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.
Time of origin of plant groups
Angiosperms
Conifers
Ferns
Mosses
Why are there do
many species?
Why are there so
many species?
West Gondwana, equivalent to
modern South America plus Africa
Gondwanaland
Two things before discussing the Angiosperms:
[A] Simple tissues of parenchyma, collenchyma and
sclerenchyma
[B] There are two classes of flowering plants,
Monocotyledons and
Dicotyledons
[A] Simple tissues of parenchyma, collenchyma
and sclerenchyma
Important structural tissues of many angiosperms
epidermis
collenchyma
sclerenchyma
xylem
pholem
parenchyma
Transverse section
Fig. 29.5, p. 502
Examples
PARENCHYMA
COLLENCHYMA
SCLERENCHYMA
Fig. 29.6, p. 502
[B] There are two classes of flowering plants, Monocotyledons and Dicotyledons
In seeds, two
cotyledons (part of
the embryo)
DICOTS
Usually four or five
floral parts (or
multiples of these)
Usually a
netlike array
of leaf veins
Basically, three
pores of furrows in
pollen grain
vascular
bundle
Vascular
bundles arrayed
as a ring in stem
In seeds only
one cotyledon
Dicotyledon –
Monocotyledon
Usually three
floral parts (or
differences
multiples of three)
MONOCOTS
Usually a parallel
array of leaf veins
Basically, one pore or
furrow in pollen grain
Vascular bundles
distributed ground
29.10, p. 503
tissue ofFig.
stem
Principal differences between
Angiosperms and Gymnosperms
1. Angiosperm leaves have finely divided venation; typically
gymnosperm foliage e.g., conifer needles, have a single
vascular strand
2. Angiosperm xylem contains vessels as well as
tracheids and parenchyma
3. Angiosperm phloem contains sieve elements with
companion cells rather than albuminous cells
4. Angiosperm ovules are protected within an enclosed
structure rather sitting on a modified leaf
5. Double fertilization in the angiosperms produces a diploid
zygote and triploid endosperm nucleus
6. In the angiosperms there are generally hermaphrodite
flowers and cross pollinating (70%). Wind pollination is
typical in the gymnosperms animal pollination
widespread in angiosperms
1. Leaves have finely divided venation
A dicotyledon
Coleus leaf cleared of cell contents and with xylem stained
So? Why is that important?
Typically veins
are distributed
such that
mesophyll cells
are close to 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.
leaf vein (one vascular
bundle inside the leaf)
xylem
cuticle of upper epidermis
phloem
Water and
dissolved
mineral ionsDiagram of a dicot leaf
move from
roots into
stems, then
into leaf vein
(blue arrow)
UPPER
EPIDERMIS
My textbook has
xylem and phloem
wrongly labeled
PALISADE
MESOPHYLL
SPONGY
MESOPHYLL
LOWER
EPIDERMIS
Products of
Photosynthesis
(pink arrow)
enter vein and
are transported
to stems, roots)
Oxygen and water
vapor escape
from the leaf
through stomata
cuticle-coated
cell of lower
epidermis
Carbon dioxide from
the surrounding
air enters the leaf
through stomata
one stoma
(opening
across the
epidermis)
Fig. 29.16, p. 507
Tomato leaf
Upper epidermis
Palisade 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
… C3 and C4 photosynthesis?
Photorespiration and biochemical
strategies to avoid it
C3
C4
RuBisCO
PEP
carboxylase
Dicots
Monocots
CAM
6CO2 + 6H2O  C6H12O6 + 6O2 (18ATP, 12 NADPH) C3
6CO2 + 6H2O  C6H12O6 + 6O2 (30ATP, 12 NADPH) C4
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
Maize
3394
2. Xylem contains vessels as well as tracheids and parenchyma
Tracheids provide better support but
less slower rates of water conduction
than vessels
Vessel
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 but superior
fluid conduction
compared to a tracheid
3. Phloem contains sieve elements with companion cells
Sieve Tube Members (STM)
Companion Cells (CC)
Cucurbita phloem
(cucumber)
Sieve plate
STMs and CCs develop from the same progenitor cell.
STMs unite vertically to form a Sieve Tube.
STMs have no nucleus at maturity and depend on CC to
regulate physiological processes.
Angelica stem
J. D. Mauseth
Four zones:
transverse section
Typical of a
dicotyledon
without
secondary
thickening.
1) epidermis
Dicotyledon stem cross section
2) cortex, in many species the
outermost part is a hypodermis
We eat Angelica
in confectionary
3) ring of vascular bundles
Stems as diverse as slender vines,
fat cacti, or as modified as potato
tubers all have this organization,
but with various zones modified.
4) pith.
Cacti have an exceptionally
thick cortex. Potato tubers have
a gigantic pith and almost no
wood.
Transverse section of corn stem, Zea mays.
There are four parts:
Transverse section of corn stem, Zea mays.
Organization of
monocotyledon
stems: numerous
vascular bundles
distributed
throughout a tissue
that may be either
parenchyma or
collenchyma
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
Monocotyledon stems: numerous vascular bundles
distributed throughout a tissue that may be either
parenchyma or collenchyma