Chapter 21 Plant Evolution (Sections 21.5 - 21.8)

1. Chapter 21Plant Evolution (Sections 21.5 - 21.8)

2. 21.5 History of the Vascular Plants • The oldest fossils of vascular plants are spores that date to about 450 million years ago (late Ordovician period) • Early vascular plants stood only a few centimeters high and had a simple branching pattern, with no leaves or roots • Fossil Cooksonia

3. From Tiny Branchers to Coal Forests • By the early Devonian, taller species with a more complex branching pattern were common worldwide

4. From Tiny Branchers to Coal Forests • Forests of giant seedless vascular plants thrived during the Carboniferous period – heat and pressure transformed the remains of these forests to coal • coal • Fossil fuel formed over millions of years by compaction and heating of plant remains

5. A Carboniferous “Coal Forest”

6. Rise of the Seed Plants • Cycads and ginkgos were among the earliest gymnosperm lineages • Early angiosperms such as magnolias evolved while dinosaurs walked on Earth

7. Reproductive Traits of Seed Plants • Seed plant sporophytes have pollen sacs, where microspores form and develop into male gametophytes (pollen grains) • Sporophytes also have ovules, where megaspores form and develop into female gametophytes

8. Key Terms • pollen sac • Of seed plants, reproductive structure in which sperm-bearing gametophytes (pollen grains) develop • microspore • Haploid spore formed in pollen sacs of seed plants; develops into a sperm-producing gametophyte (a pollen grain)

9. Key Terms • megaspore • Haploid spore formed in ovule of seed plants • Develops into an egg-producing gametophyte • ovule • Of seed plants, reproductive structure in which egg-bearing gametophyte develops • After fertilization, matures into a seed

10. How a Seed Forms

11. How a Seed Forms Microspore in the pollen sac of a sporophyte Megaspore in the ovule of a sporophyte develops into develops into Male gametophyte (pollen grain) released Female gametophyte in ovule pollination and fertilization Seed (embryo sporophyte in mature ovule) Fig, 21.17, p. 333

12. Pollination • A sporophyte releases pollen grains, but holds onto its eggs • Wind or animals can deliver pollen from one seed plant to the ovule of another • pollination • Delivery of a pollen grain to the egg-bearing part of a seed plant

13. Time Line for Plant Evolution

14. Time Line for Plant Evolution Diversification of seedless vascular plants. Bryophytes evolve, diversify; seedless vascular plants evolve. First treelike plants (fern relatives), first seed plants. Giant horsetails, club mosses relatives in swamp forests. Conifers arise late in period. Ginkgos, cycads evolve. Most horsetails and club mosses die off by end of the period. Adaptive radiations of ferns, cycads, conifers; by start of Cretaceous, conifers the are dominant trees. Flowering plants appear in the early Cretaceous, undergo adaptive radiation, and become dominant. Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Tertiary 488 443 416 359 299 251 200 146 66 Millions of years ago (mya) Fig, 21.13, p. 332

15. 21.6 Gymnosperms—Plants With Naked Seeds • Gymnospermsare vascular seed plants that produce seeds on the surface of ovules • Seeds are “naked” (not inside a fruit) • Includes conifers, cycads, ginkgos, and gnetophytes • gymnosperm • Seed plant that does not make flowers or fruits

16. The Conifers • In conifers, ovules form on the surfaces of woody cones • Conifers typically have needlelike or scalelike leaves , and tend to be resistant to drought and cold • conifer • Gymnosperm with nonmotile sperm and woody cones • Examples: pines, redwoods

17. A Conifer • Conifers include the long-lived bristlecone pines • One of these trees is now 4,600 years old

18. Cycads • An Australian cycad with its fleshy seeds • cycad • Tropical or subtropical gymnosperm with flagellated sperm, palmlike leaves, and fleshy seeds

19. Ginkgo biloba • Ginkgo’s fleshy seeds and fan-shaped leaves • ginkgo • Deciduous gymnosperm with flagellated sperm, fan-shaped leaves, and fleshy seeds • One species: Ginkgo biloba

20. Gnetophytes • Ephedra: Yellow structures on stems are pollen-bearing cones • gnetophyte • Shrubby or vinelike gymnosperm, with nonmotile sperm

