Resource Acquisition and Transport in Vascular Plants Flashcards
What is the overall function of the xylem?
Transport water and minerals from roots to shoots.
What is the overall function of the phloem?
The transport of products of photosynthesis from the source of production to sinks.
What are the things that affect light absorption in a plant (5)?
- Shoot length
- Phyllotaxy - leaves are not directly side by side in most angiosperms (alternate, spiral) which minimizes shade covering leaves below
- Canopy depth - Lower leaves (more shaded) are shed when the respire more than they photosynthesize
- Leaf area index - percentage of ground area covered by the plant
- Leaf orientation - horizontal leaves capture more light in low-light conditions, but, vertical leaves are less damaged by the sun and allow light to reach lower leaves in sunny conditions
What are some characteristics of roots that help in their acquisition of water and minerals (3)?
- grow to adjust for local conditions ( branch more near high NO3)
- Are less competitive with other roots of the same plant than with roots of another plant
- Form mutualistic relationships with fungi called mycorrhizae (helped plants to colonize land, increased surface area for absorption of water and minerals)
What are the two major pathways through plants and what do they consist of?
Apoplast - Everything external to the plasma membrane
Symplast - the entire mass of cytosol, including the plasmodesmata (cytoplasmic channels that connect cells)
What are the three transport routes for water and solutes in a plant?
Apoplastic - through cell walls and extracellular spaces
symplastic - through the cytosol and plasmodesmata
transmembrane - across cell walls AND plasma membrane
How is the membrane potential of the plasma membrane established in regards to the short distance transport of solutes across the plasma membrane?
Proton pumps that use ATP the transport protons (H+) out of the cell to create a membrane potential
What are some ways that protons (H+) are used in the short-distance transport of solutes across the plasma membrane? How do some Ions cross the membrane?
Neutral solutes (such as sugars like sucrose) can be cotransported into the cell by using H+ as cotransporters
Cotransporters can also be used for ions (important for the uptake of nitrates in plants)
There are also ion channels that open and close in response to voltage, allowing for specific ions to diffuse across them.
In regards to the short-distance transport of water across the plasma membrane, what is water potential?
Water potential is a measurement of solute concentration + physical pressure.
How does water potential determine the direction of water movement? What is the unit that water potential is measured in?
Water travels from areas of higher potential to areas of lower potential.
megapascals (MPa)
What does MPa of 0 equal?
pure water at sea level at room temperature
This is equilibrium
What is the equation for water potential?
Water potential = solute potential + pressure potential
Ws = solute potential
Wp = pressure potential
Why does an increase in solute concentration cause a decrease in solute potential?
Solute potential will always be negative because there will always be some solutes added to water, it will never be pure water.
Whens solutes are added to water they bind the the water molecules, leaving less free water molecules to do work.
Can pressure potential be both positive or negative?
What is the pressure potential in a plant usually?
What can be used to describe the pressure potential?
YES, it is all relative to the atmosphere.
In a plant the pressure potential is usually under positive pressure
Turgor pressure - the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast, this includes the plasma membrane.
If a cell is placed in a solution that has a higher water potential than inside the, what will happen? What about if the water potential is lower than inside the cell?
Water potential higher outside = water moves inside the cell, becomes turgid
Water potential lower outside = water moves out of cell, becomes plasmolyzed
Be able to use algebra to solve for different variable in the water potential equation.
Look at notes in powerpoint for reference.
When a plant loses its turgor what happens to it? Can this be reversed?
It becomes wilted, can be reversed with water movement into the cell.
What are aquaporins? Do they affect water potential?
These are transport proteins in the cell membrane that facilitate the passage of water and affect the rate of water movement across the membrane
They DO NOT affect water potential
What is bulk-flow (long-distance transport)? Where does this occur? What makes this type of movement so efficient?
This is the movement of fluid and solutes driven by pressure.
This occurs in the tracheids and vessel elements of xylem, and sieve-tube elements of phloem
What makes this efficient is the fact that tracheids and vessel elements lack cytoplasm, and sieve-tube elements have very few organelles in their cytoplasm. Cytoplasm and organelles act as “clogs in the plumbing”, by removing these bulk flow is better facilitated.
