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To observe and study the cell structure in an onion peel (cataphyll) using staining and mounting techniques.
Objective
To observe and study the cell structure in an onion peel (cataphyll) using staining and mounting techniques. |
Materials
Fresh onion bulb
Microscope slides
Cover slips
Forceps
Dropper
Safranin stain / Iodine solution (0.5%)
Distilled water
Microscope |
Procedure
Step 1: Preparing the Onion Peel |
1. Carefully peel off a thin, translucent layer from the inner surface of an onion bulb (cataphyll).
2.Place the onion peel on a clean microscope slide. |
Step 2: Staining the Onion Peel |
3. Using a dropper, add a few drops of safranin /0.5% iodine solution onto the onion peel. Ensure the entire surface is covered.
4. Allow the safranin / iodine solution to sit for 1-2 minutes to stain cell contents |
Step 3: Mounting the Onion Peel |
5. Gently lower a clean cover slip onto the onion peel, avoiding air bubbles. Angle it slightly to allow even spreading of safranin / iodine solution.
6. Press down gently to secure the cover slip. |
Step 4: Microscope Observation |
7. Place the prepared slide on the microscope stage.
8.Start with the lowest objective lens (usually 4x or 10x) and focus using coarse and fine adjustments.
9. Increase magnification (40x or 100x) and refocus as needed.
10. Observe onion peel cells, noting structures like cell wall, membrane, nucleus, and organelles |
Step 5: Recording Observations |
11. Draw representative onion peel cells in your lab notebook. Label cell structures observed.
12. Note any variations in cell structure within the onion peel. |
Step 6: Cleaning Up |
13. Remove the slide from the microscope stage.
14.Dispose of onion peel and cover slip in designated waste container.
15. Clean microscope lenses and stage using lens cleaning paper and solution if needed. |
Safety Precautions |
Handle equipment and chemicals with care.
Be cautious with iodine solution, which can stain skin and clothing.
Wash hands thoroughly after the experiment. |
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Observations: Safranin stained onion cells
Observation Table
Observation |
Description |
Cell Shape |
Rectangular |
Cell wall |
Rigid, outermost layer |
Cell Membrane (Plasma Membrane) |
Thin, semi-permeable layer beneath the cell wall |
Cytoplasm |
Granular, semi-transparent, filling the cell interior |
Nucleus |
Large, round, centrally located, darker staining |
Vacuole |
Large, clear, centrally located |
Cell Arrangement |
Regular pattern with adjacent cells |
Variation in Cell Size |
Some variations in cell size |
Safranin / Iodine Staining |
Effective staining of cell contents, enhancing visibility |
Conclusion
This experiment allowed us to observe and study the cell structure of an onion peel using staining and mounting techniques. The iodine / safranin stain highlighted various cell components, including the cell wall, cell membrane, and nucleus. This observation provides insight into the organization and characteristics of plant cells. |
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