In this article, I have given a detailed account of how to prepare a temporary mount of a leaf peel. The various precautions to be followed in doing this experiment are also given. Along with the experiment, I have mentioned some important questions as well as answers related to the experiment which will be useful for those preparing for final practical or theory exams of various Boards.
Aim of the experiment
To prepare a temporary mount of a leaf peel showing stomata.
Stomata are small microscopic openings present on the epidermal surface of leaves. In dicot leaves, the lower epidermal surface includes more stomata. In monocot leaves, both epidermal leaf surfaces have an equal number of stomata.
Each stoma (singular) is made up of two kidney-shaped guard cells in dicot leaves. These guard cells are modified epidermal cells which are surrounded by some supporting cells. The inner surface of the guard cells is concave with thick non-elastic walls. The outer surface of the guard cells is convex with thin elastic walls. 'Stoma' is the opening present between the two concave surfaces of the guard cells. Guard cells include chloroplast in them while supporting cells do not have chloroplasts. When guard cells become turgid, stoma gets opened but when they become flaccid stoma gets closed. Stomata of leaves facilitate the exchange of respiratory gases and transpiration. The guard cells of monocot leaves are dumb-bell shaped.
Procedure to prepare a temporary mount of a leaf peel
Take a freshly cut leaf of Tradescantia or Balsam.
Bend or fold the leaf at the middle. A thin peel can be seen at the folded place. Now with the help of forceps pull out the peel and carefully transfer it to the watch glass containing distilled water.
Add few drops of safranin stain on the leaf peel with the help of a brush.
Now transfer one of the thin peel on to the middle of a clean glass slide. With the help of a sharp blade make the peel into a square shaped one.
Now with the help of a dropper add a few drops of glycerine on the leaf peel.
Now take a clean coverslip and place it over the leaf peel carefully with the help of a needle. No air bubble should be formed while placing a coverslip over the peel.
Excess stain and glycerine found around the coverslip should be wiped out with blotting paper.
First observe the peel under low power microscope i.e. 10X and then 45 X.
Epidermal surface of the leaf consists of single layer of closely packed epidermal cells. No intercellular spaces present between the cells.
In between the epidermal cells minute openings called stomata are present.
Each stoma is formed of two kidney-shaped cells.
The guard cells include green chloroplasts.
The wall of the guard cell is t6hick on the inner side and thinner on the outer side.
Open Stomata in a Leaf Peel (image by author)
Closed Stomata in a Leaf Peel (image by author)
Precautions to be taken during the experiment
A freshly plucked leaf should always to be used for this experiment.
A thin leaf peel should be taken from the ventral or back surface of the leaf.
After taking the leaf peel immediately it has to be kept in a watch glass containing distilled water.
Too much of safranin stain should not be used.
The peel should be kept at the ce4nter of a clean glass slide without folding with the help of brush.
Few drops of glycerine should be placed over the stained peel before keeping the coverslip.
Excess stain and glycerine should be wiped out with the help of blotting paper.
Questions based on the experiment from various Boards
Why leaf peel should be taken from back or ventral surface of the leaf? Ans. The leaf peel should be taken from the back or ventral surface of the leaf because more stomata are present on the ventral surface of a dicot leaf.
After pulling a leaf peel it has to be immediately transferred to watch glass containing water. Why? Ans. To keep the cells of leaf in hydrated condition otherwise, the cells become flaccid.
Why safranin stain used in preparing the mount? Ans. Staining the leaf peel with safranin makes the cells of a leaf peel and stomata appear clearly.
Why glycerine is used before keeping the coverslip over the mount? Ans. Glycerin keeps the leaf peel moist and prevents drying of the peel.
What precaution should be taken while placing the coverslip? Ans. Coverslip should be placed gently with the help of a needle so that no air bubbles formed under the coverslip.
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