Final answer:
Photoreactivation repair is the DNA repair mechanism involving the enzyme photolyase, which directly breaks down thymine dimers with the help of visible light, also known as direct repair or light repair.
Step-by-step explanation:
The type of DNA repair in which thymine dimers are directly broken down by the enzyme photolyase is known as photoreactivation repair. This process involves the enzyme photolyase binding to the thymine dimer and, in the presence of visible light, breaking apart the dimer, thereby restoring the base pairing of the thymines with complementary adenines on the opposite DNA strand. This direct repair mechanism, also called light repair, is particularly important for organisms that do not have the luxury of avoiding ultraviolet light, such as plants and some bacteria. In contrast, nucleotide excision repair is a more complex process that involves cutting the DNA strand on both sides of the damage, removing the damaged section, and then filling in the gap with the correct nucleotides.