Biology: Life on Earth Lecture for Chapter 21 The Diversity of Plants Teresa Audesirk • Gerald Audesirk • Bruce E. Byers Biology: Life on Earth Eighth Edition Lecture for Chapter 21 The Diversity of Plants Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 21 Outline 21.1 What Are the Key Features of Plants? p. 404 21.2 What Is the Evolutionary Origin of Plants? p. 405 21.3 How Have Plants Adapted to Life on Land? p. 406 21.4 What Are the Major Groups of Plants? p. 407

Section 21.1 Outline 21.1 What Are the Key Features of Plants? Plants Have Alternating Multicellular Haploid and Diploid Generations Plants Have Multicellular, Dependent Embryos Plants Play a Crucial Ecological Role Plants Provide Humans with Necessities and Luxuries Plants Are Adapted to Life on Land

Key Features of Plants Multicellularity Ability to photosynthesize (most) Exhibit alternation of generations (a multicellular diploid generation alternates with a multicellular haploid generation)

Alternation of Generations Diploid sporophyte plant produces haploid spores through meiosis Spores divide by mitosis and develop into haploid gametophyte plants Haploid gametophyte plant produces haploid gametes through mitosis Gametes fuse to form diploid zygotes, which divide by mitosis and develop into diploid sporophytes

FIGURE 21-1 Alternation of generations in plants As shown in this generalized depiction of a plant life cycle, a diploid sporophyte generation produces haploid spores through meiosis. FIGURE 21-1 Alternation of generations in plants As shown in this generalized depiction of a plant life cycle, a diploid sporophyte generation produces haploid spores through meiosis. The spores develop into a haploid gametophyte generation that produces haploid gametes by mitosis. The fusion of these gametes results in a diploid zygote that develops into the sporophyte plant. The spores develop into a haploid gametophyte generation that produces haploid gametes by mitosis. The fusion of these gametes results in a diploid zygote that develops into the sporophyte plant.

Multi-cellular Dependent Embryos Have multi-cellular, dependent embryos Zygotes develop into multi-cellular embryos Embryos are retained within, and receive nutrients from the gametophyte parent

Crucial Ecological Role Through photosynthesis, plants provide food, directly or indirectly, for ALL of the animals, fungi, and non-photosynthetic microbes on land Plants produce oxygen gas as a byproduct of photosynthesis, continually replenishing oxygen in the atmosphere

Crucial Ecological Role Plants help create and maintain soil Dead plant material is decomposed by fungi, prokaryotes, and other decomposers Decomposed plant tissue becomes part of the soil, making it more fertile Roots of living plants help hold soil together, preventing erosion by wind and water

Human Necessities and Luxuries Plants provide shelter Wood is used to construct housing Plants provide fuel Wood: important fuel for warming and cooking in many parts of the world Coal: derived from the remains of ancient plants that have been transformed by geological processes

Human Necessities and Luxuries Plants provide medicine Many medicines and drugs were originally found in and extracted from plants, e.g. aspirin, Taxol, morphine Plants provide pleasure Flowers, gardens, and lawns Coffee, tea, and wine

Section 21.2 Outline 21.2 What Is the Evolutionary Origin of Plants? Green Algae Gave Rise to Plants The Ancestors of Plants Lived in Fresh Water

The Plant Evolutionary Tree Certain anatomical features represent milestones in the evolution of plants Appearance of vascular tissue and lignin Appearance of pollen and seeds Appearance of flowers and fruits

FIGURE 21-2 Evolutionary tree of some major plant groups

Green Algae Several lines of evidence support the hypothesis that green algae gave rise to plants: DNA comparisons show that green algae are plants’ closest living relatives Both use the same type of chlorophyll and accessory pigments in photosynthesis Both store food as starch Both have cell walls made of cellulose

Section 21.3 Outline 21.3 How Have Plants Adapted to Life on Land? Plant Bodies Resist Gravity and Drying Plant Embryos Are Protected and Plant Sex Cells May Disperse Without Water

Terrestrial Adaptations Roots or root-like structures Anchor plant Absorb water and nutrients from soil Waxy cuticle covers leaves and stems Reduces evaporative water loss

Terrestrial Adaptations Stomata (singular, stoma) Allow gas exchange when open Reduce evaporative water loss when closed Conducting vessels Transport water and nutrients throughout plant Lignin Stiffening agent found in cell walls; supports plant body

Reproduction Without Water Pollen A reduced male gametophyte that allows wind (instead of water) to carry sperm to eggs Seeds Nourish, protect, and help disperse developing embryos Flowers Attract pollinators Fruits Attract animals to disperse seeds

