If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of radioactivity will be found in the cells'Group of answer choicesDNA and proteins.DNA.proteins.phospholipids.DNA and phospholipids.

The answer is "DNA and proteins." Here's why:

1. Amino acids are the building blocks of proteins. Therefore, if cells are grown in a medium containing amino acids labeled with radioactive nitrogen (15N), the proteins synthesized by the cells will contain the radioactive nitrogen.

2. DNA (deoxyribonucleic acid) also contains nitrogen in its structure. Nitrogen is a component of the nitrogenous bases (adenine, guanine, cytosine, and thymine) that make up the DNA molecule. Therefore, if cells are grown in a medium containing amino acids labeled with radioactive nitrogen (15N), the DNA synthesized by the cells will also contain the radioactive nitrogen.

3. Phospholipids, on the other hand, do not contain nitrogen. They are composed of a phosphate group, a glycerol molecule, and two fatty acid chains. Therefore, they would not incorporate the radioactive nitrogen from the amino acids in the medium.

So, most of the radioactivity will be found in the cells' DNA and proteins.