Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: You consist of a great many cells, but like all other organisms, you started life as a single cell. How did you develop from a single cell into an organism with trillions of cells? The answer is cell division. After cells grow to their maximum size, they divide into two new cells. These new cells are small at first, but they grow quickly and eventually divide and produce more new cells. This process keeps repeating in a continuous cycle. Answer: cell division
[A]: What process allows an individual to develop from a single cell into an organism with trillions of cells?

[Q]: Passage: Chemical reactions constantly occur inside the cells of living things. However, under the conditions inside cells, most biochemical reactions would occur too slowly to maintain life. That's where enzymes come in. Enzymes are catalysts in living things. Like other catalysts, they speed up chemical reactions. Enzymes are proteins that are synthesized in the cells that need them, based on instructions encoded in the cells' DNA. Answer: enzymes
[A]: What proteins synthesized in cells act as catalysts?

[Q]: Passage: The other ammonium ions are changed into nitrogen gas by denitrifying bacteria. Answer: denitrifying bacteria
[A]:
The other ammonium ions are changed into nitrogen gas by what?