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Roots (external structure of roots (structure of individual roots (simple,…
Roots
external structure of roots
seed plants
root system
radicle
single prominent taproot
larger than
lateral roots
can become prominently swollen like taproot
sweet potato
tropical vegetable maniac
branch roots
after germination
becomes the largest in root system
market foods with these
carrots
beets
turnips
eudicots
undergo secondary growth
resulting in wood
aka xylem
in roots
in trunk
monocots
can’t undergo secondary growth
some monocots
do increase their size by
rhizomes
stolons
their horizontal shoots
branch
produce adventitious roots
monocots and some eduicots
fibrous root system
adventitious roots
increase the absorptive and transportive capacities
structure of individual roots
root tip
region where growth in length occurs
root hair zone
epidermal cells zone
root hair
root apical meristem
zone elongation
protected by
root cap
secrete a complex polysaccharide
mucigel
lubricates passage of the root through the soil
rich in
carbohydrates
amino acids
simple
no leaf axils
no leaf scars
no leaves
no axillary buds
elongate only at small meristematic regions
root is embedded in a solid matrix
impossible for all parents to extend at once
internal structure of roots
root apical meristem
root is more orderly than shoot
experiences no disruptions because of
leaf primorda
leaf traces
axillary buds
cells files
extend at center meristem
quiescent center
reserve of healthy cells
if root apical meristem or root cap is damaged
quiescent center becomes active
form new apical meristem
after
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important because root apex is damaged by
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root cap
must have a specific structure and growth pattern
cells
pushed closer to cap
structure and metabolism change dramatically
middle lamella
breaks down and releases cells
cells are crushed by expansion of the root
in layer closest to
root meristem
meristematic
small meristematic
formed at base of root cap
push forward
develop dense starch grains
endoplasmic reticulum
zone of maturation/ root hair zone
merges gradually with
zone of elongation
minerals do not have free access to
vascular tissue
because the innermost layer of cortical cells
differentiates into a cylinder
aka endodermis
cells have tangential walls
the bands of altered walls
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between vascular tissue end endodermis
are parenchyma cells
irregular region
pericycle
root hairs grow outward
increasing absorption of water and minerals
zone of elongation
similar to shoots sub apical meristem region
cells differentiate
into epidermis
in center
provascular tissue
primary phloem
primary xylem
form earliest
closest to meristem
protophloem
protoxylem
behind root apical meristem
region where cells expand greatly
older
further from root tip
metaphloem
metaxylem
tissues are quite permeable
mature portions of the root
passages cells
represent passage ways for absorption of minerals
causes powerful absorption of water and a water pressure
root pressure
other types of roots and root modifications
storage roots
for carbohydrates
accumulate during summer photosynthesis
used to produce a new shoot
in autumn
stem dies
in biennial species
also perennials
roots are the only permanent organs
with permanent shoots
store significant amounts of nutrients
annual plants can survive without storage capacity
