SXConline
Cytology
Onion

Objectives:


To know the arrangement of cells
To know the shape and size of the cells
To know the different parts of the cells
Requirements: A compound microscope, watch glass, cover slip, scissors, forceps, brush, needle and dropper.
Materials: Onion scale leaf
Chemicals: Dilute aqueous safranin and dilute glycerin


Procedure:
( i ) Peeling => A fleshly onion scale leaf was taken and bent transversely. Then, the epidermal layer of concave (inner) side was peeled
off and was immediately placed into a watch glass containing water.
( ii ) Staining => 3-4 drops of safranine was added in the watch glass containing material with the help of dropper. Then it was stirred
well with brush for homogenous mixing of the stain and then it was leaved for 20-30 seconds. Then the materials was washed in slow
running tap water until the water ran clear. Then the stained material was cut into small (2-5 mm) rectangular or square pieces with the
help of scissors.
( iii ) Mounting => One to two drops of glycerin was put in the center of a clean dry slide. Then a piece of the prepared material was
transferred to the glycerin by using brush. The material was spread properly with the help of brush and needle to avoid folding. Then it
was covered by a clean and dry cover slip without trapping any air bubbles.
Then the prepared slide was observed in low and high power of microscope.


Microscopic Observations
1) The cells were compactly arranged and appeared as bricks on the walls.
2) The cells were almost rectangular in shape, microscopic but variable in size.
3) All the cells were found to be covered externally by cell wall.
4) Inner to cell wall, every cells were enclosed by a thin cell membrane.
5) The cells were filled by transparent, granular fluid, the cytoplasm in the peripheral region.
6) Within the cytoplasmic region, a dark coloured rounded structure, identified as nucleus was present.
7) The central region of the cell was occupied by a large vacuole.

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