9.2 Water Transport in Multicellular Plants

Question 1

What is the function of transport systems in multicellular plants?

Answer 1

SUPPLY useful molecules to cells

REMOVE waste from cells

Question 2

What are the uses of water in plants?

Answer 2

TURGOR PRESSURE

ROOT PRESSURE

COOLANT

METABOLITE

TRANSPORT MEDIUM

Question 3

What is turgor pressure?

Answer 3

pressure exerted by PLASMA MEMBRANE

on CELLULOSE CELL WALL

Question 4

What is root pressure?

Answer 4

ACTIVE TRANSPORT of MINERAL IONS

into the xylem by root cells.

Produces OSMOSIS of water into xylem.

Question 5

Describe how water + dissolved mineral ions move into the root

Answer 5

Root hair cell has lower ψ than soil (high solute concentration)

water + dissolved mineral ions move in by OSMOSIS

Question 6

What are the adaptations of a root hair cell?

Answer 6

LONG PROJECTION - increase SA

MICROSCOPIC SIZE - penetrate between soil particles

THIN SURFACE LAYER - short diffusion distance

CONTAINS SOLUTE - amino acids, mineral ions&raquo_space; low ψ

Question 7

How does water move across the root using the SYMPLAST pathway?

Answer 7

1. Root hair cell has HIGHER ψ than neighbouring cell
2. Water moves by OSMOSIS from root hair cell ⟶ neighbouring cell.
   
   • next cell along always has lower ψ
   • ∵ H2O has left root hair cell ψ DROPS, maintaining steep ψ gradient.
3. Continues until ENDODERMIS reached.

Question 8

What is the apoplast?

Answer 8

Cell walls + intercellular spaces

of living plant cells

Question 9

What is the apoplast?

Answer 9

Cell walls + intercellular spaces

of living plant cells

Question 10

How does water move across the root using the APOPLAST pathway?

Answer 10

1. H2O fills spaces between cellulose fibres.
2. H2O forced into symplast pathway by casparian strip of endodermal cells
   Moves by osmosis into xylem vessel.
   • COHESION&raquo_space; tension in continuous flow, pulls along water with little friction

Question 11

When does root pressure come into play during the movement of water through a plant?

Answer 11

ROOT ⟶ XYLEM VESSEL

mineral ions actively transported into xylem cells

Question 12

How does water move into the xylem in the SYMPLAST pathway?

Answer 12

1. Endodermal cells ACTIVELY TRANSPORT mineral ions ⟶ xylem
   
   • ￬ xylem ψ&raquo_space; ￪ rate of osmosis into xylem cell
2. Water enters xylem VESSEL.

Question 13

How does water move into the xylem in the APOPLAST pathway?

Answer 13

1. H2O cannot pass through CASPARIAN STRIP
   
   • forced into symplast.
2. H2O moves from cell wall ⟶ cytoplasm, passes through PLASMA MEMBRANE.
   
   • impermeable to toxic solutes, so H2O filtered.
3. Joins symplast pathway.

Question 14

What is the casparian strip?

Answer 14

WATERPROOF BAND around ENDODERMAL cells

BLOCKS water in apoplast + forces into symplast.

Question 15

What is the evidence for active transport in root pressure?

Answer 15

CYANIDE REMOVES ROOT PRESSURE

￪ TEMPERATURE&raquo_space; ￪ ROOT PRESSURE

RESPIRATORY SUBSTRATE ￬&raquo_space; ROOT PRESSURE ￬

Question 16

What is the layer of cells called surrounding the xylem vessels of plants?

Answer 16

endodermis

made from endodermal cells with casparian strips

Question 17

Which cells have casparian strips?

Answer 17

endodermal cells