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Root system
1. Anchoring the plant firmly to a substrate
(soil)
2. Absorbing water and minerals
3. production of hormones
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Three types of root system
1. Tap root
from radicle
Anchorage
In dicot andgymnosperm
Secondary
growth
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2. Fibrous
After the death ofradicle
Delicate and hair-like
Absorption
No prominentenlarged primary root
In monocot
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a. brace root-arise
from main trunk stem
b. prop rootarise
from the lateral branches ofthe main stem.
Brace roots of corn
which arise from themain trunk or stem of
Zea mays
3. Adventitious do not arise from pre-existing roots
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Germinating seed showing the emergence of primary
root from the radicle.
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1. Taproot single prominent
root
2. Lateral or branch roots-
smaller and arise from the
taproot
3. Root hairs
arise fromepidermis, single celled
extension which increase
absorptive area, no line of
demarcation in the epidermal
cells.
4. Root tip- the growing portion
protected by root cap.
structure of roots
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L-section of root shows 3 zones
Zone of maturation
Zone of elongation
Zone of division/apical
meristem
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peripheral
columella
Rootcap
ROOT TIP IS PROTECTED BY A ROOT CAP
procambium
Ground meristem
protoderm
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Root cap
Slime or mucigelsecreted by the
dictyosomes of the root cap
which helps to lubricate the
passage of root through the soil.
Quiescent centeris the mitotically
inactive region of the root apical
meristem, act as reserve of
healthy cells, resistant to toxic
substances and radiations.The three zones of root apical
meristem:
1. protoderm
2. ground meristem
3. procambium
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Cross section of
Ranunculus root (Buttercup)
Internal anatomy of young dicot root
shows three general sections:
1. Dermal region epidermis with
root hairs
2. Cortex outer collenchyma
middle parenchyma
inner endodermis
3. Stele or vascular cyclinder
consists of the following:
1. pericycle outermost layer
2. primary xylem
3. primary phloem
4. vascular cambium
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B
C
D
E
b.Pericycle
c.Primary phloem
d. Vascular cambium
e. Primary xylem
Cross section of young dicot root
Beside is the enlarged view of
Vascular cylinder or stele region.
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Variations in the number of xylem strands in roots
Triarch tetrarch pentarch polyarch
Three xylem poles four xylem poles five xylem poles many xylem poles
eudicot eudicot eudicot monocot
Protostele protostele protostele siphonostele
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Endodermis- controls the
passage of minerals
across the vascular
tissues
Consist of thick-walled cells
(encrusted with
suberin and lignin)
and passage cells
(thin-walled)
Casparian stripsare bandsof lignin and suberin on the radial
walls (top, bottom and side walls)
causing the cell walls to be waterproof.
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Diffusion paths in rootsApoplastic
Water and mineral
diffuses only through
walls in intercellular
spaces
Symplastic
The material has passed
through a plasma membrane
and enters the protoplasm
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Internal anatomy of monocot root Internalanatomy of monocot rootshows 3 regions:
1. Dermal region epidermis
2. Cortex which shows:
a. outer zone of collenchyma
b. middle zone of parenchyma
c. innermost endodermid
3. Vascular Cylinder
a. pericycle
b. xylem
c. phloem
d. pith parenchyma
Siphonostele
a band of vascular
tissues surrounding a
parenchymatous pith.
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Monocot root
Epidermis
Outer collenchyma
Middle parenchyma
Endodermis
PithPericycle
Primary xylem
Primary phloem
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Vascular cylinder of monocot root
siphonostele strands of xylem and phloem
surrounding a parenchymatous pith
pithpith
O i i d D l t f L t l t
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Origin and Development of Lateral roots
Lateral root
Vascular tissues
Expaded epidermis
And cortex of parental
root
Lateral rootis iniatiated by
cell divisions in the
pericycle. As it pushes
outward, it destroys the
cells of the cortex and
epidermis that lie in its
path, ultimately destroying
endodermis.
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Old dicot root
Old dicot root shows two distinct
regions:
1. Region of secondar vascular
tissues which include the
a. secondary phloem
b. vascular cambium
c. secondary xylem
2. Region of periderm layers:
a. phellem or cork
b. phellogen or cork cambium
c. phelloderm or cork parenchyma
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Brace roots in corn plantfor additional supportand absorption
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Water retention 3. velamen in aerial roots of
orchids
photosynthesis 4. chlorophyllous roots
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Movement - Contractile roots of bulbs like onions,
gladiolus, garlic
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Parasitic (haustorial roots) for
absorption
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Buttresses- expanded roots for
great support
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Pneumatophores- breathing roots
of mangove for aeration
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enlarged fleshy tap root- carrots, ube,
tugue, radish, turnips,
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Mycorrhizae- association between
a soil fungus and roots
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Other types and root modifications
8. Protection 8. spiny roots of tugue
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Other types and root modifications
5. root nodules associations between
nitrogen fixing bacteria
and roots of legumes
such as makahiya.
6. Parasitism 6. haustorial roots of
parasitic flowering
plants like mistle toe