Section 21.4 Outline 21.4 What Are the Major Groups of Plants? Bryophytes Lack Conducting Structures Vascular Plants Have Conducting Vessels That Also Provide Support The Seedless Vascular Plants Include the Club Mosses, Horsetails, and Ferns The Seed Plants Dominate the Land, Aided by Two Important Adaptations: Pollen and Seeds

Section 21.4 Outline 21.4 What Are the Major Groups of Plants? (continued) Gymnosperms Are Nonflowering Seed Plants Angiosperms Are Flowering Seed Plants More Recently Evolved Plants Have Smaller Gametophytes

Major Groups of Plants Bryophytes (non-vascular plants) Lack well-developed structures for conducting water and nutrients Vascular plants (tracheophytes) Have a complex vascular system

Table 21-1 Features of the Major Plant Groups

The Bryophytes Lack true roots, stems, or leaves Have rhizoids, root-like anchoring structures Limited body size (most less than 2.5 cm tall) Non-vascular Cell walls lack a stiffening agent Most are restricted to moist habitats Motile sperm must swim to egg

The Bryophytes Gametophyte generation is dominant Sporophyte remains attached to and is nutritionally dependent on parental gametophyte Include liverworts, hornworts, and mosses

(b) Liverworts grow in moist, shaded areas (b) Liverworts grow in moist, shaded areas. This female plant bears umbrella-like archegonia, which hold the eggs. Sperm must swim up the stalks through a film of water to fertilize the eggs. FIGURE 21-3a Bryophytes The plants shown here are less than inch (about 1 centimeter) in height. (a) The horn-like sporophytes of hornworts grow upward from archegonia that are embedded in the gametophyte body.

FIGURE 21-3c Bryophytes (c) Moss plants, showing the stalks that carry spore-bearing capsules. FIGURE 21-3d Bryophytes (d) Mats of Sphagnum moss cover moist bogs in northern regions.

The Bryophytes: Reproduction Gametes develop within protected structures on gametophyte Archegonia (singular, archegonium) produce eggs Antheridia (singular, antheridium) produce sperm Archegonia and antheridia may be located on the same plant or on different plants

FIGURE 21-4 Moss life cycle The leafy green gametophyte (lower right) is the haploid generation that produces sperm and eggs. The sperm must swim through a film of water to the egg. The zygote develops into a stalked, diploid sporophyte that emerges from the gametophyte plant. The sporophyte is topped by a brown capsule in which haploid spores are produced by meiosis. These are dispersed and germinate, producing another green gametophyte generation. (Inset) Moss plants. The short, leafy green plants are haploid gametophytes; the reddish brown stalks are diploid sporophyte

The Bryophytes: Reproduction Sperm swim to egg Fertilization occurs and diploid sporophyte develops within archegonium of gametophyte Sporophyte produces encapsulated spores via meiosis Haploid spores disperse and germinate into new gametophytes

The Vascular Plants Have roots, stems, and leaves Have vessels impregnated with the stiffening agent lignin Sporophyte generation is dominant Include the seedless vascular plants and the seed plants

The Seedless Vascular Plants Gametes develop within archegonia and antheridia Motile sperm swim to egg Formed the first forests Gave rise to present-day coal deposits Include club mosses, horsetails, and ferns

Club Mosses Present-day club mosses are only a few inches tall Leaves are small and scalelike Lycopodium (ground pine) grows on temperate forest floors

FIGURE 21-5a Some seedless vascular plants Seedless vascular plants are found in moist woodland habitats. (a) The club mosses (sometimes called ground pines) grow in temperate forests. This specimen is releasing spores.

Horsetails Present-day horsetails (Equisetum) rarely exceed a meter in height Leaves reduced to scales on branches Outer layer of cells contain silica (glass) Abrasive texture led early European settlers to call them “scouring rushes”

FIGURE 21-5c Some seedless vascular plants Seedless vascular plants are found in moist woodland habitats. (b) The giant horsetail extends long, narrow branches in a series of rosettes. Its leaves are insignificant scales. At right is a cone-shaped spore-forming structure. .

Ferns Largest and most diverse group of seedless vascular plants Have well-developed, broad leaves Leaves emerge from coiled fiddleheads Reach significant heights in tropics

(d) Although most fern species are small, some, such as this tree fern, retain the large size that was common among ferns of the Carboniferous period. FIGURE 21-5b Some seedless vascular plants Seedless vascular plants are found in moist woodland habitats. (c) The leaves of this deer fern are emerging from coiled fiddleheads.