21. A Representative Life Cycle: Ponderosa Pine • Inside the ovule, a megaspore forms by meiosis and develops into a female gametophyte • Male cones hold pollen sacs where microspores develop into pollen grains • Pollen grains are released; pollination occurs when one lands on an ovule, and the pollen grain germinates • It takes about a year for a pollen tube to grow through ovule tissue and deliver sperm to the egg

22. A Representative Life Cycle: Ponderosa Pine (cont.) • When fertilization finally occurs, it produces a zygote • The zygote develops into an embryo sporophyte that, along with tissues of the ovule, becomes a seed • The seed is released, germinates, and grows and develops into a new sporophyte

23. Life Cycle of a Conifer: Ponderosa Pine

24. Time Line for Plant Evolution 1 A seed cone has many scales, each with two ovules on its upper surface section through one ovule (the red “cut” in the diagram to the left) surface view of seed cone scale ovule A pollen cone has many scales, each housing a pollen sac. 3 section through pollen-producing sac (red cut) surface view of pollen cone scale Seed is released, germinates, and the embryo grows and develops into a new sporophyte. 9 seed coat One sperm nucleus fertilizes the egg, forming a zygote. 7 embryo nutritive tissue Ovule develops into a mature seed. 8 Diploid Stage Fertilization Meiosis Haploid Stage pollen tube 5 4 Pollination: wind deposits pollen grain on seed cone. Microspores form by meiosis, develop into pollen grains. Megaspores form by meiosis; one develops into the female gametophyte. 2 (view inside ovule) sperm-producing cell 6 eggs Pollen grain matures into male gametophyte. Two nonflagellated sperm nuclei form as pollen tube grows through ovule tissue. female gametophyte Fig, 21.19, p. 335

25. 1 A seed cone has many scales, each with two ovules on its upper surface section through one ovule (the red “cut” in the diagram to the left) surface view of seed cone scale ovule A pollen cone has many scales, each housing a pollen sac. 3 section through pollen-producing sac (red cut) surface view of pollen cone scale Seed is released, germinates, and the embryo grows and develops into a new sporophyte. 9 seed coat One sperm nucleus fertilizes the egg, forming a zygote. 7 embryo nutritive tissue Ovule develops into a mature seed. 8 Diploid Stage Fertilization Meiosis Haploid Stage pollen tube 5 4 Pollination: wind deposits pollen grain on seed cone. Microspores form by meiosis, develop into pollen grains. Megaspores form by meiosis; one develops into the female gametophyte. 2 (view inside ovule) sperm-producing cell 6 eggs Pollen grain matures into male gametophyte. Two nonflagellated sperm nuclei form as pollen tube grows through ovule tissue. female gametophyte Time Line for Plant Evolution Stepped Art Fig, 21.19, p. 335

26. Time Line for Plant Evolution Fig, 21.19.1, p. 335

27. Time Line for Plant Evolution Fig, 21.19.3, p. 335

28. Time Line for Plant Evolution Fig, 21.19.9, p. 335

29. ANIMATION: Pine life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

30. Key Concepts • Gymnosperms • Seed plants make pollen grains that allow fertilization to occur even in dry times • They also make eggs in an ovule that develops into a seed • Gymnosperms such as pine trees are seed plants with “naked” seeds – their seeds do not form inside an ovary

31. 21.7 Angiosperms—The Flowering Plants • Angiosperms are seed plants that make flowers and fruits • angiosperms • Largest seed plant lineage • Only group that makes flowers and fruits • flower • Specialized reproductive shoot of a flowering plant • fruit • Mature flowering plant ovary; encloses a seed or seeds

32. Flowers • A flower consists of modified leaves arranged in concentric whorls of sepals and petals • The stamens of a flower produce pollen. • Eggs form in the female part of the flower (carpel) • An ovary at the base of the carpel holds one or more ovules

33. Key Terms • stamen • Male reproductive part of a flower • carpel • Female reproductive part of a flower • ovary • Of flowering plants, floral chamber that encloses ovule

34. A Cherry Flower

35. A Cherry Flower stamen carpel filament anther stigma style ovary ovule (forms within ovary) petal (all petals combined form the flower’s corolla) sepal (all sepals combined form flower’s calyx) receptacle Fig, 21.20, p. 336

