Vascular Transport in Plants Flashcards
How does primary growth in plants (leaves, specifically) help with water transport?
Leaves evaporate H2O and help pull up xylem sap.
How does secondary growth (in wood) help with water transport?
Stablizes stem and forms new xylem every year.
How does water loss occur in leaves?
H2O evaporates at the leaf surface, also 95% through stoma: H2O vapour diffuses from moist air spaces inside leaf to drier air outside (steep H2O gradient)
How is water loss in leaves regulated?
Cuticle prevents H2O loss at the surface. Stoma are regulated by their density and pore opening/closing.
What are some factors that affect stoma opening/closing?
K+ ions (in = open, out = close), light (dark = close), CO2 status and distribution (high conc = close, low = open), circadian rhythm (day = open, night = close), environmental stress (steeper H2O potential gradient and stoma close).
What are the three different pathways/routes for the short distance transport of water and nutrients?
Apoplastic, symplastic, transmembrane
Describe the function of the apoplastic route
The apoplastic route is an easy route for water and nutrient transport; h2o and dissolved materials move through the cell wall only.
Describe the function of the symplastic route
The symplastic route is an easy route for water and nutrient transport; through plasmodesmata and cytosol.
Describe the function of the transmembrane route.
The transmembrane route for water and nutrient transport is more difficult as they have to pass the lipid bilayer more than once. (In and out of cytosol and cell wall)
What are some examples of the transmembrane route?
Active, passive, and co-transport
What are aquaporins?
Bidirectional channel proteins that only allow h2o molecules to pass (faster than diffusion)
How does water uptake in roots occur (5 steps)
1, 2) Enter root hairs through apoplastic or symplastic route. 3) Unloading into cytosol on way to casparian strip. 4) Casparian strip is symplastic only. 5) Tracheary element unloading (transmembrane), w/ xylem is apoplastic only.
Why is water and nutrient uptake through the casparian strip symplastic only?
Casparian strip is a selective barrier and the endodermis surrounding it is super hydrophobic, so everything needs to be through living cells (plasmodesmata). You can’t go around it; you have to go through it.
How is water transported between roots and leaves?
By the cohesion-adhesion hypothesis.
What is the cohesion-adhesion hypothesis?
Based on definitions of cohesion and adhesion, molecules pull each other along using bulk flow: driven by evaporation and the difference in pressure potential. Cells do not need to be alive.
What is cohesion?
H2O molecules stick together via H-bonds
What is adhesion?
H2O molecules stick to walls of cells via H-bonds
What is cavitation?
When H-bonds break
What is water potential?
The potential energy of H2O under given conditions compared to pure H2O under reference conditions.
What is the direction of water flow driven by?
Water potential, measured in mPa
How does free water move, in accordance to water potential?
From regions of high water potential to areas of low water potential.
What is water potential affected by?
Pressure and solute concentration potential. Water potential = Solute conc. potential + Pressure potential
What is solute potential?
The osmotic potential of a solution is directly proportional to its molarity. Solutes have a negative effect on water potential by binding water molecules.
What is pressure potential?
The physical pressure of a solution. Positive pressure has a positive effect on water potential by pushing water. Negative pressure (tension) has a negative effect on water by pulling it.
