1. Chapter 29 Plant Diversity I How Plants Colonized Land

2. Requirements for successful life on land  Supporting mechanism (vascular tissue and lignin  Absorptive structures (above and below the ground)  Conducting tissues (move fluids)  Anti-desiccation (non-drying) adaptations for body of plant and gametes  Airborne gamete dispersal

3. General Characteristics of Land Plants  Most have stomata (except Liverworts) for gas exchange  Secrete cuticle to reduce desiccation  Most have vascular tissue for bulk transport of water and nutrients  Most have seeds for protection of embryo

4. Proposed Ancestors of Plants  Charophyceans are the green algae most closely related to land plants. Chara, a pond organism (a) 10 mm Coleochaete orbicularis, a disk- shaped charophycean (LM) (b) 40 µm

5. Lines of evidence to support the phylogenetic connection between land plants and green algae.  Share many characteristics of land plants  Multicellular, eukaryotic, photosynthetic autotrophs  Cell walls made of cellulose  Chloroplasts with chlorophyll  Other characteristics shared with only the Charophyceans:  Plasma membranes possess rosette cellulose synthesizing complexes  Higher percentage of cellulose in cell walls  Presence of peroxisome enzymes  Similar structure of flagellated sperm  Certain details of cell division

6. Classification  Charophyceans Bryophytes (nonvascular plants) Seedless vascular plants Gymnosperms Angiosperms

7. Traits in land plants not seen in charophyceans  Apical meristems  Alternation of generations  Multicellular embryo –dependent on the parent plant  Sporangia, produce walled spores  Gametangia that produce gametes

8. Derived terrestrial adaptations of Land Plants

9. Alternation of Generations  Multicellular diploid (2N) plant is sporophyte  (like our animal cells do – 2 sets of chromosomes)  Produces spores (which are N) through meiosis  Spores will develop into the gametophyte generation  Multicellular haploid (N) plant is gametophyte  Produce gametes (egg and sperm)  The gametophyte is haploid itself and produces haploid cells  Phyla can have different dominant stages of gametophyte and sporophyte.

10. Alternation of Generations  Haploid multicellular organism (gametophyte) Mitosis Gametes Zygote Diploid multicellular organism (sporophyte) Alternation of generations: a generalized scheme MEIOSISFERTILIZATION 2n2n 2n2n n n n n n Spores Mitosis ALTERNATION OF GENERATIONS Bryophytes- the dominant generation is the gametophyte (N) What we think of as the main plant Vascular plants the dominant generation is the sporophyte (2N) and comprises the main plant

11. Walled Spores  Spores  Haploid-grow into gametophytes by mitosis  Sporopollenin makes walls of spores tough and resistant to harsh environments.  See concept maps

12. Multicellular gametangia  Produce gametes  Multicellular organs  Female – archegonium (produces a single egg)  Male – antheridia – produce many sperm  Sperm have flagella and swim to egg  See concept maps

13. Multicellular dependent embryos  Develop from zygotes that are retained within tissues of the female parent  Known as embryophytes  Parent provides sugars and amino acids to embryo

14. Apical Meristems  Localized regions of cell division at the tips of shoots and roots  Cells produced by meristems differentiate into various tissues.  Allow plants to obtain resources above and below ground

15. Non-vascular plants Bryophytes – Mosses, Liverworts and Hornworts

16. Non-Vascular Plants Mosses and Bryophytes life cycles  See concept map

17. Ecological and economic benefits of Bryophytes  Compound in cell walls absorb damaging levels of radiation preseent in deserts and at high altitudes  Can exist in very cold or dry habitats  Can lose most of their body water and then rehydrate when moisture again becomes available

18. Ecological and economic benefits of Bryophytes  Sphagnum – a wetland moss  Abundant and widespread  Forms deposits of undecayed organic material, called peat  Regions of this are called peat bogs  Organic materials do not decay readily  Used in past for diapers and as a natural antiseptic material for wounds  Used today as a soil conditioner and for packing plants roots  Peatlands play an important role as carbon reservoirs stabilizing atmospheric carbon dioxide levels.

19. Sphagnum - peatmoss  A bog body is a human cadaver that has been naturally mummified in a peat bog.

20. Vascular Plants  First 100 million years, terrestrial communities dominated by bryophytes  Vegetation became taller-vascular plants evolved  Evolution of Vascular plants  Main characteristics of modern vascular plants  dominant sporophytes  Transport in xylem and phloem  Evolution of roots and leaves  Sporophylls and spore variations

21. Characteristics of Modern Vascular Plants  Dominant sporophytes  Among living vascular plants, the sporophyte generation is the larger and more complex plant  Ex: leafy fern plants  Gametophyte reduction is most extreme in seed plants

22. Characteristics of Modern Vascular Plants Transport in Xylem and Phloem. Two types of vascular tissue  Xylem  Xylem conducts most of the water and minerals  Includes tracheids  Tube shaped cells that carry water and minerals up from roots  Lignified, strengthened by lignin  Phloem  Living tissue, nutrient conducting cells are arranged itno tubes that distribute sugars, amino acids and other organic products  Also lignified

23. Characteristics of Modern Vascular Plants  Evolution of Roots  Organs that anchor vascular plants  Enable plants to absorb water and nutrients from soil  Allow shoot system to grow taller  Also lignified tissue

24. Characteristics of Modern Vascular Plants  Evolution of Leaves  Organs that increase surface area of vascular plants  Capture more solar energy for photosynthesis  Microphylls (seen in all lycophytes)  Small leaves with a single unbranched vein  Megaphylls  Highly branched vascular system  Deliver water and minerals to the leaf  Export larger quantities of sugars from the leaf  Support more photosynthetic activity

25. Characteristics of Modern Vascular Plants  Sporophylls and Spore Variations  Contain sporophylls – modified plants that bear sporangia  Vary greatly  Ferns produce clusters of sporangia called sori  Gymnosperms produce groups to form a cone or strobili  Homosporous and Heterosporous species  Homosporous – produce a single type of spore  Becomes bisexual gametophyte  Male and female gametes  Most ferns  Heterosporous – produce two kinds of spores  Megaspores become female gametophytes  Microspores become male gametophytes  All seed plants and a few seedless vascular plants are heterosporous

26. Seedless vascular plants  Clades  Lycophytes  Club mosses, spike mosses and quillworts  Pterophytes  Ferns, horsetails, whisk ferns See concept map for lifecycle

27. Ferns  Different generations exist as distinct individuals Fronds – sporophyte Dominant stage of life cycle Ferns with gametophye and sporophyte sections Christmas fern with sporangia

28. Fern lifecycle http://www.botany.wisc.edu/courses/botany_401/pdf/401_03Crypto.pdf Link to examples of homosporus and heterosporus species

29. Significance of seedless vascular plants  Increased the removal of CO2 in the atmosphere  During the Carboniferous period this caused global cooling and widespread glacier formation  First forests gave rise to modern day coal  Dead plant matter turned to layers of peat, marine sediments piled on top, heat and pressure converted peat to coal.