Where does the absorption of of water begin the transport of water and solutes?
Near the root tips where the root hairs are located (epidermis is permeable to water), root hairs account for most of the surface area of the root
Once the root hairs absorb the soil solution (water and mineral mix) how does this help with the overall absorption of the solution?
Root hairs absorb the solution and the solution travels along the cell walls of the EPIdermal cells and passes freely into the extracellular space of the cortex cells, this increases the exposure to soil solution to more than just the outer EPIdermal cells by also including exposure to the cortex cells.
If the soil typically has lower mineral concentrations than in the root cells, how do the minerals get inside the cells?
ACTIVE TRANSPORT
What is the ENDoderm? What are some special structures of this? What is its function?
These are the innermost layer of cells in the root cortex that surround the vascular cylinder.
Function: the final checkpoint in the selective passage of mineral from cortex to the vascular cylinder
The CASPARIAN STRIP blocks the apoplastic transport of water and minerals from the cortex to the vascular cylinder. THis means that water and minerals have to pass the selectively permeable plasma membrane of the endordermal cell before entering the vascular cylinder
How can water and minerals cross the cortex?
the symplastic or apoplastic route.
What is the casparian strip made of?
Suberin - a waxy material that is impervious to water and dissolved minerals.
LOOK AT 36.3 PICTURE OF DIFFERENT TYPES OF TRANSPORT.
DO IT.
What is the substance that is being transported from the roots to the leaves via bulk transport?
XYLEM SAP
What is transpiration?
The evaporation of water from a plants surface, this evaporated water is replaced as water travels up roots
Is sap pushed by roots or pulled by leaves?
BOTH
Describe how root pressure pushes xylem sap.
AS water flows in from the root cortex, root pressure is generated, which pushed xylem sap towards leaves (this is a smaller pressure exertion)
What happens to the water potential of the xylem in roots at night?
root cells continue to to push mineral ions into the vascular cylinder even though no transpiration is occuring. these ions cant be pushed back out into soil because of the casparian strip. This causes a lowering the water potential.
A root pressure is generated w/o transpiration occuring, this can result in GUTTATION, the exudation of water droplets on the tips or edges of leaves. THIS IS NOT DEW.
What is guttation?
The exudation of water on the tips or edges of leaves due to the increased root pressure w/ lack of transpiration.
What is the cohesion-tension hypothesis?
transpiration and water cohesion PULL water from roots to shoots.
What type of pressure is xylem sap normally under?
Negative, meaning tension
What is cohesion, adhesion, and surface tension?
cohesion - water molecules bind to one another
Adhesion - water binds to other polar molecules
Surface tension - layer of H2O acts as a membrane due to cohesion
Go in depth on transpirational pull (cohesion-tension hypothesis).
Water vapor of a in the airspace of a leaf is diffused down its water potential gradient leaving the leaf via the stomata
As the water evaporates the air-water interface retreats further into the mesophyl cell walls
The surface tension of this causes a negative pressure that pulls water from the xylem into the leaf
THIS PULL IS TRANSMITTED FROM THE LEAVES TO THE ROOTS
look at picture 36.3 in powerpoint that describes the transpirational pull
do it
From roots to leaves, what is the water potential?
High to low
Describe the cohesion and adhesion portion of the cohesion-tension hypothesis.
Water molecules are attracted to the cellulose in xtlem cell wall (adhesion), this helps to offset the force of gravity.
Water molecules are attracted to each other by cohesion (this creates the pull of the sap)
Why dont the walls of the vessel elements and sieve-tubes of the xylem collapse with the negative pressure of the force of gravity acting on the water that adheres the the walls.
They have secondary walls that prevent this.
What is cavitation?
This is the break in the chain of water molecules from root to shoots and decreasing traspirational pull, causing a pocket of water vapor. This occurs during increased drought stress or freezing conditions.
Does transpiration require energy?
NO NO NO
How does bulk flow differ from diffusion?
it is driven by differences in pressure potential, NOT solute potential
bulk flow occurs in hollow, dead cells, not across the membrane of living cells.
