The Plant Kingdom: Seed Plants Chapter 28

Learning Objective 1 Compare the features of gymnosperms and angiosperms

Two Groups of Seed Plants Gymnosperms seeds are totally exposed or borne on the scales of cone ovary wall does not surround the ovules Angiosperms flowering plants produce seeds within a fruit (a mature ovary)

Gymnosperm and Angiosperm Evolution

Gymnosperms Angiosperms Gnetophytes Ginkgoes Conifers Cycads Evolution of flowering plants Figure 28.2: Gymnosperm and angiosperm evolution. This cladogram shows one hypothesis of phylogenetic relationships among living seed plants, based on structural evidence and molecular comparisons. The arrangement of the phyla shown here may change as future analyses help clarify relationships. Evolution of seeds Fig. 28-2, p. 602

KEY CONCEPTS Seed plants include gymnosperms and angiosperms

Learning Objective 2 Trace the steps in the life cycle of a pine Compare its sporophyte and gametophyte generations

Conifers

Gymnosperms Angiosperms Gnetophytes Ginkgoes Conifers Cycads Figure 28.3: Conifers. (a) Colorado blue spruce (Picea pungens) is a coniferous evergreen tree native to Colorado, Wyoming, Utah, and New Mexico. Spruces are important ornamental plants, as shown in this New Jersey garden. (b, c) Leaf variation in conifers. (b) Needles of white pine (Pinus strobus). (c) Small, scalelike leaves of American arborvitae (Thuja occidentalis). Fig. 28-3 (1), p. 603

Fig. 28-3 (a-c), p. 603 Figure 28.3: Conifers. (a) Colorado blue spruce (Picea pungens) is a coniferous evergreen tree native to Colorado, Wyoming, Utah, and New Mexico. Spruces are important ornamental plants, as shown in this New Jersey garden. (b, c) Leaf variation in conifers. (b) Needles of white pine (Pinus strobus). (c) Small, scalelike leaves of American arborvitae (Thuja occidentalis). Fig. 28-3 (a-c), p. 603

Pine Life Cycle 1 Pine tree Pine gametophytes a mature sporophyte extremely small nutritionally dependent on sporophyte generation

Pine Life Cycle 2 Pine is heterosporous produces microspores and megaspores in separate cones Male cones produce microspores that develop into pollen grains (immature male gametophytes) carried by air currents to female cones

Pine Life Cycle 3 Female cones produce megaspores One of each four megaspores (meiosis) develops into a female gametophyte within an ovule (megasporangium)

Pine Life Cycle 4 Pollination Pollen tube After fertilization transfer of pollen to female cones Pollen tube grows through megasporangium to egg within archegonium After fertilization zygote develops into embryo encased inside seed adapted for wind dispersal

Pine Life Cycle

Each scale bears two microsporangia 2 Microsporangium Microspores, each of which develops into a pollen grain Scale from a male cone Pollen grains are transferred to the female cone by wind 3 Male cone 3 4 Scale from a female cone Female gametophyte Each scale bears two ovules (megasporangia) Megasporangium Megaspore Growing pollen tube Ovule HAPLOID (n) GAMETOPHYTE GENERATION Meiosis Immature female cone Fertilization DIPLOID (2n) SPOROPHYTE GENERATION Zygote 5 Papery wings Second sperm nucleus Sperm nucleus united with egg nucleus Figure 28.4: Life cycle of pine. One major advantage of gymnosperms over the seedless vascular plants is the production of wind-borne pollen grains. See text for a detailed description. Pollen tube Seed coat Male cones (pollen cones) 1 6 Mature female cone (seed cone) Embryo Two seeds on the upper surface of the scale Newly germinated seedling Female gametophyte (nutritive tissue) Pine (mature sporophyte) Fig. 28-4, p. 604

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Learning Objective 3 What features distinguish gymnosperms from bryophytes and ferns?

Gymnosperms Are vascular plants Produce seeds unlike bryophytes Produce seeds unlike bryophytes and ferns Produce wind-borne pollen grains unlike ferns and other seedless vascular plants

KEY CONCEPTS Gymnosperms produce exposed seeds, usually in cones borne on the sporophytes

Learning Objective 4 What are the four phyla of gymnosperms?

