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Laboratory Investigation on Cells
Observing Plant Cells
3. Looking at Onion Cells
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Cut an onion in half. Take out one of the inside onion leaves. From the outside of the leaf peel off a tiny piece of the outer cell layer. The layer that you peel off is as thin as a piece of cling film. Place this onto a microscope slide. The piece of onion should be no bigger than 1cm2. Cover this with one drop of iodine solution and place the cover slip over this. Observe the cells using the x10 objective lens.

Labels for the onion cell: the cell wall allows the plant cells to be more rigid, the cell membrane surrounds the cell (here it is difficult to see as it is pressed right up against the cell wall), the nucleus contains the hereditary information and is really in the cytoplasm which borders the cell membrane. The sap vacuole is the large, fluid-filled space inside the cell. The sap vacuole is found only in plant cells and it helps to keep the shape of the cell.