A scientist is comparing the outer structure of an onion cell, structure X, to the outer structure of a human skin cell, structure Y. Which generalization is true about the types of structures being examined? Structure X is not living, and structure Y is living. Structure X can be found in some human cells, and structure Y can be found in some plant cells. Structure X is only found in plant cells, and structure Y is found in plant and animal cells. Structure X is semipermeable, and structure Y is selectively permeable.