A fetus is more susceptible to radiation damage because it has

• A. More rapidly reproducing cells
• B. Higher bone density
• C. Greater fat content
• D. Larger organs

Answer: (A)

Radiosensitivity tracks with how active and immature the cells are. Cells that are rapidly dividing and not yet differentiated are most vulnerable to ionizing radiation because damage to DNA during replication can disrupt development or cause cell death. A fetus contains many developing tissues with high mitotic activity, especially during organ formation, so exposure can have widespread and more serious effects. That’s why a fetus is more susceptible to radiation damage.

The other traits listed don’t drive sensitivity in the same way. Bone density, fat content, or organ size reflect maturation or composition but don’t inherently increase the likelihood of radiation-induced cellular damage.