HORTICULTURE

Detailed explanation-1: -The correct option is A. Stimulus. Any change in the environment to which an organism responds is called stimulus. The stimuli initiates an appropriate electrical impulse in the sensory neurons which transmits it to the brain or spinal cord.

Detailed explanation-2: -A stimulus is a change in the external or internal environment that produces a physiological response. When applied to sensory receptors, it provokes behavior or response. Internal stimuli (such as changes in blood pressure) and external stimuli (tactile, sound, smell, taste, vision, etc.).

Detailed explanation-3: -Receptors are groups of specialised cells. They detect a change in the environment stimulus. In the nervous system this leads to an electrical impulse being made in response to the stimulus. Sense organs contain groups of receptors that respond to specific stimuli.

Detailed explanation-4: -Therefore, sensitivity is the ability of an organism to respond to external stimulus.