Ques. 1AIPMT 2003
In which one of the following nitrogen is not a constituent ?
- Pepsin
- Invertase
- Idioblast
- Bacteriochlorophyll
Answer
(3) Idioblast
Solution
Pepsin and invertase are enzymes, i.e., proteins; as per NCERT, amino acids have an amino group, so proteins always contain nitrogen.
Bacteriochlorophyll, like chlorophyll, has a tetrapyrrole (porphyrin) ring with four nitrogen atoms around a Mg atom, so it also contains nitrogen.
An idioblast, on the other hand, is a specialised plant cell that stores substances such as tannins, oils, resins or crystals of calcium oxalate (CaC2O4), and these stored substances contain no nitrogen.
∴ Nitrogen is not a constituent of idioblast (its stored material).
Answer: (3)