Download Lec 5: Stems

4/24/2014
Stems
BI 103: Plant & Animal A & P
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Outline:
Stems: monocots vs
dicots--handout
Woody plant growth
Discussion problems
Monocots & Dicotsoutside
Learning Objectives
What are the differences between monocots and
dicots?
What is the functions of the plant stem?
How are specific cells and tissues adapted in the stem
in order to help it function?
How are tissues in the stem different from the leaves
& root?
How does the process of transpiration move water
through the plant?
How does secondary growth occur in woody plants?
What are examples of specialized stems?
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Plant Anatomy: Vegetative Organs
Leaves:
Photosynthesis
Gas exchange
Light absorption
Stem:
Support
Transport
Storage
Roots:
Anchorage
Storage
Transport
Absorption
Form = Function
Tissue Patterns in Stems
Cotyledons - Seed leaves attached to
embryonic stems
Function: Store food needed by young seedling
1. Dicotyledons (Dicots) - Flowering plants
that develop from seeds having two
cotyledons
2. Monocotyledons (Monocots) - Flowering
plants that develop from seeds with a single
cotyledon
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Number of
Cotyledons
Leaf
Venation
Vascular
bundle pattern
in stem
Number of
Plant Anatomy: Mocot vs.
Flower Parts
Monocot
Dicot
Roots
Dicot
F.
I.
B.
H
.
G.
C.
E
.
D.
A.
J.
Plant Anatomy: Monocot vs.
Dicot
Activity: In lab groups, identify whether
each picture is associated with a
monocot or dicot. Write number
associated with pic in correct column.
~~5 minutes
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Number of
Cotyledons
Leaf
Venation
Vascular
bundle pattern
in stem
Number of
Plant Anatomy: Mocot vs.
Flower Parts
Monocot
Dicot
Roots
Dicot
F.
I.
H
.
B.
G.
C.
E
.
D.
J.
A.
Plant Anatomy: Monocot vs.
Dicot
Number of
Leaf
Cotyledons Venation
Monocot
Roots
Vascular
bundle pattern
in stem
Number of
Flower Parts
G.
B.
D.
I.
H.
Dicot
F.
C.
J.
E.
A.
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Organs: STEM
DICOT
MONOCOT
Herbaceous Dicot Stems
Have discrete vascular bundles arranged in a cylinder.
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Tissue Patterns in Stems Monocots
Have neither a vascular cambium nor a cork
cambium.
Produce no secondary vascular tissues or cork
Primary xylem and phloem in discrete vascular bundles
scattered throughout the stem
– Vascular bundles
oriented with xylem
closer to center of
stem and phloem
closer to surface.
Cross
section
– Parenchyma (ground
of
tissue) surrounds
monocot
stem
vascular bundles.
Typical herb vascular bundle
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Transpiration
Transpiration
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Specialized Stems:
Rhizome
1. Rhizome:
underground stem
Ferns
Potatoes
Ginger
Specialized Stems: Runners
2. Runners:
Horizontal stems
that grow above
ground and have
long internodes.
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Specialized Stems
3. Stolons – Arching
stem produced beneath
the surface of the
ground.
Dogwood:
Cornus serecia
Specialized Stems
4. Corms - Resemble
bulbs, but composed
almost entirely of stem
tissue, with papery
leaves
Store food
Crocus and gladiolus
5. Cladophylls Flattened, leaf-life
stems of cactus
Prickly pear cactus
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Stem Growth
1. Primary Growth
A. Apical meristem – increases length
B. Ground meristem – makes cortex & pith
2. Secondary growth
A. Vascular cambium – produces
secondary Xylem & Phloem
B. Cork cambium– produces bark to
reduce water loss & protects stem (in
woody plants only).
Primary vs. Secondary growth
Primary Growth
 All plants
Secondary Growth
 Woody plants only
 (only Dicots)
 Vertical growth
 up or down
 Horizontal growth: girth
 Plant gets taller
 Plant gets wider
 Where: Meristem tissue
in roots & buds
 Where: vascular
cambium, cork cambium
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Origin and Development of Stems
Narrow band of cells between the primary
xylem and primary phloem is the vascular
cambium.
Cells produced by the vascular cambium become
the secondary xylem toward center and
secondary phloem toward surface.
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Woody plants
Joshua tree (Yucca
• Plants brevifolia)
with secondary
growth
is
NOT a woody plant
• Think bark
because it doesn’t have
secondary growth!
External Form of A Woody Twig
Deciduous trees and
shrubs (lose all leaves
annually) - After
leaves fall, have
dormant axillary buds
with leaf scars below
Bundle scars mark food
and water conducting
tissue within leaf scars.
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