Module 3 - Water Transport in Multicellular Plants

Question 1

what is hydrostatic pressure (turgor pressure)?

Answer 1

is a result of osmosis in plants cells provide a hydrostatic skeleton to support the stem and levaves
also drives cell expansion - the force that allows roots to puch through concrete and soil

Question 2

what are the other features of water transport in plants?

Answer 2

evapouration of water from leaves to keep plant cool
mineral ions produced during photosynthesis of plants are transported in aquous solution
water is a raw matertial of photosynthesis

Question 3

where is water taken into the body of the plant?

Answer 3

root hair cells

root hair is long extension of root hair cell

Question 4

how are root hairs suited to their role as an exchnage surface?

Answer 4

• microscopic size = can penetrate the soil
• each one has a large SA:V
• each has a thin surface layer = diffusion and osmosis occur quickly
• maintains water potential gradient between soil and cell

Question 5

what are the two main pathways that H2O and solvents can take?

Answer 5

apoplastic pathway
symplastic pathway

both interchangeable

Question 6

features of the symplastic pathway:

Answer 6

slower pathway - H2O moves slowly
consists of continuous cell cytoplasm and plasmodesmata
water moves via osmosis through semi-permable membrane

Question 7

features of the apoplasitc pathway:

Answer 7

faster pathway - transpiration rates are high
consists of intracellular spaces and space between cell walls
H2O moves via diffusion as it doesnt travel though semi-permiable membranes
when H2O reaches impermiable casperian strip (layer of suberin (thick,waxy material) that water cannot penetrate) it moves into the symplastic pathway

Question 8

how does water move into the xylem?

Answer 8

• water moves in down the potential gradient
  > water moves in via the endodermis once it reaches the end of the symplastic and apoplastic pathway (layer of cells surrounding the xylem and phloem)
  > casperian strips connect endodermis to endodermis creating a waterproof layer
  > water can then nolonger move through apoplastic pathway ad if forced inot the cytoplasm joining the water in the symplastic pathway
  > water must pass through semi-permiable membrane removing any potentially toxic solutes
  > once water moves into the vascular bundle it returns to the apoplastic pathway = pumps minerals inot the plant which results in root pressure - gives water the push up the xylem

in most cases root presure is not majorly involved in water movement

Question 9

what is the evidence for the role of active transport in root pressure?

Answer 9

• some posions affect mitochondria and prevent the production of ATP
• root pressure increases with a rise in temperature and falls with a fall in temperature - suggest chem reactions are involved
• if levels of oxygen falls so does the root pressure