Practicals for 9th

Practical no I

Instructions

1 To be written in practical file with diagram (use sharp pencil)

2 Index --whole aim has to  written in index 

To prepare stained temporary mount of onion peel.

Materials Required
Onion, slides, cover slips, watch glass, petridish, forceps, needles, dropper, glycerin, blotting paper, blade/knife, safranin solution and a microscope.

Procedure

1.    Take a medium sized onion, cut its outer surface with knife.

2.    Use forceps to remove the peel of onion.

3.    With the help of needle separate the small portion of epidermis (peel)

4.    Keep dilute safranin solution in a watch glass.

5.    Put this small peel in this watch glass with brush and allow it to stain for 3-5 minutes.

6.    Transfer the stained peel to another watch glass that contains distilled water in it, to remove extra stain.

7.    Take a clean dry slide and place two drops of water/glycerine on the centre of the slide.

8.    Transfer the stained peel with needle and brush on the middle of the slide, if the peel curls straighten it and flatten it with brush and needle, do this gently.

9.    With the help of blade cut the peel into a square shape.

10. Take a dry and clean coverslip and gently place it on the slide with the help of needle such that no air bubbles enter in it.

11. Gently press the coverslip with needle for even spreading of glycerine.

12. Remove the extra stain and water with the help of blotting paper.

13. Clean the sides of the coverslip with dry blotting paper and place it under the lens of the microscope and record your observations.


Observations

The cells under observation are the plant cells. It consists of cell wall and large vacuoles. The nucleus is very prominent and is clearly visible.

Inference
Plant cell shows the following:

1.    It consists of cell wall.

2.    The nucleus is prominent and present at the periphery of cytoplasm.

3.    Large vacuoles are seen at the centre of the cell.

4.    A lightly stained cytoplasm is present in the cell.

Precautions

1.    Use dilute stain for staining.

2.    Avoid the formation of air-bubbles while placing the coverslip on the slide.

3.    Take very thin peel of onion to get a single layer of cells, no overlapping of cells should be seen.

4.    Use dry and clean slide, wipe out extra stain or water present on the sides of the slide.

Practical no 2

. To prepare stained, temporary mount of human cheek cells.

Materials Required
Slide, coverslip, watch glass, methylene blue stain, blotting paper, toothpick, needle, dropper, brush, microscope and glycerine.

Procedure

1.    Make a dilute methylene blue solution in a watch glass.

2.    Keep a clean slide with a drop of distilled water at the middle of the slide.

3.    Take a clean/unused toothpick and scrap the inner wall of your mouth/cheek gently to obtain the epithelial animal tissue, (use the blunt side of toothpick)

4.    Transfer the scrap on the middle of the glass slide and put a drop of methylene blue solution on it, to stain the cells.

5.    After 2-3 minutes place the coverslip gently on the cheek cell with the help of needle and avoid the air bubble. (A drop of glycerine can be spread on the cheek cells, it is optional)

6.    With the help of blotting paper remove the extra stain/water present on the slide.

7.    Place the slide under microscope and observe it.

Observations

1.    Cells with irregular shapes are seen.

2.    A prominent nucleus is seen in the middle of the cell.

3.    A thin membrane called plasma-membrane is visible at the boundary of each cell.

4.    The cells do not show any intercellular space.

5.    No big vacuoles and cell wall is seen.

 

Inference
The cells observed under the microscope do not have cell wall and big vacuoles, these are the cells of animal.

Precautions

1.    Use unused/new toothpick for scraping of cheek cells.

2.    Placing of coverslip should be done carefully to avoid air bubbles.

3.    Avoid overstaining.

4.    Use clean/dry mounted slide while placing it under the lens of the microscope.

5.    Avoid overlapping of the cells.

VIVA VOCE

Question 1:
Name the type of microscope used to observe the slide of animal/plant cell.
Answer:
One should use compound microscope with lens having the magnification of 10X, 40X and 100X.

Question 2:
Why do we use stain for mounting the slide?
Answer:
The stain makes cell wall, nucleus, cell membrane visible as they take up the stain.

Question 3:
Why can’t we see all the cell-organelles under microscope?
Answer:
The other cell organelles do not take up the stain and are too small to be seen under the lab microscope.

Question 4:
Give the use of glycerin in slide preparation.
Answer:
Glycerin prevents drying of specimen. The material remains wet and do not dry.

Question 5:
How many types of lenses are present in a compound microscope?
Answer:
It consists of two lenses—objective lens and eyepiece.

Question 6:
Give one example of epithelial cell.
Answer:
Cheek cell.