Plant Transport System

Question 1

What do all transport systems posess?

Answer 1

A system of vessels
A fluid transport medium
A driving mechanism to move the substances

Question 2

What is the transport system in plants?

Answer 2

The vascular system - composed of xylem and phloem

Question 3

What is xylem tissue?

Answer 3

Specialised tissue for the transport of water and dissolved mineral ions from the roots to the leaves. Substances move in only one direction.

Question 4

What types of cells is xylem tissue made of?

Answer 4

The xylem tubes are either made of xylem vessels, or xylem tracheids, both of which are strengthened with lignin. These tubes have other structural cells including parenchyma and other fibres in between.

Question 5

Describe xylem tracheids.

Answer 5

Long cells with tapering end walls, the ends overlap. At these ends, small holes called pits align for the transport of water and ions up the plant.

Question 6

Describe xylem vessels.

Answer 6

Xylem vessels ‘stack’ on top of each other, forming one continuous tube. The end walls of these vessels break down to form these tubes. The cells contents die to allow for substance movement.

Question 7

Describe the role of fibres and parenchyma in xylem tissue.

Answer 7

Fibres give support to the xylem tissue, and parenchyma tissue conducts materials between different regions of xylem.

Question 8

What is the transpiration-choesion-tension theory?

Answer 8

The theory that currently explains the movement of substances up the xylem vessels (driving mechanism for xylem).

Question 9

What is the transpiration stream?

Answer 9

The movement of water up the xylem caused by the evaporative pull of transpiration. Evaporation of water from the leaves creates a suction, pulling up water.

Question 10

Describe how transpiration creates surface tension within the leaf and tension on the xylem column.

Answer 10

When water is lost from inner leaf space by transpiration, it is replaced by water from surface of mesophyll cells. This causes surface tension on these cells. Water is pulled up from the xylem to replace the water lost on these cells, creating tension on xylem.

Question 11

How does cohesion help the movement of water up xylem?

Answer 11

Water molecules are cohesive to each other, as they are polar molecules, where oppositely charged ends create a bond. This attraction of molecules creates a continuous water stream, with water molecules pulling each other up the xylem.

Question 12

How do adhesive forces aid movement up xylem?

Answer 12

Adhesive forces between the water and the xylem walls causes water to rise up the walls, further propelling it up the xylem.

Question 13

How are the lignin-strenghtened xylem walls suited for moving water to the leaves.

Answer 13

The narrow, lignin strengthened walls can withstand the tension created in the water column and offer little resistance to the flow of water.

Question 14

How does root pressure assist water moving up the xylem?

Answer 14

A small amount of root pressure in the roots results from the continual influx of water and ions from the soil, forcing the solution already present in the xylem further up.

Question 15

What is phloem?

Answer 15

Specialised tissue that transports sugars and other products of photosynthesis from the leaves to other parts of the plant.

Question 16

What is phloem tissue composed of?

Answer 16

Sieve tube cells and companion cells.

Question 17

Describe sieve tube cells.

Answer 17

Sieve tube cells are long with perforated sieve plate cell walls. They have some mitochondria and ER, and are stacked in a continuous tube, sharing cytoplasm.

Question 18

Describe companion cells.

Answer 18

Found alongside sieve tube cells. Have a nucleus and other organelles. They are thought to assist the effectiveness of sieve tube cells by providing ATP, nutrients and assisting the loading and unloading of sugars.

Question 19

What is the source-sink theory?

Answer 19

The theory of translocation, or the movement of substances (primarily sucrose) through the phloem. Substances move in whichever direction required, driven by the difference in pressure, from regions of high pressure, to regions of low pressure.

Question 20

What is the source in the phloem?

Answer 20

The cells where sucrose is produced.

Question 21

What is the sink in the phloem?

Answer 21

The low pressure region where the sucrose in required.

Question 22

How is a high pressure region in the phloem created?

Answer 22

At the source, energy is used to pump sugars into the phloem. This creates a concentrated solution in the phloem, which then draws water in via osmosis from xylem. This creates a high pressure region at the source.

Question 23

How is a low pressure region in the phloem created?

Answer 23

At the sink (roots, flowers), energy is required to remove the sugars from the phloem. This creates a dilute solution, which causes the water to leave the phloem via osmosis into the xylem. This creates a low pressure region.

Question 24

What does sucrose do when it reaches the cells that require it?

Answer 24

It may be converted to glucose for respiration, or converted to starch for storage.