The Diversity of Plants

The Diversity of Plants

The huge, foul-smelling flower of the stinking corpse lily Parasite
Figure: 21-CO Title: The Diversity of Plants Caption: The huge, foul-smelling flower of the stinking 惡臭corpse屍體lily is a treat for visitors to Asian rain forests.

21.1 What Is the Evolutionary Origin of Plants?
Photosynthetic protists Probably similar to today’s algae Lacked true roots, stems, leaves, and complex reproductive structures such as flowers or cones Figure Evolutionary tree of some major plant groups (p. 406)

無種子維管束植物: 維管束植物中，有些植物不產生種子，如蕨類，它們會產生風媒孢子來散播。
Bryophytes苔蘚類 Tracheophytes維管植物 seed plants Liverworts Mosses Ferns Gymnosperms Angiosperms 無種子維管束植物: 維管束植物中，有些植物不產生種子，如蕨類，它們會產生風媒孢子來散播。維管束植物: 蕨類、裸子和被子植物都具有維管束，因此具有真正的根、莖和葉等構造。維管束植物體內的維管束組織貫穿根、莖和葉等器官，使植物體內的水分和養分的輸送加快，並且可支持植物體，使其直立。因此，維管束植物長得比蘚苔植物高大。種子植物: 裸子植物和被子植物靠種子繁殖乾燥的種子不但可以長期保存，抵抗乾燥，而且在適宜環境下萌芽時，種子內儲藏的養分可以供給其內的胚發育，增加種子植物繁殖和擴張生長範圍的能力。因此，種子植物在現今地球陸地上占了大部分的生長面積無維管束植物: 僅蘚苔植物不具維管束(為輸導組織)，沒有真正的根、莖和葉等構造 Figure: 21-1 Title: Evolutionary tree of some major plant groups Caption: Ancestral green alga

Green algae gave rise to plants
Green algae, closest living relatives DNA comparisons same type of chlorophyll and accessory pigments for photosynthesis Food storage starch Cellulose cell walls The ancestors of plants lived in fresh water Highly variable Temperature Chemicals in water Periods of dryness

Key Features of Plants Multicellular Photosynthetic
Plants Have Alternating Multicellular Haploid and Diploid Generations Plants have multicellular , dependent embryos Plants are adapted to life on land

Plants have alternating multicellular haploid and diploid generations
Alternation of generations A diploid sporophyte孢子體stage Zygotes formed by the fusion of two haploid gametes a haploid gametophyte配子體stage Haploid spores produced via meiosis Haploid gametes produced via mitosis

Haploid Diploid MITOSIS FERTILIZATION MEIOSIS gametophyte (n) sperm
egg n FERTILIZATION 2n zygote Haploid MEIOSIS 2n spore mother cell n spores Figure: 21-2 Title: Alternation of generations in plants Caption: 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. Diploid 2n embryo sporophyte (2n) haploid diploid

Plants Have Multicellular, Dependent Embryos
Zygote develop into multicellular embryos that are retained within and receive nutrients from the tissues of the parent plant Dependent Embryos: Not found among photosynthetic protists; distinguish plant and algae

Environmental changes of plants living on land
No supportive buoyancy of water Not bathed in a nutrient solution Air tends to dry things out Gametes and zygotes cannot be carried by water currents or propelled by flagella

Plant Bodies Resist Gravity and Drying
Roots/root-like structures – anchor and get water and nutrients; all land plants Waxy cuticle – limits water loss; all land plants Stomata: gas exchange and limit water loss; all land plants Conducting vessels – transport water and mineral in the plant; vascular plants Lignin – increases rigidity, thereby increasing sun exposure; vascular plants

Plant Embryos Are Protected and Plant Sex Cells May Disperse Without Water
Well-protected and well-provisioned embryos Seeds wind Fruit Animal forager and dispersed the indigestible seeds Waterless dispersal of sex cells Pollens Flowers Animal pollinators

21.3 What Are the Major Groups of Plants?

苔蘚類植物 Table: 21-T1 Title: Features of the Major Plant Groups

Two major groups of land plants
Bryophytes Nonvascular plants Lack Conducting Structures Requires a moist environment ot reproduce Straddles the boundary between aquatic and terrestrial life Tracheophytes Vascular plants

