Which sequence correctly describes the levels of biological organization from smallest to largest?

• A. Atoms, molecules, cells, tissues, organs.
• B. Cells, tissues, organs, organ systems, organisms.
• C. Tissues, organs, organ systems, organisms.
• D. Cells, organs, tissues, organ systems, organisms.

Answer: (B)

Biological organization in living beings builds upward from cells to tissues to organs to organ systems to the whole organism. Cells are the basic units of life; when similar cells join together, they form tissues that perform a shared function. Organs arise when different tissues work in concert to carry out a specific job. Organ systems are networks of related organs that coordinate to support major bodily functions, and the organism is the complete living entity made up of all these systems.

This sequence fits because each level depends on the one before it: tissues come from cells, organs come from tissues, organ systems come from organs, and the organism comes from the integrated organ systems. Starting with smaller non-living building blocks like atoms or molecules would skip the cellular basis of life, and placing tissues before cells or organs before tissues would ignore how these structures are built.