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Ch 7 Roots (Other Types of Roots and Root Modification (Prop Roots…
Ch 7 Roots
Other Types of Roots and Root Modification
Storage Roots
long term storage for carbs
used to produce new shoot
Prop Roots
bases of corn and grasses
transport additional nutrients and water to stem
place tension on stem and act as stabilizers
buttress roots
upper side grows more rapidly
brace trunk against the wind
Aerial Roots of Orchids
epiphytic
living attached to the branches of trees
on surface on bark and dangle freely in air
rain forest
velamen
several layers of large dead cells
white
water proof barrier
Contractile Roots
more contraction that prop roots
uppermost portion slowly contract
contraction caused by change in cortex cells
root contraction = anchored shoot in soil
Mycorrhizae
ectomycorrhizal relationship
woody forest plants
fungi penetrate outermost cortex but do not invade cell themselves
endomyocorrhizal association
herbaceous
penetrate root cortex
cannot pass casparian strip
Root Nodules and Nitrogen Fixation
nitrogen fixation
chemical conversion of nitrogen into usable compounds
infection thread
penetrates one cell after another to the root cortex
Haustorial Roots of Parasitic Flowering Plants
haustoria
roots of parasitic plants
not all related
grows around small branch
Roots of Strangler Figs
birds eat and deposit onto other trees
possibly doesn't touch soil for years
nutrients from rainwater
penetrate rapidly
grow various angles
can kill host
Internal Structure of Roots
Root Cap
specific structure
meristematic
small cells
cells pushed towards edge of cap
constantly regenerating itself
Root Apical Meristem
orderly
central cells not synthesizing DNA
quiescent center
mitotically inactive central region
becomes active is meristem is damaged
form new apical meristem
Zone of Elongation
behind root apical meristem
cells expand greatly
tissues are permeable
outer most cell is protoderm and epidermis
inner cell is provascular tissue
Zone of Maturation/ Root Hair Zone
root hairs grow outward
greatly increasing absorption of water and minerals
endodermis
cylinder cells
casparian strips
bands of altered walls
control types of minerals that enter xylem water stream
pericycle
vascular tissue and parenchyma cells form irregular region
lateral roots
Mature Portions of the Root
root hairs function for just days and die
passage cells
once thought to be passageways for mineral absorption
root pressure
powerful water absorption and water pressure
Origin and Development of Lateral
initiated by cell division in pericycle
busts through cell
destroys cells of cortex
External Structure of Roots
Organization of Root Systems
enormous absorptive surface
lateral roots/branch roots
small
radicle
embryonic root that develops from taproot
usually becomes largest root
fibrous root system
similar sized roots
adventitious roots
increase absorptive and transport capacities
Structure of Individual of Roots
root cap
protects root apical meristem
constantly worn away
mucigel
secreted by root cap cells
complex polysaccharide
lubricates passage of root through soil
zone of elongation
cells undergo division and expansion
root hair zone
epidermal cells extend out as trichomes
lateral roots emerge
root hairs
form only on part of root that is not elongating
increase root's surface area
