An electron microscope is necessary for seeing the cell membrane since the membrane is too small to be seen under a light microscope. Although chloroplasts, nerve cells, and the nucleus can be seen under a light microscope, details of their structure not visible under a light microscope are seen with the electron microscope.  If you have already finished the cell studies lab, you   saw chloroplasts in Elodea cells.  You may not have noticed the nucleus in the cells, but if you had spent some time looking carefully, you would have also seen the nucleus.  You did see the nucleus in the epithelial cells that lined your cheeks as well as the nucleus in the cells of the pseudostratified columnar epithelial tissue and in the adipose tissue. Nerve cells can easily be seen under a light microscope as can most (if not all ) animal cells. You did see one of the smallest of the animal cells in the lab - sperm cells.