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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.
Angiosperms
Ferns
Mosses
Why Origin
are there
of so
angiosperms
many species
Time scale
Why are there so
many species?
Angiosperms probably originated in the tropics
West Gondwana, equivalent to
modern South America plus Africa
Gondwana
Gondwanaland
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%)
Monocotyledons and Dicotyledons
Examples
Grasses
Triticum, wheat
Zea mays corn
lillies
Oak trees, Quercus
Coleus
Lycopersicon,
tomato
Potato, Solanum
tuberosum
Angio-Gymno 1.
Leaves have finely divided venation
Coleus leaf cleared of cell contents and with xylem stained
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.
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.
Diagram of a dicot leaf
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
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
Leaf cross section of Bouteloua
Upper epidermis
Bulliform cells
Collenchyma
Xylem
Parenchyma with
chloroplasts
Sclerified fibers
Lower epidermis
Phloem
http://www.uri.edu/artsci/bio/plant_anatomy/99.html
Bundle sheath cells
with chloroplasts
… C3 and C4 photosynthesis?
Leaf cross section of Zea mays ("corn").
Bulliform cells
Upper epidermis
Xylem
Bundle sheath cells
with chloroplasts
Parenchyma with
chloroplasts
Phloem
http://www.uri.edu/artsci/bio/plant_anatomy/99.html
Lower epidermis
Anatomical separation of the
C4 photosynthesis
component processes
Parenchyma filled
with chloroplasts
Bundle sheath cells
filled with
chloroplasts.
CALVIN
REACTION SITE
Xylem
Phloem
Carbon skeleton
compounds
return to
parenchyma
C4 acids synthesized in the parenchyma
move to the bundle sheath
Ways in which Angiosperms are different from Gymnosperms
2. Xylem contains vessels as
well as tracheids and parenchyma
Angio-Gymno
3. Phloem contains sieve
elements with companion cells
Angio-Gymno
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
Angiosperm xylem and
phloem
Tracheids provide better support
but less slower rates of water
conduction than vessels
Vessel
Vessels
A vessel is
composed of
several vessel
elements
Tracheid
Tracheids lack perforation plates but their
end walls contain numerous pits.
Wide vessel element:
This kind of cell is
better for fluid
conduction than
physical support.
These vessel elements
have completely
perforated end walls
Elongated vessel
element: This cell
provides moderate
support and fluid
conduction.
Sieve Tube Members (STM)
Companion Cells (CC)
Cucurbita phloem
(cucumber)
Phloem
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.
J. D. Mauseth
Dicotyledon stem cross section
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
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
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