Component 3.2 - Endodermis

Question 1

Why cannot water enter the xylem from the apoplast pathway ?

Answer 1

Because lignin makes xylem walls waterproof, water can only pass from the symplast or vacuolar pathways.

Question 2

How does water leave the apoplast pathway?

Answer 2

The endodermis walls are impregnated with a waxy, suberin, forming a distinctive band called the casparian strip. Suberin is waterproof so the Casparian strip prevents water moving further in the apoplast and drives it into the cytoplasm.

Question 3

How does the plant achieve a lower water potential in the xylem than the endodermis cells?

Answer 3

1) The water potential of the endodermis cells is raised by water being driven in by the casparian strip
2) The water potential of the xylem is decreased by active transport of mineral salts, mainly sodium ions from the endodermis and pericycle into the xylem

Question 4

How do minerals move into the root hair cells?

Answer 4

In the soil minerals are present in very low concentrations, so generally, minerals are absorbed into the cytoplasm by active transport.

Question 5

How do mineral ions move through the root cortex?

Answer 5

Along the apoplast pathway, in solution

Question 6

How do mineral ions enter the xylem from the apoplast pathway?

Answer 6

When the minerals reach the endodermis, the casparian strip prevents further movement in the cell walls, so they enter the cytoplasm by active transport, and then diffuse or are actively transported into the xylem.

Question 7

How is active transport important at the endodermis?

Answer 7

It allows the plant to absorb the ions selectively