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Plant Evolution & Diversity

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Presentation on theme: "Plant Evolution & Diversity"— Presentation transcript:

1 Plant Evolution & Diversity

2 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.

3 The line between Kingdom Protista and Kingdom Plantae is still being discussed……
Fig 29.4

4 II. Plant Origins

5 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

6 Fig 28.30 Volvox - freshwater Ulva – sea lettuce Caulerpa - intertidal

7 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


9 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.

10 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?

11 Then why move onto land? B. Advantages 1. 2. 3. 4.

12 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

13 1. Apical Meristems – localized regions of cell division at tips of roots and shoots

14 2. Alternation of Generations

15 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

16 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

17 sporocytes

18 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.


20 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.

21 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.

22 f. Lignin in cell walls to provide structural support for
shoots g. A vascular system that transports food & water from roots to shoots and vice versa.

23 V. Plant Phyla

24 Fig 29.7

25 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:

26 2. Moss life cycle Fig 29.8

27 a. Hepatophyta – liverworts
3. Bryophyta Phyla a. Hepatophyta – liverworts

28 b. Anthocerophyta – hornworts

29 c. Bryophyta - mosses

30 Peat bogs – d. sphagnum moss (stores carbon, doesn’t decay, fuel source)
Fig 29.10

31 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

32 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)

33 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)

34 Phylum Lycophyta: club mosses, spike mosses, quill warts

35 Phylum Pterophyta: ferns, horsetails, whisk ferns

36 c. Fern Life Cycle Fig 29.12

37 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

38 3. Terrestrial Adaptations of Seed Plants a
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.

39 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)

40 b. Reduction of the gametophyte:
Similar to Fig 30.2

41 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

42 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

43 Fig 30.3

44 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

45 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 leaves to reduce water loss during drought

46 Phylum Cycadophyta

47 Phylum Ginkophyta

48 Phylum Gnetophyta

49 Phylum Coniferophyta

50 iii. Gymnosperm life cycle
Fig 30.6 iii. Gymnosperm life cycle

51 ii. One phylum: Anthophyta
b. Angiosperms i. Characteristics Flowering plants, Most diverse, and Evolved from gymnosperms: Sporophylls rolled together to form ovaries. ii. One phylum: Anthophyta Seeds are enclosed in the moist reproductive tissue of the sporophyte generation (Ovary). More insects and animals for pollination, less dependent on wind. Formerly only 2 classes: monocots & dicots. Now 4 clades (evolutionary lines): Basal angiosperms, Magnoliads, Monocots, & Eudicots



54 iii. Evolutionary success of Angiosperms
Increased water transport efficiency due to improvement in xylem tissue: tracheid cells, fiber cells, vessel elements (gymnosperms only have tracheids) Flowers – attract pollinators Fruits – many forms for variety of dispersal mechanisms

55 iv. Angiosperm life cycle
Fig 30.3

56 Notice the triploid stage!
Each pollen grain (male gametophyte) produces two sperm Sperm travel down the pollen tube & into the ovule. Double fertilization – one sperm unites with the egg to form the 2n zygote, other sperm unites with the two nuclei of the female gametophyte to form a 3n endosperm – becomes food for the developing embryo Ovule matures into the seed – contains sporophyte embryo & endosperm (food). Ovary (female sporangium tissues) matures into the fruit.

57 Moss life cycle Fig 29.8

58 Fern life cycle Fig 29.12

59 Fig 30.6 Gymnosperm life cycle

60 Fig 30.3 Angiosperm life cycle

61 VI. Kingdom Fungi Fungi were once included in the plant kingdom because they produce spores, have cell walls, and are not animals.

62 A. Characteristics 1. Their cell walls do not contain cellulose
(like plants), but do contain chitin (like insects, arthropods). 2. Their bodies are filamentous. 3. The organization of large structures such as mushrooms and morels is completely different from plants. 4. They are heterotrophs (acquire nutrients by absorption). Hence the boot!!

63 B. Fungal life cycle

64 C. Ecological Roles of Fungi:
1. Decomposers – absorb nutrients from dead organic matter, thereby decomposing it. Recycle nutrients to the soil.

65 2. Parasites – absorb nutrients from living hosts.
ex. pathogens on crops

66 3. Mutualists with plants – absorb nutrients from host, but
aid host in mineral uptake from soil. ex. mycorrhizae

67 C. Lifestyles of Fungi 1. Molds: rapid growing, asexually reproducing fungi 2. Yeasts: single-celled fungi inhabiting moist habitats. Raise bread & ferment alcohol

68 3. Lichens: symbiotic association of cyanobacteria or green algae and fungi.
a. Fungus provides shape b. Algae provides food, N to the fungus c. Lichens are very sensitive to air pollution; used as indicators of air quality.


70 4. Mycorrhizae: mutualistic association of plant roots and fungi.
a. Fungus increases the absorptive surface area of roots, increasing water and potassium uptake b. Fungus receives food from the root exudates.

71 2 down and 7 to go!!

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