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Plant Evolution & Diversity. I. Kingdom Protista: Algae & Protozoa. A. Characteristics. 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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I. Kingdom Protista: Algae & Protozoa A. Characteristics 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
B. Suspects and Evidence 1. Characteristics of Green Algae - Chlorophytes a. Mostly freshwater, but some are marine. b. Have plant-like chloroplasts. c. There are unicellular and multicellular forms d. Can live symbiotically with fungi as lichens
Fig 28.30 Volvox - freshwater Ulva – sea lettuce Caulerpa - intertidal
2. Characteristics of Green Algae - Charophyceans a. fresh water ponds b. They are considered to be the closest ancestors of true plants. Evidence: i. Both have same type of cellulose-synthesizing complexes in cell membrane ii. Both have peroxisomes for enzyme storage iii. Both have same type of flagellated sperm iv. Both form a cell plate during cell division v. Genetic evidence – charophyceans share a greater % of similar DNA with true plants than any other algae
III. Plants Shared Characteristics A. Plants are multicellular eukaryotes that are photosynthetic autotrophs. B. Shared pigments C. Cellulose cell walls D. Store glucose as starch E. Etc.
IV. What challenges did plants face when they “moved” onto land? A. Issues Faced 1. Acquire, transport, and conserve water 2. Protect from UV radiation 3. Resist pathogens (bacteria) and herbivores (later) 4. Others?
Then why move onto land? B. Advantages 1. 2. 3. 4.
C. 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 Fig 29.5
2. Alternation of Generations Fig 29.5
a. 2 multicellular life stages: • i. 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. • ii. 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
sporocytes Fig 29.5
4. Multicellular gametangia • a. Gametangia = multicellular organs within the • gametophyte that produce the gametes by mitosis. • b. 2 types of gametangia: • i. Archegonia – produce eggs • ii. Antheridia – produce sperm • c. Sperm travel to the egg, fertilizing it within the • archegonia.
5. Multicelled 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.
6. Other examples of adaptations to life on land: (not all plants have the following): a. Cuticle – waxy covering to prevent desiccation & microbial attack b. Secondary compounds – odors, toxins, tastes, etc. to attract pollinators and defend against herbivores c. Roots - absorb water and minerals from the soil d. Shoots - stems and leaves to make food. e. Stomata – openings in the leaf surface to allow gas exchange for photosynthesis and to regulate water loss.
f. Ligninin cell walls to provide structural support for Shoots g. A vascular system that transports food & water from roots to shoots and vice versa.
A. Nonvascular Land Plants: Bryophyta 1. Characteristics a. Earliest land plants b. Phyla: Hepatophyta – liverworts, Anthocerophyta – hornworts, and Bryophyta– mosses c. Inhabit most environments, including extremes d. Peat moss (Sphagnum): doesn’t decay rapidly, stores 400 billion tons of carbon e. Gametophyte is the dominant generation f. No true roots nor leaves
2. Moss Life Cycle Fig 29.8
3. Bryophyta Phyla a. Hepatophyta – liverworts
Peat bogs – d. Sphagnum moss (stores carbon, doesn’t decay, fuel source) Fig 29.10
B. Vascular Plants 1. Characteristics a. Vascular tissue Xylem = water & mineral transport and Phloem = food (carbohydrates) transport b. Dominant generation = sporophyte c. Sporophytes branched, independent of gametophyte parent d. Leaves = Micorphylls to Megaphylls e. Root development
2. Groups a. Seedless Vascular Plants i. Characteristics Tiny gametophytes living just above or below soil surface Egg & Sperm need moist environment to fertilize (similar to bryophytes) Microphyll leaves
b. Two phyla of seedless vascular plants: i. Phylum Lycophyta (Club Mosses) They diverged first from bryophytes with an unbranched vascular system, flammable spore clouds, and were tree-like in the Carboniferous period ii. Phylum Pterophyta • Whisk ferns – no true leaves or roots • Horsetails – hollow air-filled stems (adaptation to water-logged, • low O2 environment) • Ferns – produce clusters (sori) of sporangia on underside of • leaves (fronds)
c. Fern Life Cycle Fig 29.12
d. Factors forest changes of the Carboniferous period (290-360 mya) i. Lycophytes (tree-like) & Pteridophytes ii. First forests iii. Swampy forests – slow decay in low O2, formed deep layers of organic matter iv. Heat + pressure + time => coal v. Pulled lots of CO2 out of atmosphere, cooling the earth & forming glaciers vi. Larger species died out when climate became drier
3. Terrestrial Adaptations of Seed Plants a. Seeds replace spores as main means of dispersal. i. Why? ii. More resistant to harsh environ b/c multicellular iii. old way (ferns & mosses) = spores released from sporangia to disperse and develop into gametophytes iv. new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophyte develops within the spore.
v. ovule = female sporangium + female spore. Female gametophyte develops within the spore & produces eggs. vi. after fertilization, the ovule becomes the seed vii. seed = sporophyte embryo + food supply (mature ovule tissues)
b. Reduction of the gametophyte: Similar to Fig 30.2
c. Heterospory – separate male & female gametophytes i. Old way: sporangia spores bisexual gametophyte (antheridia sperm, archegonia eggs) ii. New way: Megasporangia megaspores female gametophyte eggs Microsporangia microspores male gametophyte sperm
d. Ovules and seed production i. Megasporangia protected by layers of tissue called integuments. ii. Ovule = integuments, megasporangia, & megaspore iii. Megaspore female gametophyte egg & food supply iv. After fertilization, embryo develops, ovule becomes a seed
e. Pollen & Pollination i. Microsporangia microspores male gametophyte sperm ii. Pollen = male gametophyte iii. Pollination = transfer of pollen to ovule by wind or animals iv. Pollen tube brings sperm to egg within the ovule
4. Two types of seed plants: a. Gymnosperms i. Characteristics Evolved first and “Naked seed” – seeds develop on surface of specialized leaves called sporophylls • ii. Four phyla: • Ginkophyta – only Ginko biloba • Cycadophyta – Cycads (look like palms) • Gnetophyta – Gnetophytes (tropical trees) • Coniferophyta – Conifers – cone-bearing trees • Dominate forests of the N. hemisphere • Most are evergreen • Needle-shaped Megaphyll leaves to reduce water loss during drought
