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Laboratory Investigation on Cells
3. Looking at Onion Cells
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.
4. Observing Leaf Cells from Freshwater Pond Weed
Take one leaf of Canadian pond weed. Place it onto the microscope slide and add one drop of water. Place the cover slip on the slide. Observe the slide using the x10 objective.
Can you see cells that look like the one shown in the diagram below?
The labels for this cell are the same as the onion cell with one addition : Chloroplasts. These green, round structures can absorb sunlight energy and can turn it into food for the plant.
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