Bryophytes Lack true roots, leaves, and stems
Rootlike anchoring structure--- rhizoids Bring water and nutrients into the plant body Lack well-developed structures for conducting water and nutrients Nonvascular Diffusion or poorly developed conducing tissues to distribute water and other nutrients Body size is limited No stiffening agent in their bodies Body size is less than 1 inch (2.5cm)

苔蘚類植物具有直立的假莖，其上著生假葉，並有假根固著在土壤內。
Liverworts grow in moist, shaded areas. This female plant bears umbrella-like archegonia 造卵器, which hold the eggs. Sperm must swim up the stalks through a film of water to fertilize the eggs. 苔蘚類植物具有直立的假莖，其上著生假葉，並有假根固著在土壤內。 Figure: 21-3 part a Title: Bryophytes part a Caption: 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. 蘚苔植物是最先出現在陸地的植物。它們的外表演化出角質層，可以保護植物，以防止水分的過度散失；但由於植株尚未演化出維管束，所以水分和養分的運輸速度很慢，且個體都很小。此外，蘚苔植物的受精作用需要外界的潮濕環境；因此，在潮溼的地面、牆壁或樹幹上，常常可以發現這一群綠色矮小的植物。蘚類植物如地錢，其綠色的植物體平鋪於地面上，腹部的假根則固著在土壤內，以吸收水分。

Moss plants, showing the stalks that carry spore-bearing capsules.
苔蘚類植物，植物體平鋪於地面上，腹部的假根則固著在土壤內，以吸收水分 Some mosses have a waterproof covering that retains moisture preventing water loss and can survive in deserts (on bare rock) or in far northern and southern latitudes where humidity is low and water is scarce for much of the year Figure: 21-3 part b Title: Bryophytes part b Caption: (b) Moss plants, showing the stalks that carry spore-bearing capsules. Question Why are all bryophytes short?

The Reproductive Structures of Bryophytes Are Protected
Archegonia (singular, archegonium) Where eggs develop Antheridia (singular, antheridium) Where sperm are formed Egg emits a chemical attractant Sperm swim through a film of water Fertilized egg is retained in the archegonium, where the embryo grows and matures into a small sporophyte

The leafy green gametophyte (lower right) is the haploid generation that produces sperm and eggs.
emerging gametophyte archegonium Figure: 21-4 main bottom Title: Life cycle of a moss main bottom Caption: 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. antheridium leafy gametophyte haploid diploid Copyright © 2005 Pearson Prentice Hall, Inc.

capsules MEIOSIS emerging sporophyte capsules Sporophyte develops within gametophyte Figure: 21-4 main top Title: Life cycle of a moss main top Caption: 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. The sporophyte is topped by a brown capsule in which haploid spores are produced by meiosis. FERTILIZATION

Life cycle of a moss haploid spores capsules MEIOSIS emerging
sporophyte capsules capsules MEIOSIS Life cycle of a moss haploid spores emerging gametophyte leafy gametophyte FERTILIZATION Figure: 21-4 Title: Life cycle of a moss Caption: 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 sporophytes. haploid diploid

Figure: 21-4 Title: Life cycle of a moss Caption: (Inset) Moss plants. The short, leafy green plants are haploid gametophytes; the reddish brown stalks are diploid sporophytes. Haploid Gametophyte stage of their alternation of generations is the most prominent phase

Bryophytes lack conducting structures
Rhizoids Limited size – lack of vascular tissue and lignin Reproductive structures a. Archegonia – produce eggs b. Antheridia – produced swimming sperm Gametophyte stage of their alternation of generations is the most prominent phase

Vascular plants Vessels
A specialized groups of conducting cells Allow water and nutrients absorbed by the roots to move to the upper portions of the plant That are impregnated with the stiffening substance Lignin adds extra support, Vascular plants grow taller than nonvascular plants Sporophyte stage is larger and more conspicuous than the gametophyte

苔蘚類植物 Table: 21-T1 Title: Features of the Major Plant Groups

The seedless vascular plants
include the club mosses, horsetails, and ferns Produce swimming sperm, so water is essential for reproduction Do not produce seeds, they propagate by spores Diminished in size compared to their ancestors Dominated the landscape hundreds of millions of years ago

The club mosses grow in temperate forests (few inches in height, ground pine)
Figure: 21-5 Title: Some seedless vascular plants Caption: 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. (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. (c) The leaves of this deer fern are emerging from coiled fiddleheads. Question In each of these photos, is the pictured structure a sporophyte or a gametophyte? deer fern The giant horsetail (scouring rush)

