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Roots (Other types of roots & modifications (roots of strangler figs…
Roots
Other types of roots & modifications
storage roots
root is typically only permanent organ
stored carbs used to produce new shoot in spring
aerial roots of orchids
grow along tree bark and dangle in air
prop roots
grow thru air
transport additional nutrients and O2 to stem
stabilize stem
mycorrhizae
roots have symbiotic relationship with fungi
roots of ~ 80% of seed plants
ectomycorrhizal relationship
endomycorrhizal relationship
root nodules and nitrogen fixation
conversion of atm. nitrogen to usable compounds
symbiotic relationship with nitrogren-fixing bacteria
cortical cells form root nodule
roots of strangler figs
roots cling to tree branch
grow rapidly downward
eventually strangles tree
get nutrients from rain until reaching soil
haustorial roots of parasitic flowering platnts
roots of parasitic plants=haustoria
modified to penetrate host
contractile roots
uppermost portions contract
anchor into soil
stability
Internal structure
root cap
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protection of apical meristem
apical meristem
quiescent center
backup for apical meristem
zone of elongation
behind apical meristem
region where cells expand
zone of maturation (root hair zone)
#
root hairs increase surface area for abs. of H2O & minerals
innermost layer becomes endodermis
casparian strips (rings) control what minerals that enter xylem
selectively permeable
cells become fully differentiated and functional
root hairs die/degenerate after several days
mature root
passage cells
mature endodermis keeps root pressure from H2O under control
mature endodermis is sheath around vascular tissues
External Structure
organization of root systems
fibrous
mass of many similar sized roots
lateral roots
AKA branch roots
numerous and small
tap root
single and prominent
develops from radicle
carrots, beats, turnips
adventitious roots
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increase absorptive and transport capacities
do not arise from pre-existing roots and are not radicles
structure of individual roots
root cap
secretes mucigel which lubricates passage of the root thru soil
zone of elongation
where cells undergo division and expansion
root hair zone
increase surface area
Origin and development of lateral roots
initiated by cell division in pericycle
initiated deep within root
formed in mature regions of root
destroys cells in its path (epidermis/endodermis/cortex)
