Chapter 35 Flashcards
(38 cards)
Transpiration
Water loss via evaporation from leaves when stomata are open and air surrounding leaves is drier than air inside leaves
Leaves with large amount of surface area lose large amounts of water through transpiration
Water potential
Tendency of water to move from one area to another
Determines direction that water moves (from areas of high water potential to areas of low potential)
When the solute potential inside the cell and in surrounding solution is the same there is no net movement of water
Water-potential gradient
High potential in soil; low potential in air
To move up plant, water moves down water-potential gradient in soil, tissues and atmosphere
How is water absorbed into the root epidermis
Absorbed through osmosis
Travels through root cortex towards vascular tissues via three pathways
Transmembrane route, Apoplastic pathway, symplastic pathway
Casparian strip
Ring of hydrophobic waxy compound in cell walls of endodermal cells
Blocks apoplastic pathway at endodermis and force liquids to cross the plasma membrane of endodermal cells.
How water move from roots to shoots
A. Root pressure
B. Capillary action
C. Cohesion-tension
Root pressure
A hypothesis that explains how water moves from roots to shoots
Stomata close at night to minimize water loss, and roots accumulate ions and H2O from soil
Creates a positive pressure that forces water up xylem
Guttation
when water is secreted from the tips of the leaves of plants
Capillarity
A hypothesis that explains how water moves from roots to shoots
Happens in response to 3 forces
Adhesion
Cohesion
Surface tension
Adhesion
Attraction of unlike molecules
Water and solutes stick to sides of tube and results an upward pull
Cohesion
Water molecules are bound together through hydrogen bonding
As a result of cohesion, as one molecule moves, it pulls up another water molecule
Surface tension
When H20 molecules are being held together by cohesion
Measure of how much the molecules at the surface of the liquid are being pulled inward due cohesion
Cohesion-tension theory
Leading hypothesis to explain water movement in vascular plants
- Water vapor diffuses out of leaf
Pressure decreases - Water evaporates inside leaf
- Water is pulled out of xylem
- Water pulled up xylem
- Water pulled out of root cortex
- Water diffuses from soil into root (osmosis)
Sun provides energy to move water through xylem
Photosynthesis-transpiration
Balance between conserving H2O and maximizing photosynthesis
Plants from dry habitats and modified leaves have adaptations that slow transpiration to limit water loss.
Translocation
Movement of sugars using bulk flow through phloem from sources to sinks
Source
Tissue where sugar enters phloem
Sugar concentrations are high
Sink
Tissue where sugar exits phloem
Sugar concentrations are low in sinks
This is where sugars are used or stored (roots and fruits of a plant)
Sieve tube elements
Part of the phloem
Long thin cells that have perforated ends called sieve plants
Responsible for transporting sugars throughout the plant
Alive at maturity and lack secondary cell walls and nucleus
Companion cells
Part of phloem
Provide materials to maintain the cytoplasm and plasma membrane of sieve-tube elements
Controls the metabolic activity of sieve tube elements
Pressure-Flow hypothesis
Explains how sugars move through phloem
Pressure based on cohesion and phloem loading/unloading
Phloem loading
Sugar is moved by active transport from source cells through companion cells to sieve tube members,
Water follows passively from xylem to sieve tube elements
Turgor pressure builds up in sieve tube elements in the source region
Phloem unloading
Sucrose transfers into the sink from by passive or active transport
Water goes back into the xylem and turgor pressure in sieve tube elements drop due to the loss of solutes
Result of phloem loading and unloading
High turgor pressure near source and low turgor pressure near sink
drives phloem
sap from source to sink via
bulk (pressure) flow
One-way flow of sucrose
& continuous loop of water
movement occurs, as water
supplied to & from xylem
Result of phloem loading and unloading
High turgor pressure near source and low turgor pressure near sink
drives phloem sap from source to sink via bulk (pressure) flow
One-way flow of sucrose & continuous loop of water
movement occurs, as water supplied to & from xylem
