Mass transport plants exam q

Question 1

Explain how pressure is generated in phloem tube / mass flow

Answer 1

• Sucrose moves by active transport into the phloem
• Decreasing the water potential
  -Water moves by osmosis from the xylem into the phloem down gradient

Question 2

Why does phloem pressure decrease during the day

Answer 2

Higher rate of transpiration in the xylem
More tension in the xylem
Less water movement from xylem to the phloem

Question 3

Give measurements that are taken in order to measure rate of water movement

Answer 3

-Time taken for water movement
- Number ox xylem vessles
- Initial and final mass of beaker anc contents

Question 4

Describe how tarsnpiration occours

Answer 4

Water evaporates from leaves causing a low water potential in this area, pulling up more water by osmosis creating tension
Hydrogen bonds create cohesion of water maintaining the colum of water

Question 5

Describe cohesion tension theiry

Answer 5

Water lost from leaf due to evaporation of water/ diffusion from mesophyll
through stomata / from leaves;
2. Lowers water potential of mesophyll / leaf cells;
3. Water pulled up xylem (creating tension);
4. Water molecules cohere / ‘stick’ together by hydrogen bonds;
5. (forming continuous) water column;
6. Adhesion of water (molecules) to walls of xylem;

Question 6

Why might the rate of water loss through a plant be different to rate of water los through a whole plant

Answer 6

• Plant has roots
• Xylem cells are very narrow

Question 7

Method of rate of water loss over surface area of plant

Answer 7

draw round (each) leaf on graph paper and count squares;
Of both sides of (each) leaf;

Question 8

Describe mass transport theory

Answer 8

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