Indirect action effects on cells are associated with which cellular component?

• A. Ribosomes
• B. DNA molecules
• C. Mitochondria
• D. Water molecules

Answer: (D)

Indirect action effects come from the radiolysis of the abundant water inside the cell. When ionizing radiation deposits energy, it primarily splits water molecules to form reactive species such as hydroxyl radicals, hydrogen atoms, and other reactive oxygen species. These radicals diffuse through the cytoplasm and into the nucleus, where they chemically attack and damage critical biomolecules like DNA, proteins, and lipids. Because water is so plentiful, most radiation-induced damage arises from these secondary radicals rather than from direct ionization of DNA or other structures. So, the cellular component associated with indirect action is the water molecules themselves.