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Cellular Division and Replication

AIM:                                                                                                   

To view mitosis in cells as it is happening.

HOW DOES THE FOLLOWING WORK?

Time allocation: 10 Min Preparation of Onion
Time allocation: 72 – 96 Hours growing of roots
Time allocation: 45 Min Making the Slide & Observation

Cellular division is important for cellular growth and repair. In this experiment the onion is encouraged to grow and samples are taken from its sprouted roots. This means that the onion’s cells in the roots are growing hence they will have some cells in the process of mitosis. As the onion root is in the growing phase students should be able to identify at least 1 of the 6 phases of mitosis.

In the preparation of the slide students will use Eosin Y dye. The Eosin Y dye leaks into the cells and stains the various components of the cell. Unlike other dyes that have been used till now, the Eosin Y staining process needs to be exposed to certain conditions to get to the point where it can dye the various components of the tissue that needs to be dyed.  These conditions among many include an acidic medium. The hydrochloric acid is added to the sample that will be observed in order for the dye to react with and consequently dye the cellular components various colours.

APPARATUS:

  • 600 ml glass beaker
  • Glass Petri dish
  • Tooth picks
  • Hydrochloric acid 32% Concentration
  • Bunsen burner
  • Microscopic slides
  • Cover slides
  • Microscope (optional)
  • Scalpel
  • Eosin Y Stain
  • Toothpicks
  • Steel Tong
Supplied By Educator
  • Onion that has sprouted roots (Big enough to fit in the opening of a 600ml beaker)

PRECAUTIONS:

  • When working with the cover slips act with caution as they break easily.
  • During the experiment students must wear gloves.
  • Place the samples in a sink before dying to prevent bench top stains.

METHOD:

  1. Place a suitable size onion, so that it will balance on top of the 600ml glass beaker. With the base of the onion in the glass beaker. (If it is too small use toothpicks)
  2. Fill the beaker with water so that the onion is half submerged by the water.
  3. Place the beaker, with the onion in a dark place (cupboard) for approximately 72 -96 hours until the onion sprout roots and the roots are approximately 20mm in length.
  4. Cut 5 mm from the root tips and place them in the petri dish.
  5. Cover the root tips with one drop of Eosin Y stain and one drop of diluted Hydrochloric acid 32% solution.
  6. Warm the slide evenly with a tong for one to two minutes. Do not cook or dry out the root.
  7. Rinse the root with distilled water.
  8. Cut the root tip (2mm), place the root tip on a microscopic slide and drop one drop of Eosin Y stain on the slide. Wait five minutes for the Eosin Y to be absorbed into the root tip.
  9. Cover the root tip with a cover slide, by placing the cover slide edge down from one side to the other spreading the slide from out. Press down firmly with a paper towel to flatten the root tip as well as remove all the air bubbles and to clean off the excess Eosin Y stain.
  10. Heat the slide by running the slide over the flame three to four time, to set and seal the slide.
  11. Place on table of microscope and study and lower magnification, carry on to higher magnifications.

 

CONCLUSION:

The onion samples taken by the students were all in growth phase, students should have been able to identify the phases of Mitosis or at least 1 of the 6 phases of mitosis.

 

OBSERVATION

View 40x Magnification                VS           1000x Magnification                      VS           Scientific Drawing

PRECAUTIONS:

  • When working with the cover slips act with caution as they break easily.
  • During the experiment students must wear gloves.
  • Place the samples in a sink before dying to prevent bench top stains
  • When working with a Bunsen burner never leave the flames unattended as this could lead to dangerous laboratory fires.
  • If accidentally exposed to chemicals:
    • Eye contact – Irrigate thoroughly with water for at least 10 minutes, if not better within 10 min, obtain medical observation
    • Ingestion – Wash out mouth thoroughly with water and give plenty of water to drink, obtain medical attention.
    • Inhalation – Remove from exposure, rest and keep warm. In severe cases, or if exposure has been great, obtain medical attention.
    • Skin contact – Drench the skin thoroughly with water. Remove contaminated clothing and wash before re-use. Unless contact has been slight, obtain medical attention.
  • If chemicals are accidentally spilled:
    • Wear appropriate protective clothing. Inform others to keep at a safe distance.
    • Spread soda ash liberally over the spillage. If local regulations permit, mop up cautiously with plenty of water and run to waste, diluting greatly with running water. Otherwise transfer to container and arrange removal by a disposal company. Wash site of spillage thoroughly with water.
    • For large spillages liquids should be contained with sand or earth and both liquids and solids transferred to salvage containers. Any residues should be treated as for small spillages.
    • Ventilate area and remove sources of ignition. Absorb spill with inert material and containerize for disposal.
    • When dealing with cover slips work with caution, as these are very fragile and can cause severe cuts.