Ferns 1200 species most diverse seedless vascular plants
Ferns are the only seedless vascular plants that have Broad leaves Sporangia produce spores on special leaves of sporophyte Spores are dispersed by the wind give rise to tiny, haploid gametophyte which produce sperm and eggs

Gametophytes of ferns Retains two traits that are reminiscent of the bryophytes 1. small pametophytes lack conducting vessels 2. as in bryophytes, the sperm must swim through water to reach the egg

The dominant plant body is the diploid sporophyte.
masses of sporangia sporangium leaf MEIOSIS stem root Figure: 21-6 main top Title: Life cycle of a fern main top Caption: 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, sheetlike 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. 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. haploid diploid The dominant plant body is the diploid sporophyte.

FERTILIZATION archegonium gametophyte sperm antheridium Figure: 21-6 main bottom Title: Life cycle of a fern main bottom Caption: 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, sheetlike 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. haploid sheetlike 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. diploid

sporophyte masses of sporangia sporangium leaf MEIOSIS root stem
FERTILIZATION masses of sporangia sporangium MEIOSIS stem root leaf gametophyte Figure: 21-6 Title: Life cycle of a fern Caption: 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, sheetlike 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. haploid diploid

Figure: 21-6 Title: Life cycle of a fern Caption: (Inset) Underside of a fern leaf, showing clusters of sporangia.

The seed plants dominate the land
Distinguished from bryophytes and seedless vascular plants by pollen and seeds pollen Pollen grains – tiny structures that carry sperm-producing cells transport the sperm without water; dispersed by wind or animals Seeds –consists of an embryonic plant, a supply of food for embryo, and protective coat Seed coat – protects embryo and maintains dormancy Stored food used by embryo until it does its own photosynthesis Dispersed by wind, water, or animals

embryo stored food seed coat Pine seed Bean seed (gymnosperm)
(angiosperm) Figure: 21-7 Title: Seeds Caption: 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'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 oceans. Question Can you think of some adaptations that help protect seeds from destruction by animal consumption?

Gametophytes of seed plants
are microscopic Female gametophyte is a small group of haploid cells Male gametophyte is the pollen grain

Two major groups of seed plants
Gymnosperms ---- Lack flowers Angiosperms ---- flowering plants

Gymnosperms Are Nonflowering Seed Plants
Evolved earlier than the flowering plants Conifer 500 species Pines, firs, spruce hemlocks and cypresses Habitats: in the Cold latitudes of the Far north and At high elevations where conditions are dry

Three ways of conifers to adapt the cold and dry environment
1. retain green leaves through out the year, enabling these plats to continue photosynthesizing and growing slowly evergreens 2. leaves are covered with a thick waterproof surface that minimizes evaporation 3. produce an antifreeze in their sap that enables them to continue transporting nutrients in below-freezing temperature Give their fragrant piney scent

E. Gymnosperms 裸子植物 are nonflowering seed plants
1. Conifers – adapted to dry, cold conditions a. Thin needles retained year round and “antifreeze” are adaptations to dry, cold conditions (Figure 21-12) b. Male cones produce pollen dispersed by the wind (Figure 21-8) c. Female cones produce female gametophytes that develop and produce eggs d. e. Embryos are enclosed in (naked) seeds dispersed when the scales of the female cone open 2. and (Figure 21-9)

Reproduction of conifers
The tree is the diploid sporophyte Develops both male and female cones Male cones are relatively small (2 cm or less) Release clouds of pollen during the reproductive season and then disintegrate Female cones consists of a series of woody scales At the base of each scale are two ovules (immature seeds) Within which diploid spore cells form and undergo meiosis to produce haploid female gametophytes then develop and produce egg cells

Life cycle of the pine scale of female cone ovule scale of male cone
spore-forming cell mature sporophyte MEIOSIS MEIOSIS seedlings Figure: 21-8 Title: Life cycle of the pine Caption: 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. Male gametophyte (pollen) female gametophyte seed egg cell pollen Tube (14 months) embryo haploid diploid FERTILIZATION

Ginkgos 銀杏 probably the first modern-day seed plants to evolve
Figure: 21-9 part a Title: Two uncommon gymnosperms part a Caption: (a) This ginkgo, or maidenhair tree, is female and bears fleshy seeds the size of large cherries. Ginkgo biloba Ginkgos 銀杏 probably the first modern-day seed plants to evolve And widespread during the Jurassic period (208 million yrs ago)

