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Chapter 7 (internal structure of roots (zone of elongation (center is…
Chapter 7
internal structure of roots
root cap
meristematic
cells closest to root meristem
forming files of cells
cells undergoing cell division
root apical meristem
where cells originate
more orderly than shoot
central cells don't synthesize DNA
central area is inactive
inactive area is called Quiescent center
cells more resistant to radiation
reserve of healthy cells
can create apical meristems
zone of elongation
great cell expansion
area behind apical meristem
some meristematic activity
similar to shoots subapical meristem
cells differentiate into pattern
outermost cells are protoderm
differentiate into epidermis
center is provascular tissues
develop into primary xylem
develop into primary phloem
tissues quite permiable
zone of maturation
root hairs grow outwards
increases water absorption
increases minerals
thin cuticle appears to be present
zone of elongation emerges
no boundary between zones
minerals don't have access to vascular tissue
mature portions of the root
root hairs die and degenerate
causes water absorption to decrease
water absorption doesn't stop entirely
endodermis cells don't change
cells with only casparian strips
called passage cells
slow to develop
powerful absorption of water
root pressure
when roots keep water in
External structure of roots
prominent taproots
carbohydrate storage
main root anchor
grows straight down
tapering gradually
grows lateral or branch roots
lateral roots grow more lateral roots
results in highly ramified set
lateral roots can swell
radicles
what taproots develop from
AKA embryonic roots
present in the seed
grows after germinization
Carrots, beets, turnips
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secondary growth
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lateral root swelling
tree bark
monocots and dicots
fibrous root system
formed by root primordia
root primordia grows from radicle
adventitious roots
increase absorptive transport
no radicles
don't arise on pre-existing roots
mass of same sized roots
radicle dies after germination
Dicots
perinneal
secondary growth
functional wood in roots
functional wood in trunk
causes increase in leaves
increases # of roots
monocots
no secondary growth
after stem forms-
set # of vascular bundles
Set # of tracheary elements
Set # if sieve tubes
cant increase conducting capacity
extra leaves cant get water
increase size by stolons or rhizomes
horizontal roots produce adventitious roots
roots in new stem tissue
transports water into shoot
they can produce more roots this way
individual root structure
more simple then stems
root tip
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where growth occurs
growth by discrete apical meristem
localized growth
root cap
thick layer of cells
protects root apical meristem
constantly worn away
always rejuvenating
mucigel
root cap secretion
allows lubricated passage
makes soil release ions
rich in amino acid
rich in carbohydrates
Zone of elongation
behind the root cap and apical meristem
only a few millimeters long
cells undergo division and expansion
root hair zone
behind zone of elongation
epidermal cells extend into trichomes
other types of roots/ root modification
storage roots
long term storage for carbohydrates
biennial and perennials
roots are the only permanent part
most stem dies in autumn
carbs stored create new shoot
prop roots
monocots
wider stems with more vascular bundles
adventitious roots extend to soil
extensive growth in air
act as a stabalizer
transport additional materials
secondary growth makes stornger
Ariel roots of orchids
many orchids are epiphytic
meaning living attached to trees
roots dangle from branches
adapted for drought
velamen doesn't allow water to escape
contractile roots
after anchoring, roots contact
pulls stem downward
contraction due to cortex cells
keeps stems at proper depth
Bulbs, Corms, Rhizomes
origin and development of lateral roots
initiated by cell division in pericycle
more densely cytoplasmic
lateral roots initiated within root
secondary growth in the form of wood
storage roots are used by taproots
interworking of the root cap
