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Ch. 7 Roots (Internal Structure of Roots (Zone of Elongation (cells expand…
Ch. 7 Roots
Internal Structure of Roots
Root Apical Meristem
relationship to root tisses
quiescent center
mitocally inactive central region
nuclei do not become radioactive
resistant to harmful agents
radiation
toxic chemicals
reserve to healthy cells
Zone of Elongation
cells expand greatly
begin to differentiate into pattern
some meristematic activity
similar to shoot's subapical meristem
tissues are permeable
minerals penetrate deeply
Zone of Elongation
/30%3A_Plant_Form_and_Physiology/30.3%3A_Roots/30.3A%3A__Types_of_Root_Systems_and_Zones_of_Growth)
Zone of Maturation
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Root hair zone
root hairs grow outward
increases absorption of water/minerals
transfer minerals to epidermis
to vascular tissue
Cortical intercellular spaces
allows oxygen to diffuse
root from soil/stem
endodermis
tangential walls
thin primary walls
Casparian strips
bands of altered walls
controls types of minerals
impermeable
pericycle
parenchyma cells
between vascular tissue/endodermis
irregular region
lateral roots produced
Mature portions of roots
passage cells
passageways for absorption
slow to develop
root pressure
absorption of minerals
powerful absorption of water
Root Cap
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Origin/Development of Lateral Roots
initiated by cell divisions
in pericycle
some cells become densely cytyoplasmic
smaller vacuoles
resume mitotic activity
localized to few cells
creates small root primordium
organizes into root apical meristem
pushes outward
lateral root destroys
cells of cortex
epidermis
swells into cortex
endodermis may tear/crush
undergo cell division
Lateral Roots
Other Types of Roots & Root Mods
Prop roots
make contact with soil
transport additional nutrients/water
to stem
acts as stabilizers
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undergo secondary growth
become woody
extremely strong supports
permits branch to extend
buttress roots
brace trunk from being blown over
Contractile Roots
firmly anchored
uppermost portion contracts
caused by cortex cells shape change
shorten/expand radially
simultaneously
loses 1/2 to 2/3 of height
vascular tissue buckle
become undulate
continue conducting
stem pulled downward
kept at soil level
bulbs buried deeper
Mycorrhiaze
symbiotic relationship w/fungi
endomycorrhizal
fungal hyphae
penetrate outermost root cortex
pass through walls of cortex
slender, threadlike cells
invade cell
do not break
plasma membrane
vacuole membrane
inside cell
branch repeatedly
form arbuscule
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fill with membranous vesicles
ectomycorrihizal
woody forest plants
Mycorrhizae
External Stuctures of Roots
Organization of Root Systems
Tap roots
Lateral (branch) roots
radicle
fibrous root system
radicle dies
Carbohydrate storage
fibrous root system
monocots & some eudicots
eudicots are perennial
undergo secondary growth
increased quantity wood
trunk
roots
monocots cannot undergo secondary growth
radicle dies during/after germination
root primordia
grows out
form 1st stages of fibrous root system
more initiated in stem tissue
adventitious roots
increase absorptive
increase transport capacities
Structure of Individual Roots
no leaves/leaf scars
no leaf axils/axillary buds
root tip
growth in length
roots
growth discrete apical meristem
longitudinal growth
elongate meristematic regions
embedded in solid matrix
impossible to extend at once
root cap
protects root apical meristem
zone of elongation
root hair zone
new lateral roots
thick layer of cells
constantly worn away
renewed by cell mulitplication
dictyosomes
secrete complex polysaccharide
mucigel
lubricates passage of roots
soil releases nutrient ions
ions diffuse more rapidly
rich in carbohydrates/amino acids
rapid growth of soil bacteria
same info
merges
adds tension