Onions in focus

Essay by blacky_187Junior High, 7th gradeA, March 2006

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Aim: To investigate onion cells and to practise using the microscope.

Materials & Equipment:

- Glass slide

- Cover slip

- Onion layer (1 cell thick)

- Iodine stain

- Microscope

- Water & syringe


1) If necessary, carefully clean the cover slip and glass slide (always hold the glass by the edges)

2) From a piece of onion, carefully peel a layer of its skin (one cell thick) and put it on the glass slide.

3) Once you have made sure that the onion layer is perfectly flat, place two drops of water on the onion, then carefully lower the cover slip over the onion.

4) Using low power objective lenses, look for a pattern on the slide.

5) Take the slide from the microscope and on one side of it place two drops of "iodine stain". On the slide of the slide, use paper to absorb the water so it drags the "iodine stain" throughout the onion layer.

6) Put the slide back under the microscope and focus on the onion on the low magnification and work your way to the higher magnifications.


Slides and cover slips should be held by the sides so that they won't be affected by fingerprints.

It is important to use a very thin onion layer so that light can shine through and make it easier to see the cells.

We must place the cover slip onto the slide carefully so that no air gets trapped underneath. Trapped air makes it harder to see.

We stained the onion skin with "iodine stain" to make the cells stand out.

We should avoid getting air bubbles trapped under the cover slip to have a clear view of the cells.


In this experiment I have learned how to better use...