Concept 1.1 Biologists explore life from the microscopic to the global scale Life’s basic characteristic is a high degree of order. Each level of biological organization has emergent properties. Biological organization is based on a hierarchy of structural levels, each building on the levels below. At the lowest level are atoms that are ordered into complex biological molecules. Biological molecules are organized into structures called organelles, the components of cells. Cells are the fundamental unit of structure and function of living things. Some organisms consist of a single cell; others are multicellular aggregates of specialized cells. Whether multicellular or unicellular, all organisms must accomplish the same functions: uptake and processing of nutrients, excretion of wastes, response to environmental stimuli, and reproduction. Multicellular organisms exhibit three major structural levels above the cell: similar cells are
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