Concept: This question tests your knowledge of the classification and function of biological molecules, specifically focusing on the role of dopamine in the body.

Why (B) is correct: Dopamine is a crucial neurotransmitter, a chemical messenger that transmits signals between neurons (nerve cells) in the brain and other parts of the nervous system. It plays a significant role in reward, motivation, pleasure, motor control, and various cognitive functions.

Why other options are wrong:

• (A) hormone: While some neurotransmitters can also act as hormones (e.g., adrenaline), dopamine primarily functions as a neurotransmitter within the nervous system. Hormones are typically secreted into the bloodstream to act on distant target cells.
• (C) polysaccharide: Polysaccharides are complex carbohydrates (e.g., starch, glycogen, cellulose) and have structural or energy storage roles, not signaling.
• (D) enzyme: Enzymes are biological catalysts that speed up biochemical reactions; dopamine does not perform this function.

NEET Tip: Remember that many biological molecules can have multiple roles, but it's important to identify their primary or most characteristic function as asked in the question. Dopamine's primary role is as a neurotransmitter.

Correct Answer: (B)