Plant Transport

Question 1

Transpiration

Answer 1

Water evaporates from mesophyll cells in the leaf
Water vapour diffuses out of leaf through stomata
Water potential in leaf cells decreases
Water moves out of xylem into leaf cells
Creates a tension on the column of water in xylem
Water molecules joined by hydrogen bonds
Water molecules does not break because of adhesion with xylem walls
Water enters root hair cells by osmosis
because active uptake of mineral ions has created a water potential gradient water moves through the root by osmosis to xylem

Question 2

Xerophytes

Answer 2

Waterproof thick waxy cuticle so stops water leaving the leaf
Sunken stomata increase humidity around stomata
Hairy leaves traps water vapour around leaf
Small leaves reduce surface area
Leaves rolled up reduces surface area and increases humidity
Reduced number of stomata reduced SA for water loss

Question 3

Translocation

Answer 3

At source sucrose is actively transported into the phloem.
By companion cells
Lowers water potential in phloem
Water enters by osmosis
Produces high hydrostatic pressure
Mass transport towards sink
At sink sugars are removed
Sugar used in respiration or storage as starch

Question 4

Describe the cohesion-tension theory of water transport in the xylem

Answer 4

-Water lost from leaf because of transpiration / evaporation of water
(molecules)
-through stomata / from leaves;
-Lowers water potential of mesophyll / leaf cells;
-Water pulled up xylem (creating tension);
-Water molecules cohere / ‘stick’ together by hydrogen bonds;
(forming continuous) water column;
-Adhesion of water (molecules) to walls of xylem;