Besides urea, what other compound must be available for the urease enzyme to break down urea?

Besides urea Other compounds that are available for the break down of urea is Water.It is important for the hydrolysis of urea that results into production of  carbon dioxide and ammonia. As ammonia is produced the pH rises and the pH can be maintained by adding acid.The amount of acid added is the measure of rate of hydrolysis.

          Urea + Water = Carbon dioxide +Ammonia

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.