Transport in Plants - Water Transport

Question 1

define water potential

Answer 1

the tendency of water molecules to leave a solution

Question 2

what is the function of root hairs

Answer 2

increase the root’s surface area and absorb water and mineral ions

Question 3

how are mineral ions absorbed and why

Answer 3

• absorbed by active transport
• these minerals together with sugars and amino acids lower the water potential of the cytoplasm and vacuolar sap
• water then moves in by osmosis

Question 4

does soil water have a low or high water potential

Answer 4

high so it has a very low concentration of dissolved minerals

Question 5

does the cytoplasm and vacuolar sap of the root hair cell have a low or high water potential

Answer 5

low as they contain many solutes

Question 6

how does water enter the root and what happens as a result

Answer 6

• water moves into the root cell by osmosis down the water potential gradient
• the cell becomes turgid
• the adjacent cell will have a lower water potential than the root hair cell
• water will continue moving from cell to cell by osmosis

Question 7

how can water move across the root

Answer 7

• symplast pathway
• apoplast pathway

Question 8

describe the symplast pathway

Answer 8

• water travels through the cytoplasm of cells
• the cytoplasm’s of the cells in the root are connected by plasmodesmata through holes in the cell walls

Question 9

what are plasmodesmata

Answer 9

composed of thin strands of cytoplasm

Question 10

describe the apoplast pathway

Answer 10

• water moves through the gaps in the cellulose cell walls (adhesion)
• dissolved mineral ions are carried with the water
• it does not pass through the cell membranes
• the water moving up the xylem together with the cohesion between water molecules means there is continuous flow

Question 11

is the cellulose cell wall permeable

Answer 11

it is fully permeable
the open structure of cellulose offers little resistance to this continuous flow

Question 12

where does the apoplast pathway stop

Answer 12

the endodermis

Question 13

What is the casparian strip and where is it found

Answer 13

• band of water proof material
• found in cells in the endodermis

Question 14

What is the casparian strip made from

Answer 14

Waxy suberin

Question 15

Which pathway does the casparian strip block

Answer 15

The apoplast pathway, so water is forced into cells via the symplast pathway

Question 16

How does the casparian strip cause water to move into the xylem

Answer 16

• water has to pass through the cell surface membrane which is selectively permeable
• transport proteins in the cell surface membrane carry out active transport to move mineral ions into the xylem
• lowering water potential means water will enter the xylem by osmosis

Question 17

Can water pass back into the cortex once it has entered the xylem

Answer 17

No, as the apoplast pathway is blocked

Question 18

what are the three ways water can move up the stem

Answer 18

• root pressure
• transpiration pull
• capillary action

Question 19

how does root pressure move water up the stem

Answer 19

• mineral ions are actively transported into the xylem vessels at the roots
• this lowers the water potential, causing water to enter by osmosis and forces water up the stem

Question 20

what is root pressure affected by

Answer 20

metabolic poisons, temperature and oxygen concentrations (all affect active transport)

Question 21

how does transpiration pull move water up the stem

Answer 21

• water molecules are attracted to each other by cohesive forces
• this forms a long continuous column of water in the xylem
• as water is lost at the top via transpiration, the column is pulled up through the xylem

Question 22

what does the pull of water caused by transpiration create

Answer 22

this creates tension in the column. the lignin prevents the xylem collapsing inwards with this tension

Question 23

what happens if the column is broken

Answer 23

water can flow into adjacent xylem vessels via the pits

Question 24

how does capillary action move water up the stem

Answer 24

adhesive forces between water molecules and lignin in the narrow walls of the xylem vessels help pull the water up the xylem vessels

Question 25

why does capillary action only work in a narrow container

Answer 25

greater proportion of water in contact with the walls = greater adhesive forces