Ch. 36 Transport in Plants Flashcards
big idea: understand symplasty/apoplasty, casparian strip, transpiration, translocation, and water potential
what is the relationship between shoot height and light capture?
taller height = more light capture but
taller height = thicker stems to support height
-more branches give more access to light, but require more energy to grow
what is phyllotaxy?
-arrangement of leaves on a stem
-leaves are usually organized to minimize self shading and maximize usable leaf area
-shaded leaves can be lost via self pruning
how do roots capture minerals and water / increase their effective surface area?
-roots branch more towards nutrient rich areas, but will not overcrowd other roots of same species
-plants have evolved mutualistic relationships with fungi to capture nutrients and water better = MYCORRHIZAE
how does water enter and exit a plant?
enters via roots
leaves via leaves [stomata]
how does sugar enter a plant?
as CO2 from the atmosphere [photosynthesis]
what is apoplasty?
transport of water/minerals OUTSIDE of cell membranes (cell walls are hydrophilic)
what is symplasty?
transport INSIDE the cytosol of living cells (from cell-cell through the cytoplasm and plasmodesmata)
what is transmembrane transport?
-substances moving out of one cell, through the cell wall, and into another cell
-requires multiple membrane proteins
how do plant cells establish an electrochemical proton gradient?
-proton pump pumps H+ out of cell against concentration gradient
-this sets up an electrochemical gradient that can be used for many things
how do cells use electrochemical gradients?
- cotransporting neutral solutes - sucrose
- cotransporting ions - NH3 in roots
- creating gradients to affect cation movements - K+ to regulate stomata openings
what is water potential?
water potential = psi = Ψ
-depends on solute concentration inside and outside cell wall
water moves from high Ψ -> low Ψ
what is the equation for total water potential?
total water potential = pressure potential + solute potential
Ψ = Ψp + Ψs
how is Ψ measured?
-measured in KPa
-Ψ = 0KPa in pure water
-Ψ = 0.5 KPa in most plant cells
what is Ψs? how is it measured?
Ψs = solute potential
=0 for water
= <0 in all solutions
what is Ψp? how is it measured?
Ψp = physical pressure on a solution
-can be positive or negative
= -2MPa in xylem, + in living cells
= 0MPa in standard conditions
what is osmosis?
the movement of water molecules due to the presence of a solvent
-water moves from high concentration of water molecules to a lower concentration of water molecules
what is bulk flow?
movement of fluid using pressure gradients
-faster way to move substances long distances
how do xylem use bulk flow?
transpiration = negative pressure
negative pressure = xylem can pull up minerals and water
how does phloem use bulk flow?
positive pressure = phloem can transport sap through sieve-tube member
how do roots get water and minerals into them?
active transport pumps minerals from soil into root = decreased Ψs
-root cells are now hypertonic to soil
-water will flow into the root
what is the casparian strip?
a thick layer of lipids right before the stele / vascular cylinder
-acts as a filter and holds xylem sap in place
what is root pressure?
-occurs @ night when transpiration is low
-low Ψs and low Ψp = water moves into xyelm from root
-water is pushed up xylem and drips from leaves, creating guttation fluid
how does water move up xylem?
-bulk flow of water is driven primarily by Ψp
-active transport of into root moves water into root
-cohesion pulls water up roots
-adhesion to cell walls overcomes force of gravity
-main force that lets water move up is transpiration due to low Ψp in atmosphere
what is cavitation?
formation of a water vapour pocket = water cannot move up xylem
what are the 5 steps to opening the stomata and letting water into the roots?
- H+ is pumped out of cell
- this creates -ve charge in guard cells
- K+ flows into guard cell down its gradient
- This decreases Ψs
- Water flows into cell and cell becomes turgid
What is the closing mechanism for stomata?
- proton pump is turned off, H+ returns to cell
- K+ diffuses out of cell
- Ψs increases, and water flows out
what stimuli control the opening of the stomata?
light: circadian rhythm
CO2 = stomata will open when levels are low
humidity: if high, stomata will be open
wind: if high, stomata will be closed
how do environmental conditions [high temp, low h2o) affect the stomata?
dry conditions = closed stomata
high temperatures = closed stomata
this results in reduced CO2 intake = less photosynthesis = less growth
what is sap composed of?
sugar, amino acids, regular acids, hormones, pigments, RNA, lots of other things
what are “sinks”?
a location in the plant that uses or stores phloem sap, such as growing roots/shoots, stems and fruits
what are sap “sources”?
where sap was made - is usually close to the sink
what are the two methods of sap transport?
- sap transported into sieve tube member via symplastic route - done when sugar can flow down its gradient
- sap moves via apoplastic route, companion cells work to actively transport sap against its gradient into a sieve-tube member
how does phloem translocation via pressure flow work?
- loading of sugar into phloem cells creates a low Ψs, so water from xylem moves into phloem
- pressure due to osmosis pushes phloem sap towards sink
- some water will pass into sink, some into xylem to be recycled
- solvent follows pressure gradient down into sink
how does phloem unloading at the sink work?
-sink usually has lower sugar concentration than phloem, so passive transport is used
