Vasculature Flashcards
Describe the cohesion-tension theory
- As water evaporates out of the leaves, more water is drawn up the xylem because of the cohesiveness of the water molecules
- Water moving along the potential gradient
- Negative pressure generated
What vessel moves water through the plant?
The xylem
In theory, how tall of a water column can be maintained by cohesive forceS?
> 300 m
What factors affect cohesiveness?
Gravity, friction
Other than the size of the water column supported, what else needs to be considered for water supply in plants?
The flow rate.
How is the vasculature system protected when leaves fall off?
Xylem is sealed at the leaf scar
What are protective layers in plants made of?
Suberin
What are abscission layers?
Preemptively fill with suberin, undergo programmed cell death when leaf sheds
Can water movement be attributed to root pressure?
No, too slow.
Can capillary action explain movement of water?
No, again not enough.
Why doesn’t the xylem implode?
Xylem elements (tracheids, vessels) are strengthened by lignified secondary cell walls; can withstand negative pressure.
What happens to tree trunks when transpiration is high?
Slightly shrink in diameter
What is cavitation?
Introduction of vapor bubble in the xylem
What is the issue with cavitation?
Interrupts water flow
Is cavitation more deterimental in tracheids or vessels?
Vessels
Why is heartwood unfunctional?
Becomes filled with air
Is water conducted in sapwood or heartwood?
Sapwood, specifically younger
With sufficient water, what is the rate of water movement determined by?
The leaf and its environment.
What moves through the phloem?
Products of photosynthesis (sugars, amino acids, etc.)
What is girdling? What does it do?
Removal of phloem. Accumulation of sugars above the girdle, roots starved of photosynthate, plant dies.
Explain the mass flow hypothesis.
Sugar produced in leaves, eaves load sugar into phloem, water moves through phloem along potential gradient, sugars move with it, eventually leave through roots. Leave resupplied with water by the xylem.
What is the most common translocation sugar in plants?
Sucrose
List source and sink tissues.
Source: mature photosynthetic organs (leaves)
Sink: roots, young leaves, flowers
