chapter 29, 30 & 31

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Plant Diversity I: How Plants Colonized Land

Biology in Focus: Ch. 26—The colonization of land by plants and fungi

Chapter 29, 30 & 31


Key Concepts1.Fossils show that plants colonized the land more

than 470 million years ago

2.Fungi played an essential role in the colonization of land

3.Early land plants radiated into a diverse set of lineages

4.Seeds and pollen grains are key adaptations for life on land

5.Land plants and fungi fundamentally changed chemical cycling and biotic interactions


Overview: The Greening of Earth

• Looking at a lush landscape, it is difficult to imagine the land without any plants or other organisms

• For more than the first 2 billion years of Earth’s history, the terrestrial surface was lifeless

• Since colonizing land, plants have diversified into roughly 290,000 living species

• Plants supply oxygen and are the ultimate source of most food eaten by land animals


Concept 1: Evidence of Algal Ancestry

• Green algae called charophytes are the closest relatives of land plants


Morphological and Molecular Evidence

• Many characteristics of land plants also appear in a variety of algal clades, mainly algae

• However, land plants share four key traits only with charophytes:

– Rose-shaped complexes for cellulose synthesis

– Peroxisome enzymes

– Structure of flagellated sperm

– Formation of a phragmoplast


• Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants

• Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes

Fig. 29-3

40 µm

5 mm Chara species, a pond organism

Coleochaete orbicularis, adisk-shaped charophyte thatalso lives in ponds (LM)


Adaptations Enabling the Move to Land

• In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out

• The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens

• Land presented challenges: a scarcity of water and lack of structural support


• The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants

• Systematists are currently debating the boundaries of the plant kingdom

• Some biologists think the plant kingdom should be expanded to include some or all green algae

• Until this debate is resolved, we will retain the embryophyte definition of kingdom Plantae

Fig. 29-4

ANCESTRALALGA

Red algae

Chlorophytes

Charophytes

Embryophytes

ViridiplantaeStreptophyta

Plantae


Derived Traits of Plants

• Four key traits appear in nearly all land plants but are absent in the charophytes:

– Alternation of generations (with multicellular, dependent embryos)– http://education-portal.com/academy/lesson/alternation-of-ge

nerations-the-gametophyte-and-sporophyte.html

– Walled spores produced in sporangia

– Multicellular gametangia

– Apical meristems

http://education-portal.com/academy/lesson/alternation-of-generations-the-gametophyte-and-sporophyte.html

http://education-portal.com/academy/lesson/alternation-of-generations-the-gametophyte-and-sporophyte.html


• Additional derived traits such as a cuticle and secondary compounds evolved in many plant species

• Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients


Alternation of Generations and Multicellular, Dependent Embryos

• Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations

• The gametophyte is haploid and produces haploid gametes by mitosis

• Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis


• The diploid embryo is retained within the tissue of the female gametophyte

• Nutrients are transferred from parent to embryo through placental transfer cells

• Land plants are called embryophytes because of the dependency of the embryo on the parent

Fig. 29-5a

Gametophyte(n)

Gamete fromanother plant

n

n

Mitosis

Gamete

FERTILIZATIONMEIOSIS

Mitosis

Sporen

n

2n Zygote

Mitosis

Sporophyte(2n)

Alternation of generations

Fig. 29-5b

EmbryoMaternal tissue

Wall ingrowthsPlacental transfer cell(outlined in blue)

Embryo (LM) and placental transfer cell (TEM)of Marchantia (a liverwort)

2 µm

10 µm


Walled Spores Produced in Sporangia

• The sporophyte produces spores in organs called sporangia

• Spore walls contain sporopollenin, which makes them resistant to harsh environments

Fig. 29-5c

SporesSporangium

Sporophyte

Longitudinal section ofSphagnum sporangium (LM)

Gametophyte

Sporophytes and sporangia of Sphagnum (a moss)

Fig. 29-5d

Female gametophyte

Malegametophyte

Antheridiumwith sperm

Archegoniumwith egg

Archegonia and antheridia of Marchantia (a liverwort)


Apical Meristems

• Plants sustain continual growth in their apical meristems

• Cells from the apical meristems differentiate into various tissues

Fig. 29-5e

Apicalmeristemof shoot

Developingleaves

Apical meristems

Apical meristemof root Root100 µm 100 µmShoot


The Origin and Diversification of Plants

• Fossil evidence indicates that plants were on land at least 470 million years ago

• Fossilized spores and tissues have been extracted from 450-million-year-old rocks

(a) Fossilized spores

(b) Fossilized sporophyte tissue


Concept 2: Essential role of fungi in colonization

• How did early land plants obtain nutrients without roots and leaves?

