Question

Identify and define 'A' and 'B' in relation to uptake of water by the root :

Hint:

A simple way to remember: \textbf{A}poplast = \textbf{A}way from the cytoplasm (in the cell walls). \textbf{S}ymplast = \textbf{S}haring cytoplasm (through plasmodesmata).

Answer 1

The image shows two pathways for water uptake by a plant root.

A is the Apoplast Pathway: This is the pathway where water moves from the root hair to the xylem through the non-living parts of the root—the intercellular spaces and the cell walls. This pathway is blocked by the Casparian strip in the endodermis, forcing water to enter the symplast.
B is the Symplast Pathway: This is the pathway where water moves through the living parts of the cells—the cytoplasm and plasmodesmata (cytoplasmic channels connecting adjacent cells). Water enters the cytoplasm of a root hair cell and moves from cell to cell through the plasmodesmata, crossing the cortex and endodermis to reach the xylem.