Which sequence correctly represents the cellular hierarchy from smallest to largest unit?

• A. tissue, cell, organ, organ system, organism
• B. cell, tissue, organ, organ system, organism
• C. cell, organ, tissue, organ system, organism
• D. organism, organ system, organ, tissue, cell

Answer: (B)

Understanding the order of biological organization from smallest to largest is what this question is about. The smallest unit that carries out life functions is the cell. Similar cells group together to form tissues, which provide a specific function. Tissues then come together to form organs, each with a specialized role in the body. Organs collaborate within organ systems to perform broader physiological tasks, and all of these systems together make up the organism. So the correct progression is cell → tissue → organ → organ system → organism.

The other sequences place levels out of order. Starting with tissue assumes cells aren’t the smallest unit; placing organ before tissue ignores that organs are built from tissues; starting with the organism places the whole being before its parts.