Draw the diagram of the cell of onion peel observed under microscope.
Answers
Answer:
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.
Place7 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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The diagram of the cell of the onion peel observed under the microscope is in the attachment below.
Preparation a temporary stained slide of an onion bulb peel :
Aim :
To prepare a temporary stained slide of an onion bulb peel.
Requirements:
Onion bulb, glass slide, glycerine, watch glass, coverslip, forceps, scalpels, needles, iodine solution or methylene blue, microscope, etc.
Procedure :
1. Take out a thin onion scale from an onion.
2. Tear it from the concave side to get a transparent, thin, and membranous onion peel piece called the epidermis.
3. Now, keep this onion peel piece in a watch glass containing water.
4. Cut out a small piece of this onion peel and place it flat on a glass slide on a drop of water with the help of a thin paint brush.
5. Add a drop of an iodine solution or methylene blue stain.
6. Drain the excess stain and mount the onion peel in a drop of glycerine under a coverslip.
7. Observe the slide under a compound microscope's low and high powers.
Observations :
- The stain used to observe the nucleus in the onion peel is iodine solution or methylene blue.
- The epidermal parenchymal onion peel cells can be seen as linear/ rectangular compartments with rigid cell walls.
- The nucleus in the onion peel is pushed towards the periphery due to the presence of a central vacuole.
Precautions:
1. Immediately put the peel of the onion bulb in water containing petri-dish to avoid the folding and drying of the onion peel.
2. Spread the onion peel uniformly on the slide.
3. Excess stain should be drained off.
4. There should be no air bubbles under the coverslip.
***Similar observations are found in the peel taken from the undersurface of a leaf of Tradescantia or Rhoe or temporary mounts of peels of onions of different sizes.
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