lesson 3 Flashcards
how can water move from roots to the top of tall trees?
-1 way movement from roots to leaves using xylem
-carbohydrates move up or downward using phloem
transport between cells
-active and passive transport mechanisms
-plasmodesmata
*pores between cells
-aquaporins facilltate diffusion
water potential
-potentials are a way to represent free energy
-measured in megapascals (MPa)
-can predict the movement of water by comparing water potential values
-always moves from an area of high potential to low potential
calculation of water potential
2 components:
-pressure potential= physical forces such as plant cell wall or gravity (p)
-solute potential= concentration of solute in each solution (s)
total water potential w=p+s
water and mineral absorption
-root hairs provide surface area
-surface area further increased by mycorrhizal fungi
-water and minerals must move across cell layers until they reach the vascular tissues
3 transport pathways through cells
-apoplastic pathway
-symplastic pathway
-transmembrane pathway
apoplastic pathway
move through non-living portion of the plant
symplastic pathway
move through living portions of plant utilizing plasmodesmata
transmembrane pathway
move across membranes, provides the most control
endodermis
-endodermis: single layer surrounding the stele (primary xylem and phloem)
-casparian strips surrounds endodermal cells and are impenetrable
-only select solutes are allowed to enter
-through this process, the endodermis restricts harmful solutes and promotes uptake of water
water transport through the plant
-transpiration is the evaporation of water through stomata
-cohesive and adhesive properties maintain tension
*tension forces pull the column of water up the xylem
*cohesion pulls water from the soil
-constant water potential gradient is maintained throughout the plant
cavitation
-small diameter of tracheids and vessels maintains tensile strength of water
*stabilized by adhesive forces
-Cavitation: air bubbles can break column of water
-Damage can be minimized by anatomical adaptations
*pit connections between cells create alternate pathways
stomata open and close to control transpiration
rate of transpiration controlled by stomata
*open and close as needed, promote gas exchange
*typically open during the day, close at night
-guard cells form the stoma (singular)
*distinctive walla construction
-turgor changes cell shape
*uptake of ions (K, Cl, Malatate)
*water potential decreases
*cells accumulate water
abscisic acid promotes stomatal closing
stomata close:
-Abscisic acid (ABA) increase
-CO2 levels are high
-temperature exceeds 30-34 C
-unfavorable water conditions
phloem transport: translocation
-carbohydrates
*sucrose
*other sugars
-plant hormones
-mRNA
-Amino acids
-organic acids
-proteins
-ions
pressure-flow hypothesis
-movement of carbohydrates in phloem
-carbohydrates move from sources to sinks
-source: photosynthetic material (leaves)
-sink: developing tissues requiring sugar resources
-phloem loading
*active transport of sugars into phloem
*reduces water potential
*water follows
