What does the prefix iso- mean?

• A. Equal
• B. Large
• C. Small
• D. Different

Answer: (A)

iso- signals sameness or equality. It’s attached to a root to show that the property being described is the same as a reference standard. For example, an isotonic solution has the same osmolarity as body fluids, an isometric exercise keeps muscle length the same, and an isothermal process maintains constant temperature. Because iso- means equal, this is the best fit for describing the prefix in the question. The other options describe size or difference, which isn’t what iso- conveys.