Answer: irritability
Explanation:Response to stimuli is an important characteristic of life. Anything that causes a living organism to react is called a stimulus (plural is stimuli) Stimuli can be external or internal.
For instance, if you feel like going to the bathroom, it is an internal stimulus that is controlled by the brain. If the sun comes up on a warm day, it is an external stimulus that can cause a snake to come out and busk. The ability of the organism to react is called ‘irritability