NCERT Class 9 Science Lab Manual – Slide of Onion Peel and Cheek Cells

NCERT Class 9 Science Lab Manual – Slide of Onion Peel and Cheek Cells

Aim
To prepare stained temporary mounts of

1. onion peel and
2. human cheek cells and to record observations and draw their labelled diagrams.

Theory

1. Plant cell to be studied in lab: Onion peel
2. The cells are very clearly visible as compartments with prominent nucleus in it.
3. The cell walls are very distinctly seen under the microscope.
4. The big vacuoles are also seen in each cell.
5. The cells can be stained very easily using safranin solution.
6. Animal cell to be studied in lab: Cheek cell
7. The cells are flat and irregular in shape, with no cell wall.
8. The nucleus can be seen very prominently in the center of the cell.
9. The nucleus of the cell is stained easily with the methylene blue stain.
10. The cell membrane and the cytoplasm can also be studied through these cells.
11. Functions of the Organelles:
    • Nucleus: Contains nucleic acid, DNA (genetic material) , which controls cell activities
    • Cytoplasm: Most chemical reactions take place here; controlled by enzymes
    • Cell membrane: Controls substances that move in and out of cell. It is partially permeable.
    • Cell wall :It is made up of cellulose, strengthens and protects the cell and gives definite shape to the cell.
    • Chloroplasts: Contain chlorophyll, which absorbs light energy and is a site for photosynthesis.
    • Mitochondrion: Site of respiration. It is known as the powerhouse of the cell.
    • Vacuole: Large, and filled with cell sap to help keep the cell turgid. Acts as a store of water, sugars, in some cases, of waste products that the cell needs to excrete.

A. To prepare stained temporary mount of onion peel.

Materials Required
Onion, slides, coverslips, watch glass, petridish, forceps, needles, dropper, glycerine, 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.

B. 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 glycerine in slide preparation.
Answer:
Glycerine 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.

PRACTICAL BASED QUESTIONS

Question 1:
What should be the lens magnification when you place the slide under microscope?
Answer:
Initially the lens with lower power i.e., 10X should be used to see the material and for viewing under higher power use higher magnified lens.

Question 2:
What is the position/location of nucleus in animal cell and plant cell?
Answer:
In plant cell nucleus is present on one side of the cell whereas in animal cell the nucleus is present in the middle of the cell.

Question 3:
Why is nucleus present on one side of the plant cell?
Answer:
The plant cell consists of big vacuoles which occupies the maximum space in the cell hence nucleus is present on the side.

Question 4:
What is the function of cover slip in slide mounting?
Answer:
A cover slip keeps the slide mounted material at a fixed position, the covering prevents the material from drying and also protects the lens of the microscope from getting in contact with the material which can lead to fungul growth on the lens.

NCERT LAB MANUAL QUESTIONS 

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

Question 2:
Name the stained parts of the cell.
Answer:
In onion peel the parts of the cell stained are cell wall, nucleus and cytoplasm.

Question 3:
Pick the odd one out.
(a) plastids
(b) large vacuoles
(c) cell wall
(d) centrioles
Answer:
Centrioles is odd here as it is present in animal cell and rest all the other organelles are present in plant cell.

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

Answer:
(b) is rightly labelled.

Question 5:
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 coverslip 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 6:
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 7:
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 8:
Why are cheek epithelial cells always moist?
Answer:
The cheek cells are moist due to the secretion of saliva in mouth.

Question 9:
Name two structures which you would see in cheek cells if you were using a very high magnifying power of microscope?
Answer:
Nucleus and cytoplasm.

MULTIPLE CHOICE QUESTIONS (MCQs) 

Questions based on Procedural and Manipulative Skills

Question 1:
Which of the following liquids is not used in the preparation of stained temporary mount of onion peel?
(a) water
(b) safranin
(c) glycerine
(d) methylene blue.

Question 2:
Put cover slip gently on the slide to
(a) avoid entry of air bubbles
(b) avoid crushing of peel
(c) avoid oozing of stain
(d) see the material clearly.

Question 3:
The correct method of obtaining onion peel is to:
(a) take the thinnest bit after mashing an onion leaf,
(b) make thick sections of a thick scale leaf using blade.
(c) make thick section of a scale leaf.
(d) use a needle and forceps to remove a thin peel from convex surface of a scale leaf.

Question 4:
The cover slip is used in temporary mount to cover material to
(a) avoid drying of the material
(b) avoid the entry of air bubbles
(c) avoid the leak out of glycerine
(d) to increase the visibility.

Question 5:
A slide prepared is to be viewed under a compound microscope and the coarse adjustment is:
(a) 15X
(b) 10X
(c) 40X
(d) 100X.

