Transport in plants Flashcards
What are the two major angiosperm clades?
monocots
eudicots
What is a monocot?
one cotyledon (seed leaf) examples are orchids palms and grasses
What are eudicots?
two cotyledons (seed leafs) examples are roses, sunflowers peas, oaks, maples
Tissue organization of roots of vascular plants:
What is a characteristic of the epidermis?
it lacks a cuticle
Tissue organization of roots of vascular plants:
the ground tissue or cortex has what three uses?
storage
conduction of water and minirals from the root surface to the vascular tissue
innermost layer of cortex= endodermis; acts as selective barrier
Tissue organization of roots of vascular plants:
vascular tissues outer most layer is what?
outer most layer of vascular cylinder is called the pericycle and it gives rise to lateral roots
Tissue organization of the stem:
epidermis has a what?
a cuticle
Tissue organization of the stem:
ground tissue (cortex and pith) is used for what?
support
storage
photosynthesis
Tissue organization of the stem:
what is the arrangement of vascular bundles?
in eudicots
in monocots
eudicots: arranged in a ring
monocots: scattered throughout cortex
The ascent of water in a plant: how does it happen?
what are the four options?
diffusion
root pressure
capillary action
suction pump
Tissue organization of the stem:
diffusion characteristics?
water moved for short distance (>100 micro meters)
Tissue organization of the stem:
Root pressure characteristics?
water pushed upward from roots (least important)
Tissue organization of the stem:
capillary action characteristics?
cohesion and adhesion help fight gravity
Tissue organization of the stem:
suction pump characteristics?
water pulled up from roots by leaves
what do Fungi help do?
help plants absorb water and nutrient from soil
Where are the three places that water needs to move to and from?
from soil into roots (into epidermal cell)
across root (from cell to cell and across tissue)
across whole plant (roots–> leaves, leaves–> roots)
short and long distance transport
short distance transport of water across plasma membrane:
what does water potential(Ψ) predict?
predicts direction in which water will flow
what is Ψp?
pressure potential
what is Ψs?
solute potential (osmotic potential)
what is Ψ measured in?
units of pressure: megapascals( MPa); 1 MPa = 10 atmospheres)
What is Ψp when it is positive?
what is Ψp when it is negative?
Ψp is positive when a solution is compressed, negative when a solution is stretched (under tension)
what is going on when Ψs is zero?
Ψs is negative what is happening?
Ψs = zero for pure water
Ψs is negative if solutes are present
water moves in what direction?
doesn a water potential gradient
regions of high Ψ to region of low Ψ
what do aquaporines do?
facilitate water transport
flaccid plants are what?
limp: cell in surroundings where there is a tendancy for water to leave
Turgid plants are what?
very firm: cells have greater (solute) than surrounding
water enters
Plasmolysis plants are what?
cells loses water –> plasma membrane pulls away from cell walls
Short distance transport from outer root cells to inner cells of roots is called what?
lateral transport
What are the three routes in short distance transport of water within tissues and organs?
three routes
transmembrane route –> repeated crossings of plasma membranes
via symplast –> one crossing of plasma membrane
via apoplast
What is Bulk flow function?
used for long distance transport
Bulk flow: movement of a fluid driven by pressure
independent of solute concentration
in xylem (tracheids and vessel elements) and phloem (sieve- tube elements)
in xylem: root pressure and negative pressure
What is pushing xylem sap?
root pressure
pulling xylem sap: cohesion tension hypothesis.
what drives this process?
transpiration
as water evaporates from the leaves, the water column is pulled up
pulling xylem sap: cohesion tension hypothesis.
what are the key elements in this process?
water moves down a potential gradient
water column in xylem is under tension
weight of water column is supported by cohesion amoung water molecules and adhesion to the xylem
The casparian strip of the endodermis enforces symplastic movement of water and dissolved minirals
What problems do bubbles pose?
serious problem for a plant
the xylem and water columns must be continuous for the cohesion tension mechanism to work
Why do water columns break?
dissolved gasses can form bubbles when frozen xylem water thaws in the spring
dry soil can hold water so tightly that the tensile strength of water is exceeded
solutions to the bubble problem?
be a small annual plant
make new xylem every year
use tracheids (smaller diameter), not vessels
vary the diameter of water conducting cells during the growing season
re establish continuous water columns by pushing water up from below–> root pressure
what is the major pathway for water loss?
stomata
Stomata: major path for water loss
Why do plants transpire?
unavoidable when stomata are open
water and minerals are transported up the xylem column to aerial parts of the plant
transpiration provides evaporative cooling
How do the stomata work?
guard cells have bands of cell wall thickening
mechanism of opening:
Ψs in the guard cell falls –> water enters the guard cell down the Ψ gradient –> stomatal aperture opens
active transport of H+ out of the guard cells generates membrane potential
K+ from epidermal cells enters guard cells through K+ channels
water enters by osmosis
cells become more turgid
stomata open
Photosynthesis- transpiration compromise
factors involved in stomatal opening and closing?
Water balance of the plant
internal clock
CO2
(low –> stomata open)
(high–> stomata close)
hormones: abscisic acid (ABA)
produced in roots and leaves in response to water deficiency
single guard cells to close stomata
Light
blue light
activation of blue light receptors stimulates activity of proton pump in the plasma membrane of guard cells –> promotes absorption of K+
independent of photosynthesis and 10X more effective than red light
red light:
works indirectly by increasing photosynthesis –> increase demand for CO2 –> decrease CO2
Bulk flow by postive pressure: phloem transport
what are minerals transported?
sugars, (sucrose), AA, Minerals, Hormones
Bulk flow by postive pressure: phloem transport
direction of transport?
from sources to sink
may change with season of plant’s developmental stage
Bulk flow by postive pressure: phloem transport
sources?
plant organ that is a net roducer of sugar, by photosynthesis of by starch breakdown
Bulk flow by postive pressure: phloem transport
sink?
organ that is a net consumer or depository of sugar
Pressure flow model of phloem transport
sugar is loaded into companion cells and sieve tubes
water follows sugar by osmosis down Ψ gradient
uptake of water generates positive pressure
sugar is pushed along sieve tube by bulk flow
sugar is unloaded from phloem at the sink, moves by facilitation diffusion from phloem into sink tissue
