Ch. 36 Flashcards
stems
1) conduct water and nutrients
2) support leaves
trade-off between growing tall and branching
more energy in branching means less energy to grow
phyll
leaf
taxi
movement toward or away from
phyllotaxy
arrangement of leaves on a stem
angio
seed vessels
What is the angle between leaves that minimize shading of lower leaves
137.5 degrees
horizontal leaves
capture more sunlight
verticle leaves
less damaged by the sun
stomatal pores
tiny openings on leaf that facilitate diffusion of CO2 into photosynthetic tissue of leaves. release oxygen as byproduct
How much water is lost by stomatal pores
90%
roots branch extensively into pockets of high _______ availability and grow straight through pockets of low _______ availability
nitrate
roots and hyphae of soil fungi form
mycorrhizae associations
what does mycorrhizal fungi do?
increase the surface area for absorbing water and minerals (especially phosphate P)
apoplastic route
transport of water and solutes through cell walls and extracellular spaces
symplastic route
transport of water and solutes across plasma membrane once and then through cytosol and plasmodesmata
transmembrane route
transport of water and solutes repeatedly across plasma membranes
apo
away, furthest point
sym
with, in company, together
trans
cross
plastic
to grow or form, capable of being deformed without rupture
what controls short-distance movement of substances?
plasma membrane permeability
do plants have active or passive transport?
both
How is membrane potential established in plants?
pumping of H+ by proton pumps
how is membrane potential established in animals?
pumping Na+ by sodium-potassium pumps
explain a proton pump
a pump that uses energy from ATP hydrolysis to transport H+ across a membrane against its concentration gradient
explain a cotransporter pump
the potential gradient energy from H+ allow for transport of other ions across the membrane
explain an ion channel
An ion channel is a membrane protein that facilitates the selective movement of ions across a cell membrane
What is osmosis?
the diffusion of water in or out of a cell affected by solute concentration and pressure
What makes up water potential?
solute potential + pressure potential
which way does water diffuse
from higher water potential to lower water potential
potential
ability to do work
solute potential (2)
1) also called osmotic potential
2) inversely proportional to molarity, lower the molarity the higher the solute potential
pressure potential (2)
1) physical pressure of the solution
2) positive (pushing), negative (sucking)
What is turgor pressure?
positive pressure exerted by plasma membrane against the cell wall and against the protoplast
What is the protoplast?
the living part of the cell
What is plasmolysis
when the protoplast pulls away from the cell wall
flaccid
limp
ton
tension
ic
pertaining to or relating to
hyper
above
iso
the same
hypo
below
aquaporins
transport proteins in cell membrane that facilitate the passage of water
what is bulk flow
the movement of a fluid driven by a pressure gradient
water and solutes move together through what of the xylem and what of the phloem
1) tracheids and vessel elements of the xylem
2) sieve-tube elements of the phloem
what do branching veins in leaves ensure?
they ensure that all living cells are within a few cells of vascular tissues
mature tracheids and vessel elements lack ________
cytoplasm
sieve tube elements have few _____ in cytoplasm
organelles
what connects vessel elements?
perforation plates
what connects sieve-tube elements
sieve plates
What connect tracheids?
pits
where does most water and mineral absorption occur, and how?
1) root tips where root hairs are located
2) the epidermis is permeable to water
what accounts for much of the surface area of roots?
root hairs
cortical cell membranes do what?
enhance uptake of water and selected minerals
what does active transport enable?
it allows minerals to accumulate in higher concentrations in the roots compared to the soil
in the root cortex, what is the innermost layer of the cells
the endodermis
what does the endodermis do?
1) it surrounds the vascular cylinder
2) it is the last checkpoint of selective passage of minerals from Cortex to vascular tissue
what does the Casparian strip do?
blocks apoplastic transfer of water and minerals from cortex to vascular cylinder
describe water movement from endodermal cells to tracheids and vessel elements
1) Endodermal cells discharge water and minerals from their protoplasts into their own cell walls. (diffusion and active transport)
2) once in apoplast, water and minerals can enter tracheids and vessel elements
what is xylem sap?
1) contains water and dissolved minerals
2) transported from roots to leaves by bulk flow
transpiration
the evaporation of water from a plant’s surface
What is root pressure?
generated from water flow from root cortex
a push of xylem sap
guttation
the exudation of water or droplets on tips or edges of leaves
how do root cells lower water potential at night?
they continue pumping mineral ions from soil into xylem (soil(10) ->root cell(-5) ->xylem(-10)
- allows movement of water up plant even though there is less transpiration
cohesion-tension hypothesis
transpiration and water cohesion pull water from roots to shoots
transpiration pull
1) water vapor in air spaces of leaf diffuse down its water potential gradient and exit leaf via stomata
2) surface tension of water at air-water interface creates negative pressure potential
how does pressure potential affect water potential
negative pressure potential lowers water potential (directly correlated)
what force helps offset gravity
adhesion (water molecules to xylem cell walls)
What is cavitation?
the formation of a water vapor pocket
what element of vessel elements and tracheids prevent it from collapsing under negative pressure?
thick secondary walls
How can xylem sap transport be continued after cavitation? (4)
1) move through pits
2) move from xylem to phloem and back again
3) cavitation can be repaired
4) new xylem is added by secondary growth
differences between bulk flow and diffusion
1) driven by differences in pressure potential not solute potential
2) occurs in dead hollow cells, not membranes of living cells
3) moves entire solution, not just water or solutes
4) much faster
changes in what pressure open and close stomata
turgor pressure (turgid open, flaccid close)
what do guard cells do?
open and close stomata to help balance water conservation with gas exchange
changes in turgor pressure in stomata result from?
reversible uptake and loss in potassium ions (K+) by guard cells
what generates membrane potential required to move K+ across the plasma membrane
proton pumps generate the membrane potential required to move K+ across the plasma membrane
stomatal opening at dawn is triggered by
1) light
2) CO2 depletion
3) internal clock of guard cells
what causes stomatal closing during daytime (2)
1) drought stress
2) hormone: abscisic acid (ABA)
effects of transpiration (3)
1) some water loss through cuticle
2) plant will wilt if water cant be replaced
3) evaporative cooling from transpiration cools leaf
What affects transpiration rates (4)
1) Sun
2) Warmth
3) dryness
4) wind
Xero
dry
xerophytes
plants adapted to arid/dry climates
how xerophytes combat arid climates
1) complete life cycle during rainy season
2) fleshy stems that store water or leaf modifications that reduce transpiration
3) CAM
translocation
products of photosynthesis are transported through phloem
sugar source
organ that is a net producer of sugar (leaves)
sugar sink
organ that is net consumer of sugar (buds, roots, fruits)
What is phloem sap? How does it travel?
1) an aqueous solution that is high in sucrose
2) travels from source to sink
seasonal dependency of storage organs
sink in summer, source in spring
sugar must do what before it can be exported to sinks
loaded into sieve-tube elements
depending on the species sugar may move by:
1) symplastic
2) symplastic and apoplastic
What is the function of companion cells?
enhance solute movement between apoplast and symplast
in angiosperms, ___________ are the conduits for _________
Sieve-tube elements, translocation
phloem loading requires
active transport
how do companion cells accumulate sucrose
cotransport of sucrose and H+
The H+ gradient is created by proton pumps
at the sink, ________ diffuse from the ________ to sink tissues and are followed by _______
sugar molecules
phloem
water
how does phloem sap move through sieve tube?
bulk flow driven by positive pressure (pressure flow)
______ of soil fungi form mutualistic associations with mycorrhizae
hyphae
