• Although fundamental molecular and cellular processes are conserved, biological systems and organisms are extraordinarily diverse. Unlike atoms and simple molecules studied in chemistry and physics, no two cells are identical.

  • Biological systems maintain homeostasis by the action of complex regulatory systems. These are often networks of interconnecting partially redundant systems to make them stable to internal or external changes.

  • Cells are fundamental units of living systems. Three fundamental cell types have evolved: bacteria, archea, and eukaryotes.

  • Living organisms have behavior, which can be altered by experience in many species.

  • Information encoded in DNA is organized into genes. These heritable units use RNA as informational intermediates to encode protein sequences, which become functional on folding into distinctive three-dimensional structures. In some situations RNA itself has catalytic activity.

  • Most biological processes are controlled by multiple proteins, which assemble into modular units to carry out and coordinate complex functions.

  • Lipids assemble with proteins to form membranes, which surround cells to separate them from their environment. Membranes also form distinct compartments within eukaryotic cells.

  • Communication networks within and between cells, and between organisms, enable multicellular organisms to coordinate development and function.

  • In multicellular organisms, cells divide and differentiate to form tissues, organs, and organ systems with distinct functions. These differences arise primarily from changes in gene expression.

  • Many diseases arise from disruption of cellular communication and coordination by infection, mutation, chemical insult, or trauma.

  • Groups of organisms exist as species, which include interbreeding populations sharing a gene pool.

  • Populations of species interact with one another and the environment to form interdependent ecosystems with flow of energy and materials between multiple levels.

  • Humans, as well as many other species, are members of multiple ecosystems. They have the capacity to disrupt or preserve the ecosystems upon which they depend.

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