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ROOTS (Internal structure of roots (zone of elongation (the outermost…
ROOTS
Internal structure of roots
root apical meristem
Quiescent center
mitotically inactice center region
these cells are more resistant to various types of harmful agents
radiation
toxic chemicals
act priarily as a reserve of healthy cells
if part of root apical meristem is damaged, quiescent center cells become active and form new apical meristem
after a new apical meristem is established, its central cells become inactive forming a new quiescent center
zone of elongation
just behind root apical meristem
region where cells expand and enlarge
some meristematic activity continues
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the outermost cells are protoderm
differentiate into epidermis
center cells make up provascular tissue
develop into primary xylem or primary pholem
cells farther from the root tip, older, larger, develop into metaxylem and metapholem
cells between the provasscular tissue and the protoderm, make up ground tissue
these differentiate into root cortex
Zone of Maturation
also called root hair zone
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root hairs grow outward
greatly increases absorption of water and minerals
in some a thin cuticle appears to be present on root epidermal cells
the zone of elongation gradually merges with the zone of maturation
no distinct boundary exists because the differences between the two represent the the gradual continued differentiation of the cells
cortex cells
continue to enlarge
trasfer minerals from the epidermis to the vascular tissue
done through:
diffusion through walls and intercellular spaces
apoplastic transport
absorption into the cytoplasm of a cortical cell and then transferal from cell to cell
Mature portions of the root
root cap
function:
to remain in place
provide effective protection for the root apical meristem
meristematic
undergoing cell division with transverse walls and forming files of cells that are pushed forward.
cells are small and meristematic when first formed at base of root cap
as pushed forward, they develop dense starch grains and their endoplasmic reticulum becomes displaced to the forward end of the cell
External structure of roots
Organization of root systems
branch roots
same as lateral roots
radicle
Embryonic Root
lateral roots
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smaller roots
fibrous root system
many similarly sized roots
adventitious roots
roots that do not arise on pre-existing roots
structure of individual roots
root cap
thick layer of cells protecting the root apical meristem
mucigel
complex polysaccharide secreted by root cap of dictyosomes
root hair zone
a region in which many of the epidermal cells extend out as narrow trichomes
zone of elongation
just behind the root cap and the root apical meristem
root hairs
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Origin and Development of Lateral Roots
Other Types of Roots and Modifications
