Which sequence correctly lists the organization from simplest to most complex?

• A. From tissue, organ, organ system to organism.
• B. From organ system, organ, tissue to organism.
• C. From tissue, organ system, organ to organism.
• D. From organ, organ system, tissue to organism.

Answer: (A)

Think about how living things are built from simple to more complex units. A tissue is a group of similar cells doing a specific job. When tissues come together, they form an organ. Groups of organs work together as an organ system, and all the organ systems together make up the entire organism. So the order from simplest to most complex is tissue, organ, organ system, organism. The other sequences mix these levels—for example, placing an organ before tissue ignores that organs are built from tissues, or putting an organ system before organs skips the actual organs that compose that system.