CBSE Class 9 Science Practical Skills – Slide of Onion Peel and Cheek Cells

CBSE Class 9 Science Practical Skills – Slide of Onion Peel and Cheek Cells

EXPERIMENT (a)

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

1. 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.
2. Place the peel in water in a watch glass.
3. Add a few drops of stain safranin, to the watch glass containing the peel for staining.
4. Now, wash the leaf peel with water and transfer it on to a clean slide with the help of brush.
5. Remove extra water from the slide surrounding the peel with the help of blotting paper.
6. To this slide, add a drop of glycerine over the peel and place the coverslip in a manner to avoid entry of air bubbles.
7. Soak away the extra glycerine with blotting paper.
8. Examine slide under the microscope.
   

OBSERVATIONS

1. A large number of rectangular cells with distinct cell wall can be observed.
2. Cytoplasm is seen as thin layer of deep coloured substance on inner surface of cell wall.
3. A big central vacuole is present in the cell.
4. A deeply stained round body called nucleus is seen in each cell.
   

RESULT

1. The epidermal peel of onion comprises of rectangular shaped cells. Each cell comprises of a nucleus, a central vacuole, thin layer of cytoplasm and cell wall.
2. As cell walls and large prominent vacuole are present in each cell, the cells placed under observation are plant cells.

PRECAUTIONS

1. Always take a clean slide and hold it by its edges to avoid making the slide dirty.
2. Peel should be properly stain. Avoid under-staining or excessive staining of the peel.
3. Always transfer the peel with the help of brush.
4. Mounting of the peel should be done in centre of slide.
5. Avoid folding of the leaf peel.
6. Remove extra glycerine with the help of blotting paper.
7. Avoid entry of air bubbles while placing the cover slip.

 

EXPERIMENT (b)

AIM
To prepare stained temporary mount of human cheek cells and to record observations and draw labelled diagrams.

MATERIALS REQUIRED
Slide, coverslip, needle, blotting paper, tooth pick, methylene blue, watch glass, compound microscope.

THEORY
Animal cells lack cell wall and prominent vacuole. In these cells a semi-permeable membrane called cell membrane surrounds the cytoplasm. In comparison to plant cell, in animal cell cytoplasm is dense and occupies larger space. Vacuoles are absent or very small in size. In animal cells, the position of nucleus is usually central.Cheek cells are part of squamous epithelium. They are thin and flat cells. They found arranged like pavement tiles, i.e., arranged end to end forming a delicate lining.

PROCEDURE

1. Rinse your mouth to remove any food particles.
2. With the help of the toothpick scrap the inner side of the cheek to get some epithelial cells.
3. Place the scrappings in a drop of water over a clean slide.
4. Spread the scrappings with the help of needle.
5. Add a drop of methylene blue over the slide.
6. Wait for 2 minutes and then remove the extra stain with blotting paper.
7. Add a drop of glycerine on the slide.
8. With the help of needle, gently place the coverslip over the slide to avoid entry of air bubbles.
9. Observe the slide under the microscope.

OBSERVATIONS

1. Large number of flat polygonal cells with irregular boundaries attached edge to edge are seen.
2. The cells have thin membrane called cell membrane which encloses jelly like substance called
   

RESULT
Cells under observation do not have cell wall and large prominent vacuole. So, cells of specimen on the slide are animal cells.

PRECAUTIONS

1. Scrap the cheek cells gently with help of clean toothpick to avoid injury.
2. Always rinse the mouth before scrapping the tissue so as to remove any food particles from mouth.
3. Place coverslip gently to avoid entry of air bubbles.
4. Remove extra glycerine with blotting paper.
5. Spread the scrappings so that cells are properly distributed.

INTERACTIVE SESSION

Examiner :
Name the basic structural and functional unit of life.
Examinee:
Cell is the basic unit of life.

Examiner :
State the difference between plant cell and animal cell with respect to outer membranes.
Examinee:
Plant cell possesses a cell wall along with a cell membrane. Cell wall provides shape, protects and supports the plant cell. In contrast to this, animal cells lack cell wall. Cell membrane is the outermost covering in animal cells.

Examiner :
What is the cell wall in plants made up of?
Examinee:
Cell wall is made up of cellulose.

Examiner :
Do both plant and animal cells possess cell membrane?
Examinee:
Yes.

Examiner :
What is the significance of having a cell membrane around a living cell?
Examinee:
Cell membrane around a cell acts as a boundary membrane and encloses the protoplasm. Cell membrane is selectively permeable and helps in transport of materials in and out of cell.

