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Plant Evolution.

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Presentation on theme: "Plant Evolution."— Presentation transcript:

1 Plant Evolution

2 The Plant Kingdom Nearly all are multicelled
Vast majority are photoautotrophs Energy from sun Carbon dioxide from air Minerals dissolved in water

3 Setting the Stage for Plants
Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer

4 Invading the Land Cyanobacteria were probably the first to spread into and up freshwater streams Later, green algae and fungi made the journey together Every plant is descended from species of green algae

5 Adaptations to Land Root systems Shoot systems Vascular tissues
Waxy cuticle for water conservation

6 Evolutionary Trend in Plant Life Cycles
Algae and bryophytes put most energy into making gametophytes Land plants put energy into structures that produce spores and retain, nourish, and protect gametes

7 Evolutionary Trend

8 Milestones in Plant Evolution
charophytes bryophytes lycophytes horsetails ferns cycads ginkgos conifers gnetophytes flowering plants seed plants plants with true leaves vascular plants land plants (closely related groups)

9 Pollen Pollen grains are sperm-bearing male gametophytes that develop from microspores Allows transfer of sperm to egg without water Can drift on air currents, or be carried by pollinators

10 Seeds Ovules are female reproductive structures that become seeds
Consist of: Female gametophyte with egg cell Nutrient-rich tissue Jacket of cell layers that will form seed coat

11 Nonvascular Plants Bryophytes Include 24,000 species of: Liverworts
Hornworts Mosses

12 Bryophytes Small, nonvascular, nonwooody
Gametophyte dominates life cycle; has leaflike, stemlike, and rootlike parts Usually live in wet habitats Flagellated sperm require water to reach eggs

13 Moss Life Cycle Development of mature sporophyte (still attached to gametophyte) Zygote Diploid Stage Fertilization Meiosis Haploid Stage Spores released male gametophyte tip Sperm Male gametophyte female gametophyte tip Female gametophyte Egg

14 Marchantia: A Liverwort
Reproduces asexually by way of gemmae cups Sexual reproduction Gametophytes are male or female Gametes are produced on elevated structures

15 Vascular Plants Majority of plants
Have internal tissues that carry water and solutes Two groups Seedless vascular plants Seed-bearing vascular plants

16 Seedless Vascular Plants
Produce spores but no seeds Main groups: Lycophytes Horsetails Ferns

17 Seedless Vascular Plants
Like bryophytes: Live in wet, humid places Require water for fertilization Unlike bryophytes: Sporophyte is free-living and has vascular tissues

18 Ferns 12,000 species, mostly tropical Most common sporophyte structure
Perennial underground stem (rhizome) Roots and fronds arise from rhizome Young fronds are coiled “fiddleheads” Spores form on lower surface of some fronds

19 Fern Life Cycle zygote Diploid Stage Haploid Stage
The sporophyte (still attached to the gametophyte) grows, develops Sori zygote rhizome Diploid Stage fertilization meiosis Haploid Stage Spores are released Spores develop egg-producing structure egg mature gametophyte (underside) sperm-producing structure sperm Spore germinates gametophyte

20 Seed-Bearing Vascular Plants
Gymnosperms arose first Cycads Ginkgos Conifers Angiosperms arose later Monocots Dicots

21 Seed-Bearing Plants Microspores that give rise to pollen grains
Megaspores inside ovules More water-conserving than seedless vascular plants

22 Special Traits of Seed-Bearing Plants
Pollen grains Arise from megaspores Develop into male gametophytes Can be transported without water Seeds Embryo sporophyte inside nutritive tissues and a protective coat Can withstand hostile conditions

23 Gymnosperms Plants with “naked seeds” Seeds don’t form inside an ovary
Conifers Ginkgos Cycads

24 Conifer Characteristics
Woody trees or shrubs Most are evergreen Bear seeds on exposed cone scales Most produce woody cones

25 Cycads Only 130 living species Two species of Zamia are native to U.S.
Palmlike appearance Pollen-bearing and seed-bearing cones on different plants

26 Ginkgos Only surviving species, Ginkgo biloba, is native to China
Deciduous tree with fan-shaped leaves Trees are male or female Female trees produce seeds covered with a fleshy, foul-smelling coat

27 Pine Cones Woody scales of a “pine cone” are the parts of where megaspores formed and developed into female gametophytes Male cones, where microspores and pollen are produced, are not woody

28 Pine Life Cycle Female cone Sporophyte Ovule Male cone Pollen sac Seed
Fertilization Meiosis Egg View inside ovule Microspores Megaspores Pollen tube

29 Angiosperms Flowering plants Dominant land plants (260,000 species)
Defining feature: Ovules and (after fertilization) seeds are enclosed in an ovary Two classes: Monocots and dicots

30 Plants and Pollinators
Pollen: Sperm packed inside a nutritious package Transferred first by wind currents Later transferred by insects Plants that attracted insect pollinators with flowers had a reproductive advantage

31 Pollen Formation Each anther has four pollen sacs
Inside the pollen sacs, cells undergo meiosis and cytoplasmic division to form microspores Microspores undergo mitosis to form pollen grains

32 Double Fertilization A pollen tube grows down through the ovary tissue
It carries two sperm nuclei When pollen tube reaches an ovule, it penetrates embryo sac and deposits two sperm One fertilizes the egg, other fuses with both nuclei of endosperm mother cell

33 Endosperm Formation Occurs only in angiosperms
Fusion of a sperm nucleus with the two nuclei of the endosperm mother cell produces a triploid (3n) cell This cell will give rise to the endosperm, the nutritive tissue of the seed

34 Seeds and Fruits The seed is the mature ovule
wall of ovary The seed is the mature ovule The fruit is the mature ovary

35 Structure of a Seed Protective seed coat is derived from integuments that enclosed the ovule Nutritious endosperm is food reserve Embryo has one or two cotyledons Monocot has one Eudicot has two

36 Seed Formation Fertilization of the egg produces a diploid sporophyte zygote The zygote undergoes mitotic divisions to become an embryo sporophyte Seed: A mature ovule, which encases an embryo sporophyte and food reserves inside a protective coat

37 Seed Dispersal Fruit structure is adapted to mode of dispersal
Some modes of seed dispersal: Wind currents Water currents Animals

38 Double Fertilization Distinctive feature of angiosperms
Male gametocyte delivers two sperm to an ovule One fertilizes egg; other fertilizes a cell that gives rise to endosperm that supports embryo

39 Flower Structure

40 Flowering Plant Life Cycle
Diploid Double fertilization Meiosis Meiosis Haploid Mitosis without cytoplasmic division Microspores Pollination Two sperm enter ovule Female gametophyte

41 Deforestation Result of demand for wood as fuel and lumber; cultivation of land for agriculture Greatest occurrence in Brazil, Indonesia, Columbia, and Mexico

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