To prepare stained permanent mount of onion peel and study of its cells under the microscope.

Aim

To prepare stained permanent mount of onion peel and study of its cells under the microscope.

Material Required

Bulb of onion, knife, forcep, watch glass, slide, cover slip, iodine solution, brush, water, glycerine, nail polish and compound microscope.

Theory

Onion peel is made up of several plant cells. Each cell has a rigid cell wall made up of cellulose. A plant cell has a large central vacuole and plastids.

Procedure

1. For the observation of cells of onion, first of all, prepare the temporary stained slide of the membrane of the ; bulb of onion. For this, first of all, remove the outer tunic of the onion bulb.
2. Now, cut it into two scale leaves situated inside pieces with a knife and take out fleshy scale leaves situated inside it.
3. Hold the fleshy scale leaf by the hand and remove its upper membrane with the help of forcep very carefully and keep it in watch glass filled with water.
4. Cut this membrane into small pieces with the help of scissors.
5. Keep any one of the piece of membrane on the slide by the help of brush and put 1-2 drops of iodine solution on it.
6. Now, wash this piece of membrane with water and keep it on another slide and mount it with glycerine.
7. Now make a ring of nail polish on the edge of this cover slip in such a way that it sticks to the slide and glycerine does not come out from it.
8. Now keep the slide in the air for a while.
9. Now, observe it under microscope and draw the diagrams of the prepared slide.

Observation

1. Numerous rectangular cells close to each other are seen in the membrane.
2. Each cell is surrounded by a cell wall.
3. Cytoplasm is present inside the cell.
4. A nucleus is present in the cell.
5. Numerous vacuoles are present in the cell.

Result

On observing the slide under microscope, it is known that the cells of onion peel are parenchyma.

Precautions

• The membrane should immediately be dropped into the water as soon as it is removed from scaly leaf so that it may not dry up.
• Only one piece of membrane should be mounted.
• While placing on the slide, membrane should not be overlapped because in that case cells will not be seen distinctly.
• Cover slip should be kept on the membrane carefully so that there may be no air bubbles in between.

Viva Questions and Answers

Question-1: Define cell.

Answer: Cell is the structural and functional unit of plants and animals.

Question-2: Who discovered cell ?

Answer: The English scientist Robert Hooke (1665) discovered cell.

Question-3: By which stain the membrane of onion is stained ?

Answer: By methylene blue solution.

Question-4: What is the shape of cells of onion ?

Answer: Rectangular.

Question-5: What is cell wall made of ?

Answer: Cell wall is made of cellulose.

Question-6: What are seen inside the plant cell ?

Answer: Cytoplasm, nucleus and vacuoles are seen inside the cell.