Concept: This question tests your understanding of root systems, specifically the characteristic root system found in monocotyledonous plants.

Why (D) is correct: In monocotyledonous plants like wheat, the primary root that develops from the radicle is short-lived. It is then replaced by a large number of roots that originate from the base of the stem. This type of root system, where roots arise from the stem base and form a cluster of thin, fibrous roots, is known as a fibrous root system.

Why other options are wrong:

• (A) Primary roots: The primary root is short-lived and replaced, so it doesn't constitute the main system.
• (B) Secondary roots: Secondary roots are branches of the primary root, which is not the case here.
• (C) Tap roots: Tap roots are characteristic of dicotyledonous plants, where the primary root persists and grows deep, giving rise to lateral roots.

Common Mistake: Students often confuse the terms 'primary root' and 'tap root' or 'fibrous root' and 'adventitious root'. While fibrous roots are a type of adventitious root system, not all adventitious roots are fibrous.

NEET Tip: Remember that monocots = fibrous roots and dicots = tap roots. This is a fundamental distinction often tested.

Correct Answer: (D)