water transport in multicellular plants-transport in plants

Question 1

function of water in plants

Answer 1

• turgor pressure/ hydrostatic pressure provides a hydrostatic skeleton to support the stems and leaves, also drives cell expansion
• loss of water via evaporation keeps cells cool
• mineral ions and products of photosynthesis transported in aqueous solutions
• is a raw material for photosynthesis

Question 2

adaption of root hair cells

Answer 2

• microscopic size =penetrate easily between soil particles
• large SA:VOL
• thin= rapid diffusion
• concentration of solutes in the cytoplasm of root hair cells maintains water potential gradient between soil water and the cell (soil contains high water potential, root hair lower)

Question 3

2 diff pathways the water through to get to xylem

Answer 3

• symplast pathway

- apoplast pathway

Question 4

role of symplast pathway

Answer 4

-

Question 5

definition of symplast and apoplast

Answer 5

• symplast, the continuous cytoplasm of the living plant cells that is connected through the plasmodesmata
• apoplast, the cell walls and intercellularspaces

Question 6

casparian strip + role

Answer 6

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

Question 7

movement of water into the xylem

Answer 7

• water moves across the root in the apoplast and symplast pathways until it reaches the endodermis- the layer of cells surrounding the vascular tissue (xylem and phloem) of the roots.
• water in the apoplast pathway can go no further due to the casparian strip so it is forced into the cytoplasm of the cell, joining the water in the symplast pathway
• the diversion into the cytoplasm means the water must pass through a selectively permeable membrane=excludes toxic solutes
• water potential in xylem is much lower than the endodermal cells= water moves down a potential gradient through the symplast pathway into xylem

Question 8

water movement once inside the xylem

Answer 8

• the water returns to the apoplast pathway to enter the xylem itself and move up the plant
• active pumping of minerals into xylem creates root pressure, producing movement of water by osmosis
• root pressure gives water a push up the xylem but not a major factor

Question 9

evidence for the role of active transport in root pressure(4)

Answer 9

• some poisons, such as cyanide, affect the mitochondria and prevent the production of ATP. Root pressure disappears if cyanide is applied to root cells as there is no energy supply
• root pressure increases with a rise in temp and falls with a decrease suggesting chemical reactions are involved
• if levels of oxygen or respiratory substrates fall, root pressure falls
• xylem sap may exude from the cut end of stems at certain times

Question 10

Explain the significance of the relationship between rate of diffusion and the surface area
to volume ratio for large plants.

Answer 10

Explain the significance of the relationship between rate of diffusion and the surface area
to volume ratio for large plants.