9.2 water transport in multicellular plants

Question 1

what is turgor pressure?

Answer 1

hydrostatic pressure - provides a hydrostatic skeleton to support the stems and leaves.

Question 2

what keeps plant cool?

Answer 2

the loss of water by evaporation

Question 3

what are transported in aqueous solutions?

Answer 3

mineral ions and the products of photosynthesis

Question 4

what cells are the exchange surface in plants where water is taken into the body?

Answer 4

root hair cells

Question 5

what are root hair cells?

Answer 5

a long thin extension from a root hair cell, a specialised epidermal cell found near the growing root tip

Question 6

how are root hair cells adapted as exchange surfaces.

Answer 6

• microscopic (penetrate easily in between soil particles)
• hair has a large SA:V ratio
• hair has a thin surface layer (diffusion and osmosis can happen quickly)
• concentrations of solutes in its cytoplasm maintains the water potential gradient

Question 7

how does water move into the root hair cell by osmosis.

Answer 7

soil water has a low concentration of dissolved minerals (high water potential)
howevere the cytoplasm and vacuolar sap of root hair cell contains many solvent (low water potential)

Question 8

how does water move across the root to the xylem?

Answer 8

either the symplast pathway or the apoplast pathway

Question 9

what is the symplast pathway

Answer 9

water moves through the symplast by osmosis
root hair cell has a higher water potenital than the next cell
water diffsues in from the soil, cytoplasm is now more dilute
so water now moves from the root hair cell into the next cell osmosis

Question 10

what is the symplast

Answer 10

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

Question 11

what is the apoplast pathway

Answer 11

water moves through the apoplast
water fills the spaces between the open network of fibres in the cellulose cell wall
as water is moving into the xylem, more water is pulled through the apoplast behind due to the cohesive forces between water
this creates a tension which means there is a continuous flow of water through the open structure of the cell wall, no resistance

Question 12

what is the apoplast/

Answer 12

the cell walls and the intercellular spaces

Question 13

where does water reach before the xylem during either pathway?

Answer 13

endodermis

Question 14

what is the endodermis?

Answer 14

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

Question 15

why is the endodermis noticeable in the roots?

Answer 15

because of the casparian strip

Question 16

what is the casparian strip?

Answer 16

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

Question 17

what happens to the water in the apoplast pathway once it reaches the casparian strip?

Answer 17

can go no further and is forced into the cytoplasm of the cell, joining the water to the symplast pathway

Question 18

why does water in the apoplast pathway stop at the casparian strip?

Answer 18

water must pass through the selective permeable cell surface membrane, which stops any toxic solutes reaching living tissues

Question 19

how do endodermal cells move mineral ions into the xylem?

Answer 19

active transportw

Question 20

why do endodermal cells move mineral ions into the xylem by active transport?

Answer 20

the solute concentration in the cytoplasm of the endodermal cells is dilute compared to the cells in the xylem

Question 21

what has the lower water potential, endodermal cells or xylem cells?

Answer 21

xylem cells, as they have the higher solute concentration

Question 22

what happens when the water reaches inside the vascular bundle?

Answer 22

water returns to the apoplast pathway to enter the xylem itself and move up the plant

Question 23

what leads to root pressure?

Answer 23

active pumping of minerals into the xylem to produce movement of water by osmosis

Question 24

what is root pressure?

Answer 24

gives water a push up the xylem, but under most circumstances it is not the major factor in the movement of water up from the roots to the leaves

Question 25

what evidence is there that active transport is used to get water from the endodermis to the xylem?

Answer 25

• root pressure increases with a rise in temperature and falls with a fall in temperature (chemical reactions must be involved)
• if levels of oxygen falls, so does root pressure
• some poisons affect the mitochondrias production ATP, if it applied to root cells so there is no energy supply, root pressure disappears