1.1 The scientific method is a deliberate way of asking and answering questions about the natural world.

Observations are used to generate a hypothesis, a tentative explanation that makes predictions that can be tested. page 4

On the basis of a hypothesis, scientists design experiments and make additional observations that test the hypothesis. page 5

A controlled experiment typically involves several groups in which all the conditions are the same and one group where a variable is deliberately introduced in order to determine if that variable has an effect. page 5

If a hypothesis is supported through continued observation and experiments over long periods of time, it is elevated to a theory, a sound and broad explanation of some aspect of the world. page 6

1.2 Life works according to fundamental principles of chemistry and physics.

The living and nonliving worlds follow the same chemical rules and obey the same physical laws. page 8

Experiments by Redi in the 1600s and Pasteur in the 1800s demonstrated that organisms come from other organisms and are not spontaneously generated. page 10

Life originated on Earth about 4 billion years ago, arising from nonliving matter. page 11

1.3 The fundamental unit of life is the cell.

The cell is the simplest biological entity that can exist independently. page 12

Information in a cell is stored in the form of the nucleic acid DNA. page 12

The central dogma describes the usual flow of information in a cell, from DNA to RNA to protein. page 13

The plasma membrane is the boundary that separates the cell from its environment. page 14

Cells with a nucleus are eukaryotes; cells without a nucleus are prokaryotes. page 14

Metabolism is the set of chemical reactions in cells that build and break down macromolecules and harness energy. page 14

A virus is an infectious agent composed of a genome and protein coat that uses a host cell to replicate. page 15

1.4 Evolution explains the features that organisms share and those that set them apart.

When there is variation within a population of organisms, and when that variation can be inherited, the variants best able to grow and reproduce in a particular environment will contribute disproportionately to the next generation, leading to a change in the population over time, or evolution. page 15

Variation can be genetic or environmental. The ultimate source of genetic variation is mutation. page 16

Organisms show a nested pattern of similarity, with humans more similar to primates than other organisms, primates more similar to mammals, mammals more similar to vertebrates, and so on. page 16

Evolution can be demonstrated by laboratory experiments. page 18

1.5 Organisms interact with one another and with their physical environment, shaping ecological systems that sustain life.

Ecology is the study of how organisms interact with one another and with their physical environment in nature. page 19

These interactions are driven in part by the anatomy, physiology, and behavior of organisms, that is, the basic features of organisms shaped by evolution. page 19

1.6 In the 21st century, humans have become major agents in ecology and evolution.

Humans have existed for only the most recent 1/200 of 1% of life’s 4-billion-year history. page 20

In spite of our recent arrival, our growing numbers are leaving a large ecological and evolutionary footprint. page 21

Solving biological problems requires an integrated understanding of life, with contributions from all the fields of biology, including molecular biology, cell biology, genetics, organismal biology, and ecology, as well as from chemistry, physics, and engineering. page 22