A band of suberin layer develops all around the cell in the middle of the transverse and radial walls. This suberin is called ________ strip.
Show Hint
The Casparian strip acts as an physiological filter in plant roots. It forces water out of the cell wall spaces (apoplast) and into the living cytoplasm (symplast), allowing the plant to regulate nutrient absorption.
Step 1: Understanding the Concept:
The Casparian strip is a specialized band of cell wall material found in the endodermis of plant roots.
It is composed primarily of suberin, a hydrophobic, waxy substance that acts as a barrier to water and dissolved minerals. Step 2: Detailed Explanation:
Let us analyze how water moves through plant roots and the role of the Casparian strip:
- Water absorbed by root hairs moves through the cortex toward the vascular cylinder (stele) via two primary pathways: Apoplast pathway: Water moves through the non-living cell walls and intercellular spaces. Symplast pathway: Water moves from cell to cell through the living cytoplasm connected by plasmodesmata.
- When water moving via the apoplast pathway reaches the endodermis, it encounters the Casparian strip embedded in the radial and transverse cell walls.
- Because the Casparian strip is composed of suberin, it is impermeable to water.
- This hydrophobic barrier blocks the apoplastic movement of water and dissolved solutes, forcing them to cross the selectively permeable plasma membrane into the symplast pathway.
- This allows the plant to regulate the uptake of ions and minerals before they enter the xylem vessel.
Therefore, the band of suberin is known as the Casparian strip, named after the German botanist Robert Caspary, who first described it. Step 3: Final Answer:
The correct option is (D).
