AP Biology Chapter 29 Seedless Plants: Bryophytes and Ferns Objectives 1. Name the protist group from which plants are hypothesized to have descended, and describe supporting evidence. 2. Discuss some environmental challenges of living on land, and describe how several adaptations meet these challenges. 3. Summarize the features that distinguish bryophytes from green algae and from other plants. 4. Name and briefly describe the three phyla of bryophytes. Algae •Plantlike (autotrophic) protists •Unicellular or Colonial •Aquatic (live in water) The Chlorophytes (green algae) appear to be ancestral to the plants Phylogeny of the Plants Terrestrial (Land) Plants The move from aquatic habitat to land creates a number of problems: ◦ Protection against drying ◦ Transport of sperm to egg ◦ Structural support Plants that have specialized adaptations to solve these problems can live in drier environments, while those that do not are restricted to moist environments Protection against drying Water loss in plants is called Transpiration Terrestrial plants are protected against transpiration by: ◦ Epidermis ◦ Waxy “cuticle” ◦ Stomata Transport of sperm to egg Algae and aquatic plants, since they live in water, have a natural unbroken water pathway for sperm to swim to the egg Seedless plants can only reproduce sexually under moist conditions. The “gametophyte” is low to the ground and only grows in moist habitats Seed plants are less restricted because they provide an internal water pathway in a specialized “pollen tube” Structural Support Algae and aquatic plants are supported by the buoyancy of the water they live in. ◦ Bryophytes, which lack strong supportive tissues, are very small and low to the ground ◦ Tracheophytes, supported by a series of hollow tubes with thickened cell walls, can grow much taller And now, some video. http://www.youtube.com/watch?v=X4L3r _XJW0I Distinguishing Plants from Algae Alternation of Generations Multicellular, dependent embryo Walled spores produced in sporangia Multicellular gametangia Apical meristems See pages 602-603 in textbook Alternation of Generations Gametophyte (n) produces gametes (n) Gametes fuse to form zygote (2n) Zygote develops into a dependent, multicellular embryo (2n) Embryo grow into the sporophyte (2n) Sporophyte produces spores (n) by meiosis Spores grow and develop forming the gametophyte (n) Multicellular Embryo The zygote will develop into an embryo within the parent plant The parent provides protection and nourishment Spores and Sporangia Haploid spores will be produced in specialized organs on the sporophyte generation plant called sporangia The spores are protected by a protective wall Gametangia (produce gametes) Moss Archegonium – Note the mature eggs Moss Antheridium – will produce sperm cells Apical Meristem Growth of multicellular organisms begins with cells that have not yet differentiated. In plants, undifferentiated tissue is called meristem. Meristem tissue at the tip (apex) of a root or shoot is “apical” meristem Bryophytes •Lack vascular tissue •Reproduce with spores Mosses Liverworts Classes of Bryophytes Bryophyte Classes Hornworts Liverworts Mosses See page 608 in Textbook Objectives 5. Describe the life cycle of mosses, and compare their gametophyte and sporophyte generations. 6. Discuss the features that distinguish ferns and other seedless vascular plants from algae and bryophytes. 7. Describe the life cycle of ferns, and compare their sporophyte and gametophyte generations. 8. Compare the generalized life cycles of homosporous and heterosporous plants. 9. Name and briefly describe the four phyla of seedless vascular plants. Life Cycle of Mosses Mosses – Comparing generations Sporophyte Generation ◦ Temporary ◦ Dependent upon the gametophyte ◦ Taller, grows from the top of the gametophyte ◦ Not photosynthetic Gametophyte Generation ◦ Permanent/Long lived ◦ Independent ◦ Shorter, grows from the soil/anchored with rhizoids ◦ Photosynthetic Tracheophytes – Vascular plants Vascular tissue provides advantages ◦ Efficient transport of water and nutrients ◦ Structural support Tracheophyte phylogeny Tracheophytes include all plants with vascular tissue The tracheophytes are subdivided into seedless plants and seed plants Seed plants are subdivided into gymnosperms and angiosperms (flowering plants) Vascular Seedless Plants Ferns and Horsetails •Have vascular tissue •Reproduce with Spores http://www.youtube.com/watch?v=xN8c_X0LNcg Fern Life Cycle The gametophyte generation is small, flat and nonvascular, resembling a liverwort The gametophyte dies once the sporophyte is established The sporophyte is the prominent generation ◦ Vascular ◦ Long lived Ferns – Comparing Generations Sporophyte ◦ Permanent/Long lived ◦ Independent once established ◦ Produces a rhizome for storage and asexual reproduction ◦ Forms “fronds” Gametophyte ◦ Temporary, dies once the sporophyte is established ◦ Nonvascular, small and low to the ground ◦ Resembles liverwort ◦ Flattened form captures and holds water Homosporous and Heterosporous Homosporous Plants ◦ Most seedless vascular plants ◦ Single type of spore ◦ Spores give rise to monoecious (bisexual) gametophytes Heterosporous Plants ◦ All seed plants and some seedless vascular plants ◦ Two types of sporangia, each producing a different type of spore ◦ Megaspores give rise to the female gametophyte ◦ Microspores give rise to the male gametophyte Seedless Vascular Plants Lycophytes ◦ Most ancient group of vascular plants ◦ “club mosses” and “spike mosses” ◦ Superficially resemble mosses, but vascular Whisk Ferns ◦ Branching stems, but no roots Horsetails ◦ Photosynthetic stems with rings of branches or small leaves Ferns ◦ Horizontal stems with large “fronds” divided into leaflets Lycophytes Whisk Ferns Horsetails Ferns AP Biology Chapter 30 Seed Plants: Gymnosperms and Angiosperms Chapter 30 Objectives 1. Compare the features of seeds with those of spores and discuss the advantages of plants that reproduce primarily by seeds rather than by spores. 