chapter29 plant diversiy i

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 29Chapter 29

Plant Diversity IHow Plants Colonized Land

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• Overview: The Greening of Earth

• Looking at a lush landscape

– It is difficult to imagine the land without any plants or other organisms

Figure 29.1


• For more than the first 3 billion years of Earth’s history

– The terrestrial surface was lifeless

• Since colonizing land

– Plants have diversified into roughly 290,000 living species


• Concept 29.1: Land plants evolved from green algae

• Researchers have identified green algae called charophyceans as the closest relatives of land plants


Morphological and Biochemical Evidence

• Many characteristics of land plants

– Also appear in a variety of algal clades


• There are four key traits that land plants share only with charophyceans

– Rose-shaped complexes for cellulose synthesis

30 nmFigure 29.2


– Peroxisome enzymes

– Structure of flagellated sperm

– Formation of a phragmoplast


Genetic Evidence

• Comparisons of both nuclear and chloroplast genes

– Point to charophyceans as the closest living relatives of land plants

Chara, a pond organism

(a)10 mm

Coleochaete orbicularis, a disk-shaped charophycean (LM)

(b)

40 µm

Figure 29.3a, b


Adaptations Enabling the Move to Land

• In charophyceans

– A layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out

• The accumulation of traits that facilitated survival on land

– May have opened the way to its colonization by plants


• Concept 29.2: Land plants possess a set of derived terrestrial adaptations

• Many adaptations

– Emerged after land plants diverged from their charophycean relatives


Defining the Plant Kingdom

• Systematists

– Are currently debating the boundaries of the plant kingdom

Plantae

Streptophyta

Viridiplantae

Red algae Chlorophytes Charophyceans Embryophytes

Ancestral algaFigure 29.4


• Some biologists think that the plant kingdom

– Should be expanded to include some or all green algae

• Until this debate is resolved

– This textbook retains the embryophyte definition of kingdom Plantae


Derived Traits of Plants

• Five key traits appear in nearly all land plants but are absent in the charophyceans

– Apical meristems

– Alternation of generations

– Walled spores produced in sporangia

– Multicellular gametangia

– Multicellular dependent embryos


APICAL MERISTEMSApicalmeristemof shoot

Developingleaves

100 µm

Apical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root.

Apical meristemof root

Root 100 µmShoot

Figure 29.5

• Apical meristems and alternation of generations

Haploid multicellularorganism (gametophyte)

Mitosis Mitosis

Gametes

Zygote

Diploid multicellularorganism (sporophyte)

Alternation of generations: a generalized scheme

MEIOSIS FERTILIZATION

2n2n

n

n

nn

nSpores

Mitosis

ALTERNATION OF GENERATIONS


• Walled spores; multicellular gametangia; and multicellular, dependent embryos

WALLED SPORES PRODUCED IN SPORANGIA

MULTICELLULAR GAMETANGIA

MULTICELLULAR, DEPENDENT EMBRYOS

SporesSporangium

Longitudinal section ofSphagnum sporangium (LM)

SporophyteGametophyte

Sporophyte and sporangium of Sphagnum (a moss)

Female gametophyte

Archegoniumwith egg

Antheridiumwith sperm

Malegametophyte

Archegonia and antheridia of Marchantia (a liverwort)

EmbryoMaternal tissue

2 µm

Wall ingrowths

Placental transfer cell

10 µm

Embryo and placental transfer cell of Marchantia

Figure 29.5


• Additional derived units

– Such as a cuticle and secondary compounds, evolved in many plant species


The Origin and Diversification of Plants

• Fossil evidence

– Indicates that plants were on land at least 475 million years ago


• Fossilized spores and tissues

– Have been extracted from 475-million-year-old rocks

Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right).

(a)

Fossilizedsporophyte tissue. The spores were embedded in tissue that appears to be from plants.