Ferns: Reproduction Sporophyte produces haploid spores within sporangia (singular, sporangium) Spores disperse and germinate into tiny, independent gametophytes Archegonium produces egg Antheridium produces sperm Sperm swim to egg Fertilization occurs and zygote develops into a diploid sporophyte

FIGURE 21-6 Fern life cycle The dominant plant body (upper left) is the diploid sporophyte. Haploid spores, formed in sporangia located on the underside of certain leaves, are dispersed by the wind to germinate on the moist forest floor into inconspicuous haploid gametophyte plants. On the lower surface of these small, sheet-like gametophytes, male antheridia and female archegonia produce sperm and eggs. The sperm must swim to the egg, which remains in the archegonium. The zygote develops into the large sporophyte plant. (Inset) Underside of a fern leaf, showing clusters of sporangia.

The Seed Plants Produce pollen and seeds Pollen grains contain sperm-producing cells Dispersed by wind or pollinators Eliminate need for sperm to swim to egg Seeds consist of: Embryonic plant Seed coat (protects embryo) Food supply (nourishes emerging plant)

FIGURE 21-7a,b Seeds Seeds from (a) a gymnosperm and (b) an angiosperm. Both consist of an embryonic plant and stored food confined within a seed coat. Seeds exhibit diverse adaptations for dispersal, including (c) the dandelionﾍs tiny, tufted seeds that float in the air and (d) the massive, armored seeds (protected inside the fruit) of the coconut palm, which can survive prolonged immersion in seawater as they traverse ocean

Seeds May remain dormant for days, months, or years May possess adaptations for dispersal by wind, water, and animals

FIGURE 21-7d Seeds Seeds exhibit diverse adaptations for dispersal, including (c) the dandelion’s tiny, tufted seeds that float in the air and (d) the massive, armored seeds (protected inside the fruit) of the coconut palm, which can survive prolonged immersion in seawater as they traverse ocean.

The Seed Plants Gametophytes greatly reduced in size and dependent on sporophyte for nutrition Female gametophyte is a small group of haploid cells Male gametophyte is pollen grain Include gymnosperms and angiosperms

Gymnosperms Non-flowering seed plants First fully terrestrial plants to evolve Includes ginkgos, cycads, gnetophytes, and conifers

Gymnosperms: Ginkgos Present-day ginkgos represented by a single species, Ginkgo biloba (maidenhair tree) Trees are either male or female Female trees bear foul-smelling, fleshy seeds Male trees extensively planted in U.S. cities (resistant to pollution) Ginkgo extract purportedly improves memory

FIGURE 21-8a Gymnosperms (a) This ginkgo, or maidenhair tree, is female and bears fleshy seeds the size of large cherries.

Gymnosperms: Cycads Probably evolved from ferns Most abundant in tropical or subtropical climates Are either male or female Grow slowly and live for a long time One Australian specimen estimated to be 5000 years old

FIGURE 21-8b Gymnosperms (b) A cycad. Common in the age of dinosaurs, these are now limited to about 160 species. Like ginkgos, cycads have separate sexes.

Gymnosperms: Gnetophytes 70 species of shrubs, vines, small trees Leaves of Ephedra species contain compounds used as stimulants and appetite suppressants The leaves of gnetophyte Welwitschia mirabilis may be hundreds of years old…

FIGURE 21-8c Gymnosperms (c) The leaves of the gnetophyte Welwitschia may be hundreds of years old.

Gymnosperms: Conifers Include pines, firs, spruce, hemlocks, and cypresses Most abundant in cold latitudes and at high elevations Adapted to dry, cold conditions: Retain green leaves throughout the year (evergreen) Thin, needle-like leaves covered with waterproofing material to reduce evaporation Produce an “antifreeze” in sap

FIGURE 21-8d Gymnosperms (d) The needle-shaped leaves of conifers are protected by a waxy surface layer.

