Biology is the study of life. The document outlines several key characteristics of life including that all living things are made of cells, use energy through metabolism, maintain homeostasis, grow and develop, reproduce, respond to their environment, and evolve over time. It also discusses several core themes of biology such as emergent properties, the central role of the cell, heritable information, the relationship between structure and function, interactions between organisms and their environment, regulation of homeostasis, and the unity and diversity of life.