Question 6:
The commonly used stain for preparing onion peel slide is:
(a) safranin
(b) methylene blue
(c) glycerine
(d) iodine solution.

Question 7:
In the preparation of onion slide the following material is not used:
(a) glycerine
(b) water
(c) safranin
(d) methylene blue.

Question 8:
An onion slide when viewed under the microscope showed pink stained nucleus, the stain used is
(a) rose water
(b) methylene blue
(c) safranin
(d) iodine solution.

Question 9:
Which one of the following is the correct method of obtaining an onion peel?
(a) Mash the onion leaf and select the thinnest part,
(b) Take a thick scale leaf and make thin sections using a blade.
(c) Draw out a thin and transparent piece from the concave surface of a scale leaf using forceps.
(d) Use needle and forceps to remove a thin peel from the convex surface of a scale leaf. .

Question 10:
The types of lenses present in compound microscope are:
(a) 3 types
(b) 2 types
(c) 4 types
(d) 1 type.

Question 11:
Cheek cells are collected by:
(a) gently peeling of the inner cheek epithelium with a forcep.
(b) scraping the inside of the cheek with a toothpick.
(c) pulling out the inner layer of skin inside the cheek with a scalpel.
(d) none of these.

Question 12:
Which one of the following is the correct step, in the procedure of making a temporary slide of human cheek cells?
(a) Place the cheek cells scrapings in a watch glass containing water.
(b) Place cheek cell scrapings in the centre of a clean slide.
(c) Dip the toothpick, containing cheek cell scrapings in the stain and then transfer to a clean slide.
(d) Obtain the cheek cells, directly on the slide.

Question 13:
To prepare a temporary mount of the cheek cells
(a) scrapings are taken from outer surface of the cheek.
(b) scrapings are taken from the inner surface of the cheek.
(c) sediments are collected from a beaker after gargling.
(d) a mucous from the throat region is used.

Question 14:
While preparing a temporary mount of human cheek cells the excess glycerine on the slide
(a) is left as it is
(b) is drained by tilting the slide
(c) is allowed to evaporate
(d) is drained by tilting the slide and then the slide is wiped using a filter paper.

Question 15:
A cover slip is placed over the specimen to:
(a) crush the cells in order to see the organelles clearly
(b) remove extra stain and water.
(c) prevent the tissue from drying
(d) prevent glycerine from leaking out.

Question 16:
Given below are four steps for preparing a temporary mount of human cheek cells.
I.     Rinsing the mouth with fresh water and disinfectant solution.
II.   Putting a drop of glycerine on the material.
III. Adding two or three drops of methylene blue.
IV. Take scraping from inner side of cheek and spreading it on a clean side.
Arrange them in correct sequence:
(a) IV, III, II, I
(b) IV, II, III, I
(c) I, IV, III, II
(d) I, IV, II, III.

Question 17:
Cheek cell is stained with
(a) methylene blue
(b) safranin
(c) acetocarmine
(d) iodine solution.

Question 18:
Given below are four operations for preparing a temporary mount of human cheek cells.
(0 taking scraping from inner side of the cheek cells and spreading it on a clean side.
(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 order of steps is:
(a) (i)-(ii)-(iii)-(iv)
(b) (iv)-(i)-(iii)-(ii)
(c) (iv)-(i)-(ii)-(iii)
(d) (i)-(iii)-(ii)-(iv)

Question 19:
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 20:
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 with a blade
(c) outer side of cheek with a toothpick
(d) inner side of cheek with a toothpick

Question 21:
We use glycerine in temporary mount of the material because
(a) it avoids drying of the material
(b) it provides medium for floating the material
(c) it increases the beauty
(d) it increases the clarity of the material

Question 22:
A student used a red stain for mounting a peel of onion. This stain is
(a) acetocarmine
(b) safranin
(c) iodine
(d) methylene

Questions based on Observational Skills

Question 23:
On observing onion peel slide under low power of compound microscope which set of structure are clearly seen?
(a) cell wall, cell membrane, nucleus, cytoplasm.
(b) nucleus, cell membrane, vacuole, chromosomes.
(c) cell wall, cell membrane, mitochondria, vacuole.
(d) cell wall, nucleus, vacuole, chromosomes.

Question 24:
Human cheek cells stained in methylene blue and mounted in glycerine were observed with the help of a compound microscope. The components of the cell which would be seen are:
(a) cell wall, cytoplasm, nucleus.
(b) plasma membrane, cytoplasm, nucleus.
(c) plasma membrane, cytoplasm, nucleus, mitochondria.
(d) cell wall, plasma membrane, cytoplasm, nucleus.

Question 25:
The outermost layer of a cheek cell is:
(a) cell wall
(b) cell membrane
(c) cellulose
(d) protoplasm.