• Fossil evidence reveals that early land plants formed symbiotic associations with fungi to aid in nutrient absorption from the soil. (mycorrhizae)


PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 31

Fungi


Overview: Mighty Mushrooms

• Fungi are diverse and widespread

• Essential to most terrestrial ecosystems because they break down organic material and recycle vital nutrients

• Fungi exhibit diverse lifestyles:

– Decomposers

– Parasites

– Mutualists


Fungal Nutrition

• Fungi are heterotrophs that feed by absorption.

• Fungi use enzymes to break down complex molecules into smaller organic compounds that can be absorbed.

• Fungi can digest compounds from a wide range of sources, living or dead.


Adaptations for Feeding by Absorption

• Most fungi have cell walls made of chitin• The most common body structures are

multicellular filaments and single cells (yeasts)

• Morphology enhances absorption. Some species grow as either filaments or yeasts; others grow as both

• Fungi consist of mycelia, networks of branched hyphae adapted for absorption


Specialized Hyphae in Mycorrhizal Fungi

• Some unique fungi have specialized hyphae called haustoria that allow them to penetrate the tissues of their host

• Mutually beneficial relationships between such fungi and plant roots are called mycorrhizae (“fungus roots”)

• Mycorrhizal fungi deliver phosphate ions and other minerals to plants in exchange for organic nutrients such as carbohydrates


Fig. 31-4b

(b) Haustoria

Plantcellwall

Haustorium

Plant cellplasmamembrane

Plant cell

Fungal hypha


Two main types of mycorrhizal fungi:

• Ectomycorrhizal fungi (ektos, out) form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex

• Arbuscular mycorrhizal fungi (arbor, tree) extend hyphae through the cell walls of root cells and into tubes formed by invagination (pushing inward) of the root cell membrane


Fig. 31-2

Reproductive structure

Spore-producingstructures

Hyphae

Mycelium

20 µm


Sexual and Asexual Reproduction

• Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually

• Plasmogamy is the union of two parent mycelia

• Hours, days, or even centuries may pass before the occurrence of karyogamy, nuclear fusion

• During karyogamy, the haploid nuclei fuse, producing diploid cells

• The diploid phase is short-lived and undergoes meiosis, producing haploid spores


Fig. 31-5-1

Spores


GERMINATION

ASEXUALREPRODUCTION

Mycelium

Key

Heterokaryotic(unfused nuclei fromdifferent parents)

Haploid (n)

Diploid (2n)


Fig. 31-5-2

Spores


GERMINATION

ASEXUALREPRODUCTION

Mycelium

Key


Haploid (n)

Diploid (2n)

SEXUALREPRODUCTION

KARYOGAMY(fusion of nuclei)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

Zygote


Fig. 31-5-3

Spores


GERMINATION

ASEXUALREPRODUCTION

Mycelium

Key


Haploid (n)

Diploid (2n)

SEXUALREPRODUCTION

KARYOGAMY(fusion of nuclei)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

Zygote

Spores

GERMINATIONMEIOSIS


Asexual Reproduction

• In addition to sexual reproduction, many fungi can reproduce asexually

• Molds produce haploid spores by mitosis and form visible mycelia

• Other fungi that can reproduce asexually are yeasts, which inhabit moist environments

• Instead of producing spores, yeasts reproduce asexually by simple cell division and the pinching of “bud cells” from a parent cell


Fig. 31-7

10 µm

Parentcell

Bud


The Origin of Fungi

• Fungi and animals are more closely related to each other than they are to plants or other eukaryotes

• DNA evidence suggests that fungi are most closely related to unicellular nucleariids while animals are most closely related to unicellular choanoflagellates


Fig. 31-8

Animals (and their closeprotistan relatives)

Other fungi

Nucleariids

Chytrids

UNICELLULAR,FLAGELLATEDANCESTOR

Fungi

Opisthokonts


The Move to Land

• Fungi were among the earliest colonizers of land and probably formed mutualistic relationships with early land plants

• Among fossil evidence, molecular studies on sym genes have shown evidence of gene conservation for hundreds of millions of years.

• Molecular analyses have also helped clarify evolutionary relationships among fungal groups, although areas of uncertainty remain


Fig. 31-11

Chytrids (1,000 species)

Zygomycetes (1,000 species)

Hyphae 25 µm

Glomeromycetes (160 species)

Fungal hypha

Ascomycetes (65,000 species)

Basidiomycetes (30,000 species)

chapter 29, 30 & 31

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