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Plant Evolution & Diversity. Kingdom Protista: Algae & Protozoa. 1. Simple Eukaryotes – mostly single-celled Amoeba, slime molds, euglenoids, algae 2. Organisms in this Kingdom don’t fit clearly into what we call plant, animal, or fungi.
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Kingdom Protista: Algae & Protozoa 1. Simple Eukaryotes – mostly single-celled Amoeba, slime molds, euglenoids, algae 2. Organisms in this Kingdom don’t fit clearly into what we call plant, animal, or fungi. 3. Most diverse eukaryotic Kingdom (>60,000 species). 4. We are interested in this Kingdom because of the Chlorophytes & Charophyceans - green algae.
The line between Kingdom Protista and Kingdom Plantae is still being discussed…… Fig 29.4
Characteristics of Green Algae - Chlorophytes 1. Mostly freshwater, but some are marine. 2. Have plant-like chloroplasts. 3. There are unicellular and multicellular forms 4. Can live symbiotically with fungi as lichens
Fig 28.30 Volvox - freshwater Ulva – sea lettuce Caulerpa - intertidal
Characteristics of Green Algae - Charophyceans 1. fresh water ponds 2. They are considered to be the closest ancestors of true plants. Evidence: A. Both have same type of cellulose-synthesizing complexes in cell membrane B. Both have peroxisomes for enzyme storage C. Both have same type of flagellated sperm D. Both form a cell plate during cell division E. Genetic evidence – charophyceans share a greater % of similar DNA with true plants than any other algae
Plants 1. Plants are multicellular eukaryotes that are photosynthetic autotrophs. 2. So how are they different from Charophyceans??
What challenges did plants face when they “moved” onto land? 1. Acquire, transport, and conserve water 2. Protect from UV radiation 3. Resist pathogens (bacteria) and herbivores (later) Then why move onto land?
Adaptation to life on Land: 1. Apical Meristems 3. Walled spores produced in sporangia 5. Multicellular, dependent embryos 4. Multicellular gametangia 2. Alternation of generations
1. Apical Meristems – localized regions of cell division at tips of roots and shoots
A. 2 multicellular life stages: • a. Sporophyte: • * Diploid • * Divides by meiosis to form spores • * Spores – haploid cells that can grow into a new, multicellular, haploid organism (the gametophyte) without fusing to another cell. • b. Gametophyte: • * Haploid • * Divides by mitosis to form the gametes (egg and sperm) • B. Egg & sperm fuse to form the diploid zygote, which divides by mitosis to form the sporophyte
3. Walled spores produced in sporangia A. Sporopollenin protects the spore from harsh environmental conditions B. Sporangia = an organ within the sporophyte that produces the spores C. Sporocytes = the diploid cells within the sporangia that divide by meiosis to form the haploid spores
4. Multicellular gametangia • A. Gametangia = multicellular organs within the gametophyte that produce the gametes by mitosis. • B. 2 types of gametangia: • a. Archegonia – produce eggs • b. Antheridia – produce sperm • C. Sperm travel to the egg, fertilizing it within the archegonia.
5. Multicellular, dependent embryos A. After fertilization, the zygote remains within the archegonia, gaining nutrients for growth from the gametophyte. B. Zygote divides by mitosis to become the sporophyte.
Other examples of adaptations to life on land: (not all plants have the following): 1. Cuticle – waxy covering to prevent desiccation & microbial attack 2. Secondary compounds – odors, toxins, tastes, etc. to attract pollinators and defend against herbivores 3. Roots - absorb water and minerals from the soil 4. Shoots - stems and leaves to make food. 5. Stomata – openings in the leaf surface to allow gas exchange for photosynthesis and to regulate water loss.
6. Lignin in cell walls to provide structural support for shoots 7. A vascular system that transports food & water from roots to shoots and vice versa.
