Download The Root

General Biology lab
Lab 12 & 13
Parts of Plant
• Three Basic Plant Organs:
1. Roots
2. Stems
3. Leaves
Leaf
Shoot
system
Stem
Root
system
• The stem
– is a part of the plant that holds up other structures such as the
leaves and flowers.
• Function of stem
• Stems support photosynthetic leaves and reproductive
structures .
• Stems supply water and minerals to shoots via the xylem
and photosynthate to roots via the phloem.
•
The Dicotolydonous Stem (Dicots
stems)
Component of dicot stem:
– Epidermis
– Ground tissue (parenchyma, collenchyma, sclerenchymta,
cortex, pith),
– Vascular tissue (xylem, phloem).
• Protoxylem vessels: are the smallest vessels, their typical location is
towards the pith.
• Metaxylem vessels: are the larger vessels, typical location is towards
the cortex.
• Fascicular cambium:
– is the area between the primary xylem and phloem.
• It is the vascular cambium found within the vascular
bundle.
• It cells were derived from procambium and maintain their
ability to undergo cell division.
Epidermis: reduce evaporation, gas exchange
Cortex: photosynthesis, collenchyma support
Vascular Bundles: conduction
Pith
outside
Vascular Bundle:
conduct CH2O away from leaf
to center
outside
Phloem Fibers: support
Functional Phloem:
Vascular Cambium:
add 2° Xylem and 2° Phloem
Xylem:
to center
conduct minerals up from soil
The Monocot stem
• Component of monocot stem:
– Epidermis
– Ground tissue (parenchyma, collenchyma, sclerenchymta)
– Vascular tissue (xylem & phloem).
• Random arrangement of the vascular bundles, and its
surrounding by sclerenchyma. These vascular bundles are
closed bundles with no are of cambium.
Stems
• In most monocot stems, the vascular bundles are scattered
throughout the ground tissue, rather than forming a ring
Phloem
Xylem
Ground
tissue
Ground tissue
connecting
pith to cortex
Pith
Epidermis
Key
to labels
Cortex
Epidermis
Vascular
bundle
Dermal
Vascular
bundles
Ground
1 mm
(a) Cross section of stem with vascular bundles forming
a ring (typical of eudicots)
Vascular
1 mm
(b) Cross section of stem with scattered vascular bundles
(typical of monocots)
The Root
• The Root
– is the organ of a plant that typically lies below the surface of the
soil.
• The root must fulfill two fundamental roles:
– absorption of water and nutrients.
– anchorage.
• Further, in many plants, roots function to store food.
The Dicotolydonous root (Dicots roots)
• An epidermis
– surrounds the entire root.
• The vascular tissue
– is in the very center of the root.
• The ground tissue
– surrounding the vascular cylinder is the cortex.
• The central region of vascular tissue is termed the
vascular cylinder.
• Note that the innermost layer of the cortex is stained red. This
layer is the endodermis which have casparian strips .
– The endodermis was derived from the ground meristems and is
properly part of the cortex.
• Xylem fills the very middle of the vascular cylinder .
• Outside of this cylinder of xylem and phloem, located
immediately below the endodermis, is a region of cells called
the pericycle. these cells give rise to lateral roots and also
important in secondary growth.
The monocotolydonous roots (monocot roots)
• The roots monocots are organized into a cortex, with
primary xylem and primary phloem alternating around
central pith.
• The endodermal cells have casparian strips.
• A uniseriate partly sclerified pericycle occurs between the
endodermis and the outermost vascular elements.
• Origin of branch roots
• Roots don’t have leave, nodes or axillary buds. In roots,
branching occurs from the pericycle.
• Observe the demonstration series of slides on the side
bench of lateral branching in salix (willow)
Plant Growth - Roots
Epidermis
Cortex
Endodermis
Vascular
cylinder
Pericycle
Core of
parenchyma
cells
Xylem
100 µm
Phloem
100 µm
(a) Root with xylem and phloem in the center
(typical of eudicots)
(b) Root with parenchyma in the center (typical of
monocots)
Endodermis
Pericycle
Key
to labels
Dermal
Ground
Vascular
Xylem
Phloem
Monocots and dicots differ in the arrangement of
vessels in the roots and stems
Dicots
Monocots
Stem
Root