5.2.2. CELL WALL

Remember the temporary mount of onion peel we prepared? We had put iodine solution on the peel. Why? What would we see if we tried observing the peel without putting the iodine solution? Try it and see what the difference is. Further, when we put iodine solution on the peel, did each cell get evenly coloured?

The cell wall is an essential part of plant cells, located outside the plasma membrane. In our earlier activity with onion peel, we used iodine solution to help visualize the cells better under a microscope. Without the iodine, the structures of the cells are not as visible, making it difficult to observe the individual cell walls. When stained, the cells may take on varying colors, allowing us to differentiate between cell components based on how they absorb the stain.

This is similar to dyeing fabric; just as dye enhances the color and details of fabric patterns, staining a cell makes its components more distinguishable under the microscope.

The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants.

The primary component of the cell wall in plant cells is cellulose, a carbohydrate that forms a rigid structure. This rigidity is crucial for maintaining the shape and integrity of the plant cells, allowing them to withstand various environmental pressures such as gravity and wind. The cell wall serves as a protective barrier that supports the plant's growth and stability.

Think of a house's walls, which provide structure and protection. Just like solid walls help keep a house standing and safe from outside elements, the cellulose walls in plant cells help keep plants upright and healthy.

When a living plant cell loses water through osmosis, there is shrinkage or contraction of the cell contents away from the cell wall. This phenomenon is known as plasmolysis.

Plasmolysis occurs when plant cells are placed in a hypertonic solution (where the concentration of solutes is higher outside the cell than inside). As water exits the cell to balance the solute concentrations, the cell membrane pulls away from the rigid cell wall due to loss of internal pressure, creating a gap between the contents of the cell and the wall. This can lead to wilting in plants.

Imagine a balloon filled with water. If you were to poke a small hole in it, the water would drain out, causing the balloon to shrink. Similarly, when plant cells lose water, they shrink from the cell wall, leading to a loss of structure.

We can observe this phenomenon by performing the following activity: Prepare a temporary mount of a Rhoeo leaf in water on a slide and examine the cells under the high power of a microscope. Note the small green granules, called chloroplasts. Put a strong solution of sugar or salt on the mounted leaf on the slide. Wait for a minute and observe under a microscope. What do we see? Now place some Rhoeo leaves in boiling water for a few minutes. This kills the cells. Then mount one leaf on a slide and observe it under a microscope. Put a strong solution of sugar or salt on the mounted leaf on the slide. Wait for a minute and observe it again. What do we find? Did plasmolysis occur now?

This activity allows us to visually observe plasmolysis. By placing the living plant cells in a concentrated sugar or salt solution, we create a hypertonic environment that encourages water to leave the cells. Under the microscope, we can see the cells shrinking as their contents separate from the cell wall, indicating that plasmolysis has occurred. In the case of boiled leaves, we can further confirm that the membrane is no longer functional, which prevents any cellular reaction to the solution put in, highlighting the importance of live materials in biological observations.

Imagine placing a fresh piece of fruit in a bowl of salt. Over time, the fruit will shrivel and lose moisture, just like the plant cells do under a hypertonic solution. Observing this change helps us understand how cells react to their environment.

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