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Onion cells


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Onion cells

  2. 2. 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.
  3. 3. Copy CELL WALLPlant cells have cell walls.• Cell walls are made up of cellulose.• They protect the cell.• Maintains the cells shape.• Prevents excessive water uptake. 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.
  4. 4. CHLOROPLASTSAre a specialised organelle thatis the site for photosynthesis.Photosynthesis is a chemical process thatcaptures light energy and transfers it intouseful chemical energy.Because photosynthesis requireslight, chloroplasts are mainly found in cellsof leaves and stems (parts that areexposed to more sunlight).
  5. 5. Do onion cells have chloroplasts?Onion cells do not have chloroplasts becausethe onion is underground (where there is nolight).Without light, chloroplasts have no purpose.The green leaves and stem of an onion plantare normally exposed to daylight and so havechloroplasts, but the onion does not.
  6. 6. INTERLOCKING CELLSInterlocking of cells gives small, thinstructures (like leaves) a large amount ofstrength.
  7. 7. STARCH GRANULESBecause the bulbs are the storage tissueof the plant, you might see some starchgranules in the slide that you create.Starch granules are small spheres thatstore excess starch. Starch is madefrom many glucose molecules joinedtogether. Glucose is the energymolecule made by photosynthesis.
  8. 8. 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
  9. 9. Copy 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)