Roots
External structure of Roots
Organization of Root System
Structure of Indivudual Roots
taproot
develops from embryonic root called the radicle
consists of lateral roots or branched roots
if the plant is perennial and woody, roots also go secodary growth
Fibrous root
most monocots and some dicots have it
this arises because the radicle diesduring or immediately after germination; root primordia at the base of the radicle grow out and form the forst stage of fibrous root system
they are also known as adventitious root
this type of root system increases the absorptive and transport capacities of the root system
most monocots have the tap root system
root cap: thick layer of cells that protects the root apical meristem
root apical meristem: root tissues that multiply and form root
zone of elongation: in the region the cell undergoes division and expansion occurs
root hair zone: a region in which many of the epidermal cells exend out as narrow trichomes
Internal Structure of Roots
Root cap
provide protection to the root apical meristem
the cells of root cap near root apical meristem are also meristemetic and undergo division
the cells of root cap detect gravity
Root Apical Meristem
cells originate and extend into the regions of mature root tissues
Zone of Elongation
region behind root apical meristem where cells expand greatly
cells are mostly enlarging
the outermost layer is protoderm and develops into epidermis
the center is the provascular tissue that late develops into primary xylem and phloem
between provascular tissue is the ground tissue
cells are permeable and minerals can pass.
Zone of maturation/ Root hair zone
root hairs grow outward increasing absorption of water and minerals
zone of elongation merges with the zone of maturation
apoplastic and sympalstic transport occurs
minerals donot 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
Origin and development of lateral roots
cell division in pericycle
formation small root primordium
cortex
growth occurs and destroys cortex and epidermis
lateral root emerge
Other types of Root and Root Modification
Storage root
long term storage for carbohydrate
carbohydrates stored in the root are used to produce new shoot in the spring
example: carrot, beets, sweet potatoes etc.
Prop Roots
the stem of 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, Ficus; Moraceae
aerial roots of orchids
roots attached to the branches of the tree
contractile roots
roots undergo alot of contraction
Example: oxalis, gladiolus