ONION CELLS

ONION PLANT

This is what a whole onion plant looks like. We will be looking at cells from the onion bulb.The bulb is the storage tissue of the whole plant.

CELL WALL

Plant cells have cell walls.• Cell walls are made up of

cellulose.• They protect the cell.• Maintains the cells shape.• Prevents excessive water

uptake.

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When staining your onion cell, you will need to wait a minute or two before viewing it under the microscope.The stain can take some time to sink in to the cells because of the barrier that the cell wall creates.

CHLOROPLASTS

Are a specialised organelle that is the site for photosynthesis.Photosynthesis is a chemical process that captures light energy and transfers it into useful chemical energy.Because photosynthesis requires light, chloroplasts are mainly found in cells of leaves and stems (parts that are exposed to more sunlight).

Do onion cells have chloroplasts?

Onion cells do not have chloroplasts because the onion is underground (where there is no light).Without light, chloroplasts have no purpose.The green leaves and stem of an onion plant are normally exposed to daylight and so have chloroplasts, but the onion does not.

INTERLOCKING CELLSInterlocking of cells gives small, thin structures (like leaves) a large amount of strength.

STARCH GRANULES

Because the bulbs are the storage tissue of the plant, you might see some starch granules in the slide that you create.Starch granules are small spheres that store excess starch. Starch is made from many glucose molecules joined together. Glucose is the energy molecule made by photosynthesis.

PREPARING SLIDES

• The torn tissue used must be thin (sliced or torn)• The tissue must be flat on the

side• Add a few drops of stain• Slowly lower coverslip so

there are no air bubbles

STAINS

• Animal cells are best stained with Methylene blue as it shows the nucleus well.

• Plant cells are best stained with Iodine as it shows the cell wall and nucleus well.

• A wet mount is made using water

• The stain should be just under the coverslip (not everywhere)

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