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Plants Elgqvist 2009 Evolution and Classification • The common ancestor of plants is green algae – Lived in water or moist environments – Reproduced asexually by – binary fission – Reproduced sexually by – conjugation Charactersitics • Plants are all – Eukaryotic – Multicellular – Photoautotrophs (use light to produce food) – Have cellulose in their cell walls – Absorb nutrients through their roots or rhizoids (a major difference from algae) – Sessile (cannot move at base) Evolution and Classification Order of major evolutionary advances from algae to flowering plants 1. Spores 2. Vascular tissue 3. Seeds 4. Flowers Evolution and Classification • Since plants came from algae, the first giant evolutionary step was to move onto land – To do this, cuticles (waxy layer around leaves) had to evolve to allow plant to prevent water loss – Reproduction with spores over reproduction by binary fission • Seedless – Reproduce with spores – Need moisture • non-vascular – Stuck low to the ground – Use rhizoids – root like structures Seedless, Nonvascular Plants Sporophyte growing from gametophyte • Mosses • • Hornworts Liverworts Evolution and Classification • Next came evolution of vascular tissue – Allowed roots to sink into ground to reach deeper water – Allowed plant to grow up and compete for sunlight – Allowed plant to have a much greater surface for photosynthesis compared to land area taken – Nutrients and water can travel much faster to all parts of the plant, allowing it to grow bigger. Seedless vascular plants • Reproduce with spores (still need moisture for sperm to swim from male gametophyte to female gametophyte - egg producing part of plant) • Can grow tall and spread leaves out Seedless vascular plants • ferns Spores found on underside of leaves (p 660) • horsetails Seedless Vascular Plants • Club mosses Evolution and Classification • Then came seeds! • Soooooooooooo many ways to disseminate! Disperse! Spread out! Scatter and otherwise get away from the parent plant! Seeds - dispersal Maple seeds come down like little helicopters Dandelion seeds float off in the breeze Ever had a bur stuck in your sock? Seeds - dispersal By animals – carried off and buried, or ingested and “dropped” somewhere else A coconut (seed for a palm tree) Floating on the currents to far away islands seeds • Advantages – Dispersal – so many ways! – Not bound to moist ground for sperm to swim to female gametophyte – yeah – true dry ground! – Protected by durable seed coat that can stay dormant for long periods – Cotelydons provide nutrition until sporophyte produces green parts (germination is complete) Vascular seed plants • Sporophyte is most prominent part of life cycle, producing gametophytes (opposite of seedless plants) • Two types: • Gymnosperms – “naked seeds” – Four main divisions • Angiosperms – Flowering plants – Ovary grows into fruit around seeds Gymnosperms • ginkgos Gymnosperms • Gnetophytes – neato! (p 618) Gymnosperms • Cycads Gymnosperms • Conifers – – cone bearing plants – Pinetrees – Leaves are long and narrow = needles – Adapted for cold and shaped not to break under weight of snow. Evolution and Classification • Finally Flowers! • Advantages: – Seeds Dressed, not Naked! - surrounded by a “fruit” – Many ways to attract pollinators – Seeds protected (and dispersed) by fruit Angiosperms – “fruit” aren’t just apples and oranges. There are sooooo many ways to disperse. Take on many shapes and sizes Angiosperms – attracting pollinators • • • • Symbiosis – mutualism Pollinators get nectar & plant gets to reproduce Pollen is male sex cell of plant Pollen is carried by pollinator from male gametophyte (stamen) to female gametophyte (pistil) Angiosperms – attracting pollinators Plant parts • What are the main functions of: • Roots? – To take in nutrients and water – To anchor the plant • Stem? – To transport nutrients and water around plant – To support plant • Leaves? – Produce food with photosynthesis • Flower? – reproduction Stems - structure • • • • • Vascular tissue – some transport down, some up What goes up? Water with dissolved nutrients from roots What goes down? Food made by leaves to feed rest of plant, and to be stored in roots for winter. • What is exception? • Food goes up in spring – sap rises – to give energy for leaves to grow back Stem – transport tissue • • • • Up vascular tissue is called Xylem Down is Phloem – think phood phloes down botany.hawaii.edu Leaves – structure See text p. 644 for diagram • • • • Main function is photosynthesis Cells filled with chloroplasts are sandwiched between: Top layer cuticle: prevent water loss Bottom layer cuticle with embedded stomata – – – – – Stomata open to let in CO2 (carbon dioxide), and let out Oxygen (O2) Stomata close at night to prevent Loss of water vapor • Running through all this is the vascular tissue transporting water and nutrients in from roots (xylem), and transporting food out (phloem). Flowering plant life cycle 1. 2. 3. 4. 5. 6. 7. Pollen is produced by stamen – (get it?) Pollen lands on female pistil Pollen travels down pollen tube – in the style Pollen fertilizes eggs inside ovary to produce zygotes Zygotes grow into seeds Ovary grows into fruit around seeds Seeds get dispersed, land and grow into new sporophyte (main plant) 8. Sporophyte produces new gametophytes (flowers), which produce pollen and eggs Tropisms – see text p. 651 • • • • • Plant responses to stimulus Stimulus = gravity Response: Gravitropism – Roots grow down and shoots grow up Tropisms • • • • • Stimulus = light Response: Phototropism Plants grow toward the light, With help of auxin – a hormone that increases growth on side of stem that’s away from light • – get it? Tropisms • • • • • Stimulus – touch Response: Thigmotropism Plants grow toward touch This is for vines that climb or use other plants/objects to support them Nastic Responses see text p. 650 • Movement independent of direction of stimulus • Can be repeated many times • Examples: – Sun flowers move to always face the sun – sunflowers move to face sun – Venus fly traps snap shut when an insect triggers the response