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Lecture 8

BIOL215 Lecture 8 Notes.pdf

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Biology (Sci)
BIOL 215
Neil Price

BIOL215 Lecture 8 Notes Plants: a story of transition from water to land: •They evolved from Green Algae (aquatic seaweed) •Plates are multicellular eukaryotes •Possess cellulose rich cell walls •They are photoautotrophic •Alternation of generations Unicellular green algae that had incorporated new genes through horizontal gene transfer and gained organelles by endosymbiosis, transformed into multicellular photosynthetic organisms Green algae and land plants share various similarities reflecting their common origins: •Green algae store their carbohydrate reserves as starch •Many species of algae have rigid, cellulose-reinforced cell walls, as do all land plants •Green algae and vascular plants use similar types of pigments in metabolic pathways, both green chlorophyll (a and b) and yellow-orange carotenoids (alpha & beta) An alternation of generation includes the sporophyte - diploid stage (2n) to a gametophyte - haploid stage (n) Sperm and egg are haploids which when they go together, become a zygote that is diploid 4 major evolutionary inventions in plants: •Silurian (430 mya): origin of plants •Early Devonian (390 mya): Vascular lineage •Late Devonian(360 mya): Seed lineage •Early Cretaceous (130 mya): Flower lineage Bryophytes: •Some of the earliest land plants •Nonvascular because they lack vascular tissue & true roots to transport water & nutrients •Thrive in damp places, althought can withstand drought •Lack lignan to strengthen cell walls: means they have to stay close to the ground Were important in two major transitions: • • Water to land; • Haploid gametophyte-dominated life cycle to a diploid sporophyte-dominated life cycle •Three major divisions of bryophytes: • Mosses Hornworts • • Liverworts Major features of seedless vascular plants: •Possess vascular tissue •Allowed plant to live in drier habitats more effectively Thrive in damn places, although can withstand drought • •Well-developed cuticle and stomata - minimize H2O loss and regulate gas exchange •Ferns are most abundant: specialized underground stem the rhizome and an aerial frond Know that cooksonia caledonica was the earliest vascular plant due to fossils and that using CT • scan, you can see evidence of stomata and vascular tissue Moving onto land required three evolutionary changes: •Reduction in the size of the gametophyte; •Evolution of easily dispersible pollen; •And encasement of spores in seeds •This allowed plants to avoid desiccation and so move away from water Early vascular plants evolved into the two major lineages of pollen-producing, seed-bearing land plants: •Gymnosperms (seeds) • The seed is invented: provides a small capsule composed of a protective seed coat, the plant embryo, and nutrients • Pollen is invented: sperm don't have to have water to swim ovule - can be transported by animals, air, moving H2O • Most common are the conifers (cone-bearing trees) • Examples: pine, fur, redwood, spruce, cedar • Sporophyte: large woody tree-like • Gametophyte: reduced and living in cones •Angiosperms (flowers) • Advertise their sex organs for all to see • 95% of modern plants are angiosperms • The major evolutionary invention is the flower: (see diagram) • Angiosperms have a complex lifecycle and have an alternation of
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