mass transport in plants

Question 1

Describe the transport of carbohydrate in plants (5)

Answer 1

      Sucrose actively transported into phloem

2.      By companion cells;

3.      Lowers water potential (in phloem) and water enters (from xylem) by osmosis;

4.      (Produces) high(er) (hydrostatic) pressure;

5.      Mass flow to respiring cells/ sink

6.      Unloaded/removed (from phloem) by active transport;

Question 2

   Describe the cohesion-tension theory of water transport in the xylem (5)

Answer 2

 1.      Water lost from leaf because of transpiration

2.      Lowers water potential of leaf cells;

3.      Water pulled up xylem (creating tension);

4.      Water molecules cohere by hydrogen bonds;

5.      (forming continuous) water column;

6.      Adhesion of water (molecules) to walls of xylem;

Question 3

explain why the diameter of the trunk is smallest at midday. (6)

Answer 3

Diameter of trunk lowest at warmest and brightest time of day

Stomata opens in light so more water loss

Water evaporates more when warm/ more heat energy

Hydrogen bonds between water molecules- cohesion

Water molecules adhere to xylem walls- adhesion

Xylem pulled inwards by faster water flow

Question 4

Describe and explain three ways in which the leaves of xerophytic plants may be adapted to reduce water loss. (3)

Answer 4

Thick waxy cuticle- impermeable to water so less water passes through

Rolling up of leaves- traps still, saturated air next to leaf surface, reduces water potential gradient so transpiration slows

Sunken stomata- saturated layer of still air outside

Small leaves- reduced SA for water loss

Less stomata- reduced SA for water loss