The onion epidermal cell provides a protective layer against unwanted viruses that may harm the sensitive tissues. Because of its simple structure and transparency it is often used to introduce students to plant anatomy. These properties also make it useful for demonstrations of plasmolysis. The clear epidermal cells consist of a single layer and do not contain chloroplasts, because the onion fruiting body (bulb) is used for storing energy, not photosynthesis. To prepare onion epidermal cells for microscopy, smaller onions that feel firm are best. Remove the epidermal layers by cutting the onion and peeling them off (they are the membrane-like sheaths between each onion layer). For advanced microscopy, such as fluorescence microscopy, the layers halfway between the outside and the centre of the onion are best.
If you are using these layers for biolistics, it is important to note that bombarding with the cells facing up or down, on the media that they're placed, on can't make a difference.
Famous quotes containing the words onion and/or cell:
“I had rather munch a crust of brown bread and an onion in a corner, without any more ado or ceremony, than feed upon turkey at another man’s table, where one is fain to sit mincing and chewing his meat an hour together, drink little, be always wiping his fingers and his chops, and never dare to cough nor sneeze, though he has never so much a mind to it, nor do a many things which a body may do freely by one’s self.”
—Miguel De Cervantes (1547–1616)
“What Mrs. Thatcher did for women was to demonstrate that if a woman had enough desire she could do what she wanted, do anything a man could do.... Mrs. Thatcher did not have one traditional feminine cell in her body.”
—Julie Burchill (b. 1960)