3.4 Mass transport Flashcards
What are the layers in blood vessels?
Elastic tissue in wall, muscle layer, endothelium
How are arteries adapted for their function?
Folded endothelium, thicker muscular walls, smaller lumen, elastic tissue in wall
- Allows stretch and recoil of vessel as heart beats to maintain high pressure
How is tissue fluid formed?
1) At arteriole end high hydrostatic pressure in capillary forces liquid out
2) Hydrostatic pressure reduces and so is lower at venule end
3) Due to fluid loss and conc. of proteins = high w.p
4) Water re enters via osmosis
What is a capillary bed?
Network of capillaries in tissue
Describe the structure of xylem vessel
Long, tube like structures made of dead cells joined end to end
Describe the water cohesion tension theory
- Transpiration occurs at leaves (top of xylem)
- This creates tension which pulls water to leaf
- Water is sticky hence the whole column of water moves upwards
- Low water conc. in roots therefore water moves in
What is transpiration?
Loss of water from a plants surface
What factors affect transpiration rate
Light - Stomata open in light
Temperature - High heat = evaporation
Wind - Blows water away
Humidity - Decreases conc. gradient
Describe the structure of phloem
Sieve tube element with sieve plates imbetween
Companion cell for each sieve tube element
What is translocation
The movement of solutes in a plant
- Solutes == assimilates
Describe the mass flow hypothesis
1) Active loading of solutes from companion cells into the sieve tube at source
2) Lowers Ψ at source and so water enters sieve tube from xylem and companion cell
3) High pressure created
4) At sink end solutes used and so water potential lowered
5) Low pressure created
6) Pressure gradient drives movement of assimilates
Why are arteries adapted for their function?
- Allows stretch and recoil of vessel as heart beats to maintain high pressure
