Lec 5: Stems
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4/24/2014 1 Stems BI 103: Plant & Animal A & P Outline: 1. Stems: monocots vs dicots--handout 2. Woody plant growth 3. Discussion problems 4. Monocots & Dicots- outside 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?
Transcript of Lec 5: Stems
4/24/2014
1
Stems BI 103: Plant & Animal A & P
Outline:
1. Stems: monocots vs
dicots--handout
2. Woody plant growth
3. Discussion problems
4. Monocots & Dicots-
outside
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:
Roots:
Stem:
Form = Function
Photosynthesis
Gas exchange
Light absorption
Anchorage
Storage
Transport
Absorption
Support
Transport
Storage
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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Plant Anatomy: Mocot vs.
Dicot
A.
B.
C.
D.
E
.
F.
H
. G.
J.
I.
Number of
Cotyledons
Leaf
Venation Roots
Vascular
bundle pattern
in stem
Number of
Flower Parts
Monocot
Dicot
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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Plant Anatomy: Mocot vs.
Dicot
A.
G.
C.
D.
E
.
F.
H
. B.
J.
I.
Number of
Cotyledons
Leaf
Venation Roots
Vascular
bundle pattern
in stem
Number of
Flower Parts
Monocot
Dicot
Plant Anatomy: Monocot vs.
Dicot Number of
Cotyledons
Leaf
Venation Roots
Vascular
bundle pattern
in stem
Number of
Flower Parts
Monocot
Dicot
G.
B.
C.
D.
J.
F.
E.
H. I.
A.
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DICOT MONOCOT
Organs: STEM
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.
– Parenchyma (ground
tissue) surrounds
vascular bundles.
Cross
section
of
monocot
stem
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
Vertical growth
up or down
Plant gets taller
Where: Meristem tissue
in roots & buds
Secondary Growth
Woody plants only
(only Dicots)
Horizontal growth: girth
Plant gets wider
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
• Plants with secondary growth
• Think bark
Joshua tree (Yucca
brevifolia) is
NOT a woody plant
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.