Examiner :
How are plant cells different from animal cells?
Examinee:

Examiner :
Name any four cell organelles found both in plant cell and animal cell.
Examinee:
These include nucleus, endoplasmic reticulum, ribosomes and mitochondria.

Examiner :
Name the two cell organelles which apart from nucleus contain DNA
Examinee:
Mitochondria and chloroplast.

Examiner :
Name the stain used for staining the human cheek cell during the experiment.
Examinee:
Methylene blue.

Examiner :
Even after staining of slide with methylene blue, certain cell organelles like mitochondria are not visible in the microscope. Why?
Examinee:
All the cell organelles do not get stained with methylene blue, so they cannot be seen under the microscope.

Examiner :
Why is glycerine used for mounting of the onion cell or human cheek cell?
Examinee:
Glycerine is hygroscopic in nature and hence, does not allow the cells to dry up.

Examiner :
Why is teasing or spreading the cells important in case of cheek cell slide?
Examinee:
Teasing is important as it helps in proper dispersion of cells.

Examiner :
Why is it essential to place the coverslip gently to avoid entry of air bubbles?
Examinee:
Entry of air bubbles on the slide should be avoided as these would mask the structure to be observed.

Examiner :
Name the stain used for staining of onion peel
Examinee:
Safranin.

Examiner :
Compare the shapes of onion peel cells with human cheek cells.
Examinee:
Onion peel cells are rectangular in shape, having distinct cell walls whereas human cheek cells are flat polygonal cells with irregular boundaries.

Examiner :
Name the cell organelle found only in cheek cells (animal cells) but absent in onion peel cells.
Examinee:
Centrosome.

Examiner :
What is the function of centrosome?
Examinee:
Centrosome helps in spindle fibre formation during cell division.

Examiner :
What is the function of nucleus of a cell?
Examinee:
Nucleus controls all the activities of cell.

Examiner :
Why should you rinse your mouth before scrapping the epithelial cells from inner side of cheek? Rinsing helps in removal of any food particles left in the mouth and which may come with the cells. Why is staining done before mounting?
Examinee:
Rinising helps in removal of any food particless left in the mouth and which may come with the cells.

Examiner :
Why is atinin done before mounting?
Examinee:
Staining provides colour to the cell, hence making it visible under microscope.

NCERT LAB MANUAL QUESTIONS
EXPERIMENT NO. 14 (a)

Question 1:
What is the size of nucleus in relation to size of cell?
Answer:
The size of nucleus is very small.

Question 2:
Name the stained parts of the cell.
Answer:
Cell wall, nucleus, cytoplasm.

Question 3:
Pick the odd one out.

1. Plastids
2. Large vacuoles
3. Cell wall
4. Centrioles.

Answer:
(d) Centrioles (as these are present in animal cells and absent in plant cells.)

Question 4:
Which of the following is a correctly labelled cell of an onion peel?

Answer:
(b) is correctly labelled

EXPERIMENT NO. 14 (b)

Question 1:
Arrange the following steps in correct sequence-
(i) Putting a drop of glycerine on the cheek cells on a slide.
(ii) Scrapping the inner side of cheek,
(iii) Adding methylene blue stain, and
(iv) Placing the cover slip over the material.
(a) (i), (ii), (iii), (iv)
(b) (ii), (i), (iv), (iii)
(c) (iv), (ii), (iii), (i)
(d) (ii), (iii), (i), (iv)
Answer:
(d) (ii), (iii), (i), (iv)

Question 2:
Which one of the following is absent in animal cells?
(a) Cell membrane
(b) Nucleolus
(c) Cell wall
(d) Cytoplasm
Answer:
(c) Cell wall

Question 3:
Cheek epithelial cells are an example of
(a) squamous epithelial cells.
(b) cuboidal epithelial cells.
(c) columnar epithelial cells.
(d) all of these.
Answer:
(a) Squamous epithelial cells.

Question 4:
Why are cheek epithelial cells always moist?
Answer:
Due to presence of saliva.

Question 5:
Name two structures which you would see in cheek cells if you were using a very high magnifying power of microscope.
Answer:
Nucleus, Cytoplasm.

