Question

Lab activity on onion peal cells

Answer 1

AIM

To prepare stained temporary mount of onion peel cells and to record observations and draw labelled diagrams.

MATERIALS REQUIRED

Onion, plain slides, coverslip, watch glass, needles, forceps, brush, blade, safranin, blotting paper, glycerine and compound microscope.

THEORY

Onion is a multicellular plant. Like other plant cells, the cell of onion peel consists of a cell wall, cell membrane, cytoplasm, a large vacuole and a nucleus. The nucleus lies at the periphery of cytoplasm and vacuole is located in the centre. Presence of large vacuoles and cell wall confirms that cells of onion peel are plant cells.

PROCEDURE

Take a piece of onion and bend it to remove the transparent membranous structure called onion epidermal peel. With help of forcep remove the peel from its inner side.

Place the peel in water in a watch glass.

Add a few drops of stain safranin, to the watch glass containing the peel for staining.

Now, wash the leaf peel with water and transfer it on to a clean slide with the help of brush.

Remove extra water from the slide surrounding the peel with the help of blotting paper.

To this slide, add a drop of glycerine over the peel and place the coverslip in a manner to avoid entry of air bubbles.

Soak away the extra glycerine with blotting paper.

Examine slide under the microscope.

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OBSERVATIONS

A large number of rectangular cells with distinct cell wall can be observed.

Cytoplasm is seen as thin layer of deep coloured substance on inner surface of cell wall.

A big central vacuole is present in the cell.

A deeply stained round body called nucleus is seen in each cell.

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RESULT

The epidermal peel of onion comprises of rectangular shaped cells. Each cell comprises of a nucleus, a central vacuole, thin layer of cytoplasm and cell wall.

As cell walls and large prominent vacuole are present in each cell, the cells placed under observation are plant cells.

PRECAUTIONS

Always take a clean slide and hold it by its edges to avoid making the slide dirty.

Peel should be properly stain. Avoid under-staining or excessive staining of the peel.

Always transfer the peel with the help of brush.

Mounting of the peel should be done in centre of slide.

Avoid folding of the leaf peel.

Remove extra glycerine with the help of blotting paper.

Avoid entry of air bubbles while placing the cover slip.

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Answer 2

Answer:

• Fill a watch glass with some distilled water.
• Using the forceps, remove a portion of the transparent onion peel (epidermis) from the leaf after removing a leaf from the half of the onion.
• Place the epidermis in the water-filled watch glass.
• Safranin solution should be dispensed into a different watch glass using a dropper.
• Put the peel into the watch glass holding the safranin solution with a brush.
• This should soak in the Safranin solution for 30 seconds to stain the peel.
• Using the brush, remove the peel from the Safranin solution and put it in the watch glass with the distilled water.
• Using a dropper, add a few drops of glycerine to the centre of a dry glass slide.
• Put the peel on the glycerine-filled slide with the brush.
• With the help of a needle, delicately lay a cover slip on the peel.
• A piece of blotting paper can be used to remove the surplus glycerine.
• View it by setting this glass side on the compound microscope's stage.
• Observations:

1. There are numerous regularly shaped cells lining up next to one another, and each one has a unique cell wall.
2. Each cell has a separate nucleus that is located on the outside.
3. Each cell has cytoplasm that has been lightly dyed.
4. Each cell has a sizable vacuole at its core, which is encircled by cytoplasm.

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