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roots (other types of roots/root modifications (roots of strangler figs #,…
roots
other types of roots/root modifications
storage roots
provide long term storage for carbohydrates
only permanent organs in some plants
carbs stored are used to produce new stems
annual plants can survive without a storage system
prop roots
some roots are capable of growing through air
do make contact with the soil
roots can be strong if it has undergone secondary growth and became woody
act as stabilizers
aerial roots of orchids
many orchids
roots spread alongside the surface of the bark
contractile roots
more common that appreciated
may be by means by which the shoot becomes anchored into the soil
mycorrhizae
in nearly all woody forest plants have an ectomycorrhizal relationship
fungal hyphae penetrate between the outermost root cortex cells, never invade the cells themselves
herbaceous plants have an endomycorrhizal association
hyphae penetrate root cortex as far as epidermis
root nodules and nitrogen fixation
nitrogen fixation- conversion of atmospheric nitrogen into usable nitrogen
root nodule- adjacent cortical cells undergo mitosis
haustorial roots of parasitic flowering
must adhere firmly to their host
penetration- forcing a shaft of cells through host's dermal system
grows inside host
roots of strangler figs
#
grows as epiphytes
grows on host tree
roots sometimes never touch the ground
strangler figs' roots circle the tree, enclosing the tree
internal structure of roots
root cap
root apical meristem is protected by the root cap
cells are small and meristematic
as cells are pushed towards the edge of the cap, structure/ metabolism change
root apical meristem
quiescent center- cells are more resistant to types of radiation and toxic chemicals
inactive central cells form this center
active quiescent center cells form a new meristem
zone of maturation/root hair zone
root hairs grow outwards
a thin cuticle appears to be present
zone of elongations merges with zone of maturation
innermost layer of cortical cells differentiates into the endodermis
development of casparian strips
development of the pericycle between vascular tissue and endodermis
zone of elongation
just behind the root apical meristem
area where cells began to differentiate
outermost cells are protoderm and differentiate into epidermis
the center is provascular tissue which turns into primary xylem and phloem
in zone, tissue are all permeable
short zone- little absoption
mature portions of the root
passage cells- cells that only have casparian strips
root pressure- absorption of minerals via root hairs
origin and development of lateral roots
lateral roots are initiated by cell division in the pericycle
new lateral root destroys cells of cortex and epidermis, breaking the endodermis
root cap is formed by the time the lateral root emerges
lateral roots are initiated deep within the root
external structure of roots
organization of roots systems
lateral roots/ branch roots
lateral roots can produce more lateral roots
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lateral roots can become swollen like taproot
monocots and some eudicots have roots that have a fibrous root system
adventitious roots
do not arise from pre-existing roots
are not radicles
increase absorptive transport capacities of root system
most monocots, rhizomatos, and some eudicots have this feature
structure of individual roots
root tip- where growth in length occurs
growth by discrete apical meristem- only type of longitudinal growth
root apical meristem is protected by the root cap
zone of elongation- cells undergo division and expansion
root hair zone- region where epidermal cells extend out as narrow trichomes
root hairs only form in part of the root that is not elongating
root hairs increase roots surface area
#
lateral roots develop from the pericycle
this is an image of a root cap and its meristem
this is an image of a lateral root and a taproot
this is an image of a prop root
root hairs form in the zone of maturation
this is an image of strangler fig roots
all roots have these structures
