What is Life?
1.1 What Are the Characteristics of Life?
1. A living organism is distinguished from an inanimate object by the presence of a combination of characteristics.
2. An organism is organized as structures of increasing size and complexity, from biochemicals, to cells, to tissues, organs, and organ systems, to individuals, populations, communities, ecosystems, and the biosphere.
3. Emergent properties arise as the level of organization of life increases and are the consequence of physical and chemical laws.
4. Life requires energy to maintain its organization and functions. Metabolism directs the acquisition and use of energy.
5. Organisms must maintain an internal constancy in the face of changing environmental conditions, a state called homeostasis.
6. Organisms develop, grow, and reproduce.
7. Organisms respond to the environment, through irritability in the short term and by adaptation over generations. Natural selection eliminates inherited traits that decrease chance of survival and reproduction in a certain environment.
1.2 How is Life Diverse?
8. Biologists classify organisms with a series of names that reflect probable evolutionary relationships.
9. The three domains of life are distinguished by cell structure and organization. Cell complexity, mode of nutrition, and other factors distinguish members of kingdoms.
10. Evolution through natural selection explains why organisms are alike yet diverse and how common ancestry unites all species.
1.3 How Do Scientists Study the Natural World?
11. Scientific theories are ideas based on hypotheses that have survived rigorous testing. They attempt to explain natural phenomena.
12. Scientific inquiry, which uses the scientific method, is a way of thinking that involves observing, questioning, reasoning, predicting, testing, interpreting, concluding, and posing further questions.
13. Scientific inquiry begins when a scientist makes an observation, raises questions about it, and reasons to construct an explanation, or hypothesis.
14. Experiments test the validity of the hypothesis, and conclusions are based on data analysis. Experimental controls ensure that the data is the result of the variables in the experiment, and not other factors.
15. Placebo-controlled, double-blind experiments minimize bias.
16. The scientific method does not always yield a complete answer or explanation or may produce ambiguous results. Discoveries may be unusual, unexpected, or serendipitous.