Section 8 - Xylem and Phloem

Question 1

By what process does water from the soil enter the roots

Answer 1

Osmosis

Question 2

What are the two ways by which water can travel through the roots?

Answer 2

• The symplast system
• The apoplast system

Question 3

Describe the symplast system

Answer 3

Some water moves through the root via the cytoplasm of the root cells. The water has to cross the cell membrane, which regulates the passage of the water and dissolved minerals.

Question 4

Describe the apoplast system

Answer 4

• The water moves through the cell walls and the spaces between the cells.
• There are no membranes to regulate the passage.

Question 5

Describe the apoplast system

Answer 5

• The water moves through the cell walls and the spaces between the cells.
• There are no membranes to regulate the passage.

Question 6

Describe the cells that make up the vessels of xylem tissue

Answer 6

Dead, waterproof, hollow

Question 7

What are the three factors by which water is pulled up through the xylem tissue?

Answer 7

Cohesion, tension and adhesion

Question 8

Describe how water is pulled up through the xylem tissue by cohesion, tension and adhesion (6)

Answer 8

1) Water evaporates from inside the leaf having a high concentration of solutes.
2) Water from the nearest xylem vessel enters by osmosis.
3) Water molecules stick together because of weak hydrogen bonds between them - this is called cohesion.
4) As water molecules leave the xylem vessel they pull up further molecules, so the whole column of water is pulled up.
5) Evaporation pulls the water column upwards and gravity pulls it down, so the water column is under tension.
6) The adhesion of water molecules to the sides of the xylem vessels stops the column breaking

Question 9

As water travels through the xylem tissues, what stops the columns from breaking?

Answer 9

The adhesion of water molecules to the sides of the xylem vessels stops the column breaking

Question 10

What does phloem tissue transport?

Answer 10

Sugar and other organic compounds

Question 11

What structures is phloem tissue arranged in so the solutions of sugar can move through easily?

Answer 11

Sieve tubes

Question 12

What is translocation? (3)

Answer 12

• The movement of carbohydrates and other organic compounds in plants.
• It occurs in the sieve tubes of the phloem tissue.
• Companion cells next to the sieve tubes are believed to actively transport sugar into the sieve tubes, and then water follows by osmosis.