Conifer Seeds Develop in Cones Male cones are relatively small Produce pollen (male gametophytes) by meiosis Pollen dispersed by wind Pollen grain germinates and forms a pollen tube if it lands near female gametophyte Pollen tube slowly burrows into female gametophyte (may take 14 months)

Conifer Seeds Develop in Cones Female cones consist of numerous woody scales arranged spirally around a central axis Two ovules (immature seeds) located at base of each scale Cells within each ovule undergo meiosis to produce haploid female gametophytes Female gametophytes produce egg cells

Conifer Seeds Develop in Cones Pollen tube releases sperm when it comes into contact with egg Fertilization occurs and seed develops Seeds released when cone is mature Seeds dispersed by wind Seeds germinate to form sporophyte trees

FIG 21-9 Pine life cycle The pine tree is the sporophyte generation (upper left) and bears both male and female cones. Haploid female gametophytes develop within the scales of female cones and produce egg cells. Male cones produce pollen, the male gametophytes. A pollen grain, dispersed by the wind, may land on the scale of a female cone. It then grows a pollen tube that penetrates the female gametophyte and conducts sperm to the egg. The fertilized egg develops into an embryonic plant enclosed in a seed. The seed is eventually released from the cone, germinates, and grows into a sporophyte tree.

Seed Plants: Angiosperms Seed plants that produce flowers and fruits Most diverse and widespread of all plants Have broad range in size Smallest is duckweed (3 mm in diameter) Largest is eucalyptus tree (100 meters in height)

FIGURE 21-10a Angiosperms (a) The smallest angiosperm is the duckweed, found floating on ponds. These specimens are about 1/8 inch (3 millimeters) in diameter. (b) The largest angiosperms are eucalyptus trees, which can reach 325 feet (100 meters) in height. Conspicuous flowers, such as those on a eucalyptus tree (b, inset), entice insects and other animals that carry pollen between individual plant

Seed Plants: Angiosperms Three major adaptations have contributed to dominance of angiosperms Flowers Fruits Broad leaves

Flowers Flowers are reproductive structures in which both male and female gametophytes are formed Believed to have evolved when gymnosperm ancestors formed an association with animals Animals benefited by eating some of the protein-rich pollen Plants benefited by using animals as pollinators

Flowers Most flowers are showy and attract animal pollinators (e.g. insects)

Flowers Some flowers are inconspicuous and rely on wind for pollination FIGURE 21-10b Angiosperms Both (c) grasses and many trees, such as (d) this birch, in which flowers are shown as buds (green) and blossoms (brown), have inconspicuous flowers and rely on wind for pollination.

Life Cycle of an Angiosperm Flowers develop on dominant sporophyte plant Male gametophytes (pollen) develop inside anthers Female gametophyte develops from an ovule inside the ovary Egg develops within female gametophyte

Life Cycle of an Angiosperm Pollination occurs when pollen grain lands on the stigma of a flower Fertilization occurs when growing pollen tube releases sperm into the ovule Fertilized ovule develops into a seed Seed is dispersed and germinates to form a sporophyte plant

FIGURE 21-11 Life cycle of a flowering plant The dominant plant body (upper right) is the diploid sporophyte, whose flowers normally produce both male and female gametophytes. Male gametophytes (pollen grains) are produced within anthers. The female gametophyte develops from a spore within the ovule, and contains one egg cell. A pollen grain that lands on a stigma grows a pollen tube that burrows down to the ovule and into the female gametophyte. There it releases its sperm, one of which fuses with the egg to form a zygote. The ovule gives rise to the seed, which contains the developing embryo and its food source. The seed is dispersed, germinates, and develops into a mature sporophyte.

Fruits Encourage Seed Dispersal Fruits are mature ovaries that contain developing seeds Various fruit adaptations help disperse seeds Edible fruits entice animals to eat them (seeds pass through digestive tract unharmed) Burrs cling to animal fur Winged fruits are carried through the air

Broad Leaves Broad leaves of angiosperms collect more sunlight for photosynthesis than narrow leaves of gymnosperms Temperate angiosperms drop leaves to conserve water when it is in short supply (fall, winter) Tropical and subtropical angiosperms are evergreen May shed leaves during dry season

Broad Leaves Photosynthetic advantage is offset by fact that broad, tender leaves are more appealing to herbivores than tough, waxy needles of conifers Angiosperm defenses include Physical defenses (thorns, spines, resins) Chemical defenses (make plant tissue poisonous or distasteful)

Chemical Defenses Many defensive compounds have been exploited by humans for medicinal and culinary uses Medicines (aspirin, codeine) Stimulants (nicotine, caffeine) Spicy flavors (mustard, peppermint)

Smaller Gametophytes ‘Evolve’ Earliest plants (nonvascular plants) Gametophyte dominates Small, dependent sporophyte attached to larger gametophyte Later plants (seedless vascular plants) Sporophyte dominates Small gametophyte is independent of sporophyte Recently evolved plants (seed plants) Microscopic, dependent gametophyte attached to larger sporophyte