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Roots
Chapter 5
Botany
How Roots Develop
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
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
Seed germinates into radicle
From radicle ( immature plantlet)
Forms first root
Becomes thick taproot with adventitious
roots or a fibrous root system
Root Structure
Composed of four zones:
1.
2.
3.
4.
Root cap
Region of cell division
Region of elongation
Region of maturation
Root Cap
Thimble shaped
mass of parenchyma
cells that cover the
tip of each root
Root Cap Functions
1. Protect delicate young root
2. Make slime for lubrication of root
3. Promote bacteria growth-increases
Nitrogen reserve
4. Cells live less than 1 week
5. Regenerates cells
6. Contains amyloplasts (starch grains)
7. Act as gravity sensors
Gravitropism
 Plant roots grow
“down”
 If you move a plant
the roots turn toward
the center of the
earth within 30
minutes
Region of Cell Division
1.
2.
3.
4.
5.
Apical meristem-region of active mitosis
Makes root cap
Cell division occurs along cap edges
Cells divide every 12 to 36 hours
Cells are cube shaped with large nuclei
and small vacuoles
Apical Meristem
Divided into three areas:
1.
2.
3.
Protoderm becomes
epidermis
Ground meristem
produces parenchyma
cells of cortex
Procambium produces
primary xylem and
primary phloem
Region of Elongation
 Merges with apical meristems and
extends from root tip
 Cells grow several times in original length
and width
 Remainder of root remains stationary as
secondary tissues and increase root girth
Region of Maturation
 Cells differentiation into cell types
 Also know as region of differentiation
 Root-hair zone
Root Hairs
 Adhere to soil particles
 Increase absorptive root
surface
 Tubular extensions of
epidermal cells-not all
separate cells
 Very numerous look like fine
down
 Transplanted plants lose root
hairs reduce ability to absorb
water and transplanted plants
must have shade water and
pruning.
Interior of Root
 Cuticle-thick cuticle on
root hairs and allows
water to be absorbed
and doesn’t against
bacteria
 Cortex- Parenchyma
cells
 Store food
 Tissue-many cells thick
 Endodermis -Cortex of
root has suberin cell
walls, suberin bands
called Casparian strips
on the radical and
transverse walls,
prevents water leaking
 Vascular Cylinder-lies to
inside of endodermis,
conducts food and water
Vascular Cylinder
 Pericycle –cells continue to divide and
make lateral branch roots
 Xylem conducts water and dissolved
minerals
 Phloem conducts dissolved glucose from
the leaves to the roots
Vascular Cylinder
 Woody plants-cork cambium gives rise to
cork cells which are dead at maturity and
impervious to moisture
 Growth –Determinate growth stops.
Indeterminate growth occurs where growth
added season after season