Notes

All living organisms are made up of one or more cells, which are considered the fundamental units of life.

Multicellular organisms—such as humans—are made up of many cells Tissues make up organs, such as the heart or lungs, which carry out specific functions needed by the organism as a whole.

Metabolism can be subdivided into anabolism and catabolism. In anabolism, organisms make complex molecules from simpler ones, while in catabolism, they do the reverse. Anabolic processes typically consume energy, whereas catabolic processes can make stored energy available.

maintenance of a stable internal environment, even in the face of a changing external environment, is known as homeostasis.

Reproduction can be either asexual, involving a single parent organism, or sexual, requiring two parents

Living organisms show “irritability,” meaning that they respond to stimuli or changes in their environment. For instance, people pull their hand away—fast!—from a flame; many plants turn toward the sun; and unicellular organisms may migrate toward a source of nutrients or away from a noxious chemical.

Populations of living organisms can undergo evolution, meaning that the genetic makeup of a population may change over time. In some cases, evolution involves natural selection, in which a heritable trait, such as darker fur color or narrower beak shape, lets organisms survive and reproduce better in a particular environment.