Question

Casparian strip is found in
A) Epidermis
B) Endodermis
C) Endothecium
D) Endothelium

Answer 1

Hint:Casparian strip is pretty much as the tight junctions in animals. They basically provide an extracellular diffusion barrier in plant roots that forces the minerals that are passively moving through apoplast.

Complete answer:
As we are aware with the fact that radial movement of ions dissolved in water occurs through both apoplastic and symplastic pathways. Apoplastic pathway involves the transport of dissolved solute through intercellular spaces between the cells. However, water and minerals cannot cross the endodermis apoplastically because of the presence of the Casparian strip.

The Casparian strip is pretty much the same as the tight junctions in animals. They basically provide an extracellular diffusion barrier in plant roots. It forces the minerals that are passively moving through apoplast to cross the plasma membrane of an endodermal cell and enter the xylem through the symplast.

Thus we came to know that in endodermal cells of roots, Casparian strips are seen along radial and tangential walls. Casparian strip is made up of chiefly Suberin and Lignin along with other proteins.
We also know that the symplastic pathway involves the movement of dissolved solutes from cell to cell through plasmodesmata. For transport of ions from the epidermis to tracheary elements of xylem which are dead cells, symplastic pathway is the chief pathway for that purpose. The ions exit the symplastic pathway by the process called xylem loading.

Hence the correct answer is option ‘B’.

Note: Endodermis is also called a Biological checkpoint due to the presence of a Casparian strip. In roots, Endodermal cells are interrupted by thin walled passage cells lying just outside the protoxylem and these cells help in passage of water from cortex to xylem.