Specialized cells perform specialized functions in multi-cellular organisms. These systems interact with one another. All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment. Regulation of an organism's internal environment involves sensing the internal environment and changing physiological activities to keep conditions within the range required to survive. Behavior is one kind of response an organism can make to an internal or environmental stimulus.
Some scientists work in teams, and some work alone, but all communicate extensively with others.
Nature of science Scientists formulate and test their explanations of nature using observation, experiments, and theoretical and mathematical models. History of science Many individuals have contributed to the traditions of science.