CBSE Biology Experiment To Prepare Slide of Onion Peel and Cheek Cells

Biology Experiment- Prepare Slide of Onion Peel and Cheek Cells

Introduction

Plants and Animals are eukaryotic organisms and contain very specific characters. They are advanced forms of organisms and are found in large populations. A eukaryotic cell contains many membrane bound organelles and a prominent nucleus with a nuclear membrane.

Table of Contents

The following article contains: - 

• Aim 

• Requirements 

• Theory 

• Methodology 

• Observations 

• Conclusion 

• Summary

• Questions

Aim 

• To study onion peel under microscope and draw accurate labeled diagrams.

Requirements

Onion, Safranin, Glycerin, Compound microscope. Slides, Coverslips, forceps,etc.

Theory

Onion is a multicellular, eukaryotic organism which belongs to Kingdom Plante. An onion peel cell contains a cell wall, cell membrane, large vacuole at the center and prominent nucleus at the periphery of the cytoplasm. Safranin is stain used for staining plant cells as it colors all the organelles with a very prominent red color hence, helping in easy detection of various organelles under a microscope.

Procedure

1. For the onion peel experiment, cut an onion into two halves and remove a transparent membranous structure which is known as epidermal peel.

2. Take the peel with the help of a forceps in a watch glass containing water.

3. Add a few drops of safranin and let it stand for staining.

4. Wash the peel with water to remove extra stain

5. Transfer the peel on a glass slide with a brush.

6. Add a drop of glycerin over the peel and place the coverslip gently.

7. Remove extra stain/ glycerin with a blotting paper.

8. Observe the onion peel under microscope.

Observations

• Red colored cells with prominent color on the periphery were observed.

• Rectangular cells with thin cytoplasm are present enclosed within the cell wall.

• Vacuole is large and centrally placed.

• Nucleus is round in shape, deeply stained and present in each cell close to the periphery. 

Result

The onion peel cell contains a large vacuole, prominent nucleus, thin cytoplasm and rectangular cells with a cell wall. Therefore, we can conclude that the above onion peel cell is a type of plant cell.

Onion peel cell diagram

• To study Cheek cells under a microscope.

Requirements

Methylene blue, Glycerin, Compound microscope. Slides,forceps, toothpicks etc.

Theory

Humans are multicellular, eukaryotic organisms which belong to Kingdom Animalia. These cells contain a semi-permeable cell membrane, dense cytoplasm and the nucleus in the cheek cell is placed in the center. Cheek cells are squamous epithelium cells which are thin and flat and form a delicate lining inside the mouth.

Procedure

1. Gargle mouth with clean water.

2. Take a toothpick and scrap the epithelial cells from the inner lining of the cheek.

3. Place these scrapings over a clean slide and add a drop of water to it.

4. Evenly spread the cheek cells over the slide.

5. Add a drop of methylene blue and allow it to stain for 2-3 mins.

6. Remove the extra stain with blotting paper.

7. Add glycerin and place a coverslip gently and remove the excess with blotting paper.

8. Observe the onion peel under a microscope.

Observations

• Large cells were seen which were irregular in shape.

• The boundaries of cells are attached with each other.

• Nucleus in cheek cells are deep blue-stained, round and present at the center of the cell.

• The cytoplasm is dense and jelly-like, surrounded by a thin-walled cell membrane.

Result

The above cells do not contain a cell wall. The cell contains a dense cytoplasm. Nucleus in cheek cells are centrally placed. Therefore, we can conclude that the above specimen cell is a type of animal cell.

Internal structure of cheek cells

Precautions

1. Do not over stain the specimen

2. Place coverslip gently and avoid air bubbles

3. Remove excess stain and glycerine

Lab Manual Questions

1. In a plant cell diagram which organelles are present?

Ans: In a plant cell diagram, a cell wall, cell membrane, nucleus and vacuoles are present. It also contains mitochondria, golgi complex, endoplasmic reticulum and chloroplast.

2. Cheek cells contain which organelle commonly?

Ans: Lysosomes are found commonly organelle in the cheek cells of the mouth.