Cycads蘇鐵 probably evolved from ferns
Figure: 21-9 part b Title: Two uncommon gymnosperms part b Caption: (b) A cycad. Common in the age of dinosaurs, these are now limited to about 160 species. Like ginkgos, cycads have separate sexes. Cycads蘇鐵 probably evolved from ferns 160 species in tropic and subtropic lands

Angiosperms Dominated Earth for more than 100 million yrs
are modern flowering seed plants Dominated Earth for more than 100 million yrs Highly diverse : 230,000 species Duckweed浮萍 Eucalyptus tree尤加利樹 Grass Cactus Corpse lilies Rule over the plant kingdom

Flowers attract pollinators
Flower develop on the dominant sporophyte plant May have evolved when gymnosperm ancestors formed an association with animals that carried their pollen from plant to plant Less pollen produced

Figure: part d Title: Angiosperms Caption: (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. 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. More conspicuous flowers, such as those on (e) this butterfly weed and on a eucalyptus tree (b, inset), entice insects and other animals that carry pollen between individual plants. Exercise List the advantages and disadvantages of wind pollination. Do the same for pollination by animals. Why do both types of pollination persist among the angiosperms?

Figure: part e Title: Angiosperms Caption: (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. 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. More conspicuous flowers, such as those on (e) this butterfly weed and on a eucalyptus tree (b, inset), entice insects and other animals that carry pollen between individual plants. Exercise List the advantages and disadvantages of wind pollination. Do the same for pollination by animals. Why do both types of pollination persist among the angiosperms?

Life cycle of angiosperm
Flowers are the structures in which both male and female gametophytes are formed Female gametophytes develop from an ovule in the ovary of a flower Male gametophytes (pollen) are formed inside a structure called the anther Pollen tubes transport sperm from the flower stigma to the egg in the ovary Plant embryo enclosed in a seed formed from the ovule

seedling flower stigma anther mature sporophyte food source embryo
ovule seed coat ovule seed spore-forming cell Figure: top Title: Life cycle of a flowering plant top Caption: 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. anther contains cells that form pollen each seed developed from one ovule MEIOSIS MEIOSIS

pollen grain stigma pollen (male gametophytes) pollen tube spore
FERTILIZATION Figure: bottom Title: Life cycle of a flowering plant bottom Caption: 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. sperm nuclei haploid female gametophyte diploid egg cell

seedling flower stigma anther mature sporophyte food source embryo
ovule stigma anther food source embryo seed coat spore- forming cell MEIOSIS anther contains cells that form pollen spore pollen (male gametophytes) ovule each seed developed from one ovule seed stigma pollen grain pollen tube FERTILIZATION female gametophyte sperm nuclei egg cell Figure: 21-11 Title: Life cycle of a flowering plant Caption: 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. haploid diploid

Fruits encourage seed dispersal
The ovary surrounding the seed matures into a fruit Help to disperse the seed Edibility seeds are undigested and dispersed Clinging to animal fur Form wings to fly in air each seed developed from one ovule stigma pollen grain pollen tube FERTILIZATION female gametophyte sperm nuclei egg cell

Broad leaves capture more sunlight
When water is plentiful Broad leaves provide and advantage by collecting more sunlight for photsynthesis When water is in shortage Seasonal leaf drop Adaptations to avoid predation by herbivores Physical defenses: Thorns, spines, and resins Chemical defenses: poisonous or distasteful compd

More Recently Evolved Plants
Evolutionary history of plants has been marked by tendency For the sporophyte generation become increasingly prominent For the longevity and size of gametophyte generation to shrink The earliest plants were similar to nonvascular plants Sporophyte is small than the gametophyte and remains attached to it Plants that originated later Sporophyte is dominant Gametophyte is a smaller independent plat Seed plants Gametophytes are microscopic

Figure: 21-12 Title: Two ways of coping with the dryness of winter Caption: The evergreen (a conifer) retains its needles throughout the year. The small surface area and heavy cuticle of the needles slow the loss of water through evaporation. In contrast, the aspen (an angiosperm) sheds its leaves each fall. The dying leaves turn brilliant shades of gold as pigments used to capture light energy for photosynthesis are exposed when the chlorophyll disintegrates.

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