Aim: -To study plasmolysis in epidermal cells of Tradescantialeaf.

 

XII  BIOLOGY

PRACTICAL-2

Q. 1 Make a temporary slide to study plasmolysis. Sketch & label the diagram.

Q. 1 Make a temporary slide to study plasmolysis. Sketch & label the diagram.

•       Preparation of slide……………… 2Marks

•       Observation / Conclusion………………1 Mark

•       Diagram of plasmolysed cell……………1 Mark

Total-4 Marks

Aim: -To study plasmolysis in epidermal cells of Tradescantialeaf.

Requirements: Fresh leaf of Tradescantia, conc. Sugar solution, distilled water, slides, cover slips, watch glass, blades, etc.

Method:

1. From the lower surface of the leaf of Tradescantia, peel off small segments of epidermis by a blade.

2. Put few peelings on a slide, mount in a drop of water, put a cover glass and study under microscope.

3. Mount some of the peelings in the drops of sugar solutions of different concentrations. Study under the microscope.

Observations:1

1. Peelings mounted in the water show clear cell structure.
2. But the peelings placed in the sugar solution show the Concentra in their cell contents.
3. More the concentration of sugar solution more is the contraction and shrinkage of cell contents.
4. Peelings mounted in very high concentrated sugar solution, when observed under microscope, show complete shrinkage of their cell contents which become round or ball-like.

• Observation:2
• The slide prepared using hypertonic solution shows shrinkage of protoplast.
• The protoplast moves away from the cell wall and becomes concentrated to the corner of the cell. This is called plasmolysis.
• Conclusion:
• Plasmolysis occurs due to exosmosis.
• A cell is placed in a hypertonic solution loses its water and shows shrinkage of protoplast.

Results:

1. Shrinkage of the cell contents in the peelings mounted in conc.sugar solution is due to the fact that the osmotic pressure of the outer sugar solution is higher than that of the osmotic pressure of the cell sap.
2. So the water from the cell sap diffuses into the external sugar solution through the semipermeable plasma membrane of the cell.
3. Thus there is a shrinkage of the cell contents and this phenomenon is known as plasmolysis
4. If slightly plasmolysed (incipient plasmolysis.)
5. cells are now kept in pure water, these will show the phenomenon of endosmosis and the cells will recover soon.
6. This indicates the phenomenon of deplasmolysis.

• Q.1. What occupies the space between the cell wall and the shrunken protoplast in the plasmolyzed cell?  
• Ans- When a cell undergoes complex plasmolysis the protoplast loses so much water that they completely detach from the cell wall. 
•  The cell wall collapses in a process called cytorrhysis.                                           Convex plasmolysis cannot be reversed and results in the destruction of the cell.
• It is one of the results of osmosis and occurs very rarely in nature.
• The hypertonic solution occupies the space between the cell wall and shrunken protoplast.
• Q 2 Define incipient plasmolysis
• Ans-The protoplasm is usually tightly pressed against the cell wall. When the plant tissue is placed in hypertonic solution the water will come out from the cell into the solution due to the process of exosmosis. 
• This excess of osmosis results in the contraction of the protoplasm from the cell wall and this phase of plasmolysis is known as the incipient plasmolysis.
• Q.3.Where do we use plasmolysis at home​                                                            
• Ans-Plasmolysis is defined as the process of contraction or shrinkage of the protoplasm of a plant cell and is caused due to the loss of water in the cell. Plasmolysis is an example of the results of osmosis and rarely occurs in nature.
• Plasmolysis helps in the preservation of meat and fish by salting.
• It is also helpful in the preservation of jellies and jams by adding concentrated sugar solution to them.
• It helps in plasmolyzing the spores of bacteria and fungi.
• Spraying of weedicides kills weeds in lawns, orchards and agricultural fields. This is due to the natural phenomena-Plasmolysis.
• Q.4. Is it possible to use plasmolysis in fish drying?                                                                             
• Ans- Yes, we can use plasmolysis in drying the fish by placing it in a hypertonic solution. Plasmolysis due to excessive loss of water from the cell due to osmotic actin  
• Q.5.Give reason of selecting the leaf peel from the lower surface of tradescantia leaf​? 
• Ans- The leaf Tradescantia results in the good quality of leaf peel.The epidermal peel is generally collected from the lower surface of the leaf body because; the lower surface of the leaf has a greater number of stomata than the upper one.