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• The loss of water vapor
form the leaves and
stems of a plant
• Water generally moves
into plants through their
roots and upwards
through the vascular
system and out of the
stomata in the leaves
• Transpiration is regulated by the stomata
• Tiny pores for gas exchange
• Occur mostly in the leaves but sometimes found in the stem
• Made of 2 elongated guard cells
• attached to normal epidermis cells on one side
• Not attached to each other
• Open and close based on turgor pressure
• Open when water is absorbed by the guard cell from its neighboring epidermis
• Water is then lost through the pore
• Close when enough water is lost that the cell becomes flaccid
• Tend to be open during the day and closed at night
• Will close during the day if plant becomes short of water
• Regulates transpiration and prevents excess water loss
• Water transport occurs in
the xylem
• Begins as elongated cells
connected end to end
• During development the
end walls are dissolved
away so long hollow tubes
• Living tissues of xylem lay
down cellulose which is
thickened by lignin
• Water lost by transpiration raises
the osmotic pressure in the cells
causing water uptake from
surrounding cells and the xylem
• As water leaves the xylem more is
pulled up through transpiration pull
and the cohesive/adhesive
• As water leaves the xylem more is
pulled into the xylem at the root
• Much of the water pulled into the
plants is lost to evaporation
• Light
• Stomata tend to be open in light
• Light can warm the leaf and raise its temperature
• Temperature
• Causes evaporation of water molecules from the surface cells of the plant
• Evaporation rate doubles for every 10 degree increase in temperature
• Wind
• Sweeps away water vapor
• Humid Air
• High water vapor surrounding the leaf
• Soil water
• Amount of intake by the roots must match transpiration
• Carbon Dioxide
• High levels cause the stomata to close
• Huge, ever growing root
systems increase the surface
area for absorption of water
and essential nutrients
• Surface area is also
increased by the addition of
root hairs
• Water enters due to higher
solute concentration than soil
• Cortex cells have a structure
that also facilitates the
uptake of water
• Minerals needed by the
plants and found in soil
• are:
N as NO3- or NH4+
K as K+
P as PO43Ca as Ca2+
• Diffusion
• Minerals are more concentrated
in the soil than in the root
• When dissolved in water the
minerals will diffuse into the
• Mass flow of water
• Uptake of water which includes
dissolved minerals
• Fungal Hyphae
• Plants work together with fungus
to absorb minerals
• Threads of the fungus grow
through the soil and absorb the
• The threads also grow into the
roots and transport the minerals
into the roots
• These minerals would not be
absorbed without the fungus
• Plants give the fungus sugars
• Use of metabolic energy to obtain minerals
• Can occur against the concentration gradient
• Cytosol of the cell holds some reserves of ions
• Allows the cells to pull in more of these ions when available
• Cells tend to horde ions
• Highly selective – plant will choose from different forms of the
same ion
• Ions cross into the cell through pump molecules
• If roots are deprived of oxygen then active transport stops
• The formation of the necessary metabolic energy is from respiration
• Thick cuticle
• Prevents water loss through the external wall of the epidermis
• Hairs on the epidermis
• Traps moist air over the leaf
• Reduction in number of stomata
• Reduces areas where loss can occur
• Rolled or folded leaves
• Reduces area for transpiration to occur
• Lower epidermis is rolled inside the leaf protecting it
• Superficial roots
• Takes advantage of condensation on the soil overnight
• Deep and extensive roots
• Allows access to the deep water
• Reduced leaf numbers
• Less surface area for transpiration
• Low growth
• Limits plant exposure to wind
• Store water to dilute salt concentrations
• Salt glands
• Expel excess salt
• Example is the mangrove
• Specialized Vacuoles
• Store Na+ and Cl• Prevents NaCl toxicity
• Protected stomata
• Stomata are recessed into the cuticle increasing the humidity and
therefore decreasing transpiration
• Reduced surface area
• Sieve tubes
• narrow elongated cells
connected end to end; no real
• Sieve plates
• end walls which have pores for
material to move through
• Companion cells
• services and maintains the
sieve tubes; attached to the
sieve tube by cytoplasm strands
• The movement of manufactured food (sugars and amino acids)
• Occurs in the phloem
• Can move in any direction
• Goes from the source to the sink
• The source is where the organic material is produced
• The sink is where the organic material is used
• Takes sugars to new growth in young plants and to storage in older
• Amino acids are produced in the roots and transported to where they
are needed for protein synthesis (usually growing parts of the plant)
• Chemicals sprayed on the plant can also be moved in this manner
• Aphid Stylets
A way of getting uncontaminated sap from the phloem
Aphids insert their stylets into the sieve tubes as a feeding mechanism
The pressure in the sieve tube pushes the sap into the stylet
Scientists can then remove the stylets and analyze its contents
• Radioactively labeled carbon dioxide
• Allows scientists to see where the carbon dioxide is fixed into sugar
• This sugar can then be used to track the flow from the source to the
• Involves active transport of the
sugars and passive transport of
• Sugar is loaded at the source
through active transport which
causes water to also enter
through osmosis
• Increased water in the sieve
tube causes and increase in
hydrostatic pressure which
causes movement of the sap
• Sugar is removed at the sink and
transformed to starch (or used)
through active transport
• Xylem then recycles the excess
• Which osmoter is the
• Which osmoter is the sink?
• Which part of the plant is
typically represented by
osmoter A?
• Which part of the plant is
typically represented by
osmoter B?