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Chapter 7: Roots (Internal Structure of Roots (Zone of Maturation/ Root…
Chapter 7: Roots
Internal Structure of Roots
Zone of Elongation
cells expand vastly
cells enlarged
differentiation
protoderm
epidermis
provascular tissue
primary xylem/ primary phloem
ground tissue
root cortex
Zone of Maturation/ Root Hair Zone
endodermis
tangential walls
encrusted with lignin and suberin
endodermis becomes waterproof
called Casparian strips
Pericycle
between vascular and endodermis
initiate lateral roots
root hairs grow outward
increasing water absorption
Root Cap
meristematic
files of cells pushed forward
detect gravity
starch settles lower side of cell
Root Apical Meristem
quiescent center
mitotically inactive
resistant to harmful agents
reserve for healthy cells
if damage done
quiescent center cells become active
new formation of apical meristem
Mature Portions of the Root
passage cells
only casparian strips
slow development
root pressure
Other Types of Roots and Root Modifications
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Prop Roots
extensive growth through air
may take months to reach ground
acts as stabilizers
buttress roots
braces the trunk
plate-like
tall
transports nutrients once ground is reached
Contractile Roots
roots firmly anchor in soil
stem is pulled downward
root surface becomes wrinkled
uppermost portions contract
Storage Roots
permanent organs in perennials
phlox
datura
daisies
permanent organs in biennials
beets
celery
carrots
carbohydrates
used to produce new shoot in spring
External Structure of Roots
Organization of Root Systems
taproot
develops from radicle
embryonic root
beats
turnips
carrots
fibrous root system
similar sized roots to taproot
highly branched root system
lateral roots
branched roots
adventitious roots
increases absorptive and transport capacities
Massive absorptive area
Structure of Individual Roots
no leaf axils
no axillary buds
no leaf scars
simple
region of growth in root tip
apical meristem
renewed by cell multiplication
dictyosomes
mucigel secretion
amino acids
aids rapid growth of bacteria
rich in carbohydrates
releases nutrients from soil matrix
thick layer of cells
zone of elongation
cells divide and expand
behind root cap
root hair zone
behind zone of elongation
epidermal cells extend out
narrow trichomes
root hairs
3 more items...
no leaves
Origin and Development of Lateral Roots
cell division in pericycle
small root primordium
organizes into root apical meristem
pushes outward
forms root cap
protoxylem/protophloem differentiates
breaking through endodermis
Other Types of Roots and Root Modifications cont'd
Roots of Strangler Figs
roots cling to bark of host tree
hugs the tree trunk
root doesn't contact soil for months
penetrates soil rapidly once reached
host tree dies and rots away
becomes self supporting tree
encases host tree trunk
grows downward rapidly
Aerial Roots of Orchids
epiphytic
adapted to drought
velamen
root epidermis
waterproof barrier
attached to branches of trees
Mycorrihizae
symbiotic relationship with soil fungi
ectomycorrhizal relationship
fungi hyphae
penetrates between root cortex cells
endomycorrhizal association
fungi hyphae
penetrates root cortex to caspian strip
invades cell
do not break plasma/vacuole membrane
Haustorial Roots of Parasitic Flowering Plants
number of angiosperms are parasites
substrate in the body of another plant
haustoria
highly modified roots
grow around branch/root
shaft cells penetrate host dermis
makes contact with xylem
contacts phloem
performs little to no photosynthesis
carries out own photosynthesis
secrete adhesive
