The Diversity of Plants Plants are in Domain Eukarya • Immediate ancestors are green algae, a type of Protista, that lived in fresh water. They share: Chapter 21 Similar DNA Same photosynthetic pigments (most plants are primary producers) Store food as starch Cell walls made of cellulose Kingdom Plantae Key feature: Alternation of generations • All are eukaryotes • A diploid sporophyte produces haploid spores. The sporophyte is usually the common form of the plant. • Cell walls made of cellulose • Haploid spores divide to become haploid gametophytes. • Most are primary producers • Haploid gametophytes produce haploid gametes (eggs and Carry out photosynthesis! sperm) Chloroplasts are sites of • Egg and sperm unite to form the diploid zygote. photosynthesis • Zygote developes into the embryo. • Some are parasites Embryo relies on nutrients from parent Example: mistletoe! • Embryo develops into the sporophyte Visual picture of plant reproduction Major groups of plants 1 Bryophytes Bryophyte reproduction • Haploid gametophyte is dominant • Examples: liverworts and (green in photo) mosses Produces gametes in specialized structures (keep gametes moist!) • Most similar to ancestral • Requires water for sperm to swim to egg green algae Egg chemically attracts the sperm Egg stays in its “archegonium” • Non-vascular: lack special attached to the gametophyte Fertilization within archegonium conducting vessels for Zygote Embryo sporophyte movement of water and • Sporophyte remains attached to gametophyte (brown stalks) materials Develops and produces spores No true roots, leaves or stems • Spores disperse; develop into gametophytes Body size limited Mosses live in wetlands • Especially bogs Moss life cycle Tracheophytes: vascular plants Major groups of plants 1: Seedless vascular plants • All vascular plants have vessels reinforced with lignin Movement of materials Support • All vascular plants have dominant sporophytes • Examples of seedless vascular plants club mosses (“ground pines”) Horsetails ferns All are found in moist woodland habitats 2 Fern life cycle Ferns: sporophyte & gametophyte • Sporophyte dominant Diploid sporangia on leaf underside produce haploid spores. • Gametophyte tiny Has specialized, egg and sperm producing structures (just like bryophytes (i.e. mosses!) Eggs retained in archegonium Sperm swims to egg; fertilization within archegonium Sporophyte Gametophyte Zygote Embryo sporophyte Tracheophytes: vascular plants Major groups of plants 2: Vascular plants with seeds • Different from the seedless vascular plants Produce seeds! Contain developing embryos Contain stored food Protected by seed coat Produce pollen Pollen grains are the sperm-producing (male) gametophytes Can disperse by wind or pollinators – Fertilization no longer tied to water! Gymnosperms: non-flowering seed plants Gymnosperms: non-flowering seed plants • Examples • Conifers Ginkgos Pines, firs, spruces, hemlocks, Probably the first “modern-day” seed plants cypresses Maintained by cultivation in Asia Many are well-adapted to cold, Pollution resistant dry conditions Does Ginkgo biloba improve memory? Retain green leaves year round; Cycads can photosynthesize and grow all year Resemble large ferns Slow-growing Waterproof coating of needles Long-lived (leaves) prevents water loss – One Australia cycad is ~5000 years old! Contain an “antifreeze” in their sap Conifers (next page) that allows for nutrient transport in sub-zero temperatures 3 Conifer life cycle Conifer (gymnosperm) life cycle • Sporophyte has male and • Fertilization within female cone female cones Pollen lands on cone; pollen tube Male gametophytes (pollen) extends slowly to ovule produced in male cones Tube takes 14 months to grow, deposit sperm Pollen grains have “wings” and disperse on the wind • After fertilization, the ovule develops into the seed with Female gametophyte is Embryo within scale of female cone Nutrients Seed coat The “ovule” contains spores that divide (meiosis) to • Seed germinates become the gametophyte • Seedling mature Gametophyte produces the sporophyte eggs. Pinyon nuts Angiosperms: flowering plants • Pinyon nuts (pine nuts) • Flowers attract pollinators (mutualistic) are the seeds of pine Pollinators move pollen (and thus trees. sperm!) from flower to flower Pollinators gain food Found only in female Flower features evolved to be cones. attractive to the pollinators • Fruits (containing seeds) promote seed dispersal (How?) Edible, but you have to • Broad leaves capture sunlight beat the squirrels to effectively Some flowering plants don’t have them. broad leaves, though… (Why not?) May also have toxins to prevent being eaten Nectar - Insects Nectar - Birds Nectar - Mammals Pollinators locate flowers via: Vision (Ultraviolet) Odor 4 How do they attract Angiosperm life cycle (unique features): pollinators? Compare to others… • Food (nectar) • Pollen produced on anthers of flower • Lands on stigma • Color Via wind or pollinator Bees like yellow flowers • Builds pollen tube to ovary that contains Hummingbirds like red ovules flowers • Fertilization in ovule • After fertilization Ovule develops into the • Odor seed Flies like smelly plants Ovary develops into fruit. Trends in plant evolution Plant phylogenetic tree • Increased prominence of sporophyte; reduction of gametophyte • Development of lignin-supported vessels (support on land; larger sizes reached) • Development of alternate (non-swimming) methods for sperm to reach egg. • Development of seeds (embryo protection) • Development of flowers/fruits: pollination and seed dispersal by animals 5.