This practical involves looking at plant cells through a microscope. Onion cells are often used as their cells are relatively big and therefore can be seen clearly however they do not contain any chloroplasts. If you wish to view chloroplasts, use a moss plant or elodea instead.
Equipment required (per set)
Students need to cut a small section of onion and then use forceps to peel away the inner surface. This inner surface looks a little like tissue paper. It is very thin.
- Piece of onion
- Iodine solution in dropper bottles
- Cover slip
- Mounted needle
The small piece of skin then needs to be placed flat onto a clean slide and a drop or two of iodine solution should be added. The iodine stains the nucleus of the cell so it stands out more clearly under a microscope.
The cover slip needs to be gently lowered onto the onion skin using the mounted needle. The cover slip flattens the skin, removing any large air bubbles and also stops the skin moving around.
The finished slide needs to be placed onto the stage of a microscope using the lowest objective lens to start with. The student should be able to see the basic structure of the cell. Using a higher power lens enables more detail to be seen.