(b)

Figure 29.6 a, b


• Whatever the age of the first land plants

– Those ancestral species gave rise to a vast diversity of modern plants

Table 29.1


• Land plants can be informally grouped

– Based on the presence or absence of vascular tissue


• An overview of land plant evolution

Bryophytes(nonvascular plants) Seedless vascular plants Seed plants

Vascular plants

Land plants

Origin of seed plants(about 360 mya)

Origin of vascular plants (about 420 mya)

Origin of land plants(about 475 mya)

Ancestralgreen alga

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• Concept 29.3: The life cycles of mosses and other bryophytes are dominated by the gametophyte stage

• Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants

– Liverworts, phylum Hepatophyta

– Hornworts, phylum Anthocerophyta

– Mosses, phylum Bryophyta


• Debate continues over the sequence of bryophyte evolution

• Mosses are most closely related to vascular plants


Bryophyte Gametophytes

• In all three bryophyte phyla

– Gametophytes are larger and longer-living than sporophytes


• The life cycle of a moss

Maturesporophytes

Youngsporophyte

Malegametophyte

Raindrop

Sperm

Key

Haploid (n)Diploid (2n)

Antheridia

Femalegametophyte

Egg

Archegonia

FERTILIZATION

(within archegonium)Zygote

Archegonium

Embryo

Femalegametophytes

Gametophore

Foot

Capsule(sporangium)

Seta

Peristome

Spores

Protonemata

“Bud”

“Bud”

MEIOSIS

Sporangium

Calyptra

Capsule with peristome (LM)

Rhizoid

Maturesporophytes

Spores develop intothreadlike protonemata.1

The haploidprotonemataproduce “buds”that grow intogametophytes.

2 Most mosses have separatemale and female gametophytes,with antheridia and archegonia,respectively.

3

A sperm swimsthrough a film ofmoisture to anarchegonium andfertilizes the egg.

4

Meiosis occurs and haploidspores develop in the sporangiumof the sporophyte. When thesporangium lid pops off, theperistome “teeth” regulategradual release of the spores.

8

The sporophyte grows along stalk, or seta, that emergesfrom the archegonium.

6

The diploid zygotedevelops into a sporophyte embryo withinthe archegonium.

5

Attached by its foot, thesporophyte remains nutritionallydependent on the gametophyte.

7

Figure 29.8


• Bryophyte gametophytes

– Produce flagellated sperm in antheridia

– Produce ova in archegonia

– Generally form ground-hugging carpets and are at most only a few cells thick

• Some mosses

– Have conducting tissues in the center of their “stems” and may grow vertically


Bryophyte Sporophytes

• Bryophyte sporophytes

– Grow out of archegonia

– Are the smallest and simplest of all extant plant groups

– Consist of a foot, a seta, and a sporangium

• Hornwort and moss sporophytes

– Have stomata


• Bryophyte diversityLIVERWORTS (PHYLUM HEPATOPHYTA)

HORNWORTS (PHYLUM ANTHOCEROPHYTA) MOSSES (PHYLUM BRYOPHYTA)

Gametophore offemale gametophyte

Marchantia polymorpha,a “thalloid” liverwort

Foot

Sporangium

Seta

500

µm

Marchantia sporophyte (LM)

Plagiochiladeltoidea,a “leafy”liverwort

An Anthoceroshornwort species

Sporophyte

Gametophyte

Polytrichum commune,hairy-cap moss

Sporophyte

Gametophyte

Figure 29.9


“Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years.

Ecological and Economic Importance of Mosses

• Sphagnum, or “peat moss”

– Forms extensive deposits of partially decayed organic material known as peat

– Plays an important role in the Earth’s carbon cycle

GametophyteSporangium attip of sporophyte

Livingphoto-syntheticcells

Dead water-storing cells

100 µm

Closeup of Sphagnum. Note the “leafy” gametophytes and their offspring, the sporophytes.

(b)

Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality.

