Irritability as a basic characteristic of

Irritability means living organisms respond to changes in their environment. Two main types of responses exist: taxis and nastism. Taxis is a directed movement toward or away from a stimulus. For example, when you see a cockroach and it runs away from light into a dark corner, that's negative phototaxis—movement away from light. Nastism is a non-directional response where the organism's movement doesn't depend on where the stimulus comes from. When you touch a sensitive plant leaf and it suddenly folds up, the leaf doesn't fold toward or away from your finger; it just contracts regardless of the direction of touch. That's nastism. Think of it this way: taxis has direction and purpose, while nastism is just a general reaction. Both show how organisms detect changes and respond appropriately to survive.

Irritability means that living organisms can sense and respond to changes in their environment. When something in the surroundings changes, living things react to it. Environmental factors that trigger these responses include light, heat, sound, chemicals, and touch. For example, when you touch a hot stove, you quickly pull your hand away because your body senses the heat and responds. Similarly, if you're sitting quietly and hear a loud noise, you jump because your ears detect the sound and your body reacts.

In Nigeria, you can observe irritability in plants too. The Mimosa pudica plant, commonly called "touch-me-not," closes its leaves when you touch it. This is the plant's way of responding to the stimulus of touch. Without irritability, organisms couldn't survive because they wouldn't be able to react to dangers or find food.