Question

Write four sequential steps of the procedure of the experiment "Preparing a temporary mount leaf peel to show stomata".

THIS QUESTION CAME IN BOARD EXAMS IN 13/3/2019

Answer 1

To prepare a temporary mount of a leaf peel to show stomata. Leaf of Tradescantia or periwinkle or balsam, slide, coverslip, forceps, needles, cotton cloth, brush, blotting paper, watch glass, blade, dropper, glycerine, safranin and compound microscope.

Answer 2

Mounting a slide

Take a clean glass slide and wipe it with cotton cloth to remove any dust ).

To locate the centre, place the slide on a paper and draw its outline. Remove the slide and draw the diagonals to mark the centre in the outline of slide. Now, place the slide on this paper over the outline drawn and hence centre point can be observed.

In a watch glass, take some stain and place the material in it for staining. After a minute, wash the material with water so that excess stain get removed.

Now, place a drop of glycerine on the centre of slide and transfer the material on to drop with the help of brush.

Place the coverslip on the slide in such a position that its one side touches the liquid on the slide.

Hold the other side edge with the help of needle, obliquely placed. Now, gently lower down the needle till the coverslip touches the slide and covers the material. In this way air bubbles will be eliminated.

AIM

To prepare a temporary mount of a leaf peel to show stomata.

MATERIALS REQUIRED

Leaf of Tradescantia or periwinkle or balsam, slide, coverslip, forceps, needles, cotton cloth, brush, blotting paper, watch glass, blade, dropper, glycerine, safranin and compound microscope.

THEORY

Stomata (singular: stoma) are tiny pores present on the surface of the leaves. Though they are found on both upper and lower epidermis of leaf but they are more in number on the lower epidermis. Each stoma is bounded by two kidney-shaped guard cells. These guard cells possess a nucleus and a number of chloroplasts. The walls of guard cells are differentially thickened and elastic, i.e. they are thickened on inner side and thinner and more elastic on outer side.

The opening and closing of stomata is operated by the change in the turgidity of guard cells. The stomata help in exchange of oxygen, carbon diodide and water vapour between atmosphere and plant.

PROCEDURE

Take a freshly plucked leaf, and remove the peel from its lower surface by tearing it.

Put the leaf peel in a watch glass containing water so that the peel does not dry.

To the watch glass containing leaf peel, add 1-2 drops of safranin to stain the peel.

With the help of a brush, place the leaf peel in the centre of a clean slide.

Put a drop of glycerine on the slide over the peel.

Now, with the help of a needle, gently place a coverslip over the peel.

Remove the excess glycerine with a blotting paper.

Observe the slide, first, under the lower magnification (i.e., 10 X) of a compound microscope and then, under the higher magnification (i.e., 45 X).

OBSERVATIONS

Epidermis or leaf peel consists of a number of cells which are irregular in outline and are arranged in single layer with no intercellular spaces.

Tiny pores called stomata are seen in the epidermal cells.

Each stoma consists of two kidney-shaped guard cells.

Each guard cell has a nucleus and many chloroplasts.

PRECAUTIONS

Peel should be taken from freshly plucked leaf.

Peel should not be allowed to dry.

Leaf peel should not be over stained.

The slide should not be dirty. –

Use a brush to transfer the leaf peel from watch glass to slide.

Peel should be placed in centre of slide.

Curling of peel should be avoided while placing it on slide.

The epidermal peel should be small in size.

Place the coverslip gently to avoid entry of air bubbles.

Excess stain and glycerine should be removed with blotting paper

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