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Roots (Internal Structure of Roots (Zone of Elongation zone of elongation…
Roots
Internal Structure of Roots
Root Apical Meristem
cells originate and extend into the regions of mature root tissues
Zone of Elongation
the outermost layer is protoderm and develops into epidermis
the center is the provascular tissue that later develops into primary xylem and phloem
cells are mostly enlarging
between provascular tissue is the ground tissue
region behind root apical meristem where cells expand greatly
cells are permeable and minerals can pass
Root Cap
provide protection to the root apical meristem
the cells of root cap near root apical meristem are also meristematic and undergo cell division
the cells of root cap detect gravity
Zone of Maturation/ Root Hair Zone
zone of elongation merges with the zone of maturation
apoplastic and symplastic transport occurs
root hairs grow outward increasing absorption of water and minerals
minerals do not have easy access to vascular tissues because of endodermis
Casparian strip controls the minerals going in the xylem water stream
root hair function for several after which they die and regenerate
Other Types of Root and Root Modification
Storage root
carbohydrates stored in the root are used to produce new shoot in the spring
example: carrots, beets, sweet potatoes etc.
long term storage for carbohydrate
Prop roots
the stem of the monocot can produce adventitious roots which are known as prop roots
provide additional water and nutrients to the stem
they act as stabilizers
example: corn, Moroceae, Ficus
Aerial roots of Orchids
roots attached to the branches of the tree
Contractile roots
roots undergo a lot of contraction
example: Oxalis, gladiolus
External Structure of Roots
Organization of Root System
Tap Root
consists of lateral roots or branched roots
most dicots have the tap root system
develops from embryonic root called the radicle
if the plant is perennial and woody, roots also go secondary growth
Fibrous Root
this arises because the radicle dies during or immediately after germination; root primordia at the base of the radicle grow out and form the first stage of fibrous root system
they are also known as adventitious root
most monocots have the fibrous root system
this type of root system increases the absorptive and transport capacities of the root system
Structure of Individual Roots
root apical meristem: root tissues that multiply and form root
zone of elongation: in the region the cell undergoes division and expansion occurs
root cap: thick layer of cells that protects the root apical meristem
root hair zone: a region in which many of the epidermal cells extend out as narrow trichomes
Origin and Development of Lateral Roots
Cell division in pericycle
formation of small root primordium
cortex
growth occurs and destroys cortex and epidermis
lateral root emerge
