To distinguish microscopically between cheek cell and onion cell mount, one should look for the presence or absence of
(a) Mitochondria
(b) Plastids
(c) Cell membrane
(d) Nucleus

Hint: Human cheek cells have different characters as compared to the onion cell as they are both taken from the different organisms. One is taken from the humans while the other is taken from the plant resulting in a change in structure and function.

Complete answer:
Difference between cheek cell and onion cell mount


Additional information
-The cheek cells constitute a well-defined nucleus with a nuclear membrane. They are found to be an actively dividing cell thus it becomes easier to observe under the microscope. While in the case of the onion cells the nucleus is not well defined.
-the human cheek cells are obtained by scraping the cheek from the inside with the help of a toothpick or a sterilized needle. While in the case of the onion cell they can be obtained from the peeling of the transparent layer present on the onion.

Note:
The cheek cell and the onion cell are both epithelial cells that can be obtained easily. They are both transparent and thus can be stained easily. They both have various cell organelles, cell membrane, and nucleus except plastids or chloroplast, which is absent in the case of the human cheek cell.