Connecting to Your World In 1928, Alexander Fleming, a Scottish scientist, noticed that a bacteria he was studying did not grow in the presence of a yellow-green mold. Other scientists had made the same observation, but Fleming was the first to recognize its importance. He assumed that the mold had released a chemical that prevented the growth of the bacteria. That chemical was penicillin, which can kill a wide range of harmful bacteria. In 1945, Fleming shared a Nobel Prize for Medicine with Howard Florey and Ernst Chain, who led the team that isolated penicillin. In this section you will study the methods scientists use to solve problems.

Key Concepts

• How did alchemy lay the groundwork for chemistry?

• How did Lavoisier help to transform chemistry?

• What are the steps in the scientific method?

• What role do collaboration and communication play in science?

Vocabulary

• scientific method

• observation

• hypothesis

• experiment

• manipulated variable

• responding variable

• theory

• scientific law

Reading Strategy

Building Vocabulary After you read this section, explain the difference between a theory and a scientific law.

Guided Reading and Study Worksheet