Why are KD and EC50 usually not the same Question 17 options

Why are KD and EC50 usually not the same? Question 17 options: A. Not all receptors are capable of activating cell response B. Not all receptors are capable of binding ligand C. Some receptors are inactive D. Some receptors bind more than one ligand E. The cell has spare receptors

Solution

Correct answer is : E. The cell has spare receptors.

Reason: Kd will be equal to EC50 only in the absence of spare receptors.