Evolution of Seed Plants – Ch. 30

1. Evolution of Seed Plants – Ch. 30 Lecture Objectives: Evolutionary adaptations of seed plants Gymnosperms vs. Angiosperms Flower parts & angiosperm lifecycle

3. Seed Plants - Transforming the World • Originated 360 mya • Dominant producers in most terrestrial ecosystems • Why seeds? • May remain dormant for days to years • Seeds have a supply of stored food • Transported long distances by wind or animals

4. Characteristics of Seed Plants • Reduced Gametophytes • develop within walls of spores that are retained within tissues of the parent sporophyte • Heterosporous • Produce Ovules • Pollen Production • Seed Production

5. Figure 30.UN05 Five Derived Traits of Seed Plants Microscopic male and female gametophytes (n) are nourished and protected by the sporophyte (2n) Reduced gametophytes Male gametophyte Female gametophyte Heterospory Microspore (gives rise to a male gametophyte) Megaspore (gives rise to a female gametophyte) Ovules Integument (2n) Ovule (gymnosperm) Megaspore (n) Megasporangium (2n) Pollen grains make water unnecessary for fertilization Pollen Seeds Seeds: survive better than unprotected spores, can be transported long distances Seed coat Food supply Embryo

6. Gymnosperms/Conifers • Better suited to drier conditions • Served as food source for herbivorous dinosaurs • “Naked Seed” Plants = seeds are exposed on sporophylls that form cones (strobili)

7. Gymnosperm Diversity • The gymnosperms consist of four divisions • Cycadophyta (cycads) • Gingkophyta (one living species: Ginkgo biloba) • Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) • Coniferophyta (pine, fir, and redwoods)

8. Division Cycadophyta • Large cones w/ palm-like leaves • *** Flagellated sperm • These thrived during the Mesozoic, but most of the few surviving species are endangered Fig. 30.7a

9. Division Ginkgophyta • Single living species, Ginkgo biloba • *** Flagellated sperm • High tolerance to air pollution Fig. 30.7b

10. Division Gnetophyta • 3 genera: Gnetum, Ephedra, and Welwitschia • Species vary in appearance, some are tropical whereas others live in deserts

11. Figure 30.7c Phylum Gnetophyta Welwitschia Gnetum Ovulate cones Welwitschia Ephedra

12. Fig. 30.7d Division Coniferophyta • Largest of the gymnosperm phyla • Most are evergreen and can carry out photosynthesis year round Doug fir European larch Sequoia

13. Figure 30.7e Phylum Coniferophyta Common juniper Wollemi pine Bristlecone pine

14. Figure 30.4 Ovule Megasporocyte (2n) Ovulate cone Integument Pollen cone Microsporocytes (2n) Pollen grains (n) Megasporangium (2n) Mature sporophyte (2n) MEIOSIS Germinating pollen grain MEIOSIS Microsporangia Microsporangium (2n) Seedling Surviving megaspore (n) Archegonium Seeds Female gametophyte Food reserves Sperm nucleus (n) Seed coat (2n) Pollen tube Key Embryo (new sporophyte) (2n) Haploid (n) FERTILIZATION Diploid (2n) Egg nucleus (n)

15. The Life Cycle of a Pine • Three key features of the gymnosperm life cycle are • Miniaturization of their gametophytes • Development of seeds from fertilized ovules • The transfer of sperm to ovules by pollen • The pine tree is the sporophyte and produces sporangia in male and female cones • Small cones produce microspores called pollen grains, each of which contains a male gametophyte • The familiar larger cones contain ovules, which produce megaspores that develop into female gametophytes • It takes nearly three years from cone production to mature seed

16. Angiosperms Flowering Seed Plants

17. Division Anthophyta (Gk. Anthos – flower) • Angiosperms have two key adaptations: • Flowers - specialized for sexual reproduction • Specialized shoot with up to 4 types of modified leaves called floral organs: • Sepals (enclose the flower) • Petals (attract pollinators) • Stamens (produce pollen) • Carpels (produce ovules) * can be complete or incomplete • Normally pollinated by insects, animals or wind • Fruits – used to protect and disseminate seeds

18. Figure 30.8 Stigma Carpel Stamen Anther Style Filament Ovary Petal Sepal Ovule Receptacle

19. ▼ Mechanisms that disperse seeds by explosive action Figure 30.11 ▼ Wings ▼ Seeds within berries and other edible fruits ▼ Barbs

20. Microsporangium Figure 30.12 Anther Carpel Microsporocytes (2n) Mature flower on sporophyte plant (2n) Microspore (n) MEIOSIS Generative cell Ovule with megasporangium (2n) Tube cell Tube nucleus Male gametophyte (in pollen grain) (n) Ovary Pollen grains MEIOSIS Germinating seed Stigma Pollen tube Megasporangium (2n) Surviving megaspore (n) Sperm Embryo (2n) Integuments Tube nucleus Endosperm (3n) Seed Micropyle Seed coat (2n) Antipodal cells Polar nuclei in central cell Style Female gametophyte (embryo sac) Synergids Egg (n) Zygote (2n) Nucleus of developing endosperm (3n) Egg nucleus (n) FERTILIZATION Key Haploid (n) Diploid (2n) Discharged sperm nuclei (n)

21. The Angiosperm Life Cycle • * Flower (sporophyte tissue) is composed of both male and female structures • * Male gametophytes are contained within pollen grains produced by the microsporangia of anthers • * Female gametophyte (embryo sac) develops within an ovule contained within an ovary at the base of a stigma • 1. Pollen grain lands on stigma & germinates  pollen tube of the male gametophyte grows down to the ovary • 2. Ovule is entered by a pore called the micropyle • 3. Double fertilization occurs when the pollen tube discharges two sperm into the female gametophyte within ovule • 4. One sperm fertilizes egg & other combines with two nuclei in the central cell of the female gametophyte to produce food-storing endosperm (3n) • 5. Within a seed, the embryo consists of a root and seed leaves called cotyledons (one or two)

22. Figure 30.16 Embryos Leaf venation Stems Roots Pollen Flowers Monocot Characteristics Root system usually fibrous (no main root) Floral organs usually in multiples of three One cotyledon Veins usually parallel Vascular tissue scattered Pollen grain with one opening Eudicot Characteristics Floral organs usually in multiples of four or five Vascular tissue usually arranged in ring Two cotyledons Veins usually netlike Taproot (main root) usually present Pollen grain with three openings

23. Products from Seed Plants • Most of our food comes from angiosperms • Six crops (wheat, rice, maize, potatoes, cassava, and sweet potatoes) yield 80% of the calories consumed by humans • Modern crops are products of relatively recent genetic change resulting from artificial selection • Many seed plants provide wood • Secondary compounds of seed plants are used in medicines

24. PLANT GROUP Figure 30.2 Ferns and other seedless vascular plants Mosses and other nonvascular plants Seed plants (gymnosperms and angiosperms) Reduced, Independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Dominant Gametophyte Reduced, dependent on gametophyte for nutrition Sporophyte Dominant Dominant Gymnosperm Angiosperm Sporophyte (2n) Microscopic female gametophytes (n) inside ovulate cone Microscopic female gametophytes (n) inside these parts of flowers Sporophyte (2n) Microscopic male gametophytes (n) inside these parts of flowers Gametophyte (n) Example Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Sporophyte (2n) Gametophyte (n)