Water transport in multicellular plants

Question 1

Why is water important in the structure and metabolism of plants? (5 reasons)

Answer 1

1) Turgor pressure provides a hydrostatic skeleton to support the stems and leaves

2) Turgor driver cell expansion

3) The loss of water by evaporation helps keep plants cool

4) Mineral ions and products of photosynthesis are transported in aqueous solutions

5) Water is a raw material for photosynthesis

Question 2

What creates turgor pressure?

Answer 2

Osmosis in plant cells

Question 3

What is cell expansion?

Answer 3

The force that enables plant roots to force their way through tarmac and concrete

Question 4

What is the exchange surface in plants?

Answer 4

Root hair cells

Question 5

What do root hair cells do?

Answer 5

Takes water into the body of the plant from the soil

Question 6

What is a root hair?

Answer 6

A long, thin extension from a root hair cell

Question 7

What type of cell is a root hair cell?

Answer 7

Specialised epidermal cell

Question 8

Where are root hair cells found?

Answer 8

Near the growing root tip

Question 9

What are the four adaptations of root hairs?

Answer 9

1) Microscopic size so they can penetrate easily through soil particles

2) Large SA:V ratio and there are thousands on each growing tip

3) Thin surface layers through which diffusion and osmosis can take place quickly

4) The concentration of solutes in the cytoplasm of root hair cells maintains a water potential gradient between the soil water and the cell

Question 10

Why does soil water have a high water potential?

Answer 10

It has a very low concentration of dissolved minerals

Question 11

What do the cytoplasm and vacuolar sap of a root hair cell contain?

Answer 11

Solvents such as sugars, mineral ions, and amino acids

Question 12

Why does a root hair cell have a lower water potential that soil water?

Answer 12

It has lots of dissolved solvents and minerals

Question 13

How does water move into root hair cells?

Answer 13

By osmosis

Question 14

Where does the water in the root hair cell go?

Answer 14

It continues to move across the root to the xylem

Question 15

What are the two pathways of the xylem?

Answer 15

Symplast and apoplast

Question 16

What is the symplast?

Answer 16

The continuous cytoplasm of the living plant cells that is connected through plasmodesmata

Question 17

How does water move through the symplast?

Answer 17

By osmosis

Question 18

How does water move through root hair cells?

Answer 18

It moves from one cell to the next cell along by osmosis

Question 19

Why does water move into the next cell along?

Answer 19

The root hair cell has a higher water potential than the next cell along

Question 20

Why does the root hair cell have a higher water potential than the next cell?

Answer 20

Diffusion of water from the soil makes the cytoplasm more dilute

Question 21

How does water leave the root hair cell?

Answer 21

By osmosis

Question 22

How is a steep water potential gradient maintained when water leaves the root hair cell?

Answer 22

The water potential of the cytoplasm falls again when the water leaves

Question 23

What is the apoplast?

Answer 23

The cell walls and the intercellular spaces

Question 24

Where does water go when it enters the apoplast?

Answer 24

It fills the spaces between the loose, open network of fibres in the cellulose cell wall

Question 25

What happens when water molecules move into the xylem?

Answer 25

More water molecules are pulled through the apoplast behind them due to cohesive forces between them

Question 26

What creates tension in the apoplast pathway?

Answer 26

The pull from water moving into the xylem and up the plant along with the cohesive forces between water molecules

Question 27

What does the tension in the apoplast do?

Answer 27

Keeps a continuous flow of water through the open structure of the cellulose wall, which offers little resistance

Question 28

How far does water travel through the apoplast and symplast pathways?

Answer 28

Until it reaches the endodermis

Question 29

What is the endodermis?

Answer 29

The layer of cells surrounding the vascular tissues (xylem and phloem) of the roots

Question 30

Why is the endodermis particularly noticeable in the roots?

Answer 30

Due to the effect of the Casparian strip

Question 31

What is the Casparian strip?

Answer 31

A band of waxy material called suberin that runs around each of the endodermal cells forming a waterproof layer

Question 32

What happens when water reaches the Casparian strip?

Answer 32

It can’t go any further and is forced into the cytoplasm of a cell, joining water in the symplast pathway

Question 33

Why is the diversion into the cytoplasm significant?

Answer 33

To get there, water must pass through the selectively permeable cell surface membranes

Question 34

Why does water have to pass through the selectively permeable cell surface membranes?

Answer 34

To exclude any potentially toxic solutes in the soil water reaching living tissues

Question 35

How is the solute concentration different in the cytoplasm of endodermal cells and xylem cells?

Answer 35

Concentration is relatively dilute in the cytoplasm of endodermal cells compared to cells in the xylem

Question 36

What do endodermal cells do?

Answer 36

Move mineral ions into the xylem

Question 37

How do endodermal cells move mineral ions into the xylem?

Answer 37

By active transport