B3 - Xylem and Phloem

Question 1

What is the xylem and phloem on plants?

Answer 1

Transport vessels for transporting materials around. Both types go to every part of the plant in a continuous system but they are totally separate.

Question 2

What do phloem tubes transport?

Answer 2

Food substances. mainly sugars, up and down the stem to growing and storing tissues

Question 3

What are phloem tubes made up of?

Answer 3

Columns of living cells called sieve tube elements.

Question 4

What allows materials to flow through phloem tubes?

Answer 4

Perforated end plates

Question 5

Sieve tube elements have no nucleus and can’t survive on their own. What allows the cells to survive and what is the purpose?

Answer 5

Each sieve tube element has a companion cells.

Theses cells carry out living functions for both them selves and their sieve cell.

Question 6

What is the movement of food substance around the plant known as?

Answer 6

Translocation

Question 7

Describe the translocation of sugar.

Answer 7

Usually translocated from photosynthetic tissue (leaves) to non-photosynthetic tissues.

The sugars enter the phloem through active transport then pushed around by water which enters the phloem by osmosis.

Question 8

What Xylem tubes carry?

Answer 8

Water and mineral ions e.g nitrates, in aquaeous solution.

Question 9

Describe the cells that make up xylem tubes.

Answer 9

Dead cells joined end to end, with no connecting cell walls between them (to create a long tube) and a hole down the middle (lumen)

Question 10

What are the thick side walls of xylem tubes made of and why?

Answer 10

Cellulose which is strong and stiff to give the plant support and strengthened with a material called lignin

Question 11

Where do xylem tubes transport water and mineral ions from and to?

Answer 11

From the roots, up the stem, to the leaves in transpiration stream.

Question 12

What is transpiration?

Answer 12

The loss of water from the plant.

Question 13

What is transpiration caused by?

Answer 13

Evaporation and diffusion of water from a plants surface.

Question 14

Where does most transpiration happen?

Answer 14

In the leaves

Question 15

Describe the transpiration stream of water through the plant.

Answer 15

Evaporation and diffusion cause a slight shortage of water in the leaf.
Water is drawn up from the plant through the xylem vessels to replace it.
This means that more water is drawn up from the roots.

Question 16

Explain why there is a continuous upward flow of water in plants (3 marks)

Answer 16

Water evaporates and diffuses from a plants surface, creating a slight shortage of water in the leaf (1 mark)
This draws more water up from the rest of the plant through the xylem vessels to replace it (1 mark)
This in turn means more water is drawn up from the roots (1 mark)