Question 26:
The organelle not observed in animal cell is:
(a) nucleus
(b) cytoplasm
(c) chloroplast
(d) plasma membrane.

Question 27:
The cellular component not seen while observing the slide of a cheek cell is
(a) chromosomes
(b) nucleus
(c) cytoplasm
(d) cell membrane.

Question 28:
The shape of onion cells appear
(a) rectangular
(b) pentagonal
(c) square
(d) hexagonal

Questions based on Reporting and Interpretation Skills

Question 29:
On examining the onion peel which statement is not correct.
(a) Intercellular space is absent
(b) Intracellular space is absent
(c) Intracellular space is present
(d) Nucleus is present.

Question 30:
In the cells of the onion peel the nucleus is seen:
(a) in the centre of the cell
(.b) on one side of the cell
(c) in the comer of the cell
(d) near the plasma membrane.

Question 31:
Which of the following are the identifying features of human cheek cells you will find in a slide given to you by your teacher?
(a) The large vacuole appears in each cell
(b) The cells are irregular flat with cytoplasm
(c) The cells are large enough lying side by side with cell walls.
(d) The cells are irregular and flat with central nucleus and cytoplasm.

Question 32:
One of the following is not visible in cheek cells.
(a) cell membrane
(b) nucleus
(c) cell wall
(d) cytoplasm.

Question 33:
The correct feature of cheek epithelium is:
(a) absence of cell wall, nucleus and plastid
(b) absence of nucleus, plastids
(c) absence of cell wall, plastids and intercellular space.
(d) absence of intercellular space and nucleus.

Question 34:
Cells are stained to:
(a) make the cells turgid
(b) nourish the cell
(c) help in cell multiplication
(d) highlight the cell organelles.

Question 35:
During observation of an onion peel, cells are first seen under
(a) high power
(b) low power
(c) medium power
(d) none of the above.

Question 36:
One end of the onion peel when focussed under microscope, the other end of the peel become 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

SCORING KEY WITH EXPLANATION

1. (d) To stain the slide of plant cell, safranin stain is used and hence methylene blue is not required.
2. (a) While placing the cover slip on the slide the air gets trapped and forms air bubble, this should be avoided.
3. (d) Mashing onion will damage the cell and thick section will not show single cell of onion.
4. (a) Cover slip prevents the water from the slide and the mount to get evaporated.
5. (b) For coarse adjustment the power is 10X.
6. (a) To stain the slide of plant cell, safranin stain is used and hence methylene blue is not required.
7. (d) To stain the slide of plant cell, safranin stain is used and hence methylene blue is not required.
8. (c) Safranin stains the mount pink/red.
9. (d) Mashing onion will damage the cell and thick section will not show single cell of onion.
10. (b) Compound microscope has two lenses.
11. (b) Forceps and scalpel may cause injury and are not safe.
12. (b) The scrapping of cheek cells should be mounted on the centre of the slide and then stain should be added on it.
13. (b) The inner scrapping of the cheek gives lot of cells which can be easily scrapped using toothpick.
14. (d) Glycerine need to be cleaned from the slide hence it is wiped off with the filter paper.
15. (c) Cover slip prevents the water from the slide and the mount to get evaporated.
16. (c) It is the right procedure to mount a cheek cell.
17. (a) Cheek cells are stained in methylene blue.
18. (b) It is the right procedure to mount a cheek cell.
19. (d) Helps in removing extra stain from the slide without drying the slide.
20. (d) The inner scrapping of the cheek gives lot of cells which can be easily scrapped using toothpick.
21. (a) Glycerine acts as anti-dehydrating solution.
22. (b) Safranin stains the mount pink/red.
23. (a) All these parts are prominent in the cell and are seen under low power of the microscope.
24. (b) All these parts are prominent in the cell and are seen under low power of the microscope.
25. (b) Cell wall is absent in animal cells hence cell membrane is the outermost layer.
26. (c) Chloroplast is not present in animal cell but is seen in plant cell.
27. (a) Chromosomes are very tiny to be seen by microscope.
28. (d) Shape of onion cells are hexagonal.
29. (b) Inside the onion cell large space is present.
30. (b) In plant cell the central big vacuole is seen that shifts the nucleus to one side of the cell.
31. (d) Human cheek cells have central nucleus but do not have large vacuole. They are irregular in shape with no cell wall.
32. (c) Only plant cells have cell wall, animal cells do not have cell wall.
33. (c) Animal cells do not have cell wall, plastids and the cells are compact with no intercellular space.
34. (d) Stain helps in making the cell organelles prominent.
35. (b) An onion is made of layers, each separated by a thin skin or membrane.
36. (a) When the mirror is focused to reflect sufficient light on the slide, then uniform light helps in focusing the slide.

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