Conifers (Phylum Coniferophyta) Largest phylum of gymnosperms Woody plants that bear needles (leaves that are usually evergreen) produce seeds in cones Most are monoecious have male and female reproductive parts in separate cones on same plant

Male and Female Cones

KEY CONCEPTS Conifers are the most diverse and numerous of the four living gymnosperm phyla

Cycads (Phylum Cycadophyta) Palmlike or fernlike in appearance Are dioecious have male and female reproductive structures on separate plants but reproduce with pollen and seeds in conelike structures

Cycads

Gymnosperms Angiosperms Gnetophytes Ginkgoes Conifers Cycads Figure 28.6: Cycads. Fig. 28-6 (1), p. 605

Female strobilus (seed cone) Figure 28.6: Cycads. Female strobilus (seed cone) Fig. 28-6a, p. 605

Figure 28.6: Cycads. Fig. 28-6b, p. 605

Phylum Ginkgophyta Ginkgo biloba only surviving species in phylum deciduous, dioecious tree Female ginkgo produces fleshy seeds directly on branches

Ginkgo

Gymnosperms Angiosperms Gnetophytes Ginkgoes Conifers Cycads Figure 28.7: Ginkgo, or maidenhair tree. Fig. 28-7 (1), p. 606

Figure 28.7: Ginkgo, or maidenhair tree. Fig. 28-7a, p. 606

Figure 28.7: Ginkgo, or maidenhair tree. Fig. 28-7b, p. 606

Gnetophytes (Phylum Gnetophyta) Share some traits with angiosperms

Gymnosperms Angiosperms Gnetophytes Ginkgoes Conifers Cycads Figure 28.8: Gnetophytes. Fig. 28-8 (1), p. 607

Gnetophytes

Learning Objective 5 What features distinguish flowering plants from other plants?

Flowering Plants Angiosperms (phylum Anthophyta) Vascular plants that produce flowers and seeds enclosed within a fruit Most diverse and successful plant group

Flowering Plants

Flowering Plants Flower Ovules enclosed within ovary sepals, petals, stamens, carpels functions in sexual reproduction Ovules enclosed within ovary unlike gymnosperms After fertilization ovules become seeds ovary develops into fruit

Floral Structure

Fig. 28-10a, p. 609 Figure 28.10: Floral structure. (a) An Arabidopsis thaliana flower. Fig. 28-10a, p. 609

Pollen grain (each will produce two sperm cells) Female floral parts Male floral parts Pollen grain (each will produce two sperm cells) Stigma PISTIL (consisting of one or more carpels) Style Anther STAMEN Ovary Filament Ovules (each producing one egg cell) Petal Figure 28.10: Floral structure. (b) This cutaway view of an Arabidopsis flower shows the details of basic floral structure. Each flower has four sepals (two are shown), four petals (two are shown), six stamens, and one long pistil. Four of the stamens are long, and two are short (two long and two short are shown). Pollen grains develop within sacs in the anthers. In Arabidopsis, the compound pistil consists of two carpels that each contain numerous ovules. This flower is both a complete and a perfect flower. Sepal Receptacle Peduncle Fig. 28-10b, p. 609

Parts of a Flower

Petals Sepals Figure 28.11: Parts of a flower. Fig. 28-11a, p. 610

Stamen Pistil Figure 28.11: Parts of a flower. Fig. 28-11b, p. 610

Simple and Compound Pistils

Stigma Ovules Style Ovary wall Ovary Fig. 28-12a, p. 611 Figure 28.12: Simple and compound pistils. Fig. 28-12a, p. 611

One carpel Ovules Stigma Style Ovary wall Ovary Fig. 28-12b, p. 611 Figure 28.12: Simple and compound pistils. Ovary Fig. 28-12b, p. 611

One carpel Ovules Stigma Style Ovary wall Ovary Stepped Art Figure 28.12: Simple and compound pistils. Stepped Art Fig. 28-12b, p. 611

KEY CONCEPTS Angiosperms produce ovules enclosed within carpels; following fertilization, seeds develop from the ovules, and the ovaries of carpels become fruits

Learning Objective 6 Explain the life cycle of a flowering plant Describe double fertilization

Flowering Plant Life Cycle 1 Sporophyte generation dominant Gametophytes extremely reduced in size nutritionally dependent on sporophyte generation Heterosporous produce microspores, megaspores in flower

Flowering Plant Life Cycle 2 Microspore develops into a pollen grain (immature male gametophyte) One of each four megaspores (meiosis) develops into embryo sac (female gametophyte)