The entire solution moves, not just water or solutes
occurs much faster
What exerts more pressure, cohesion-tension or root pressure?
cohesion-tension
What is the disadvantage of the high surface-to-volume ratio of leaves?
while photosynthesis is increased, water loss is increased through the stomata
How is the high surface-to-volume ratio and its consequence of high water loss through the stomata combated?
Guard cells open and close the stoma to help with the balance of water for gas exchange and photosynthesis
What percentage of water of a plant is lost through the stomata?
95%
How exactly does a guard cell open and close the stomata?
By changing its shape
Over the last 200 years, have the number of stomatas plants have increased or decreased?
decreased
THIS SHOWS THAT NOT ONLY ARE THE DENSITY OF STOMATA UNDER GENETIC CONTROL, BUT ALSO ENVIRONMENTAL CONTROL
How exactly do guard cells change their shape to open and close the stomata?
CHANGES IN TURGOR PRESSURE
When turgid - the cell bows outwards and the stoma opens
When flaccid - the bow is decreased and the pore closes
THE SPECIFIC BOWED SHAPE IS ALSO FORMED BY CELLULOSE MICROFIBRILS
How is the change in shape of guard cell caused?
the uptake and loss of K+ ions.
How do potassium ions help to change the shape of the guard cells?
K+ moves out, so does water, cell becomes less bowed.
K+ moves into cell, so does water, cell becomes more bowed.
What do the stomata generally do during the day, what about at night? What stimulates stomatal opening at dawn?
Open during the day - at dawn the light, CO2 depletion, and an internal clock open the stomata
Close during the night
What is a circadian rhythm?
internal clock of eukaryotes?
What can cause stomata to close during the day?
drought
high temperature
wind
What is abscisic acid?
hormone produced in response to water deficiency and closes the stomata
What happens if water is transpired and not replenished by transport of water into roots?
the plant will lose water and wilt.
What is evaporative cooling and how does transpiration affect this?
the evaporation of water causes the temperature of the leaf to lower, preventing the denaturation of enzymes involved in photosynthesis and other metabolic processes.
A LACK OF TRANSPIRATION CAN LOWER THIS EFFECT AND COULD BE BAD FOR THE PLANT
What are xerophytres?
These are plants that adapted to arid climates
What are some adaptations that xerophytes have?
some completed their life cycle during the rainy season
Some have fleshy stems that store water
some have leaf modifications that reduce the rate of transpiration
Some have a special form of photosynthesis where stomatal gas exchange occurs at night, this is called CRASSULACEAN ACID METABOLISM (CAM)
What is translocation? Where does this occur?
This is the movement of the products of photosynthesis through the phloem from a sugar source to a sugar sink (phloem sap)
This usually occurs in the sieve-tube elements
What is a sugar source?
An organ that is a net producer of sugar (such as leaves)
What is a sugar sink?
An organ that is a storer or net consumer of sugar (like a tuber or a bulb)
Can a sugar sink also be a sugar source?
YES, sometimes what is a sugar sink in the summer may be a sugar source in the winter
How does sugar travel to the phloem?
symplast or apoplast
What do companion cells do?
these have ingrowths that enhance the transfer of solute between the apoplast and symplast
How do sugars move from the apoplast to the symplastt?
Cotransport using protons.
What is pressure flow?
bulk flow of phloem sap that is driven by positive pressure. look at pressure flow hypothesis.
What is self-thinning?
the dropping of sugar sinks such as flowers, seeds, or fruits when there are more sugar sinks that sources can support (like apples falling from a tree)
Describe bulk flow by positive pressure
LOOK AT FINAL 36.5 picute in powerpoint.
- sugar is loaded into sieve-tube at the source, reducing the water potential inside the sieve-tube, THIS CAUSES THE SIEVE TUBE TO TAKE UP WATER BY OSMOSIS FROM THE XYLEM
- the water uptake creates a positive pressure that forces the sap along the tube
- As the sugar is unloaded into the sink the pressure is relieved, also causes water to be lost at the sink.
- in leaf-root translocation, the water is recycled by the xylem from sink to source
What is the overall difference between translocation and transpiration?
Transpiration - NEGATIVE PRESSURE (high water potential to low), used in the XYLEM
Translocation - POSITIVE PRESSURE made from water rushing into phloem from xlyem as sugar creates lower solute potential, performed in the phloem
