Answer:
Option (a).
Explanation:
Hormones may be defined as the chemical messengers of the body that may have short term and long term effects on the body of individual. Hormones plays an important role in the growth and metabolism.
The cell of the body respond only against a particular hormone. The cells have the receptor, these receptors have the ability to bind with the hormone. The binding of hormone with receptor initiates a signalling cascade that helps in the particular functioning of the hormone.
Thus, the correct answer is option (a).