A series of studies on mutants of Neurospora identified three classes of mutants that needed arginine added to minimal media in order to grow. The production of arginine includes the following steps: precursor → ornithine → citrulline → arginine. What nutrient (s) have to be supplied to the mutants that had a defective enzyme for the ornithine → citrulline step in order to grow?

a. the precursor

b. citrulline

c. the precursor, ornithine, and citrulline

d. either ornithine or citrulline

e. ornithine

Answer: Citrulline, Option B

Explanation:

The sequence of the formation of arginine is as follows. Precursor → ornithine → citrulline → arginine.

If there is a defective enzyme for ornithine then there will no production of citrulline or lesser production of citrulline which ultimately will affect arginine production.

So, the compound citrulline should be provided so that the production process can continue. Ornithine if not present then citrulline can alone produce arginine.

So, the correct answer is option B