Question 5b

At this point, there is no further net movement of water, and the cell remains in a plasmolyzed state.

Water Potential and Osmosis

When a plant cell is placed in a solution with a lower water potential than the cell’s internal environment, water moves out of the cell.

This occurs through the process of osmosis, where water flows from a region of higher water potential (inside the cell) to a region of lower water potential (the surrounding solution).

Cell Surface Membrane and Partially Permeable Nature

Water exits the cell via the cell surface membrane, which is partially permeable.

This membrane allows selective passage of water molecules, preventing larger solutes from crossing freely.

Role of Cell Wall and Protoplast

The cell wall is freely permeable, allowing water to move in and out of the cell’s surroundings.

However, the protoplast (the living part of the cell inside the cell wall, including the cytoplasm and organelles) begins to lose water and shrink away from the cell wall as water exits.

Cytoplasm, Vacuole, and Tonoplast

As water leaves, the cytoplasm and vacuole lose water, reducing the internal volume of the cell.

Water exits the vacuole through the tonoplast (membrane surrounding the vacuole), leading to a decrease in vacuole size.

Incipient Plasmolysis and Plasmolysed State

Incipient plasmolysis is the initial phase when the protoplast just begins to detach from the cell wall.

As water loss continues, the cell becomes fully plasmolysed, meaning the protoplast has completely pulled away from the cell wall, and the cell has lost turgor pressure.

Equilibrium

Eventually, equilibrium is reached when the water potential inside the cell equals the water potential of the surrounding solution.