Question

how does a cheek cell is different from onion cell

Answer 1

As in all animal cells, the cells of the human cheek do not possess a cell WALL. A cell membrane that is semi-permeable surrounds the cytoplasm.
Unlike plant cells, the cytoplasm in an animal cell is denser, granular and occupies a larger space. The vacuole in an an animal cell is smaller in size, or absent.