This is a good question. In general, plant cells tend to be bigger than animal cells, but as with many things, there are exceptions! Now, why are they bigger? I'm not sure that the answer to that is really known, but many people think it has to do with the fact that each cell in a plant stores food, whereas animals have specialized cells in certain parts of their bodies that serve this purpose. This means that the other cell types in the body are left to perform other functions, and in some cases don't have a vacuole (the organelle where food is stored) at all. I hope this helps!

Cells vary a lot in size. I'd guess plant cells are bigger, but that may be because plant cells are easy to see with a microscope or even a hand-held magnifying glass; plant cells have cell walls that are easy to spot.