(c)

Peat being harvested from a peat bog(a)

Figure 29.10 a–d

(d)


• Concept 29.4: Ferns and other seedless vascular plants formed the first forests

• Bryophytes and bryophyte-like plants

– Were the prevalent vegetation during the first 100 million years of plant evolution

• Vascular plants

– Began to evolve during the Carboniferous period


Origins and Traits of Vascular Plants

• Fossils of the forerunners of vascular plants

– Date back about 420 million years


• These early tiny plants

– Had independent, branching sporophytes

– Lacked other derived traits of vascular plants

Figure 29.11


Life Cycles with Dominant Sporophytes

• In contrast with bryophytes

– Sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern

– The gametophytes are tiny plants that grow on or below the soil surface


• The life cycle of a fern

Fern sperm use flagellato swim from the antheridia to eggs in the archegonia.

4

Sporangia release spores.Most fern species produce a singletype of spore that gives rise to abisexual gametophyte.

1 The fern sporedevelops into a small,photosynthetic gametophyte.

2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanismspromote cross-fertilizationbetween gametophytes.

3

On the undersideof the sporophyte‘sreproductive leavesare spots called sori.Each sorus is acluster of sporangia.

6

A zygote develops into a newsporophyte, and the young plantgrows out from an archegoniumof its parent, the gametophyte.

5

MEIOSIS

Sporangium

Sporangium

Maturesporophyte

Newsporophyte

Zygote

FERTILIZATION

Archegonium

Egg

Haploid (n)Diploid (2n)

Spore Younggametophyte

Fiddlehead

Antheridium

Sperm

Gametophyte

Key

Sorus

Figure 29.12


Transport in Xylem and Phloem

• Vascular plants have two types of vascular tissue

– Xylem and phloem


• Xylem

– Conducts most of the water and minerals

– Includes dead cells called tracheids

• Phloem

– Distributes sugars, amino acids, and other organic products

– Consists of living cells


Evolution of Roots

• Roots

– Are organs that anchor vascular plants

– Enable vascular plants to absorb water and nutrients from the soil

– May have evolved from subterranean stems


Evolution of Leaves

• Leaves

– Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis


• Leaves are categorized by two types

– Microphylls, leaves with a single vein

– Megaphylls, leaves with a highly branched vascular system


• According to one model of evolution

– Microphylls evolved first, as outgrowths of stems

Vascular tissue

Microphylls, such as those of lycophytes, may have originated as small stem outgrowths supported by single, unbranched strands of vascular tissue.

(a) Megaphylls, which have branched vascular systems, may have evolved by the fusion of branched stems.

(b)

Figure 29.13a, b


Sporophylls and Spore Variations

• Sporophylls

– Are modified leaves with sporangia

• Most seedless vascular plants

– Are homosporous, producing one type of spore that develops into a bisexual gametophyte


• All seed plants and some seedless vascular plants

– Are heterosporous, having two types of spores that give rise to male and female gametophytes


Classification of Seedless Vascular Plants

• Seedless vascular plants form two phyla

– Lycophyta, including club mosses, spike mosses, and quillworts

– Pterophyta, including ferns, horsetails, and whisk ferns and their relatives


• The general groups of seedless vascular plants

LYCOPHYTES (PHYLUM LYCOPHYTA)

PTEROPHYTES (PHYLUM PTEROPHYTA)

WHISK FERNS AND RELATIVES HORSETAILS FERNS

Isoetesgunnii,a quillwort

Selaginella apoda,a spike moss

Diphasiastrum tristachyum, a club moss

Strobili(clusters ofsporophylls)

Psilotumnudum,a whiskfern

Equisetumarvense,fieldhorsetail

Vegetative stem

Strobilus onfertile stem

Athyrium filix-femina, lady fern

Figure 29.14


Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts

• Modern species of lycophytes

– Are relics from a far more eminent past

– Are small herbaceous plants


Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives

• Ferns

– Are the most diverse seedless vascular plants


The Significance of Seedless Vascular Plants

• The ancestors of modern lycophytes, horsetails, and ferns

– Grew to great heights during the Carboniferous, forming the first forests

Figure 29.15


• The growth of these early forests

– May have helped produce the major global cooling that characterized the end of the Carboniferous period

– Decayed and eventually became coal

chapter29 plant diversiy i

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characteristics of land

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