Question

lab activity of observing nucleus in onion peel cells full format​

Answer 1

Answer:

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.

Answer 2

Experiment to observe nucleus in onion peel cells

Explanation:

Objective :

To analyze the cells of the onion peel by preparing a stained temporary mount of onion peel cells.

Theory :

All living things are made up of cells. The division of cells results in the formation of new cells. A cell is a structural and functional unit of life. In plants, cells are composed of an outermost rigid cell wall and a cell membrane beneath it. The cytoplasm, cell organelles, and nucleus are all enclosed by the cell membrane, and a nucleus

Materials required :

An onion bulb, slides, coverslips, two watch glasses, needle, brush, forceps, razor blade, compound microscope, blotting paper, methylene blue (or safranin) solution, glycerine, and water are among the items required.

Procedure :

1. Onion's fleshy scale leaf is taken. After breaking it into two, the forceps are used to pull out a thin membranous peel adhering to the inner surface of the leaf. This is called the epidermal peel.

2. The peel is cut into little rectangular pieces and placed in a watch glass filled with water.

3. The peels are transferred into another watch glass with 1 or 2 drops of methylene blue or safranin in a tiny amount of water. It takes 3 minutes for the peels to dry. To remove the extra stain,  the peel is soaked in water.

4. A  drop of glycerine is applied  in the middle of the slide and a brush is used to transfer the cleaned and stained peel to it

5. It is covered with a coverslip by carefully lowering it with a needle. Air bubbles should not be allowed to enter.

6. Excess glycerine from the corners of the coverslip is removed by using a piece of blotting paper

7. The slide is examined under the microscope, first at low magnification and then at high magnification.

8. Labeled diagram of the cells are drawn as such seen under the microscope.

Observation :

• Large numbers of rectangular cells are visible with distinct wall cells.

• Cytoplasm is visible on the inner surface of the cell wall as a thin coating of dark-colored substance.

• There is a big central vacuole in the cell.

• Each cell has a nucleus, which is a circular body that is strongly pigmented.

Conclusion :

It is clear from the observation of cell walls and large vacuoles that the cells placed for observation are plant cells.  

Precautions :

• Peel staining must be done correctly.  The peel is rinsed with water in a watch glass to remove any remaining stain.

• A brush is used to transfer the peel on the slide.

• The coverslip must be placed carefully to avoid air bubbles