why there is a need to stain onion peel and name different types of stains?
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The complexity of a tissue can be seen in the different shapes, sizes and arrangements of the cells. The advantage of using stains to look at cells is that stains reveal these details and more.
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Real Lab Procedure
Pour some distilled water into a watch glass.Peel off a leaf from half a piece of onion and using the forceps, pull out a piece of transparent onion peel (epidermis) from the leaf.Put the epidermis in the watch glass containing distilled water.Take a few drops of safranin solution in a dropper and transfer this into another watch glass.Using a brush, transfer the peel into the watch glass containing the safranin solution.Let this remain in the Safranin solution for 30 seconds, so that the peel is stained.Take the peel from the Safranin solution using the brush and place it in the watch glass containing the distilled water.Take a few drops of glycerine in a dropper and pour 2-3 drops at the center of a dry glass slide.Using the brush, place the peel onto the slide containing glycerine.Take a cover slip and place it gently on the peel with the aid of a needle.Remove the extra glycerine using a piece of blotting paper.Place this glass side on the stage of the compound microscope and view it.
Observations
There are a large number of regularly shaped cells lying side by side and each cell has a distinct cell wall.A distinct nucleus is present on the periphery of each cell.Lightly stained cytoplasm is observed in each cell.A large vacuole is present at the centre of each cell, and is surrounded by the cytoplasm.
Conclusion
As cell walls and large vacuoles are clearly observed in all the cells, the cells placed for observation are plant cells.
Precautions
Use a brush to transfer the peel from one apparatus to another.Staining of peel should neither be too dark, nor too light.Extra glycerine stain should be removed using blotting paper.
Pour some distilled water into a watch glass.Peel off a leaf from half a piece of onion and using the forceps, pull out a piece of transparent onion peel (epidermis) from the leaf.Put the epidermis in the watch glass containing distilled water.Take a few drops of safranin solution in a dropper and transfer this into another watch glass.Using a brush, transfer the peel into the watch glass containing the safranin solution.Let this remain in the Safranin solution for 30 seconds, so that the peel is stained.Take the peel from the Safranin solution using the brush and place it in the watch glass containing the distilled water.Take a few drops of glycerine in a dropper and pour 2-3 drops at the center of a dry glass slide.Using the brush, place the peel onto the slide containing glycerine.Take a cover slip and place it gently on the peel with the aid of a needle.Remove the extra glycerine using a piece of blotting paper.Place this glass side on the stage of the compound microscope and view it.
Observations
There are a large number of regularly shaped cells lying side by side and each cell has a distinct cell wall.A distinct nucleus is present on the periphery of each cell.Lightly stained cytoplasm is observed in each cell.A large vacuole is present at the centre of each cell, and is surrounded by the cytoplasm.
Conclusion
As cell walls and large vacuoles are clearly observed in all the cells, the cells placed for observation are plant cells.
Precautions
Use a brush to transfer the peel from one apparatus to another.Staining of peel should neither be too dark, nor too light.Extra glycerine stain should be removed using blotting paper.
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