Greek:

By far the most diverse group of plants that has ever existed with more than 240,000 different species.

The angiosperms

angeion case; sperma seed

Time of origin of plant groups

Why are there do many species?

Mos

ses

Fer

ns

Angiosperms

Why are there so many species?

Con

ifer

s

Gondwanaland

West Gondwana, equivalent to modern South America plus Africa

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

Fig. 29.5, p. 502

[A] Simple tissues of parenchyma, collenchyma and sclerenchyma

Transverse section

pholem

sclerenchyma

collenchyma

parenchyma

Important structural tissues of many angiosperms

xylem

epidermis

Examples

Fig. 29.6, p. 502

PARENCHYMA COLLENCHYMA SCLERENCHYMA

DICOTS

Dicotyledon – Monocotyledon

differences

MONOCOTS

Fig. 29.10, p. 503

In seeds, two cotyledons (part of the embryo)

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

In seeds only one cotyledon

Usually three floral parts (or multiples of three)

Usually a parallel array of leaf veins

Basically, one pore or furrow in pollen grain

Vascular bundles distributed ground tissue of stem

Vascular bundles arrayed as a ring in stem

vascular bundle

[B] There are two classes of flowering plants, Monocotyledons and Dicotyledons

1. Angiosperm leaves have finely divided venation; typically gymnosperm foliage e.g., conifer needles, have a single vascular strand

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

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

2. Angiosperm xylem contains vessels as well as tracheids and parenchyma

3. Angiosperm phloem contains sieve elements with companion cells rather than albuminous cells

Principal differences between Angiosperms and Gymnosperms

The network of veins also provides a supportive framework for the leaf.

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 a vein.

So? Why is that important?

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

Fig. 29.16, p. 507

Water anddissolvedmineral ionsmove fromroots intostems, theninto leaf vein(blue arrow)

Products ofPhotosynthesis(pink arrow)enter vein andare transportedto stems, roots) one stoma

(openingacross theepidermis)

cuticle-coatedcell of lowerepidermis

PALISADEMESOPHYLL

SPONGYMESOPHYLL

Carbon dioxide from the surroundingair enters the leaf through stomata

Oxygen and water vapor escapefrom the leaf through stomata

xylem phloem

leaf vein (one vascularbundle inside the leaf)

UPPEREPIDERMIS

LOWEREPIDERMIS

cuticle of upper epidermis

My textbook has xylem and phloem wrongly labeled

Tomato leaf

Upper epidermis

Lower epidermis

Palisade parenchyma: chloroplasts visible around cell periphery

Spongy parenchyma

Longitudinal section through a vascular bundle

Xylem vessel: annular thickening around cell wall

Phloem

Bundle Sheath

… C3 and C4 photosynthesis?Photorespiration and biochemical

strategies to avoid it

6CO2 + 6H2O C6H12O6 + 6O2 (18ATP, 12 NADPH) C36CO2 + 6H2O C6H12O6 + 6O2 (30ATP, 12 NADPH) C4

RuBisCO PEPcarboxylase

C3 C4 CAM

MonocotsDicots

http://www.uri.edu/artsci/bio/plant_anatomy/99.html

Leaf cross section of Zea mays ("corn").

Bulliform cellsXylem

Upper epidermis

Lower epidermis

Bundle sheath cells with chloroplasts

PhloemParenchyma with chloroplasts

Xylem

Bundle sheath cells filled with chloroplasts. CALVIN REACTION SITE

Phloem

Parenchyma filled with chloroplasts

C4 acids synthesized in the parenchyma move to the bundle sheath

Carbon skeleton compounds return to parenchyma

Anatomical separation of the C4 photosynthesis component processes

Maize3394

2. Xylem contains vessels as well as tracheids and parenchyma

Elongated vessel element: This cell provides moderate support but superior fluid conduction compared to a tracheid.

Vessel

A vessel is composed of several vessel elements

Wide vessel element: This kind of cell is better for fluid conduction than physical support.

These vessel elements have completely perforated end walls

Tracheid

Tracheids provide better support but less slower rates of water conduction than vessels

Tracheids lack perforation plates but their end walls contain numerous pits.

3. Phloem contains sieve elements with companion cells

STMs have no nucleus at maturity and depend on CC to regulate physiological processes.

Sieve Tube Members (STM)

Sieve plate

Cucurbita phloem

Companion Cells (CC)

(cucumber)

STMs and CCs develop from the same progenitor cell.

STMs unite vertically to form a Sieve Tube.

Stems as diverse as slender vines, fat cacti, or as modified as potato tubers all have this organization, but with various zones modified.

Dicotyledon stem cross section

Angelica stem transverse section Typical of a dicotyledon without secondary thickening.

J. D. Mauseth

We eat Angelica in confectionary

1) epidermis

2) cortex, in many species the outermost part is a hypodermis

3) ring of vascular bundles 4) pith.

Four zones:

Cacti have an exceptionally thick cortex. Potato tubers have a gigantic pith and almost no wood.

Transverse section of corn stem, Zea mays.

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

There are four parts:

3) vascular bundles

2) cortex with or without part differentiated into a hypodermis

1) epidermis

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