Final answer:
Option B) DNA photolyase is the enzyme activated by visible light that directly repairs thymine dimers in DNA strands through a process called photoreactivation or direct repair.
Step-by-step explanation:
The DNA repair enzyme activated by visible light that directly breaks down thymine dimers is DNA photolyase. This enzyme participates in a repair process known as photoreactivation or direct repair. Upon absorption of visible light, DNA photolyase changes conformation and splits the thymine dimers, which are lesions on the DNA caused by ultraviolet radiation. This allows the thymines to base pair correctly again.
In contrast, other DNA repair mechanisms, such as nucleotide excision repair, involve the removal of a larger portion of the damaged DNA strand, which includes the thymine dimer, and filling in the gap with correct nucleotides using DNA polymerase followed by sealing with DNA ligase.