Transport tissues 3.3.2

Question 1

State the function of the xylem

Answer 1

The xylem transport water and mineral ions from the roots up to the leaves & other parts of the plant.

Question 2

What does the xylem consist of?

Answer 2

Vessels for transport, fibres to support the plant & parenchyma cells which act as packing tissue to separate & support the vessels.

Question 3

What do the xylem walls become impregnated with?

Answer 3

Lignin

Question 4

What is the function of lignification/lignin?

Answer 4

It makes the xylem walls waterproof.
However it kills the cells but strengthens the walls and prevents them from collapsing.

Question 5

Are xylem cells living or dead?

Answer 5

Dead, apart from the living parenchyma

Question 6

What patterns form due to lignification?

Answer 6

Forms patterns which may be spiral, annular or reticulate (broken rings).

Question 7

What is the purpose of the patterns within the xylem, formed by lignin?

Answer 7

They allow the xylem to stretch as the plant grows and enables the stem to bend.

Question 8

What are the gaps known as, that are formed following the process of lignification?

Answer 8

Bordered pits

Question 9

What is the purpose of bordered pits?

Answer 9

Allows water to move sideways from one vessel to another

Question 10

What cell packs around xylem vessels?

Answer 10

Parenchyma

Question 11

What does parenchyma contain?

Answer 11

Contains tannin deposits

Question 12

What does tannin do?

Answer 12

It is a chemical which protects plant tissue from attack by herbivores.

Question 13

Why isn’t the flow of water impeded in the xylem? (3 reasons)

Answer 13

• There are no cross walls
• There are no cell contents, nucleus, or cytoplasm - as the vessel is not living.
• Lignin thickening prevents the walls from collapsing

Question 14

What is the function of the phloem?

Answer 14

Transports assimilates (sucrose and amino acids) which are dissolved in water to form sap up and down the plant.

Question 15

What is the phloem tissue made up of?

Answer 15

Sieve tube elements and companion cells

Question 16

What are sieve tube elements, and describe their structure.

Answer 16

They are elongated cells, lined end to end to form sieve tubes.
The ends have perforated walls called sieve plates, which allow for the sap to move from one sieve tube to another.
They also have no nucleus and very little cytoplasm which leaves space for the sap to flow.

Question 17

What is the function of the sieve plates?

Answer 17

They support the vessels lumen, keeping it open.
They also become blocked if the sieve tube element becomes injured which prevents the sap from escaping.

Question 18

How are companion cells linked to sieve tube elements?

Answer 18

By cytoplasmic strands through gaps in the cell wall.

Question 19

Describe the structure of companion cells

Answer 19

They have a large nucleus and lots of mitochondria, needed to help load assimilates into the sieve tubes by active transport.

Question 20

Compare the structure of xylem tissue with phloem tissue.

Answer 20

• Xylem tissue is lignified, meaning it is not living, whereas phloem tissue is living.
• The phloem transports assimilates, such as sucrose and amino acids, whereas the xylem transports water and mineral ions
• The xylem transports its containments up the plant only whereas the phloem transports substances both up and down the plant.

Question 21

Why aren’t sieve tube elements true cells?

Answer 21

As they lack key cellular components such as a nucleus and most other organelles.

Question 22

Why do xylem vessels have bordered pits?

Answer 22

To allow water to leave one vessel and pass into the next

Question 23

Suggest why the phloem does not have walls impregnated with lignin.

Answer 23

As this would kill the sieve tube elements, as phloem is a living tissue.