Question

1. The figure alongside is a diagram of a root hair. On the diagram, name the parts labelled 1 to 5.
2. What role is played in the uptake of water into the root hair by the parts numbered 1, 2 and 3?
3. What would happen if living cells of a plant were planted first in a strong solution of cane sugar and then in water?

Answer 1

a. 

b. Role played in water uptake by:

Part 1 (cell wall): It is permeable and allows water and dissolved mineral salts to pass through freely into the space surrounding the cell membrane.

Part 2 (Cell membrane): It is semi-permeable (selectively permeable). It controls the movement of water molecules into the cell by allowing them to pass through while restricting larger solute molecules.

Part 3 (Vacuole): It contains a high concentration of solutes (cell sap), creating a lower water potential than the surrounding soil water. This concentration gradient forces water to move into the root hair via osmosis.

c. If living cells of a plant were planted first in a strong solution, the sugar solution is hypertonic (more concentrated) relative to the cell sap. Water moves out of the plant cells into the solution by exosmosis. As a result, the vacuole shrinks, the cytoplasm withdraws away from the cell wall, and the cells become flaccid or plasmolysed.

If living cells of a plant were planted first in a strong solution of cane sugar and then in water. The surrounding medium becomes hypotonic (less concentrated) relative to the inside of the cell. Water moves back into the cells by endosmosis. The vacuole swells again, pushing the cytoplasm back against the cell wall and restoring the cell to its original turgid state (deplasmolysis).