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Transport in Vascular Plants

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Emily Hays

on 20 March 2014

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Transcript of Transport in Vascular Plants

Transport in Vascular Plants

Water Potential and Osmosis
Water moves through the xylem along with minerals, in a fluid known as
xylem sap

Moving Materials Upwards= Negative pressure from above (like the twizzler straws) or positive pressure from below (Positive pressure rooms)

Is the sap pushed upward, or pulled upward? Let's have a vote!
Pushing Xylem Sap Upwards
-When rate of transpiration is close to 0
-Root cells pump mineral ions in xylem of vascular cylinder
helps prevent leakage of ions
-Accumulation of minerals lowers water potential in vascular cylinder
-Water flows from root cortex, generating
root pressure
, an upward push of xylem sap
-Can cause more water to leave than is transpired =
-Not the same as dew!!!
-Minor Mechanism
Both occur!!!!
One more than the other
Pulling Xylem Sap
Root Pressure
Let's Sum it Up!
-Transpirational Pull
- Water potential outside is less
-Negative pressure develops at air water interface (which lowers water potential)
-First, water lost by transpiration is replaced by water layer around mesophyll cells
-As the
air-water interface
curves in more, surface tension increases and pressure at interface becomes more negative
-Water molecules are pulled in to
alleviate the tension.
Cohesion and adhesion
then help
offset the pull of gravity and make
a continuous column of water
-The evaporative loss of water from a plant
-A leaf may transpire more than its weight in water each day
-If transpiration can pull sufficient water up, the leaf will not wilt
-Transpiration results in evaporative cooling
-Prevents the denaturing of various enzymes involved in biological processes
-But environmental factors can increase evaporation (what are some situations?)
are plants that have adapted to minimize tranpiration. (Cacti, Succulents)
The Stomata
-90% of water escape through stomata (1-2% of leaf surface)
Waxy cuticle
limits rest of water loss
-Flanked by pair of
guard cells
-Kidney-shaped in eudicots, dumbell-shaped in monocots
-Control Diameter of stoma by changing shape
-Amount of water lost by leaf depends on the number of stomata and avg. size of holes
Let's Take A Look!
-Stomatal density can determine a lot:
-Where the plant is growing
-CO2 Levels
-Guard cells help control transpiration:
- Become turgid and bowed during water intake :
stomata open
-Become flaccid and straight during water loss:
stomata close
-Change in turgor pressure results from reversible
loss and intake of K+ ions
-Stomata open when guard cells actively accumulate
K+ from neighboring epidermal cells
-The water potential lowers, and water rushes in, causing the guard cells to become turgid and open once more.
More on Stomata
Three Stimuli that Stomata Respond To
Anyone? Anyone?
Ooooohh... Aaaaah...
- Light
-Internal clock
Anyone? Anyone know?
-Light Stimulates guard cells to accumulate K+ and become turgid
-Triggered by illumination of blue-light receptor in plasma membrane of guard cells
-Activation stimulates activity of ATP-powered proton pumps, and promote uptake of K+
Depletion of CO2
-Depletion of CO2 within air spaces of leaf occurs when photosynthesis begins in mesophyll
-A plant will actually open its stomata at night if it is placed in a chamber devoid of CO2
Cycles with intervals of approx. 24 hours are called...
Circadian Rhythms!
Internal Clock
-Guard cells have internal clocks and patterns of opening and closing
-Even in the dark, stomata have been observed to open and close
Phloem, a Vein of Thought
the transport of organic nutrients in the plant
Sieve-tube members
are specialized cells, arranged to form long sieve tubes
Phloem Sap
Sucrose (C12H22O11)
Amino acids
Where does it go?
Travels in the "opposite" direction of xylem
direction can vary
Sugar source --> Sugar sink
Sugar source
is an organ that produces sugar (by photosynthesis or catabolic reaction)
Sugar sink
is the recipient of the sugar obtained by the sugar source (ex: growing roots, buds, stems, fruits)
Flow rate 1 meter per hour
How is Phloem sap moved?
The diffusion of water molecules across a plasma membrane down their concentration gradient
Concentration Gradient
Water Potential
Pressure Potential + Solute Potential
Pressure Potential
The pressure of the cell wall that prevents the intake of water
Solute Potential
The concentration of the solute
- higher concentration = lower water potential -> water will move into the solution
A difference in concentrations of solutes on different sides of a membrane
What do they do?
absorb nutrients and water (
soil solution
Where does the
soil solution
absorbed through the permeable
root hairs
into the
(ground tissue)
across the
(single-cell wall)
Casparian Strip
into the
vascular cylinder
which contains the vessels and tracheids of the xylem
Out of the Sugar Source:
Some species
: From the sugar source (mesophyll cell) to the sieve tube member through plasmodesmata (through the symplast)
Other species
: Sugar travels via the symplast and apoplast
There are two types of root systems
Eudicots and Angiosperm
Monocots and seedless vascular
Mycorrhizae, a symbiotic relationship
Root hairs and root tips can't do all the work themselves - they get help from fungi
Roots and fungi come together to create symbiotic structures
More surface area
Older parts of root can still absorb nutrients
Owen Phloem
Dude, does maple syrup come from the phloem of maple trees?

Dude, I thought plants make glucose from photosynthesis not sucrose?
Take that! Gravity!
Brought to you by the BAE
Thanks for Watching!
Three Compartments of
Vacuolated Plant Cells
-Transport is regulated by compartmental structure of plant cells-
Cell Wall, Cytosol, Vacuole
Apoplast and Symplast
When a plant cell has a greater water potential than its environment, it will undergo ______________, the shrinking of the cytoplasm away from the cell wall.

When a plant cell has an equal water potential as its environment, it will be _______________. This is seen in a wilting plant.

A plant is at its best condition (is happiest) when it is _______________.
Bulk Flow
Moves through sieve tubes by bulk flow, driven by pressure
Pressure built up at source, and reduction of pressure at sugar source moves the sap along
Joke (with humor subject to controversy )
What type of instrument would a plant play?
A xyle-phloem!!!!!
Lateral Transport
Bulk Flow
-Osmosis/Diffusion and just the work of hydrogen bonds is efficient for short distances
-For long distances,
bulk flow
is necessary
-Movement of fluid is driven by pressure
-Water and solutes move through tracheids and vessels of xylem
-Tension in xylem due to transpiration
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