Roots Flashcards
main function of roots
- anchorage: stability, proper orientation
- absorption: w/ cylindrical shape that has an ideal surface-volume ratio
- hormone production: produce cytokinin & gibberellin imported to
the shoot system
two classifications of root system based on origin
- taproot system
- fibrous root system
taproot system is derived from an embryonic root called ____. example: radish, carrots, etc.
radicle
the emerging branching of a taproot system is ___ while its primary root grows ____.
lateral; downward
taproot system is common to ____.
eudicots
dense, fine network of roots that arises when radicle dies during or immediately after germination
fibrous root system
fibrous root system grows ____ and is common to ____.
horizontally; monocots
fibrous root system forms roots that develop outside the root system. what is this called?
adventitious roots
external structures of individual roots
- root tip
- root cap
- root hairs
- rhizodermis/epiblem
a root’s external structure that refers to the extreme tip pushing thru the soil
root tip
a root’s external structure that protects the root apical meristem and is formed by terminal _____ cells. this structure constantly worn away and must be renewed.
root cap; parenchyma
the root cap provides lubrication to the root tip as they grow downwards (glycoprotein + pectin)
true
dictyosomes of root cap cells secrete this polysaccharide for lubrication
mucigel
a root’s external structure that provides increased surface area for absorption
root hairs
root epidermis with root hairs that also produces mucigel and never develops cuticle
rhizodermis/epiblem
the rhizodermis/epiblem has stomata. true or false?
false
rhizodermis is different from root pericycle. true or false?
true
rhizodermal cells that give rise to root hairs
trichoblasts
cells that do not produce root hairs
atrichoblasts
internal structures of roots: longitudinal section
- root cap
- zone of division
- root apical meristem
- quiescent zone
- zone of elongation
- zone of maturation
- root hair zone
- zone of primary permanent tissues
- zone of secondary permanent tissues
cells in the central portion divide, and the root cap grows forward. on the edges, cells divide and expand in such a way that the cells flow radially outward. true or false?
true
site of gravisensing found at the center of the root cap containing ____.
columella; amyloplasts
amyloplasts of columella cells
statoliths
statolith-containing cells of columella cells
statocysts
located at the apex of the root proper but is buried under the root cap
root apical meristem
cells produced in the RAM id more orderly than those produced in SAM. true or false?
true
do all cells undergo cell division?
no, some are in quiescent stage
mitotically inactive central region where cells are resistant to various types of harmful agents and act primarily as a reserve of healthy cells
quiescent center
are nuclei in the quiescent center radioactive?
no
where most cells continue to enlarge; cells begin to differentiate into a visible
pattern
zone of elongation
zone of elongation differentiation:
protoderm: ___
procambium: ___
ground meristem: ___
rhizodermis
vascular cylinder
root cortex
tissues in the zone of elongation are all ___.
permeable
where several processes occur more or less simultaneously:
* root hairs grow outward
* thin cuticle appears to be present in some micrograph
* cortex continues to enlarge; able to
transfer minerals from epidermis to the
vascular tissues
zone of maturation
internal structure of roots: cross section
- rhizodermis
- cortex
- endodermis
- pericycle
- stele (vascular cylinder)
the outermost region of a root’s cross section
rhizodermis
ground tissues between rhizodermis and vascular tissues derived from ____.
root cortex; ground meristem
innermost cortical layer with casparian strip
endodermis
in the zone of maturation, minerals
do not have a free access to the
vascular tissues due to endodermis. true or false?
true
fuunction of casparian strip
controls the types of minerals that enter the vascular tissues
casparian strip is made up of what components?
lignin
suberin
four routes in transporting materials from root hairs to vascular tissues
- apoplastic route
- symplastic route
- transmembrane route
- endodermal route
describe apoplastic route
thru cell wall
describe symplastic route
thru plasmodesmata
describe transmembrane route
from the apoplastic route to the protoplasm via symplast
describe endodermal route
casparian strip blocks passage of water and minerals; mineral in symplast/entering the pathway by crossing the plasma membrane of an endodermal cell can pass
parenchyma cells between endodermis and vascular tissues; gives rise to lateral roots
pericyclela
lateral roots (pericycle) are derived endogenously which means what?
they are derived from the root interiors/deep within the roots
the central vascular cylinder of the root
stele
stele is bound by the ___ to the exterior.
endodermis
stele contains what components?
xylem
phloem
some parenchyma
pericycle
describe a eudicot stele
xylem form a solid mass at the center surrounded by phloem
eudicot stele has a pith. true or false?
false. it has no pith
inner wide cells in eudicot stele
metaxylem
outer narrow cells in eudicot stele
protoxylem
phloem occurring outside the eudicot stele
protophloem
phloem occurring inside the eudicot stele
metaphloem
describe monocot stele
strand of xylem and phloem are scattered in the ground tissues = atactostele
type of roots based on support
- buttress: plate-like and brace the trunk against being blown over by wind; rubber trees
- brace: thrives in intertidal marshes and strong currents; provides stability; mangrove; ex: rhizophoraceae
- prop roots: provide support and help aerate those in low o2 substrate; observed in monocots; ex: pandanaceae
- clinging roots: roots spread along the surface of the bark; ex: orchid
- strangling/drop roots: roots cling to the bark of host tree and grow rapidly downward; ex: strangler fig
type of roots based on storage
- food storage: manihot esculenta
- water storage: desert plants; ex: turbinicarpus
- contractile roots: plants with bulbs; ex: hyacinthus ep.
- nodular roots: legumes; ex: pea roots
modified roots for protection may possess ___ to deter herbivores
spines
modified roots for aeration allow root to perform ___; common in pneumatophores of mangroves
gas exchange
modified roots for photosynthesis have _____ capable of photosynthesis; common in aerial roots of orchids; ex: taeniophyllum (orchidaceae)
chlorophyllous
modified roots for reproduction have ___ roots that give rise to another plant; ex: kalanchoe; kataka-taka
adventitious
plants that cling to rocks
lithophyte
plants found in branches/trunk
epiphyte
underground storage organs of plants
bulb
