Purine and pyramidine both get N from:

24. Ans: a (Aspartate) Ref: Vasudevan, 4th ed, p. 388, 392; 5th ed, p. 407, 411Carbamoyl phosphate is formed by ammonia and glutamine with the help of CPS-II.From the above explanation it is clear that aspartate is directly involved in providing nitrogen atom to both purine and pyramidine. In purine synthesis glutamine provides nitrogen atom directly but in pyramidine synthesis glutamine is first converted to carbamoyl phosphate which in turn provides nitrogen atom. Though both provides nitrogen atom, aspartate is definitely a the better option.