Nonvascular Land Plants: Bryophytes • 1. Earliest land plants • 2. 3 Phyla: • A. Hepatophyta – liverworts • B. Anthocerophyta – hornworts • C. Bryophyta - mosses • 3. Inhabit most environments, including extremes • 4. Peat moss (sphagnum): doesn’t decay rapidly, stores 400 billion tons of carbon • 5. Gametophyte is the dominant generation:
Moss life cycle Fig 29.8
Peat bogs – sphagnum moss (stores carbon, doesn’t decay, fuel source) Fig 29.10
Vascular Plants • 1. Vascular tissue: • A. Xylem = water & mineral transport • B. Phloem = food (carbohydrates) transport • 2. Dominant generation = sporophyte • 3. Sporophytes branched, independent of gametophyte parent
Seedless Vascular Land Plants 1. Tiny gametophytes living just above or below soil surface 2. Egg & Sperm need moist environment to fertilize (similar to bryophytes)
Two phyla of seedless vascular plants: • 1. Phylum Lycophyta (Club Mosses) • A. diverged first from bryophytes • B. unbranched vascular system • C. flammable spore clouds • D. were tree-like in the Carboniferous period 2. Phylum Pterophyta • A. Whisk ferns – no true leaves or roots • B. Horsetails – hollow air-filled stems (adaptation to water-logged, low O2 environment) • C. Ferns – produce clusters (sori) of sporangia on underside of leaves (fronds)
Forests of the Carboniferous period (290-360 mya) 1. Lycophytes (tree-like) & Pteridophytes 2. First forests 3. Swampy forests – slow decay in low O2, formed deep layers of organic matter 4. Heat + pressure + time => coal 5. Pulled lots of CO2 out of atmosphere, cooling the earth & forming glaciers 6. Larger species died out when climate became drier
Terrestrial Adaptations of Seed Plants • 1. Seeds replace spores as main means of dispersal. • A. Why? • B. More resistant to harsh environ b/c multicellular • 2. Gametophytes became reduced and retained within reproductive tissue of the sporophyte • 3. Heterospory – separate male & female gametophytes • 4. Zygote develops into an embryo packaged with a food supply within a protective seed coat. • 5. Pollen & Pollination - freed plants from the requirement of water for fertilization.
1. Seeds replace spores as main means of dispersal. A. old way (ferns & mosses) = spores released from sporangia to disperse and develop into gametophytes B. new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophyte develops within the spore. C. ovule = female sporangium + female spore. Female gametophyte develops within the spore & produces eggs. D. after fertilization, the ovule becomes the seed E. seed = sporophyte embryo + food supply (mature ovule tissues)
2. Reduction of the gametophyte: Similar to Fig 30.2
2. Heterospory – separate male & female gametophytes A. Old way: sporangia spores bisexual gametophyte (antheridia sperm, archegonia eggs) B. New way: a. Megasporangia megaspores female gametophyte eggs b. Microsporangia microspores male gametophyte sperm
3. Ovules and seed production A. Megasporangia protected by layers of tissue called integuments. B. Ovule = integuments, megasporangia, & megaspore C. Megaspore female gametophyte egg & food supply D. After fertilization, embryo develops, ovule becomes a seed
4. Pollen & Pollination A. Microsporangia microspores male gametophyte sperm B. Pollen = male gametophyte C. Pollination = transfer of pollen to ovule by wind or animals D. Pollen tube brings sperm to egg within the ovule
Two types of seed plants: • 1. Gymnosperms • A. Evolved first • B. “Naked seed” – seeds develop on surface of specialized leaves called sporophylls • 2. Angiosperms • A. Flowering plants • B. Most diverse • C. Evolved from gymnosperms: Sporophylls rolled together to form ovaries.
Gymnosperms • Four phyla: • 1. Ginkophyta – only Ginko biloba • 2. Cycadophyta – Cycads (look like palms) • 3. Gnetophyta – Gnetophytes (tropical trees) • 4. Coniferophyta – Conifers – cone-bearing trees • A. Dominate forests of the N. hemisphere • B. Most are evergreen • C. Needle-shaped leaves to reduce water loss during drought
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