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Chapter 18Evolution of Plants and

Fungi

The Evolution of Plants Spans 500 Million Years

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18.1 Evidence suggests that plants evolved from green algae Plants - multicellular, photosynthetic eukaryotes

that range in size from the duckweed to the giant coastal redwoods Important ecologically, industrially, and medically

Believed to have evolved from freshwater green algae over 500 million years ago Evidence - Both green algae and plants

Contain chlorophylls a and b and various accessory pigments

Store excess carbohydrates as starch Have cellulose in their cell wall

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Figure 18.1 Close algal relatives of plants

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18.2 The evolution of plants is marked by four innovations

Nourish and protect a multicellular embryo that completes the life cycle

Have vascular tissue transporting water and solute to cells when the plant body is surrounded by air

Produce seeds that contain an embryo and stored organic nutrients within a protective coat

Flowers that attract pollinators, such as insects, and give rise to fruits, food for animals to help disperse the seeds

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Figure 18.2A Representatives of the four major groups of plants

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Figure 18.2B Evolutionary history of plants

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18.3 Plants have an alternation of generations life cycle

Alternation of Generations A sporophyte represents the diploid generation

and a gametophyte represents the haploid generation Sporophyte (2n) produces spores by meiosis

A spore is a haploid reproductive cell that develops into a new organism without needing to fuse with another reproductive cell

A spore undergoes mitosis to become a gametophyte Gametophyte (n) produces gametes

In plants, eggs and sperm are produced by mitosis A sperm and egg fuse, forming a diploid zygote that

undergoes mitosis and becomes the sporophyte

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Figure 18.3 Alternation of generations

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18.4 Sporophyte dominance was adaptive to a dry land environment Reproductive Adaptation to the Land Environment Sporophyte dominance can be associated with an increasing

adaptation for reproduction in a dry, terrestrial environment Ferns are seedless vascular plants with a dominant sporophyte

The sporophyte produces spores that disperse (scatter) separate gametophytes

The gametophyte is a small, heart-shaped structure that has no vascular tissue and can dry out if the environment is not moist

Each archegonium on the surface of a gametophyte produces an egg that is fertilized by a flagellated sperm, which must swim to the archegonium in a film of external water

Other Adaptations to the Land Environment Cuticle - relatively impermeable layer and provides an effective barrier

to water loss, but it also limits gas exchange Leaves have little openings called stomata (sing., stoma) that let carbon

dioxide enter while allowing oxygen and water to exit 18-11

Figure 18.4A Reduction in the size of the gametophyte as sporophyte becomes dominant

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Flowering plants are seed plantswith a dominant sporophyte

In flowering plants: Sporophyte produces seeds that disperse separate

sporophytes protected by seed coats Female gametophyte is microscopic and retained and

protected within an ovule, a structure located within the tissue of a flower

The male gametophytes are pollen grains that are transported by wind, insects, or birds They do not need external water to reach the egg

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Figure 18.4B Protection of eggs and embryos

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Figure 18.4C Features of the leaves of vascular plants

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Plants Are Adapted to the Land Environment

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18.5 Bryophytes are nonvascular plants in which the

gametophyte is dominant Nonvascular plants lack a specialized means of

transporting water and organic nutrients They do not have true roots, stems, and leaves

bryophyte (lowercase b) - general term for nonvascular plants

The Generations of Bryophytes Gametophyte is the dominant generation Female gametophyte produces eggs in archegonia, and the male

gametophyte produces flagellated sperm in antheridia Sperm swim to the vicinity of the egg in a continuous film of water Zygote becomes a sporophyte embryo that is protected from

drying out within the archegonium The lack of vascular tissue and the need for sperm to

swim to archegonia in a film of water largely account for the limited their height 18-17

Figure 18.5A Representative bryophytes

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Figure 18.5B Moss life cycle, Polytrichum sp

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18.6 Ferns and their allies have a dominant vascular sporophyte

Today’s seedless vascular plants Club mosses, horsetails and ferns

Ferns (phylum Pterophyta) include approximately 11,000 species Ferns are most abundant in warm, moist, tropical regions, but

can also be found in temperate regions Range in size from less than 1 cm to giant tropical tree ferns that

exceed 20 m Large leaves of ferns, called fronds, are commonly divided into

leaflets

Economic Value of Ferns Often used by florists in decorative bouquets and as ornamental

plants in the home and garden18-20

Figure 18.6A Sporophyte of a club moss

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Figure 18.6B Diversity of fern fronds

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Figure 18.6C Fern life cycle

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18.7 Most gymnosperms bear coneson which the seeds are “naked”

Diversity of Gymnosperms Four groups of living gymnosperms: cycads,

ginkgoes, gnetophytes, and conifers All of these plants have ovules and subsequently

develop seeds that are exposed on the surface of cone scales or analogous structures

Conifers (phylum Coniferophyta) Consist of about 575 species of trees

Many are evergreens such as pines, spruces, firs, cedars and hemlocks

Economic Value of Conifers Wood of conifers is used extensively in construction

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Figure 18.7A Gymnosperm diversity

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Figure 18.7B Pine life cycle

