Which one of the following parts of the pitcher plants becomes modified into a pitcher?

Answer: (b) Leaf

The pitcher is a modified leaf blade; the lid grows from the leaf tip.

The idea

Plants often change one organ to do a new job. In the pitcher plant it is the leaf: the leaf blade is rolled into a jug, and the leaf tip forms the lid.

Leaf → pitcher (pitcher plant), spine (cactus), tendril (pea) → Stem → potato tuber, ginger rhizome, flat green pad of a cactus → Root → carrot, radish, sweet potato

Why the others are wrong

(d) The petiole (leaf stalk) forms the tendril-like part, not the pitcher itself.

The trap

The pitcher hangs on a stalk, which makes “petiole” tempting.

Also know

A quick test for a stem: it has buds or “eyes”. A potato has eyes, so it is a stem; a sweet potato has none, so it is a root.