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Roots (Other Types of Roots and Root Modifications (Prop Roots (Buttress…
Roots
Other Types of Roots and Root Modifications
Storage Roots
provide long term storage for carbs
Prop Roots
Transport nutrients & water to stem
Buttress roots
upper side grows faster than other parts of root
Aerial Roots of Orchids
epiphytic
living attached to the branches of trees
Roots spread along surface of bark
dangle freely in the air
adapted to drought conditions
Contractile Roots
stem is pulled downward
caused by changes in the shape of cortex cells
shorten and expand radially
Mycorrhizae
symbiotic relationship with soil fungi
both organisms benefit
ectomycorrhizal relationship
fungal hyphae penetrate between
the outermost root cortex cells
never invade the cells
endomycorrhizal association
penetrate root cortex as far as the endodermis
Root Nodules and Nitrogen Fixation
nitrogen fixation
chemical conversion of atmospheric nitrogen
into usable compounds
Haustorial Roots of Parasitic Flowering Plants
Haustoria
roots of parasitic plants that are highly modified
Roots of Strangler Figs
seed germinates
roots cling to the bark of the host tree branch
grow downward
Internal Structure of Roots
Root Cap
Thick layer of cells
Protects root apical meristem
Root Apical Meristem
Root tip that divides cells
Zone of Elongation
region where cells expand greatly
Cells differentiate into a visible pattern
Cells do not mature
Zone of Maturation/Root Hair Zone
Root hairs grow outward
increasing absorption of water and minerals
Endodermis
innermost layer of cortical cells
differentiates into a cylinder
Casparian strips
bands of altered walls
control types of minerals that enter xylem water stream
Mature Portions of the Root
Passage cells
cells that have only Casparian strips
slow to develop
Root pressure
powerful absorption of water, and a water pressure
External Structure of Roots
Organization of Root Systems
Radicle
taproot develops from the embryonic root
Fibrous root system
mass of many similarly sized roots
Adventitious roots
transport capacities of root system
increase absorptive
Structure of Individual Roots
No leaves
No leaf scars
No leaf axil
No axillary buds
Root cap
Thick layer of cells
Protects root apical meristem
Mucigel
lubricates passage of root through soil
Zone of elongation
cells undergo division & elongation
Root hair zone
epidermal cells extend out
narrow trichomes
Root hairs
form only in part of root that is not elongating
Origin and Development of Lateral Roots
Lateral roots
Initiated by:
Cell division in the pericycle