36. Pollinators • Many flowering plants coevolved with pollinators • pollinator • Animal that moves pollen, facilitating pollination

37. Fruits and Seeds • After pollination, the flower’s ovary becomes a fruit that contains one or more seeds • A flowering plant seed includes an embryo sporophyte and endosperm, a nutritious tissue • A variety of dispersal-related traits help disperse seeds to new habitats where they can thrive

38. Major Lineages of Flowering Plants • Two major lineages differ in seed structure and other traits: • Monocots include orchids, palms, lilies, and grasses • Eudicots include most herbaceous (nonwoody) plants such as tomatoes, cabbages, roses, poppies, most flowering shrubs and trees, and cacti

39. Key Terms • monocots • Lineage of angiosperms with one cotyledon • Do not produce true wood • Includes grasses, orchids, and palms • eudicots • Lineage of angiosperms with two cotyledons • Includes herbaceous plants, woody trees, and cacti

40. Monocot Life Cycle (Lilium) 1. Sporophyte dominates the life cycle 2. Pollen forms inside pollen sacs of stamens 3. Eggs develop in an ovule within an ovary 4. Pollination occurs; a tube grows from the pollen grain into the ovule, delivering two sperm 5. Double fertilization occurs 6. The resulting seed grows into a sporophyte

41. Double Fertilization • Double fertilization occurs in all flowering plant life cycles • One sperm fertilizes the haploid egg • One fertilizes a diploid cell, yielding a triploid cell that divides to form endosperm,which nourishes the embryo sporophyte • endosperm • Nutritive triploid tissue in angiosperm seeds

42. Life Cycle of Lily (Lilium)

43. Life Cycle of Lily (Lilium) 1 1 A sporophyte dominates this life cycle. 2 Pollen forms inside pollen sacs of stamens. 6 ovules inside ovary seedling pollen sac, where each one of many cells will give rise to microspores 3 Eggs develop in an ovule within an ovary. cell in ovule that will give rise to a megaspore seed coat 4 Pollination occurs and a tube grows from the pollen grain into the ovule, delivering two sperm. embryo (2n) endosperm (3n) seed 5 Diploid (2n) Phase Meiosis Meiosis Double fertilization Haploid (n) Phase 2 5 Double fertilization occurs in all flowering plant life cycles. One sperm fertilizes the haploid egg. The other fertilizes a diploid cell, yielding a triploid cell that divides to form endosperm, a tissue that nourishes the embryo sporophyte. ovules inside ovary pollen grain (the male gametophyte) 4 pollen tube sperm (n) sperm (n) cell from which endosperm will form 3 6 egg The resulting seed will grow into a new sporophyte. pollen tube delivering two sperm to an ovule ovary that holds many ovules female gametophyte inside ovule Fig, 21.21, p. 337

44. 1 6 ovules inside ovary seedling pollen sac, where each one of many cells will give rise to microspores cell in ovule that will give rise to a megaspore seed coat embryo (2n) endosperm (3n) seed 5 Diploid (2n) Phase Meiosis Meiosis Double fertilization Haploid (n) Phase 2 pollen grain (the male gametophyte) 4 pollen tube sperm (n) sperm (n) cell from which endosperm will form 3 egg pollen tube delivering two sperm to an ovule ovary that holds many ovules female gametophyte inside ovule Life Cycle of Lily (Lilium) Stepped Art Fig, 21.21, p. 337

45. ANIMATION: Monocot life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

46. ANIMATION: Flower parts

47. 21.8 Ecological and Economic Importance of Angiosperms • Dominant plants in most land habitats, flowering plants are ecologically important – and essential to human existence • Angiosperms feed and shelter animals, and they provide us with food, fabric, oils, medicines, drugs, and more…

48. Flowering Plants Feed Animals • Angiosperms provide food and shelter for a variety of animals • This hummingbird is sipping nectar, which is mainly sucrose, from a columbine flower

49. Angiosperms as Crop Plants • Nutrient-rich endosperms of angiosperm seeds are staples of human diets throughout the world • Mechanized harvesting of wheat, a monocot

50. Commercial Products • Angiosperms supply us with fiber, wood, and oils • Field of cotton, a eudicot