Question

Apoplast is the system of adjacent cell walls that is continuous throughout the plant except at the
(a)Plasmodesmata
(b)Vessel element
(c)Casparian strip of endodermis
(d)Tracheids

Answer 1

The apoplast is the space outside the plasma membrane within which material can freely diffuse. Structurally an apoplast is formed by the fusion of cell walls of adjacent cells as well as extracellular spaces, forming a tissue level compartment comparable to the symplast. The apoplast facilitates the transport of water and solutes across a tissue or organ. This process is known as apoplastic transport. The apoplast is important for all plant’s interaction with its environment.

Complete answer:
The apoplastic pathway is the cell wall to cell wall diffusion of water through the apoplast ( cell wall and intercellular space). So it exclusively occurs through the cell wall, without crossing the protoplast. The absorbed water takes a radio route from root his to root xylem through the root cortex. This radial movement across three routes, namely vascular pathway or osmotic pathway, symplastic pathway or symplastic diffusion, and apoplastic pathway or apoplastic diffusion. The constant removal of water from the root cortex to the root xylem provides the necessary osmotic gradient for the first mechanism and necessary diffusion gradient for the others. In the roots, ions diffuse into the apoplast the epidermis before diffusing into the simplest. Similarly, all gaseous molecules emitted and received by plants such as plant hormones and other pheromones must pass the apoplast. The apoplast is composed mostly of intercellular spaces and porous cell walls. They are interrupted by the Casparian thickness of endodermis.

Additional Information: -The radial construction of water occurs through three routes; vascular pathway, symplastic pathway, and apoplastic pathway.
-Vascular pathway is the transmembrane, vacuole to vacuole osmotic flow of water by a relay mechanism, under the influence of osmotic forces. So it is called the transmembrane pathway or osmotic pathway.
-Symplastic pathway is the cell to cell diffusion of water through plasmodesmata and plasma membrane. Plasmodesmata serve as free channels for this flow.
- In the case of passive transport water conduction is mostly through the apoplast route which consists of cell wall intercellular spaces.
So, the correct answer is ‘ Casparian strip of endodermis.’

Note: The mechanism of water absorption in plants is of two main kinds, namely active and passive absorption. In passive absorption, absorption is mainly an activity of shoot and leaves, whereas in active absorption of water is mainly an activity of roots and root hairs. Passive absorption occurs due to suction force developed in xylem vessels due to transpiration pull. In active absorption, water is absorbed by osmotic and nonosmotic mechanisms.