Being aware of its environment is not very important, because it does not need to search for food or be aware of potential predators. However, the brain and peripheral nerve network of free-living flatworms represent the most primitive nervous systems currently under investigation. It consists of a small but well-defined brain (right panel) and numerous peripheral motoneurones connected by longitudinal nerve cords and transverse commissures. So to answer your answer your question, this nervous system enables flatworms to perceive environmental changes and to respond to internal and external stimuli.
An example of an external stimulus is a painful prick (and any other stimulus that happens OUT side the organism ). The organism could respond by pulling away from the pain caused by the stimuli. An example of an internal stimulus is the feeling of hunger or thirst (or any other stimulus that happens IN side the organism). The organism could respond by eating or drinking. a behavior
external
external for A~plus
external is thunder
Earthworms do not respond to darkness per say, but they do respond to light. although they do not have eyes, they are light sesitive.
Generalization is the tendency to respond to a stimulus that is similar but not identical to a conditioned stimulus.
The difference between an external stimulus and an internal stimulus is that an external stimulus is a stimulus that comes from outside an organism. But an internal stumulus is a stimulus that comes from inside an organism. An example for an external stimulus can be that when you are cold, you put on a jacket. An example for an internal stimulus is that when you feel hungry, you eat food.
There are a number of ways that an organism could respond to an external stimulus. For instance, if a child was at the zoo and heard a loud roar, she might run over to the lion exhibit to investigate the sound.
A stimulus causes your body to react, a response is something that is caused by a stimulus. Work it out, does the virus respond to you more or you to the virus?
If you poke a worm, it wriggles. The poke is the stimulus and the wriggling is the reaction. Also, a worm moves away from light and moves to a moister area in the ground.
It is an external stimulus.
External Stimulus