This document defines key terms related to anatomy, physiology, and cell biology. It provides an overview of the organization of the human body from atoms to organ systems. Key points include: - Anatomy studies body structure, physiology studies functions, and pathology studies abnormalities. - The body is made of cells, tissues, organs, and systems organized into body cavities. - The human cell contains organelles like the nucleus, mitochondria, and endoplasmic reticulum, surrounded by a plasma membrane. - Cells divide through mitosis and meiosis to produce genetically identical or variant cells. - Substances move across the cell membrane through passive, active, or bulk transport processes.