Which statement describes the hierarchical levels of organization from cells to organisms?

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

Answer: (A)

Understanding how the body is organized starts with the basic unit of life: the cell. Similar cells join to form tissues that perform a common function. Tissues come together to build organs, which are structures with specific tasks. Organs act in concert within organ systems, where groups of organs coordinate to carry out broader physiological processes. All of these levels work together to form a whole organism, the living being.

This sequence—cells → tissues → organs → organ systems → organism—fits the natural progression from simple units to a complete living being.

Other options mix in levels that come before cells (like atoms and molecules) or omit a level (such as skipping tissues), or reorder the tiers (placing organs before tissues or organ systems after organisms).