3. The DNA double helix is stabilized by hydrogen bonds between:

Explanation:

hope it helps

The structure of the DNA helix is stabilized by van der Waals forces, hydrogen bonds between complementary organic bases (a base pair), and hydrophobic interactions between the nitrogenous bases and the surrounding sheath of water

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation:

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.