Question

Casparian strip is
A. Lens-like thickenings of endodermal cells
B. Strip of thickening found on the outer side of endodermis
C. Ligno-suberin band running in endodermal cell walls
D. layer of cells between endodermis and cortex

Answer 1

Hint:-In land plants, the endodermis is the central most layer present in the cortex. The endodermis is a layer of cylindrical shaped cells. The cells of the endodermal layer are compact and they are live cells. It forms the boundary between the cortex and the stele. The endodermis is responsible for regulation of movement of ions, water as well as hormones into and outside the vascular system.

Complete step-by-step solution:
The Casparian strip is a band of cell wall material that is settled in the radial and transverse walls of the endodermis of roots of plants. The Casparian strip is found as a thick layer on the endodermal region in the roots. It has a different chemical composition from the rest of the cell wall. While the other cell wall is composed of lignin and suberin is not found there but in the case of the Casparian strip, it is majorly of suberin and a little amount of lignin. Suberin is a type of biopolymer of lipophilic and it acts as a barrier in the case of excessive loss of water.
The endodermis with its Casparian strips may act as regulator of the flow of water between outer tissues and the vascular cylinder at the centre of the root. It acts as a hydrophobic boundary layer that separates the apoplast of the cortex from the apoplast of the vascular tissue. It causes a sort of blocking as well as divergency of material between the two. This separation applies a force on the water and solutes to move through the plasma membrane via a symplastic route with the purpose to cross the endodermis layer.
When an outward growth of the cortex is completed causes the differentiation of the Casparian strip. The primary xylem of its vascular cylinder is partly present during this phase of the root development. In gymnosperms and angiosperms, when the secondary growth has started, the roots build only endodermis with Casparian strips. In several cases, it is found that the endodermis is neglected along with the cortex. This condition takes place when the periderm develops from the pericycle. As the Casparian strip is a thick band of cells in the endodermal cells and composed of lignin and suberin, so it is a ligno-suberin band running in endodermal cell walls.
Therefore, the correct option is option C.

Note:-
In most woody plants, the endodermis is absent in the stem but are found in the roots. The main function of endodermis is regularisation of the flow of ions and molecules with water to and fro the vascular system. The radial walls of the endodermis bears a band of lignin-suberin which is known as the Caspian strips. It restricts the flow of water to enter the inside.