[This text] covers the concepts and principles of biology from the structure and function of the cell to the organization of the biosphere. It draws upon the entire world of living things to bring out an evolutionary theme that is introduced from the start. The concept of evolution is necessary to understanding the unity and diversity of life and serves as a background for the study of ecological principles. Four chapters are devoted to reviewing the ecological principles that explain how the natural world works. Frequent references are made as to how humans impact the environment. Ecological problems are considered.