Paper 1- Processes

Question 1

Describe Cohesion Tension Theory

Answer 1

Water lost from leaf because of transpiration / evaporation of water
(molecules) / diffusion from mesophyll / leaf cells;
OR
Transpiration / evaporation / diffusion 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;

Question 2

Describe Mass Flow Theory:

Answer 2

In source / leaf sugars actively transported into phloem;
By companion cells;
Lowers water potential of sieve cell / tube and water enters by
osmosis;
Increase in pressure causes mass movement (towards sink /
root);
Sugars used / converted in root for respiration for storage.