topic 3.1.3: transport in plants

Question 1

describe the process of translocation

Answer 1

1) at source, sucrose actively loaded into sieve tube elements from companions (WP lowered in STEs)
2) water enters STE from xylem and CCs (increases H pressure in STEs at source)
3) sucrose actively removed from STEs at sink (increased WP in STEs at sink)
4) water leaves phloem at sink (lowers H pressure in STEs at sink)
5) pressure gradient pushes assimilates up tube

Question 2

describe the process of active loading

Answer 2

H+ ions ATd from companion cells to source cells, then cotransported back into companion cells with sucrose which then diffuses along conc gradient to STEs

Question 3

describe the distribution of xylem and phloem tissues in the root

Answer 3

xylem like a drill, phloem in corners

Question 4

describe the distribution of xylem and phloem tissues in the stem

Answer 4

in outer circle with phloem to the outside

Question 5

describe the distribution of xylem and phloem tissues in the leaves

Answer 5

form a network of veins with phloem on bottom

Question 6

describe the apoplastic pathway water can take through plants

Answer 6

water moves through cell walls due to adhesive and cohesive nature, until Casparian strip in endodermis

Question 7

describe the symplastic pathway water can take through plants

Answer 7

water moves through cytoplasm and plasmodesmata due to water potential gradients

Question 8

why can water move up through the xylem

Answer 8

adhesive- H bonds stick together
cohesive- H bonds between water and cellulose
transpiration stream- water evaporates at leaves, tension transmitted down xylem and pulls water up