Overview of Green Plants

1. Overview of Green Plants Chapter 30

2. 2 Defining Plants The kingdom Viridiplantae includes land plants and green algae Red and brown algae are excluded All green plants arose from a single species of freshwater algae The green algae split into two major clades Chlorophytes � Never made it to land Charophytes � Did!

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4. 4 Defining Plants Land plants have two major features 1. Protected embryos 2. Multicellular haploid and diploid phases

5. 5 Defining Plants Adaptations to terrestrial life 1. Protection from desiccation by a waxy cuticle and stomata 2. Evolution of leaves which increase photosynthetic surface area 3. Shift to a dominant vertical diploid generation

6. 6 Plant Life Cycles Humans have a diplontic life cycle Only the diploid stage is multicellular Plants have a haplodiplontic life cycle Multicellular diploid stage = Sporophyte Multicellular haploid stage = Gametophyte

7. 7 Plant Life Cycles Sporophyte produces haploid spores by meiosis Spores divide mitotically, producing the gametophyte Gametophyte produces gametes by mitosis Gametes fuse to form the diploid sporophyte

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9. 9 Plant Life Cycles As more complex plants evolved: 1. Diploid stage became the dominant portion of the life cycle 2. Gametophyte became more limited in size 3. Sporophyte became nutritionally independent

10. 10 Chlorophytes Green algae have two distinct lineages Chlorophytes � Gave rise to aquatic algae Streptophytes � Gave rise to land plants Chlamydomonas Unicellular chlorophyte with two flagella Have eyespots to direct swimming Reproduces asexually as well as sexually

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12. 12 Chlorophytes Volvox -Colonial chlorophyte

13. 13 Chlorophytes Ulva -Multicellular chlorophyte -Haplodiplontic life cycle -Gametophyte and sporophyte have identical appearance

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15. 15 Charophytes Charophytes are green algae related to land plants

16. 16 Charophytes Charales (300 species) -Macroscopic -Plant-like plasmodesmata -Sister clade to land plants

17. 17 Bryophytes Bryophytes are the closest living descendants of the first land plants Called nontracheophytes because they lack tracheids (specialized transport cells) Simple, but highly adapted to diverse terrestrial environments Non-photosynthetic sporophyte is nutritionally dependent on the gametophyte

18. 18 Bryophytes Liverworts (phylum Hepaticophyta) -Have flattened gametophytes with liver-like lobes

19. 19 Bryophytes Hornworts (phylum Anthocerotophyta) -Sporophyte has stomata

20. 20 Bryophytes Mosses (phylum Bryophyta) Gametophytes consist of small, leaflike structures around a stemlike axis Anchored to substrate by rhizoids Multicellular gametangia form at the tips of gametophytes Archegonia � Female gametangia Antheridia � Male gametangia Mosses withstand drought, but not air pollution

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22. 22 Features of Tracheophyte Plants Cooksonia, the first vascular land plant, appeared about 420 MYA

23. 23 Features of Tracheophyte Plants Vascular tissues are of two types Xylem � Conducts water and dissolved minerals upward from the roots Phloem � Conducts sucrose and hormones throughout the plant These enable enhanced height and size in the tracheophytes Tracheophytes are also characterized by the presence of a cuticle and stomata

24. 24 Features of Tracheophyte Plants Vascular plants have gametophytes reduced in size and complexity relative to sporophytes Seeds Highly-resistant structures that protect the plant embryo Occur only in heterosporous plants Fruits in flowering plants add a layer of protection to seeds Also attract animals that disperse seeds

25. 25 Features of Tracheophyte Plants Vascular plants include seven extant phyla grouped in three clades 1. Lycophytes (club mosses) 2. Pterophytes (ferns and their relatives) 3. Seed plants

26. 26 Lycophytes Club mosses are the earliest vascular plants -They lack seeds

27. 27 Pterophytes The phylogenetic relationships among ferns and their relatives is still being sorted out

28. 28 Pterophytes Whisk ferns -Saprophyte consists of evenly forking green stems without leaves or roots

29. 29 Pterophytes Horsetails -All 15 living species are homosporous -Constitute a single species, Equisetum

30. 30 Pterophytes Ferns -The most abundant group of seedless vascular plants with about 11,000 species

31. 31 Pterophytes The fern life cycle differs from that of a moss Much greater development, independence and dominance of the fern�s sporophyte Fern morphology Sporophytes have rhizomes Fronds (leaves) develop at the tip of the rhizome as tightly rolled-up coils They unroll and expand

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33. 33 Pterophytes Fern reproduction -Most fern are homosporous -Produce distinctive sporangia in clusters called sori on the back of the fronds -Diploid spore mother cells in sporangia produce haploid spores by meiosis -At maturity, the spores are catapulted by snapping action

