AP BIOLOGY

Detailed explanation-1: -The two strands are held together by hydrogen bonds between pairs of bases: adenine pairs with thymine, and cytosine pairs with guanine.

Detailed explanation-2: -DNA is made up of two strands of sugar molecules and phosphate groups, with nitrogen bases in between them that are held together by hydrogen bonds.

Detailed explanation-3: -Within a molecule of DNA, pairs of bases are chemically bonded together by hydrogen bonds. These bonds hold the two strands of the molecule together.

Detailed explanation-4: -hydrogen. Covalent bonds occur within each linear strand and strongly bond the bases, sugars, and phosphate groups (both within each component and between components). Hydrogen bonds occur between the two strands and involve a base from one strand with a base from the second in complementary pairing.