Destructive changes in body molecules which result when a specific molecule such as DNA is acted upon directly by radiation.

• A. radiochemolysis
• B. direct effect
• C. indirect effect
• D. radio dystrophy

Answer: (B)

Direct effect is when radiation directly interacts with a biomolecule, such as DNA, transferring energy that ionizes or excites the molecule and causes bond breakage or structural damage. This is why destructive changes occur in the molecule itself, without intermediates. In contrast, indirect effect happens when radiation first interacts with surrounding water, producing free radicals (like hydroxyl radicals) that then damage biomolecules. High-LET radiation tends to produce more direct effects, while low-LET radiation (like X-rays or gamma rays) often causes damage mainly through indirect effects.