Dried Substances and Water

Johnleprekan

When you dehydrate a substance like an apple and then reintroduce the water back in, why does the apple not reconstitute itself and only breaks down further into smaller particles? I know an apple isn't the best example because I have seen dried fruit swell back up, but I do not know what this is called. It happens with other substances and not fruit or something that had a form to begin with. Can someone explain and give the name of this too?