34. 34 The Evolution of Seed Plants Seed plants first appeared 305-465 MYA Evolved from spore-bearing plants known as progymnosperms The seed represents an important advance

35. 35 The Evolution of Seed Plants Seed plants produce 2 kinds of gametophytes -Male gametophytes -Pollen grains -Dispersed by wind or a pollinator -Female gametophytes -Develop within an ovule -Enclosed within diploid sporophyte tissue

36. 36 Gymnosperms are plants with �naked seeds� Ovule is exposed on a scale at pollination There are four living groups Coniferophytes Cycadophytes Gnetophytes Ginkgophytes All lack flowers and fruits of angiosperms Gymnosperms

37. 37 Conifers (phylum Coniferophyta) are the largest gymnosperm phylum Include: Pines, spruces, firs, cedars and others Coastal redwood � Tallest tree Bristlecone pine � Oldest living tree Conifers are sources of important products Timber, paper, resin and taxol (anti-cancer) Gymnosperms

38. 38 Pines -More than 100 species, all in the Northern hemisphere -Produce tough needlelike leaves in clusters -Leaves have: 1. Thick cuticle and recessed stomata 2. Canals into which cells secrete resin Gymnosperms

39. 39 Pine reproduction -Male gametophytes (pollen grains) develop from microspores in male cones by meiosis -Female pine cones form on the upper branches of the same tree -Female cones are larger, and have woody scales -Two ovules develop on each scale Gymnosperms

40. 40 Pine reproduction -Each ovule contains a megasporangium called the nucellus -Surrounded by the integument -Opening � Micropyle -One layer becomes the seed coat -While scales of female cone are open, pollen grains drift down between them -Are drawn to top of nucellus Gymnosperms

41. 41 Pine reproduction -While female gametophyte is developing, a pollen tube emerges from the pollen grain -It digests its way to the archegonium -Fifteen months after pollination, pollen tube reaches archegonium and delivers its sperm Gymnosperms

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43. 43 Gymnosperms Cycads (phylum Cycadophyta) -Slow-growing gymnosperms of tropical and subtropical regions

44. 44 Gymnosperms Gnetophytes (phylum Gnetophyta) -Only gymnosperms with vessels in their xylem

45. 45 Gymnosperms Ginkgophytes (phylum Ginkgophyta) -Only one living species remains -Ginkgo biloba

46. 46 Angiosperms Angiosperms are the flowering plants -Ovules are enclosed in diploid tissue at the time of pollination

47. 47 Angiosperms Angiosperm origins are a mystery -The oldest known angiosperm in the fossil record is Archaefructus -The closest living relative to the original angiosperm is Amborella

48. 48 Angiosperms

49. 49 Angiosperms

50. 50 Angiosperms Flower morphology -Primordium develops into a bud at the end of a stalk called the pedicel -Pedicel expands at the tip to form a receptacle, to which other parts attach -Flower parts are organized in circles called whorls

51. 51 Angiosperms Flower morphology -Outermost whorl = Sepals -Second whorl = Petals -Third whorl = Stamens (androecium) -Each stamen has a pollen-bearing anther and a filament (stalk) -Innermost whorl = Gynoecium -Consists of one or more carpels that house the female gametophyte

52. 52 Angiosperms

53. 53 Angiosperms Carpel structure -Three major regions -Ovary = Swollen base containing ovules -Later develops into a fruit -Stigma = Tip -Style = Neck or stalk

54. 54 Angiosperm Life Cycle The female gametophyte (embryo sac) has 8 haploid nuclei arranged in two groups of four A nucleus from each group migrate toward the ovule�s center and become polar nuclei Cell walls form round remaining three nuclei At the micropyle end, one cell functions as the egg, and the other two are synergids At the other end, three cells are antipodals They eventually break down

55. 55 Angiosperm Life Cycle Pollen production occurs in the anthers -It is similar but less complex than female gametophyte formation -Diploid microspore mother cells undergo meiosis to produce four haploid microspores -Binucleate microspores become pollen grains

56. 56 Angiosperm Life Cycle Pollination is the mechanical transfer of pollen from anther to stigma -Pollen grains develop a pollen tube that is guided to the embryo sac -One of the two pollen grain cells lags behind -This generative cell divides to produce two sperm cells

57. 57 Angiosperm Life Cycle As the pollen tube enters the embryo sac, a double fertilization occurs One sperm unites with egg to form the diploid zygote Other sperm unites with the two polar nuclei to form the triploid endosperm Provides nutrients to embryo When the seed germinates, a young sporophyte plant emerges

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59. 59 Angiosperm Life Cycle Angiosperms include: Eudicots (about 175,000 species) Trees, shrubs, snapdragons, peas, other Use flowers to attract insect pollinators Monocots (about 65,000 species) Grasses, lilies, palms, irises, others Some rely on wind for pollination Note: Self-pollination may also occur