Introduction

• At the very simplest level, humans are made of nothing more than atoms.
• However this fails to capture its complexity.
• Instead, we recognize atoms as the first level of organization.
• Higher levels of complexity are created by combining structures from the level below.

In anatomy and physiology

• The levels of organization usually found in anatomy and physiology are:
  1. Molecules
     • Molecules are composed of atoms bonded together.
     • Examples of molecules are water, carbon dioxide, proteins, and sugars.
  2. Organelles
     • Organelles are structures inside cells that carry out a specific function.
  3. Cells
     • A cell is the smallest unit of a living organism that can function independantly.
  4. Tissues
     • A tissue is a group of similar cells that work together to perform a shared function.
  5. Organ
     • An organ is made up of at least two tissues, and performs at least one function.
  6. Organ System
     • An organ system is made up from a group of organs.
     • They perform major functions such as digestion and respiration.
     • Many organs can belong to multiple organ systems.