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Name: ( )

Name: ( )

Class: No.:

Date: 5 March 2011 .


Objective:

To find out the effect of a pickling agent on living plant cell.


Design principle:

Pickling has been a popular method of preservation long before the invention of refrigerator. Putting the food material, cooked or uncooked, into a concentrated solution of sugar, salt or vinegar will make the food free from decay. Thus, the food may be kept for a very long time.


Living cells contains a considerable amount of water and varies soluble substance in their cytoplasm. Thus, the water potential of the cytoplasm is usually negative when compared with that of distilled water. When the cell is placed in solution of different concentration, the cell may loose water or gain water or remain unchanged depending upon the difference in the respective water potential between the cytoplasm and the solution.


In order to find out the effect of the pickling agent on living plant cell, a series of sucrose solution of different concentration is used. The lower epidermis of is peeled off from freshly cut Zebrina leaf. As the lower epidermal cells contain a violet color, any change in the cell can be easily observed under a compound microscope. The effect of the selected agent, sucrose solution, can be investigated.


Materials and equipment:

Zebrina leaves

Petri dish

Compound microscope

Tissue paper

Fine forceps

dropper

Sucrose solution (10%)

scissors

Distilled water

microscope slide and cover slip


Procedure

  1. Preparing Zebrina epidermis

    1. Several parts of the lower epidermis of Zebrina were carefully peeled off with fine forceps.

    2. the epidermis was place into a petri dish with distilled water.

  2. Preparing microscope slide

    1. a portion of the epidermis was cut with scissors and placed on a microscopic slide as the specimen for investigation.

    2. a drop of distilled water was added to the specimen.

    3. a cover slip was slowly put on the specimen.

    4. the specimen was examined with a microscope at low power (x40). Cells with suitable coloration and adequately thin was selected for investigation. Unsuitable specimen was discard, the preparation procedure was repeated

    5. A drawing of the cells in this condition was prepared as a record of the initial state.

  3. Adding the pickling agent and Examine the effect

    1. sucrose solution was added, drop by drop, to the edge of the cover slip on the slide until the solution slightly accumulated at the edge.

    2. Tissue paper was carefully placed on the edge of the other side of the cover slip. Excess sucrose solution was absorbed by the paper.

    3. Careful observation was made on any change of the followings.

      1. Cell shape,

      2. sign of plasmolysis (relative position of cell membrane and cell wall)

      3. coloration of the cytoplasm

    4. Step A to C ware repeated for 5 times.

  4. A record of the observation was prepared with suitable diagram.


Result:

  1. The observable result was recorded in the drawings.

  2. The cells were in turgid state initially. The cell membrane was indistinguishable from the cell wall.

  3. After adding the pickling agent, the cell membrane was clearly seen as it started to detach from the cell wall. The purple color of the cytoplasm was becoming deeper.

  4. At the end, most of the cells became plasmolysis. Dark purple color was found in some cells.


Discussion:

Initial state

When living plant cell was put into distilled water, the water potential of the cytoplasm was lower than that of the distilled water. Water entered the cell by osmosis. The cell expanded and the cell membrane pressed against the cell wall. The cell became turgid.


Adding pickling agent

When sucrose solution was added to the specimen by "rinsing", the water potential of the medium became lower and lower. The water potential of the cytoplasm would be higher than the surrounding medium. Water moved out of the cell by osmosis. As water was lost to the medium, the cell shrank. Cell membrane detached from cell wall and resulted in plasmolysis.


Effect of pickling

As the growth of microorganism requires water and food. The pickling, to certain extend, induced the dehydration of the cell, therefore no microorganism could emerge in this state and the food could be persevered.


Choice of plant tissue

The cytoplasm of most cell is colorless, any change in the size due to increase or decrease in water content cannot be distinguished clearly. The use of Zebrina cell with natural purple color facilitates easy observation.


Disappearing of color

The purple colour of the Zebrina cell disappears after prolonged exposure to strong light. It would be better to employ concentrated sucrose in this investigation so as to shorten the experiment period.


Minimizing the evaporation from the specimen

The cover slip on the specimen reduce water loss to atmosphere due evaporation. Thus, a major error source is minimized.


Optimizing the specimen

The prepared specimen should be as thin as possible, one cell layer is the best specimen.

No air bubble is trapped in the temporary mounting.


Conclusion:

Pickling agent takes away the water from the cell. It actually acts as a dehydrating in food preservation.



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