Plant Diversity I: The Colonization of

Land

CampbeCampbell, 5ll, 5thth Edition, Chapter 29 Edition, Chapter 29

Nancy G. MorrisNancy G. Morris

VolunteerVolunteer State Community CollegeState Community College

Figure 29.3Highlights of Plant Evolution

Review of Characteristics:Review of Characteristics:

Chloroplasts with photosynthetic pigments: chlorophyll a, chlorophyll b, carotenoids

Cell walls containing cellulose– Secondary cell walls containing lignin

Food stored as amylose in plastids Classification of Kingdom (Table 29.1)

Plant Kingdom

Members show structural, chemical, & reproductive adaptations of terrestrial life

This distinguishes higher plants from the aquatic algae

Structural adaptation includes specialized structures to obtain water, minerals, carbon dioxide, light, etc.– Example: stomata – special pores

on surface for gas exchange

Plant Kingdom

Chemical adaptation includes a waxy cuticle, composed of cutin, to prevent desiccation

Cutin, lignin, sporopollenin are examples of secondary products meaning that they are produced through metabolic pathways not common to all plants

cellulose is an example of a primary product

Plants as Embryophytes

A new mode of reproduction was necessary to move from an aquatic to terrestrial existence:

1) Gametes are produced in gametangia, organs with protective jackets of sterile cells that prevent gametes from drying out. Egg is fertilized within the female organ. Figure 29.1a

Plants as Embryophytes

2) Embryos must be protected against desiccation. Zygote develops into embryo that is retained within female protective cells in the gametangia Figure 29.1b

AAlternation of lternation of GGenerationsenerations: a review

All higher green plants reproduce sexually

Most are also capable of asexual reproduction

The haploid gametophyte generation produces and alternates with a diploid sporophyte generation. The sporophyte produces gametophytes.

Figure 29.2Alternationof Generation

AAlternation of lternation of GGenerationsenerations: a review

The life cycle is heteromorphic – the gametophyte & sporophyte differ in morphology

The sporophyte is larger & more noticeable in all but the bryophytes

Reduction of the gametophyte and dominance of the sporophyte generation we move from bryophytes to angiosperms

Figure 29.5 Hypothetical Mechanism: Origin of Alternations of Generations

Keeping a low profile…Keeping a low profile…

Bryophytes: Lack woody tissue Unable to support tall plants on land Often sprawl horizontally as mats

Nonvascular Plants: 3 Nonvascular Plants: 3 DivisionsDivisions

Bryophyta

Mosses Sphagnum

Hepatophyta Liverworts Marchantia

Anthocerophyta Hornworts

Division BryophytaDivision Bryophyta

Bryon (Gr. “moss”) Grip substratum with rhizoids Cover about 3% of land surface Contain vast amounts of organic

carbon Campbell, Figure 29.7, Life Cycle of a

Moss

Division HepatophytaDivision Hepatophyta

Liverworts Sporangia have elaters, coil-shaped

cells, that spring out of capsule & disperse spores

Also reproduce asexually from gemmae (small bundles of cells that bounce out of cups when hit by rainwater)

Campbell, Figure 29.8

Division AnthocerophytaDivision Anthocerophyta

Hornworts Resemble liverworts but

sporophyte is horn-shaped Photosynthetic cells have one

large single chloroplast Campbell, Figure 29.9

Adaptation to landAdaptation to land

Antheridium produces flagellated sperm

Archegonium produces a single egg

Fertilization occurs within the archegonium

Zygote develops into an embryo within the archegonium (embryophyte condition)

Ancestral aquatic habitat evident…

Water required for reproduction Flagellated sperm cells swim from the

antheridium to the archegonium Vascular tissue is absent Water is distributed throughout the plant

by the relatively slow process of diffusion, capillary action, cytoplasmic streaming

Six terrestrial adaptations:Six terrestrial adaptations:

1) Regional specialization of the plant body:

subterranean roots that absorb water & minerals from the soil

aerial shoot system of stems & leaves to make food

Terrestrial adaptations:Terrestrial adaptations:

2) Structural support– support is provided by lignin

embedded into the cellulose matrix of cell walls

Terrestrial adaptations:Terrestrial adaptations:

3) Vascular systems evolved:

XYLEM – complex tissue that conducts water & minerals from the roots to the rest of the plant; composed of dead, tube-shaped cells that form a microscopic water-pipe system

PHLOEM – conducts sugars, amino acids, etc. throughout the plant; composed of living cells arranged in tubules

Terrestrial adaptations:Terrestrial adaptations:

4) Pollen – pollination eliminated the need for water to transport gametes

5) Seeds

6) Increased dominance of the diploid sporophyte

Vascular plants display two Vascular plants display two distinct reproductive distinct reproductive strategiesstrategies:

Homosporous plants produce one type of spore– Each spore develops into a bisexual gametophyte

with both antheridia and archegonia

Heterosporous plants produce two kinds of spores:– Megaspores develop into female gametophytes

possessing archegonia

– Microspores develop into male gametophytes possessing antheridia

ComparisonComparison

Single Eggs

Homosporous type of BisexualSporophyte spore gametophyte Sperm

Female Megaspore Gametophyte Eggs

Heterosporous Sporophyte Microspore Male Sperm Gametophyte

Seedless vascular plants: Seedless vascular plants: primitive primitive

tracheophytestracheophytes

Division Psilophyta - whisk ferns

Division Lycophyta - club mosses

Division Sphenophyta - horsetails

Division Pterophyta - ferns

Division LycophytaDivision Lycophyta

Club mosses (Fig. 29.12) Sporangia are borne on sporophylls – leaves

specialized for reproduction In some sporoangia, sporophylls are clustered at

branch tips into club-shaped strobili – hence the name club moss

Spores develop into inconspicuous gametophytes that are nurtured by symbiotic fungi.

Most are homosporous. (Selaginella is heterosporous.)

Division SphenophytaDivision Sphenophyta

(Fig. 29.13) Equisetum

Common in Northern Hemisphere in damp locations

Homosporous

Gametophyte is only a few mm

Gametophyte is free-living & photosynthetic

Division Pterophyta: FERNSDivision Pterophyta: FERNS

12,000 existing species most ferns have fronds homosporous sori on underside of leaf with

annulus to catapult spores into the air

prothallus (gametophyte) requires water

Figure 29.11Figure 29.11 Life Cycle of a Fern Life Cycle of a Fern

“Coal forests”

During the Carboniferous period, the landscape was dominated by extensive swamp forests: club mosses, whisk ferns, horsetails were gigantic plants

Organic rubble of the seedless plants accumulated as peat (Figure 29.14)

When later covered by sea and sediment, heat & pressure transformed the peat into coal