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Roots (Other Types of Roots and Root Modifications (Aerial Roots of…
Roots
Other Types of Roots and Root Modifications
Prop Roots
prop roots act as stabilizers
they transport additional water and nutrients to the stem
can produce massive trees
Aerial Roots of Orchids
orchids live attached to the branches of trees
roots dangle freely in the air
velamen = root epidermis
velaman acts as a waterproof barrier
Storage Roots
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stored carbohydrates used to produce new shoot
annual plants can survive without storage
provide long term storage for carbohydrates
roots have a stable environment
Root Nodules and Nitrogen Fixation
lack of nitrogenous compounds in soil is a growth limiting factor
nitrogen fixation = chemical conversion of atmospheric nitrogen
infection thread = hold bacteria
root nodule = swollen and occupied by bacteria
Mycorrhizae
symbiotic relationship with soil fungi
ectomycorrhizal relationship = woody forest plants
endomycorrhizal association = herbaceous plants
Contractile Roots
shoot at soil level or deeper
common
undergo much contraction
important in keeping stems at proper depth
Haustorial Roots of Parasitic Flowering Plants
very little root like structure remains
firmly adhere to host
haustoria = roots of parasitic plants
inadequate for growth in soil
Internal Structure of Roots
Root Apical Meristem
quiescent center = mitotically inactive
quiescent center has resistant cells
cells originate here
root apical meristem destroyed = quiescent center takes over
Zone of Elongation
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cells differentiate
protoderm ---> epidermis
cells expand greatly
provascular tissue --->xylem and phloem
very short zone
Root Cap
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cells close to edge of cap = change dramatically
small cells at base of root
provide protection for root apical meristem
Zone of Maturation
root hairs increase surface area
innermost layer of cortical cells = endodermis
root hairs grow
Casparian strips = control types of materials that enter the xylem
pericycle = parenchyma cells ---> lateral roots
Mature Portions of the Root
passage cells = slow to develop
root pressure = water pressure builds up
root hairs die after a couple days
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Origin and Development of Lateral Roots
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root apical meristem forms ---> pushes outward
new lateral root destroys the other cells it pushes through
initiated in pericycle
lateral root forms a root cap
External Structure of Roots
Structure of Individual Roots
root tip = site of growth
root apical meristem has a root cap
simple - (no leaves, leaf axils, buds, etc.)
root cap = thick layer of cells for protection
root cap used to bury through soil
mucigel = polysaccharide which lubricates passage of root
zone of elongation = cells undergo division and expansion
root hair zone = many trichomes
trichomes = root hairs
root hairs in area that is not elongating
root hair zone = zone of maturation
Organization of Root Systems
taproot ---> lateral roots/branch roots
taproot develops from the radicle
enormous absorptive surface
radicle = embryonic root
root systems
monocots or eudicots
fibrous root system
adventitious roots = not from pre-existing roots
taproots
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