Xylem vessels and their lignification patterns

Overview

Two functions of xylem tissue, substance that impregnates the walls of xylem vessels and why a xylem vessel must be strengthened against collapse.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   State the two functions of xylem tissue.

   Model answer

   Xylem transports water and dissolved mineral ions from the root to the rest of the plant, and it provides mechanical support.

2. 2

   Describe how a xylem vessel is formed from a column of cells.

   Model answer

   The end walls between the cells break down and the contents die away, leaving a continuous hollow tube of lignified walls.

3. 3

   Why is it an advantage that mature xylem vessels contain no cytoplasm?

   Model answer

   The empty lumen offers almost no resistance, so water can move through in a continuous unbroken column.

4. 4

   Name the substance that impregnates the walls of xylem vessels.

   Model answer

   The walls are impregnated with lignin.

5. 5

   Give two properties that lignin gives to a xylem vessel wall.

   Model answer

   Lignin makes the wall rigid and strong, and it makes it waterproof and impermeable.

6. 6

   Explain why a xylem vessel must be strengthened against collapse.

   Model answer

   Water is pulled up under tension, so the pressure inside the vessel is negative and an unstrengthened tube would be crushed inwards.

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