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Chapter 8: Roots - Coggle Diagram
Chapter 8: Roots
other types of roots and root modifications
storage roots
provide long-term storage for carbohydrates
produces new shoot in spring
permanent in biennial species
live for 2 years
beets
carrots
celery
permanent in perennials
Datura
Phlox
many daises
prop roots
extensive growth through air
may grow for months before reaching the ground
buttress roots
tall plate-like roots
braces trunk
arial roots of orchids
epiphytic
living attached to branches or trees
live in rainforests but adapted to drought conditions
root epidermis called velamen
composed of several layers of large dead cells (white in appearance)
acts as waterproof barrier for sides of root.
mychorrhizae
symbiotic relationship with soil fungi (both organisms benefit)
ectomycorrhizal relationship
wood forest plants
fungal hyphae
slender thread-like cells
penetrate between the outermost root cortex cells but never invade them
endomycorrhizal relationship
herbaceous plants
fungal hyphae penetrate root cortex as far as epidermis
cannot pass Casparian strip
contractile roots
extend through soil/ firmly anchored
uppermost portions slowly contract
stem is pulled downward
root nodules and nitrogen fixation
scarcity of nitrogenous compounds in soil
one of the main growth limiting factors
nitrogen fixation
some prokaryotes can use N2 by incorporating it into amino acids and nucleotides
when they die, the nitrogenous compounds are available to plants
plants/legumes form symbiotic relationship with
Rhizobium
nitrogen fixing bacteria
infection thread
tubelike invagination of plant cell wall
extends to the root"s inner cortex
reaches cytoplasm
proliferates rapidly
root nodule
may remain simple or could become complex
haustoria roots of parasitic flowering plants
a number of angiosperms are parasites on other plants
substrate is the body of a plant
haustoria
highly modified
secrete adhesive to adhere to host plant
grow around small branch or root
penetration occurs two ways
forcing shaft of cells through host's dermal system
expanding the haustorium radially
cracks host's epidermis
after penetration, parasitic cells make contact with the host's xylem
carry out their own photosynthesis
contact both xylem and phloem and perform little/no photosynthesis
roots of strangler figs
roots cling to bark of host tree
grow rapidly downward
hug trunk of host tree
once the soil is reached (may take months for roots to reach soil)
penetrate rapidly
encircle host's tree trunk
host tree finally dies
strangler fig becomes self-supporting tree
branch profusely
Internal structure of roots
root cap
meristematic
cells on edges grow toward side and proliferate
forms files of cells that are pushed froward
develop dense starch grains
endoplasmic reticulum becomes displaced to forward end of cell
detect gravity because of starch grains settling on lower side of cell
root apical meristem
quiescent center
mitotically inactive central region
more resistant to various types of harmful agents
radiation
toxic chemicals
reserve for healthy cells
if root apical meristem or root cap is damaged
quiescent center becomes active and forms new apical meristem
zone of elongation
just behind root apical meristem
cells expand greatly
cells begin to differentiate into a visible pattern
protoderm
outermost cells
differentiate into epidermis
provascular tissue
in center
cells develop into primary xylem and primary phloem
ground tissue
between pro vascular tissue and protoderm
differentiates into root cortex
zone of maturation/rooh hair zone
root hairs grow outward
greatly increases absorption of water and minerals
endodermis
tangential walls
closest to vascular tissue of cortex
ordinary thin primary walls
radial walls
encrusted with lignin and suberin
waterproofs wall
Casparian strips
controls minerals in xylem water stream
impermeable
mature portions of the root
passage cells
have only Casparian strips
slow to develop
root pressure
absorption of minerals in root hair zone causes powerful absorption of water and water pressure
External Structure of Roots
Organization of root systems
roots have an enormous absorptive surface
highly branched system
lateral roots
branched roots
taproot
develops from radicle
embryonic root
grows extensively and becomes largest root in the system
carrots
beets
turnips
fibrous root system
mass of many similarly sized roots
adventitious roots
increase absorptive and transport capacities of system
Structure of individual roots
simple
no leaves
no leaf scars
no leaf axils
no axillary buds
root tip is the region where growth in length occurs
apical meristems
extreme tip pushes through soil
protected by thick layer of cells
root cap
constantly being worn away
must be renewed by cell multiplication
dictyosomes of root cap cells secrete complex polysaccharide mucigel
lubricates passage of root through soil
rich in carbohydrates and amino acids
foster rapid growth of soil bacteria around root tip
releases nutrients from soil matrix
zone of elongation
just behind root cap/apical meristem
few millimeters long
cells undergo division and expansion
root hair zone
region where many epidermal cells extend out as narrow trichomes
behind zone of elongation
1 more item...
origin and development of lateral roots
initiated by cell division in the pericycle
small root primordial organizes itself into root apical meristem and pushes outward
breaks through epidermis
forms root cap/ first protaoxylem and protophloem differentiate
