The authors have updated each of the books eight units to reflect the progress in our understanding of life at many levels, from molecules to ecosystems. The sixth edition has a new chapter that introduces students to science as a way of knowing nature. A new feature highlights examples of the process of science throughout the book, and each chapter contains a process of science question that encourages students to experience science. Media activites allow additional practice with experimentation and analysis of data, and interviews with various researchers humanize science as a social activity.