Question

a scientist is studying how cells prepare for division. based on the model shown, which step must occur before a cell can successfully divide?

both strands of the original dna must remain paired while new bases are added.
the original dna strands must separate so each can serve as a template for a new strand.
one original dna strand must be removed before new strands can be built.
the original dna must dissolve completely before new dna can form.

Explanation:

Step1: Recall DNA replication process

DNA replication is semi - conservative. The double - stranded DNA molecule unwinds, and each of the original strands serves as a template for the synthesis of a new complementary strand.

Step2: Analyze each option

• Option 1: The original DNA does not dissolve completely. It unwinds, so this option is incorrect.
• Option 2: The original DNA strands are not removed. They are used as templates, so this option is incorrect.
• Option 3: The original DNA strands separate (unwind) so that each can serve as a template for a new strand. This is in line with the semi - conservative replication model.
• Option 4: The original strands do not remain paired. They separate for replication, so this option is incorrect.

Answer:

The original DNA strands must separate so each can serve as a template for a new strand.