Download Chapter 36—Transport in Vascular Plants

Chapter 36—Transport in Vascular Plants
Concept 36.1: Physical forces drive the transport of
materials in plants over a range of distances
A. 3 Levels of transport occur in plants
1. Uptake and release of water and solutes by cells
2. Sort distance transport
3. Long distance transport of sap in xylem and
phloem at whole plant level
B. Transport at cellular level depends on permability of
membranes
1. proton pumps
2. differences in water potential
3. aquaporins—water channels made up transport
proteins
 facilitate osmosis
C. 3 major compartments of a plant cell
1. cell wall
2. cytosol of the protoplast
3. tonoplastmembrane surrounding the large
central vacuole found in plant cells
D. Two of the three cellular compartments are continuous
between cells.
1. plasmodesmata connect cytosolsymplast
2. walls of adjacent cells are connectedapoplast
 both function in transport in tissues and organs
E. Lateral Transport is short distance
 Usually along the radial axis of plant organs
 Can take a symplast or apoplast route
 Water can switch routes
F. Bulk flow—long-distance transport
 Usually along vertical axis of plant
 Vascular tissue involved—transport would be too
slow
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
Transpiration reduces pressure in the xylem—
creates tension which pulls sap up from roots
Concept 36.2: Roots absorb water and minerals from
the soil
SOIL
EPIDERMIS
ROOT CORTEX XYLEM
 Absorption occurs
near root tips
 Apoplastic
route exposes
parenchymal
cortex to soil
solution
 Only minerals
using
symplastic
route enter
 Root hairs
increase surface
area
 Symplastic
route makes
selective
mineral
absorption
possible
 Apoplastic
minerals must
pass through a
Casparian strip
into an
endodermal cell
 Symbiotic with
fungi—creates
mycorrhizae—
aids in water
absorption
 Water and
minerals enter
into stele by
endodermis
cells
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Concept 36.3: Water and minerals ascend from roots to
shoots through the xylem
A. Ascent of xylem sap depends on transpiration and
properties of water
1. Pushing xylem sap—root pressure
 Transpiration low
 Decrease in water pressure
 Water flows into steleincrease pressure
and forces fluid up xylem
 Not the major mechanism
 Cannot keep up with transpiration
2. Pulling xylem sap
 Created by negative pressure
 Water creates cohesion—surface tension
 Causes water to be pulled
 Cohesion and adhesion creates a water
“chain”
 Adhesion to the sides of the xylem aid in the
pull against gravity
 Small diameter vessels aid in adhesion
effect
3. Cavitation—breaks the chain of water molecules
and the pull is stopped
 Will not function again unless filled by water
by root pressure—will only fill back up in
small plants
 Pits allow for detours around a cavitated area
 Secondary growth adds new xylem each year
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Concept 36.4: Stomata help regulate the rate of
transpiration
A. Guard cells are responsible for photosynthesis—act as
a transport compromise
1. Found on bottom of leaves away from sun
B. Transpiration benefits
1. mineral movement
2. evaporative cooling
C. Transpiration high and low water pressureplant wilts
D. Stomata help prevent wilting by opening and closing
1. Guard cells open when plant turgid—cell “buckles”
2. Plant flaccid the cells sag—guard cell closes
E. Internal and external environmental cues open and
close guard cells
1. stomata open at dawn
 light
 decrease of CO2
 internal clock—circadian rhythm
2. guard cells close during day if:
 water deficiency
 high temperatureincreases CO2
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Concept 36.5: Organic nutrients are translocated
through the phloem
A. Translocationproducts of photosynthesis transported
to rest of plant
B. Sugar sourcewhere sugar produced
C. Sugar sinkwhere sugar used or stored
1. Sugar can flow within phloem either direction
depending on location of the closest sink
D. Loading of sugar into phloem
1. Symplastic route
2. Apoplastic route
3. Transfer cells
E. Unloading of sugar to sink
1. Active transport
2. Diffusion
3. Symplastic route
4. Apoplastic routes
F. Phloem translocationbulk flow
1. Source has high pressure
2. Sink has low pressure
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