Module 3 : Section 3 - Xylem and Phloem

Question 1

What do plants need to live

Answer 1

• To remove waste products
• Water, minerals and sugars

Question 2

Like animals plants are….

Answer 2

• Multicellular, so they have small surface area : volume ratio
• they are also relatively big with a relatively high metabolic rate

Question 3

Why can’t substances be exchanged using direct diffusion in plants

Answer 3

Exchanging substances by direct diffusion would be too slow to meet their metabolic needs

Question 4

What do plants need to move substances to and from individual cells quickly

Answer 4

They need transport systems to move substances to and from individual cells quickly

Question 5

What are the two types tissue involved in transport in plants

Answer 5

• Xylem
• Phloem

Question 6

What do xylem tissues transport

Answer 6

• Water and mineral ions in solution
• these substances move up the plant from the roots to the leaves

Question 7

What do phloem tissues transport

Answer 7

• Phloem tissue mainly transports sugars in solution
• move up and down the plant

Question 8

What do the xylem and phloem both make up

Answer 8

The plants vascular system

Question 9

What is the other function of the xylem apart from transport

Answer 9

Support

Question 10

What is significance of the xylem in the root

Answer 10

In a root, the xylem is in the centre surrounded by phloem to provide support for the root as it pushes through the soil

Question 11

What is the significance of the xylem in the stem

Answer 11

In the stems, the xylem and phloem are near the outside to provide a sort of ‘scaffolding’ that reduces bending

Question 12

What is the significance of xylem in the leaf

Answer 12

In a leaf, the xylem and phloem make up a network of veins which support the thin leaves

Question 13

How are the xylem adapted for transporting water and mineral ions

Answer 13

• xylem vessels are very long, tube-like structures formed from cells(vessel elements) joined end to end
• there are no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily
• the cells are dead, so they contain no cytoplasm
• walls are thickened with woody substance, lignin, it supports the xylem vessels and stop them collapsing inwards. Lignin can be deposited in xylem walls in different ways e.g. spiral or rings
• the amount of lignin increases as the cell gets older
• water and ions move into and out of the vessel ps through small pits in the walls where there’s no lignin

Question 14

What do phloem transport

Answer 14

• Solutes (dissolved substances) mainly sugars like sucrose around plants

Question 15

Phloem cells are formed from….

Answer 15

Cells arranged in tubes. But unlike xylem, it is purely a transport tissue - it isn’t used for support

Question 16

What are the contents of the phloem

Answer 16

• Phloem fibres
• Phloem parenchyma
• sieve tube elements
• companion cells

Question 17

What are the most important cells for transport in phloem

Answer 17

• Sieve tube elements
• companion cells

Question 18

What are sieve tube elements

Answer 18

• Living cells that form the tube for transporting solutes through the plant
• they are joined end to end to form sieve tubes
• ‘sieve’ parts are the end walls, which have lots of holes in them to allow solutes to pass through
• sieve tubes elements have no nucleus, a very thin layer of cytoplasm and a few organelles
• the cytoplasm of adjacent cells is connected through the holes in the sieve parts

Question 19

What are the companion cells

Answer 19

• companion cells carry out the living function fro both themselves and their sieve cells
• e.g. they provide energy for the active transport of solutes
• the lack of nucleus and other organelles in sieve tube elements means that they can’t survive on their own
• so there’s a companion cell for every sieve tube element