PRACTICAL BASED QUESTIONS
Multiple Choice Questions/VSA

Question 1:
Which of the following components are seen in a slide of human cheek cell when observed under a microscope?
(a) Cell membrane, protoplasm, nucleus
(b) Cell wall, cytoplasm, nucleus
(c) Cell wall, protoplasm, nucleus
(d) Cell membrane, cytoplasm, nucleus

Question 2:
One end of the onion peel when focussed under microscope, the other end of the peel became out of focus. The reason is that the
(a) light coming from diaphragm is not uniform.
(b) material is overstained.
(c) material is not spread uniformly.
(d) material is understained.

Question 3:
The extra stain from the slide if present is removed by
(a) drying stain under sunlight.
(b) evaporation by heating.
(c) keeping slide under running water.
(d) soaking with filter paper.

Question 4:
To prepare a mount of human cheek cell, the sample is collected from
(a) outer side of cheek with a blade.
(b) inner side of cheek wfrh a blade.
(c) outer side of cheek with a toothpick.
(d) inner side of cheek with a toothpick.

Question 5:
A student used a red stain for mounting a peel of onion. This corresponds to Pie stain
(a) Acetocarmine.
(b) Safranin.
(c) Methylene.
(d) Iodine.

Question 6:
Pooja draws a cell with cell wall and presence of large vacuole. The cell belongs to which type of cells
(a) animal cell.
(b) bacterial cell.
(c) plant cell.
id) none of these.

Question 7:
You are viewing a prepared slide of temporary mount of cells under high magnification microscope. You would observe
(a) more number of cells and size is large.
(b) less number of cells and size of cells is large.
(c) less number of cells and small in size.
(d) more number of cells and small in size.

Question 8:
Roshini is making a temporary mount of onion peel. What precautions should be taken to avoid the entry of air bubbles on the slide?
(a) Coverslip should be dropped on to the peel from a certain height.
(b) Peel should be allowed to fold over itself once or twice.
(c) Coverslip should be gently dropped over the peel.
(d) Peel should be immersed in stain for over an hour.

Question 9:
Given below are four steps for preparing a temporary mount of human cheek cells.
(i) Taking the scrap from inner side of the cheek and spreading it on a clean slide.
(ii) Putting a drop of glycerine on the material.
(iii) Adding two or three drops of methylene blue.
(iv) Rinsing the mouth with fresh water and disinfectant solution.
The correct sequence of these steps is:
(a) (i) – (ii) – (iii) – (iv)
(b) (iv) – (i) – (iii) – (ii)
(c) (iv) – (i) – (ii) – (iii)
(d) (i) – (iii) – (ii) – (iv)

Question 10:
A compound microscope is generally used in the following manner:
(a) Objective of lOx and eye-piece of lOx
(b) Objective of 45x and eye-piece of lOx
(c) Objective of lOx and eye-piece of 15x
(d) Objective of 45x and eye-piece of 15x
The microscope is used in its high power in
(a) d
(b) b, d
(c) c, d
(d) b

Question 11:
Neha observed a slide of human cheek cells under a microscope in its (i) low magnifying power, (ii) high magnifying power settings. In the first setting, she must have observed
(a) fewer cells in a darker field of view.
(b) more cells in a brighter field of view.
(c) more cells in a darker field of view.
(d) fewer cells in a brighter field of view.

Question 12:
Diagrams of cells of an onion peel were labelled by four students as given below. The correctly labelled diagram is

(a) nucleus, cytoplasm,
(b) nucleus, vacuole.
(c) vacuole, nucleus.
(d) cytoplasm, vacuole.

Question 13:
The correct labelling of A and B is

(a) nucles, crtoplasm
(b)  nucles, vacuole
(c) vacuole ,   nucles,
(d) crtoplasm ,   vacuole

Question 14:
Following four slides were given for observation under microscope. The correct identification of the slides is

Question 15:
When an onion peel cell i solution, it will look like

(a) A
(b) B
(c) C
(d) D

Question 16:
Which of the following is not seen while studying the slide of squamous epithelium?
(a) Cell membrane
(b) Vacuole
(c) Cell wall
(d) Nucleus

Question 17:
Where does protein synthesis in a cell occur?
(a) mitochondria.
(b) ribosomes.
(c) plastids.
(d) golgi apparatus.

Multiple Choice Questions/VSA

1. (d)
2. (a)
3. (d)
4. (d)
5. (b)
6. (c)
7. (b)
8. (c)
9. (b)
10. (d)
11. (b)
12. (d)
13. (c)
14. (c)
15. (d)
16. (c)
17. (b)

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