The angiosperms

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The angiosperms
Greek angeion case sperma seed
By far the most diverse group of plants that has
ever existed with more than 240,000 different
species.
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Why are there so many species
Angiosperms
Origin of angiosperms
Time scale
Mosses
Ferns
Why are there so many species?
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Gondwana
Angiosperms probably originated in the tropics
West Gondwana, equivalent to modern South America
plus Africa
Gondwanaland
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Principal differences between Gymnosperms and
Angiosperms
1. Leaves have finely divided venation
2. Xylem contains vessels as well as tracheids
and parenchyma
3. Phloem contains sieve elements with companion
cells
4. Ovules protected within an enclosed structure
5. Double fertilization to produce diploid
zygote and triploid endosperm nucleus
6. Generally hermaphrodite flowers and cross
pollinating (70)
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Monocotyledons and Dicotyledons

Examples
Grasses Triticum, wheat Zea mays corn lillies
Oak trees, Quercus Coleus Lycopersicon,
tomato Potato, Solanum tuberosum
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Angio-Gymno 1. Leaves have finely divided
venation
A dicotyledon
Typically veins are distributed such that
mesophyll cells are close to is a vein. The
network of veins also provides a supportive
framework for the leaf.
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Leaf of a monocotyledon plant
The major venation follows the long axis of the
leaf and there are numerous joining cross veins
so that, as with the dicotyledon, mesophyll cells
are always close to a vein.
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Diagram of a dicot leaf
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Tomato leaf
Upper epidermis
Pallisade parenchyma chloroplasts visible around
cell periphery
Longitudinal section through a vascular bundle
Xylem vessel annular thickening around cell wall
Phloem
Bundle Sheath
Spongy parenchyma
Lower epidermis
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Ficus leaf
Ficus, the fig, is a xerophyte
Collenchyma forming a hypodermis
Pallisade parenchyma
Spongy parenchyma
Vascular bundle
Collenchyma above and below the vascular bundle
Lower epidermis
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Leaf cross section of Bouteloua
Upper epidermis
Bulliform cells
Collenchyma
Xylem
Parenchyma with chloroplasts
Lower epidermis
Bundle sheath cells with chloroplasts
Phloem
Sclerified fibers
http//www.uri.edu/artsci/bio/plant_anatomy/99.htm
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C3 and C4 photosynthesis?
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Leaf cross section of Zea mays ("corn").
Upper epidermis
Bulliform cells
Xylem
Bundle sheath cells with chloroplasts
Parenchyma with chloroplasts
Lower epidermis
Phloem
http//www.uri.edu/artsci/bio/plant_anatomy/99.htm
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Anatomical separation of the C4 photosynthesis
component processes
Bundle sheath cells filled with chloroplasts.
CALVIN REACTION SITE
Parenchyma filled with chloroplasts
Xylem
Phloem
Carbon skeleton compounds return to parenchyma
C4 acids synthesized in the parenchyma move to
the bundle sheath
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Ways in which Angiosperms are different from
Gymnosperms
Angio-Gymno 2. Xylem contains vessels as well
as tracheids and parenchyma
Angio-Gymno 3. Phloem contains sieve elements
with companion cells
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Angiosperm xylem and phloem
In Angiosperms Xylem and Phloem contain more
specialized cells than in Gymnosperms as well as
containing Fibers and Parenchyma.
Xylem Vessel Elements
Phloem Sieve elements, Companion cells
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Vessels
Tracheids provide better support but less slower
rates of water conduction than vessels
Wide vessel element This kind of cell is better
for fluid conduction than physical support.
A vessel is composed of several vessel elements
These vessel elements have completely perforated
end walls
Elongated vessel element This cell provides
moderate support and fluid conduction.
Tracheids lack perforation plates but their end
walls contain numerous pits.
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Phloem
Companion Cells (CC)
Sieve Tube Members (STM)
Cucurbita phloem
(cucumber)
Sieve plate
STMs and CCs develop from the same progenitor
cell. STMs, are columnar cells and unite
vertically to form a Sieve Tube. STMs have no
nucleus at maturity and depend on CC to regulate
physiological processes. Each STM has one to
several CC. The Sieve Plate is analogous to a
Perforation Plate in vessels.
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Dicotyledon stem cross section
J. D. Mauseth
Angelica stem transverse section is typical of a
dicotyledon plant without secondary thickening.
Stems as diverse as slender vines, fat cacti, or
as modified as potato tubers all have this
organization, but with various zones modified.
Cacti are so wide because they have an
exceptionally thick cortex. Potato tubers have a
gigantic pith and almost no wood.
Four zones 1) epidermis 2) cortex, in many
species the outermost part is a hypodermis 3)
ring of vascular tissues, usually a ring of
vascular bundles 4) pith.
We eat Angelica in confectionary
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Transverse section of corn stem, Zea mays.
Transverse section of corn stem, Zea mays.
This is the organization of monocot stems
numerous vascular bundles distributed throughout
a tissue that may be either parenchyma or
collenchyma
Vascular bundles
There are four parts 1) epidermis 2) cortex
with or without part differentiated into a
hypodermis 3) vascular bundles 4) a matrix of
parenchyma called conjunctive tissue or pith
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Sections you need to have read
17.10, 31.2 through 31.6
Courses that deal with this topic
Botany 443 Origins of our modern floras