People have a CNS and big fat brains that do the processing and it's extremely dynamic. Neurons are set up in dedicated patterns to carry out both instinctual and learned responses. Plants use chemical gradients across tissues to do basic things. In fact, what is cool about plants is how little processing power they need in order to do their basic little behaviors.

Example: plants establish simple things like "up", "down", "tip of primary stem", "base of primary stem", "tip of secondary stem", "base of secondary stem", and so on, mostly through simple chemical gradients. Too much of chemical X prevents another secondary stem from appearing. This is how you get spaced out branches at different angles around a tree trunk. These kinds of things are how plants do everything.

Humans do brain things. Big, dedicated processing centers that carry out our much more complex behaviors, carry our emotions, build bonds between siblings, play, problem-solving, relaxation, driving our bodies around looking for food and shelter, etc.