Exchange- Mass transport in plants

Question 1

What are the Exchange Systems in Plant?

Answer 1

 exchange systems = leaf and root
 leaf to absorb light and CO2 for photosynthesis
 roots to absorb water and minerals

Question 2

What are the Transport Systems in Plants?

Answer 2

 transport systems = xylem and phloem
 xylem transports water and minerals
 phloem transports glucose/sugars
 xylem transports in one direction from roots to leaves, phloem transports in both directions

Question 3

Function of the Xylem?

Answer 3

transport water and minerals from roots, up the plant, to the leaves

Question 4

Structure of the xylem?

Answer 4

 long continuous hollow tube (no resistance to water flow)
 narrow lumen
 wall made out of lignin
 lignin: strong, waterproof, adhesive
 wall contains pits/pores (water and minerals can leave)

Question 5

How does water move up the xylem?

Answer 5

 this is is the cohesion-tension theory
 loss of water at the leaves (transpiration)
 water moves from the top of the xylem into the leaf by osmosis (transpirational pull)
 this applies TENSION to the column of water in the xylem
 the column of water moves up as one as the water particles stick together, COHESION
 supported by capillary action, adhesion and root pressure
 (capillary action = water automatically moves up narrow lumen of xylem)
 (adhesion = water particles stick to lignin in wall of xylem)
 (root pressure = water absorbed at the roots pushes the column of water up slightly by hydrostatic pressure)

Question 6

Why does the diameter of a tree decrease during the day?

Answer 6

 more light and higher temperature
 increase rate of transpiration
 increase transpirational pull
 water pulled up xylem by cohesion-tension
 because the water particles stick to the wall of the xylem (adhesion)
 the walls of the xylem are pulled inwards