3. How is the size of the nucleus related to the size of the cell?

Ans: Cell is a bigger entity and contains various organelles such as mitochondria, vacuoles etc. Nucleus is also an organelle and is present inside the cell. Hence, as compared to the size of the cell the nucleus is very small.

4. What is the main function of cheek cells?

Ans: Cheek cells secrete mucin which is an important part of mucous which in combination with the salivary glands keep the oral cavity moist and helps in the process of digestion.

Viva Questions

1. What is the basic structural and functional unit of life?

Ans: Cells are the basic structural and functional unit of life.

2. Cell wall of plants is made up of which component?

Ans: Cell wall of plants is made up of cellulose which protects the inner parts of the cell.

3. Give two uses of cell membrane.

Ans: Cell membrane is a boundary which separates cytoplasm and all organelles from the outside environment. It is selectively permeable and hence facilitates the movement of materials across the cell.

4. Mention four organelles which are present in animal and plant cells.

Ans: Nucleus, Mitochondria, Endoplasmic Reticulum, Golgi complex are found in both animal and plant cells.

5. Which are self-replicating organelles?

Ans: Mitochondria and Chloroplast both are self-replicating as they contain their own DNA.

6. Which organelle is only seen in animal cells?

Ans: Centrosome and it facilitates spindle fiber formation in cell division.

7. Which organelle is seen only in plant cells?

Ans: Chloroplast and it performs the function of photosynthesis.

8. Mounting of cells is always done in glycerin, why so?

Ans: Glycerin is a highly dense liquid and contains ample amount of moisture and hence prevents drying out of the cells.

9. Why should air bubbles be prevented?

Ans: When air bubbles are formed they cover parts of the cell which is under observation. Therefore, they should be avoided.

10. What is the significance of teasing?

Ans: Teasing separates all cells from each other so that they can be seen clearly under the microscope.

Practical Based Questions

1. Human cheek cells are commonly stained with

1. Methylene blue

2. Safranin

3. Crystal violet

4. Glycerin

 Ans: Methylene blue

2. Nucleus in the cheek cell is________.

1. Placed centrally

2. Placed peripherally

3. Placed in the cell membrane

4. Placed inside the vacuoles

Ans: Placed centrally

3. Cheek epithelial cells are a type of_______.

1. Epithelial cells

2. Squamous epithelial cells

3. Cuboidal epithelial cells

4. None of these

Ans: Squamous epithelial cells

4. Which stain is used for staining onion peel?

1. Acetocarmine

2. Methylene red

3. Crystal violet

4. Safranin

Ans: Safranin

5. Seetha makes a cell diagram containing rectangular cells and chloroplast, mitochondria and vacuole. This cell is a_______.

1. Onion peel cell diagram

2. Animal cell diagram

3. Eukaryotic cell diagram

4. Prokaryotic cell diagram

Ans: Onion peel cell diagram

6. What is observed under the high power of a microscope?

1. Large cells, more in number

2. Small cells, less in number

3. Large cells, less in number

4. Small cells, more in number

Ans: Large cells, less in number

7. Which of the following is not seen in cells of squamous epithelium?

1. Nucleus

2. Cytoplasm

3. Cell membrane

4. Cell wall

Ans: Cell wall

8. Site of protein synthesis is ______.

1. Chloroplast

2. Ribosomes

3. Nucleus

4. Mitochondria

Ans: Ribosomes

9. To observe an object at high power; the order of lens in a compound microscope is-

1. Objective 10X, eye piece 45X

2. Objective 45X, eyepiece 10X

3. Objective 10X, eyepiece 10X

4. Objective 45X, eyepiece 45X

Ans: Objective 45X, eyepiece 10X

10. Put in correct chronological order-

i) Remove cheek cells with toothpick

ii) Stain with methylene blue

iii) Clean the mouth with water

iv) Observe under microscope

1. i, ii, iii, iv.

2. iii, i, ii, iv

3. ii, iii, iv, i

4. iv, iii, ii, i

Ans: iii, i, ii, iv

Summary

Onion and Cheek cells experiments give us information regarding plant and animal cells. A plant cell contains, large vacuole and cell wall. Animal cells contain nucleus and cell membranes. Plant cells have a definite shape whereas animal cells are irregular in shape. Staining of cells helps in better visibility of cells and their organelles.