Which type of action causes damage by ionization of a biological macromolecule?

The type of action that causes damage by ionization of a biological macromolecule is direct action. This occurs when radiation interacts directly with the DNA or other critical macromolecules, resulting in ionization and subsequent molecular damage. The energy from the radiation dislodges electrons from the atoms within the macromolecule, which can lead to structural alterations, mutations, or even cell death if the damage is severe enough.

This concept is particularly important in the context of radiation effects on living tissues, as it can help explain the mechanisms underlying radiation therapy in cancer treatment and the risks of ionizing radiation exposure. In contrast, indirect action typically involves the ionization of water molecules, resulting in free radicals that then interact with biological macromolecules. Options related to passive or reversible actions do not pertain to mechanisms of ionization and thus are not relevant in this specific context.