Pyrimidine biosynthesis is allosterically inhibited by ATP. a. requires an intermediate found in urea biosynthesis. b. does not require ATP hydrolysis. c. involves synthesizing the base while it is attached to ribose.

requires an intermediate found in urea biosynthesis

Explanation:

Both pyrimidine and urea are carbon and nitrogen containing compounds. Carbamoyl phosphate provides both carbon and nitrogen in biosynthesis pathways of both pyrimidine and urea. Hence, it is an intermediate in both the pathways.

In urea biosynthesis carbamoyl phosphate provides its carbamoyl group to ornithine. In pyrimidine synthesis it donates the carbamoyl group to aspartate. Carbamoyl phosphate synthetase synthesizes carbamoyl phosphate by joining ammonium ions to carbon dioxide and adenosine triphosphate.

Gametes are the sex cells. As in the asexual and sexual reproduction. Asexual reproduction has only 1 organism, like cloaning. And sexual reproduction is the mixing of 2 organisms. I would get into the details, but I don't have any rights on that. So basically to recap, gametes are the sex cells.
I hope this helps.