Question

What is the name of the structure that blocks water from entering the root stele/vascular cylinder? And what is the purpose of the change to the route?

What are the three major pathways of material transport in plants and which pathway uses plasmodesmata?

How is large-scale irrigation affecting the world aquifers?

Is sucrose concentration within the phloem higher near the source or the sink?

Answer 1

Ans- 1. Endodermis blocks entry of water to root stele. It is a cylindrical structure formed by living cells, the radial walls of which contain casparian strip, hydrophobic substance. Hence, blocking the flow of water. This is important to regulate the passage of water through xylem so, that water enters by crossing endodermal cells twice.

2. Pathways for material transport in plants-

a) Apoplast pathway - In this pathway, water passes from root hair to xylem through walls of intervening cells. Water does not cross any membrane or cytoplasm hence, there is least resiatance to flow of  water. The flow may be interrupted by casparian strips at endodermal cells.

b)Non-vacuolar symplast pathway- By this pathway, water passes from one cell to another by crossing the membrane at least once. The water does not enter cell vacuoles hence, non-vacuolar pathway and also, called as transmembrane pathway.

c) Vacuolar pathway- In this pathway, each root cell behaves as osmotic system. In this pathway, water entering passes through cell wall, plasma lemma, cytoplast, tonoplast and finally, cell vacuole.

PLASMODESMATA uses non vacuolar symplast pathway.

3. Large scale irrigation dilutes NO3 in groundwater and also recharges it. This helps to sustain water table level for human use.

4. Sucrose concentration is higher near the source. This is so because the sucrose is produced by source hence, having a higher concentration.