2. Trace the steps in the life cycle of a pine, and compare its sporophyte and gametophyte generations. 3. Summarize the features that distinguish gymnosperms from bryophytes and ferns. 4. Name and briefly describe the four phyla of gymnosperms. Seed Plants Seeds provide many advantages over spores • Multicellular embryo • Stored food • Protection • Mechanisms for dispersal Conifers – Pine seeds Flowering Plants – Apple seeds Life Cycle Trends Alternation of generations continues in the seed plants, but the gametophyte is diminished to the point of being microscopic By enclosing the gametophyte entirely within the sporangium, the need for a film of water for transport of sperm is eliminated. The pathway is fully enclosed. Motility in sperm is lost in most seed plants and diminished in others Life Cycle of the Pine The Pine tree is the sporophyte generation Gymnosperms are heterosporous. The megasporangium is located in an ovulate cone. The microsporangium is in a pollen cone. The female gametophyte develops entirely within the megasporangium The male gametophyte is enclosed within the pollen grain Gymnosperm Life Cycle Microsporangium The pollen cone contains microsporangia, which will produce the pollen grains The male gametophyte is within the pollen grain Megasporangium The ovulate cone contains the megasporangium The female gametophyte is enclosed within it Pollination results in the growth of a pollen tube into the ovule, directly depositing a sperm cell Same deal, different diagram Evolutionary significance The gymnosperms had advantages over seedless plants: ◦ With the gametophyte protected and sperm delivered directly by the pollen tube, gymnosperms were able to survive in much drier environments than any of the seedless plants. ◦ The climate became drier in the Mesozoic, giving the advantage not only to the gymnosperms, but also to the reptiles over the amphibians Concept check 30.1 p. 621 1. 2. 3. Contrast sperm delivery in seedless plants with sperm delivery in seed plants What features not present in seedless plants have contributed to the enourmous success of seed plants on land? If a seed could not enter dormancy, how might that affect the embryo’s transport or survival? Gymnosperms Vascular, seed producing plants “naked seed” – seeds are not completely enclosed by the ripened ovary Generally have needle-like (pines) or scale-like (cedars) leaves Gymnosperm Phylogeny (p. 622-3) Cycads ◦ Resemble palms, but are gymnosperms. The cycads were the prominent large plants of the mesozoic Gnetophytes Ginkgoes ◦ A deciduous gymnosperm, only one species still exists Conifers ◦ Pines, spruce, redwoods . . . The most diverse group of gymnosperms Chapter 30 Objectives 5. Summarize the features that distinguish flowering plants from other plants 6. Diagram the parts of a flower. Describe the structure and function of each part 7. Briefly explain the life cycle of a flowering plant and describe double fertilization. Angiosperms (Flowering Plants) Vascular seed plants Have a wide variety of adaptations for transferring pollen Seeds mature inside of the ripened ovary of the flower, forming “fruit” which protects, nourishes, and aids dispersal of the seeds Parts of a Flower What parts can you recognize? Double Fertilization Double fertilization occurs only in the angiosperms The pollen grain will produce 2 sperm cells, one which will fertilize the egg to form the zygote (2n) and another which will fertilize the diploid female gametophyte, producing a triploid cell which will form the endosperm The Endosperm and Cotyledons The endosperm contains stored food (mostly starch) which will contribute to the early growth of the embryo The endosperm will form either 1 or 2 seed leaves called cotyledons Angiosperms are categorized as either monocots or dicots based on the number of cotyledons Angiosperm life cycle Chapter 30 Objectives 8. Define fruit. Discuss adaptive advantages of fruits. Give examples 9. Contrast dicots and monocots, the two classes of flowering plants. 10. Discuss the evolutionary adaptations of flowering plants. 11. Summarize the evolution of gymnosperms from seedless vascular plants, and trace the evolution of flowering plants from gymnosperms Fruit Fruit is the ripened ovary of a flower Fruit may contain stored food and moisture Fruit provides a mechanism for seed dispersal Monocots vs. Dicots Monocots vs. Dicots Advantages of Flowering Plants Many flowering plants attract animal pollinators, which increase the likelihood of pollen grains actually resulting in pollination Seeds of flowering plants contain far more stored food than the seeds of gymnosperms. The endosperm provides for rapid growth of the embryo after germination Fruit facilitates seed dispersal through a wide variety of mechanisms: wind, water, animals Trends in Plant Evolution Animal pollinators greatly increase the rate of cross-pollination, which in turn increases the amount of genetic recombination and variation that occurs within a species Greater variation results in both more opportunities for adaptation and a more rapid rate of evolution The connection between flower and pollinator results in co-evolution. The flower and the pollinator both evolve in relation to each other Pollinator/Flower Coevolution Wasp mimicry ◦ https://www.youtube.com/watch?v=h8I3cqpgnA The hoverfly ◦ https://www.youtube.com/watch?v=MQlq5Qt RI9o Overdramatic artistic pollinator representation ◦ https://www.youtube.com/watch?v=MQlq5Qt RI9o Concept Check 30.3 p. 632 1. 2. It has been said that an oak is an acorn’s way of making more acorns. Write an explanation that includes these terms: Sporophyte, gametophyte, ovule, seed, ovary and fruit Compare and contrast a pine cone and a flower in terms of structure and function Concept Check 30.3 p. 632 3. Do speciation rates in closely related clades of flowering plants show that flower shape is correlated with the rate at which new species form, or that flower shape is responsible for this rate? Explain.