Flowering Plant Life Cycle 3 Embryo sac contains seven cells with eight nuclei Egg cell and central cell with two polar nuclei participate in fertilization

Flowering Plant Life Cycle

Developing pollen tube of mature male gametophyte Pollination Each microspore develops into a pollen grain 6 Embryo sac (mature female gametophyte) 5 Pollen grain (immature male gametophyte) Microspore Tetrad of microspores Pollen tube 3 Polar nuclei Megaspore Two sperm cells HAPLOID (n) GAMETOPHYTE GENERATION Egg nucleus Meiosis Double fertilization DIPLOID (2n) SPOROPHYTE GENERATION 7 Ovary 4 2 Endosperm (3n) Megasporocyte Zygote (2n) Figure 28.13: Life cycle of flowering plants. A significant feature of the flowering plant life cycle is double fertilization, in which one sperm cell unites with the egg, forming a zygote, and the other sperm cell unites with the two polar nuclei, forming a triploid cell that gives rise to endosperm. See text for a detailed description. Megasporangium (ovule) Fruit 8 Embryo Seed Seed coat Microsporocytes within microsporangia Seedling Anther 1 Flower of mature sporophyte Fig. 28-13, p. 612

Double Fertilization Characteristic of flowering plants Results in formation of diploid zygote triploid endosperm

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Learning Objective 7 Contrast eudicots and monocots, the two largest classes of flowering plants

Monocots (Class Monocotyledones) Most have floral parts in threes Seeds each contain 1 cotyledon Endosperm nutritive tissue in mature seeds

Eudicots (Class Eudicotyledones) Usually have floral parts in fours or fives or multiples thereof Seeds each contain 2 cotyledons Cotyledons nutritive organs in mature seeds absorbed nutrients in endosperm

Monocot and Eudicot

Learning Objective 8 What are the evolutionary adaptations of flowering plants?

Reproduction Flowering plants reproduce sexually by forming flowers After double fertilization, seeds form within fruits Wind, water, insects, animals transfer pollen grains

Structures Efficient water-conducting vessel elements in xylem Efficient carbohydrate-conducting sieve tube elements in phloem

KEY CONCEPTS Angiosperms, which compose a single phylum, dominate the land and exhibit great diversity in both vegetative and reproductive structures

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Learning Objective 9 Summarize the evolution of gymnosperms from seedless vascular plants Trace the evolution of flowering plants from gymnosperms

Evolution 1 Seed plants arose from seedless vascular plants Progymnosperms seedless vascular plants had megaphylls and “modern” woody tissue probably gave rise to conifers and seed ferns

Progymnosperm Seed Fern

Evolution 2 Seed ferns probably gave rise to cycads and ginkgo Evolution of gnetophytes, particularly their relationship to flowering plants, is unclear

Evolution 3 Flowering plants probably descended from gymnosperms with specialized features leaves with broad, expanded blades closed carpels Flowering plants likely arose only once

Fossil Angiosperms

Figure 28.17: The oldest known fossil angiosperm. This fossil of Archaefructus shows a carpel-bearing stem. Discovered in northeastern China, it is about 125 million years old. Carpel Ovule 5 mm Fig. 28-17, p. 615

Scars on reproductive axis Pistils Scars on reproductive axis Figure 28.18: Fossil flower. The fossilized flower of the extinct plant Archaeanthus linnenbergeri, which lived about 100 mya. The scars on the reproductive axis (receptacle) may show where stamens, petals, and sepals were originally attached but abscised (fell off). Many spirally arranged pistils were still attached at the time this flower was fossilized. 7 mm Fig. 28-18, p. 615

Evolution of Flowering Plants

Evolution of vessel elements Basal Angiosperms Core Angiosperms Amborella Water lilies Star anise Magnoliids Monocots Eudicots Figure 28.19: Evolution of flowering plants. Evolution of vessel elements Evolution of flowering plants Fig. 28-19a, p. 616

Figure 28.19: Evolution of flowering plants. Fig. 28-19b, p. 616

Figure 28.19: Evolution of flowering plants. Fig. 28-19c, p. 616

Figure 28.19: Evolution of flowering plants. Fig. 28-19d, p. 616

Figure 28.19: Evolution of flowering plants. Fig. 28-19e, p. 616

KEY CONCEPTS Gymnosperms and angiosperms evolved from ancestral seedless vascular plants