transport in the xylem

Question 1

outline the water uptake by roots

Answer 1

1) the surface area of roots is increased by the presence of root hairs which uptake water
2) soil contains very dilute solution of mineral salts and a high water potential
3) the vacuole and cytoplasm of the root hair cells contain concentrated solution of solutes and a lower water potential
4) water passes through the root hair cell down the water potential gradient by osmosis

Question 2

list the different pathways water can take in the root

Answer 2

1) apoplast pathway
2) symplast pathway
3) vascular pathway

Question 3

outline the apoplast pathway

Answer 3

1) water moves within the cell walls, cellulose fibres in the cell wall are separated by spaces through which water moves

Question 4

outline the symplast pathway

Answer 4

water moves through the cytoplasm and plasmodesmata

Question 5

outline the vacular pathway

Answer 5

water moves from vacuole to vacuole

Question 6

what is the fastest pathway for water to take in the roots

Answer 6

the apoplast pathway

Question 7

outline how water moves from the apoplast pathway into the symplast

Answer 7

1) water cant enter the xylem from the apoplast pathway due to the lignin in the xylem cell wall making it water proof
2) the water therefore has to move from the apoplast pathway into the symplast pathway
3) the centre of the root is surrounded by the pericycle which is surrounded by the endodermis
4) the endodermis is impregnated with suberin forming a waterproof band called the casparian strip
5) the casparian strip prevents the further movement of water in the apoplast pathway and drives it into the symplast

Question 8

outline how water moves from the root endodermis into the xylem

Answer 8

1) water moves by osmosis across the endodermal cell membrane
2) the water potential of the endodermis is raised by water being driven in by the casparian strip
3) the water potential of the xylem is decreased by active transport of mineral salts from the endodermis into the xylem
4) therefore water moves into the xylem by osmosis down the water potential gradient generating an upwards push

Question 9

what is root pressure

Answer 9

the upwards push of water entering the xylem by osmosis from the endodermis of the root

Question 10

outline the movement of minerals from the soil into the xylem

Answer 10

1) soil water is more dilute than the contents of the root hair cell therefore minerals are absorbed via active transport against their gradient
2) mineral ions also diffuse across the apoplast pathway in solution where they reach the endodermis and are driven into the symplast pathway by the capsarian strip by active transport
3) they then diffuse or are actively transported into the xylem

Question 11

outline the movement of water from the roots to the leaves

Answer 11

1) water always moves down the water potential gradient
2) the air has a much lower water potential than soil has a very high water poetntial
3) therefore water moves from the soil through the plant into the air using different mechanisms

Question 12

list the three mechanisms used during the movement of water from roots to leaves

Answer 12

1) cohesion tension
2) adhesion
3) root pressure

Question 13

outline the mechanisms of cohesion tension

Answer 13

1) as water evaporates from the leaf cells it draws water across the cells of the leaf in the different pathways from the xylem
2) as water molecules leave they ‘pull’ up other molecules of water due to the hydrogen bonds showing cohesion
3) this continuous pull causes tension in the water column

Question 14

outline adhesion

Answer 14

the charges of the water molecules also cause attraction to the hydrophilic lining of the vessels
this adhesion contributes to the upwards movement of water

Question 15

in the transpiration stream what is water drawn upwards by

Answer 15

1) the cohesive forces between water molecules

2) the adhesive forces between water molecules and the hydrophilic lining if the xylem vessels