Florida Biology EOC Practice Test 2025 – 400 Free Practice Questions to Pass the Exam

The correct choice identifies hydrogen bonds as the forces that hold the two strands of a DNA molecule together. In the double helix structure of DNA, the two strands are composed of a backbone formed by sugar and phosphate groups that are linked by covalent bonds. However, the strands are paired through complementary nitrogenous bases (adenine with thymine and guanine with cytosine) that are held together by hydrogen bonds.

These hydrogen bonds are crucial because they provide enough stability to keep the two strands aligned while still allowing for the strands to separate easily during processes such as replication and transcription. This feature is vital for the functions of DNA, allowing it to store genetic information and facilitate its transfer during cell division and protein synthesis. The relatively weaker nature of hydrogen bonds compared to covalent bonds is what makes the unwinding of DNA simpler during these processes, while still maintaining the integrity of the genetic code.