Mass transport plants exam q Flashcards
(17 cards)
Explain how pressure is generated in phloem tube / mass flow
- Sucrose moves by active transport into the phloem
- Decreasing the water potential
-Water moves by osmosis from the xylem into the phloem down gradient
Why does phloem pressure decrease during the day
Higher rate of transpiration in the xylem
More tension in the xylem
Less water movement from xylem to the phloem
Give measurements that are taken in order to measure rate of water movement
-Time taken for water movement
- Number ox xylem vessles
- Initial and final mass of beaker anc contents
Describe how tarsnpiration occours
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
Describe cohesion tension theiry
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;
Why might the rate of water loss through a plant be different to rate of water los through a whole plant
- Plant has roots
- Xylem cells are very narrow
Method of rate of water loss over surface area of plant
draw round (each) leaf on graph paper and count squares;
Of both sides of (each) leaf;
Describe mass transport theory
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.
Unlike plants, Ulva lactuca does not have xylem tissue.
Suggest how Ulva lactuca is able to survive without xylem tissue.
Short diffusion pathway for water when immersed
Steep concentration gradient for water when immersed
Treatment D is a control. Explain how the measurement obtained from this
control is used by the scientist.
Used to compare effect of other treatments / as a baseline;
2. Shows / Measures effect of substance (X);
vUsing the diagram and the table above, what can you conclude from
treatments D and E about root growth?
(D shows) substance (X) is not required for (some) root growth
production of roots;
OR
Substances (already) present in stem cause (some) root growth;
2. Substance X moves through plant;
Accept X moves through stem / phloem
3. (E shows) substance (X) causes / increases / doubles number of
roots / root growth;
Treatment D is a control. Explain how the measurement obtained from this
control is used by the scientist.
(F shows) phloem is involved;
2. (G shows) respiration / active transport is involved (in flow /
movement);
3. Because 4 °C / cooling reduces / slows / stops flow / movement;
4. The agar block is the source;
5. Roots are the sink;
Against the mass flow hypothesis
6. No bulge above ringing (in F);
7. No (role for) osmosis / hydrostatic pressure / water movement;
Accept no turgor pressure
8. Movement could be due to gravity;
vThe scientists also concluded that this heat treatment did not affect the
xylem.
Explain how the results in the table support this conclusion.
v(The water content of the leaves was) not different because (means ±
2) standard deviations overlap;
For ‘not different’ accept ‘difference is not
significant’ or ‘difference due to chance’.
2. Water is (therefore) still being transported in the xylem (to the leaf)
Describe the cohesion-tension theory of water transport in the xylem.
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;
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;
The student wanted to determine the rate of water loss per mm2 of surface
area of the leaves of the shoot in Figure 1.
Outline a method she could have used to find this rate. You should assume
that all water loss from the shoot is from the leaves.
Method for measuring area;
e.g. draw round (each) leaf on graph paper and count squares;
2. Of both sides of (each) leaf;
3. Divide rate (of water loss / uptake from potometer) by (total)
surface area (of leaves);
The rate of water movement through a shoot in a potometer may not be the
same as the rate of water movement through the shoot of a whole plant.
Suggest one reason why
Plant has roots
OR
xylem cells very narrow;
Ignore references to air bubbles / mass flow /
photosynthesis
Accept xylem damaged when cut
Describe the mass flow hypothesis for the mechanism of translocation in
plants.
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.
