic parasite, Plasmodium vivax.

• Doctors were unsure how the disease spread.

Dr. Ross observed that patients who slept in open wards were more apt to get the disease.

Hypothesis

• Ross suggested a testable explanation why this happened

• He proposed that mosquitoes were spreading the disease.

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He further hypothesized that it was the Anopheles mosquito.

Predictions

• Ross knew that if his hypothesis were correct, he could predict several consequences.

Predictions

1. If Anopheles mosquitoes were spreading the disease, then mosquitoes that had bitten infected patients would have the Plasmodium inside them.

Predictions

2. He also predicted that the Plasmodium would be alive in the mosquitoes.

Experimentation

• Testing under controlled conditions

Controlled Conditions• A group not exposed to the variable

(control group) is compared to a group that is exposed to the variable (experimental group).

• Ross compared mosquitoes that had not feasted on infected patients (control group) with those that had feasted on infected patients (experimental group).

Control Group Experimental Group

The control group did not have Plasmodium living in the stomach

The experimental group did

Ross confirmed and retested his work

• He proved that the Plasmodium moved from the mosquito’s stomach to its salivary glands.

Ross developed a theory….

• …that mosquitoes were responsible for the spread of malaria

Dr. Ross wrote a letter to the Indian government suggesting mosquito control could help combat an epidemic of malaria

Great progress in fighting the disease.

Dr. Ross won The Nobel Prize in Physiology or Medicine 1902

Theory

• unifying explanation for a broad range of observations

“Theory”

• To the public, “theory” implies uncertainty

• To scientists, “theory” refers to a generally accepted scientific principle

Theories have limited certainty

• No absolute scientific “truth” or certainty

• Future evidence may cause a theory to be revised or discarded.

Some theories will probably never be rejected.

• Theory of Gravity

• Atomic Theory

Theory of Evolution