Download Onion peel - My Dear Students

Experiment : Onion peel
A I M : To prepare stained temporary mount of onion peel , record
its observation and draw diagram
MATERIALS REQUIRED
Onion, slide, coverslip, watchglass, forceps, blade, needle, brush,
dropper, water, glycerine, knife, blotting paper, microscope.
THEORY
The cells of onion peel consist of cell wall, cell membrane, nucleus and a
large central vacuole. As the vacuole is very large and occupies most part
of the cell, so the nucleus lies at the periphery in the cytoplasm. Other
cell organelles like mitochondria, plastids, endoplasmic reticulum,
ribosomes, etc., also lie in the cytoplasm but are not stained by the
safranine stain so we cannot see them.
POCEDURE
1. Cut an onion into 5-6 pieces with a knife.
2. Take a thick scale leaf and fold it gently to break it. With the help of
a forceps pull a thin transparent peel from its concave surface.
3. Put this thin transparent peel into a watch glass, full of water.
4. With the help of dropper, add 1-2 drops of safranine to stain the
peel.
5. After two minutes, the peel turns red in colour.
6. Mount the stained peel on a clean slide in a drop of glycerine
using a brush. Cut the peel in a proper rectangular shape with the
help of a blade.
7. Cover it with coverslip.
8. Drain out excess glycerine from the slide with the help of blotting
paper.
9. Focus the peel under low power of compound microscope and
observe the cells.
10. Then observe the cells of onion peel under high power
OBSERVATIONS
1. The peel of onion leaf consists of a large number of regularly
placed rectangular cells lying side by side without any inter
cellular spaces.
2. Each cell has a distinct cell wall.
3. A darkly stained nucleus is present on the periphery of each cell.
4 . Light stained cytoplasm is also seen.
RECORD OF OBSERVATIONS
S. No
Character
Observation
1
Shape of cell,
Regular, rectangular
2
Inter cellular spaces
absent
3
Nucleus
present
4
Cell wall
present
5
Stained portion
Nucleus and cell wall
darkly stained and
cytoplasm lightly
stained.
RESULT
1. Onion peel has cell wall surrounding each cell.
2. Cells are rectangular and regularly , arranged. 3. There are no
inter cellular spaces.
4. A dark stained nucleus lies on one side of the cell due to the presence
of large vacuole in the center of the cell.
5. Cytoplasm is also towards the periphery in which nucleus lies.
PRECAUTIONS
1. The peel is very delicate so do not hold it with fingers. Use
brush.
2. Peel should not be over-stained or under-stained.
3. Peel should not become dry.
4. Peel should not get folded.
5. Hold the glass slide only by the edges.
6. The slide, coverslip and lens of the microscope should be
cleaned before use.
7. The mounting of the peel should be done in the centre of the
slide.
8. Always put the coverslip carefully so that no air bubbles enter the
slide.
Diagrams to be drawn for this experiment (Left hand side page of your
journal)