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

18.8 Carboniferous forests became the coal we use today

Our industrial society runs on fossil fuels, such as coal

During Carboniferous period (>300 MYA) a great swamp forest encompassed much of Northern Hemisphere Enormous amount of biomass Didn’t decay when trees fell in the water Remains became covered by sediment that changed

to sedimentary rock With pressure, and the organic material became coal

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Figure 18.8 Swamp forest of the Carboniferous period

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18.9 Angiosperms are the flowering plants

Angiosperms (phylum Anthophyta) 240,000 known species Evolved at beginning of the Cenozoic era (65 MYA) when the first

flying insects appeared Flower and their pollinators evolved together

Flower involved in pollination Fruit serves as a means of seed dispersal

Angiosperm Diversity Monocotyledones (or monocots)

about 65,000 species Eudicotyledones (or eudicots)

about 175,000 species

Cotyledons - seed leaves with nutrients that nourish the embryo

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Figure 18.9 Generalized flower

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18.10 The flowers of angiosperms produce “covered” seeds

Fruits Fruits of flowers protect and aid in seed dispersal

Seeds are transported by wind, gravity, water, or animals to another location

Fleshy fruits may be eaten by animals, which transport the seeds to a new location and then deposit them when they defecate

Flowers and Diversification Today there are 240,000 species of flowering plants

and 700,000 species of insects Suggests that success of angiosperms has

contributed to the success of insects, and vice versa18-31

Figure 18.10 Flowering plant life cycle

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Figure 18.10 Flowering plant life cycle (continued)

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

18.11 Flowering plants provide many services

Humans derive most of their sustenance from three flowering plants Wheat

First cultivated in the Middle East about 8000 B.C. thought to be one of the earliest cultivated plants

Corn Properly called maize, first cultivated in Central America about 7,000

years ago Rice

Originated several thousand years ago in southeastern Asia, where it grew in swamps

Used for centuries for many important items Lumber - major part of buildings (mainly comes from conifers) Rubber - first made from the thick sap (latex) of the rubber tree About 50% of all pharmaceuticals come from plants

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Figure 18.11A Some species of grain

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Figure 18.11B Uses of plants

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Fungi Have Their Own Evolutionary History

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18.12 Fungi differ from plants and animals

Fungi (domain Eukarya, kingdom Fungi) Structurally diverse group of eukaryotes

Strict heterotrophs that release digestive enzymes into the external environment and digest their food outside the body

Mycelium - fungus body, a mass of filaments called hyphae

Fungal cells are different from plant cells Lack chloroplasts and their cell wall contains chitin rather

than cellulose Fungi are adapted to life on land by producing

windblown spores during both asexual and sexual reproduction

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Figure 18.12A Fungal mycelia and hyphae

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18.13 Fungi have mutualistic relationships with algae and plants

In a mutualistic relationship, two different species live together and help each other out Lichen - a mutualistic association between a

particular fungus and a cyanobacteria or green algae Three varieties

Compact crustose lichens seen on bare rock Shrublike fruticose lichens Leaflike foliose lichens

Mycorrhizal fungi form mutualistic relationships with the roots of most plants Helps plants grow more successfully in dry or poor soils

particularly those deficient in inorganic nutrients18-40

18.14 Fungi occur in three main groups

Zygospore Fungi (phylum Zygomycota) Mainly saprotrophs, but some parasitize small protists,

worms, and even insects

Sac Fungi (phylum Ascomycota) Nearly 75% of all described fungal species Yeasts - unicellular forms mainly in Ascomycota

Club Fungi (phylum Basidiomycota) Name comes from the reproductive structure, the

basidium (pl., basidia) The basidia are located within a basidiocarp

When you eat a mushroom, you are eating a basidiocarp18-41

Figure 18.14A Black bread mold, Rhizopus stolonifer

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Figure 18.14B Sexual reproduction in sac fungi

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Figure 18.14C Asexual reproductive structures in sac fungi

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Figure 18.14D Sexual reproduction in club fungi involves a basidiocarp of which three types are shown

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

18.15 Fungi have economic and medical importance

Economic Importance Help produce medicines and many foods

Mold Penicillium was original source of penicillin

In U.S., 1.13 billion pounds of mushrooms consumed annually

Fungal pathogens are a major concern for farmers

Medical Importance Mycoses are diseases caused by fungi Tineas are infections of the skin caused by fungi

Ringworm is a cutaneous infection contracted from soil Athlete’s foot is a tinea that affects the skin between the toes

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Connecting the Concepts:Chapter 18

Both plants and fungi are multicellular organisms adapted to living on land Four plant adaptations to a dry environment

Protect the sporophyte embryo from drying out Vascular tissue transports water and solutes Seeds allow the sporophyte to be dispersed Flowers get animals to pollinate and disperse seeds

Fungi are adapted to the land environment Produce windblown spores for asexual and sexual life cycles Saprotrophic and release enzymes into the environment to digest

organic remains and absorb nutrients

Without photosynthesis from algae and plants and decomposition from bacteria and fungi, animals could not exist Animals are not essential to the biosphere, but plants and fungi

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