P lant D iversity I : T he C olonization of L and

1. Plant Diversity I: The Colonization of Land Campbell, 5th Edition, Chapter 29 Nancy G. Morris VolunteerState Community College

2. Figure 29.3 Highlights of Plant Evolution

3. Review of Characteristics: • Chloroplasts with photosynthetic pigments: chlorophyll a, chlorophyll b, carotenoids • Cell walls containing cellulose • Secondary cell walls containing lignin • Food stored as amylose in plastids • Classification of Kingdom (Table 29.1)

4. Plant Kingdom • Members show structural, chemical, & reproductive adaptations of terrestrial life • This distinguishes higher plants from the aquatic algae • Structural adaptation includes specialized structures to obtain water, minerals, carbon dioxide, light, etc. • Example: stomata – special pores on surface for gas exchange

5. Plant Kingdom • Chemical adaptation includes a waxy cuticle, composed of cutin, to prevent desiccation • Cutin, lignin, sporopollenin are examples of secondary products meaning that they are produced through metabolic pathways not common to all plants • cellulose is an example of a primary product

6. Plants as EmbryophytesA new mode of reproduction was necessary to move from an aquatic to terrestrial existence: • 1) Gametes are produced in gametangia, organs with protective jackets of sterile cells that prevent gametes from drying out. Egg is fertilized within the female organ. Figure 29.1a

7. Plants as Embryophytes • 2) Embryos must be protected against desiccation. Zygote develops into embryo that is retained within female protective cells in the gametangia Figure 29.1b

8. Alternation of Generations: a review • All higher green plants reproduce sexually • Most are also capable of asexual reproduction • The haploid gametophyte generation produces and alternates with a diploid sporophyte generation. The sporophyte produces gametophytes.

9. Figure 29.2Alternationof Generation

10. Alternation of Generations: a review • The life cycle is heteromorphic – the gametophyte & sporophyte differ in morphology • The sporophyte is larger & more noticeable in all but the bryophytes • Reduction of the gametophyte and dominance of the sporophyte generation we move from bryophytes to angiosperms

11. Figure 29.5 Hypothetical Mechanism: Origin of Alternations of Generations

12. Keeping a low profile… Bryophytes: • Lack woody tissue • Unable to support tall plants on land • Often sprawl horizontally as mats

13. Nonvascular Plants: 3 Divisions

14. Division Bryophyta • Bryon (Gr. “moss”) • Grip substratum with rhizoids • Cover about 3% of land surface • Contain vast amounts of organic carbon • Campbell, Figure 29.7, Life Cycle of a Moss

15. Division Hepatophyta • Liverworts • Sporangia have elaters, coil-shaped cells, that spring out of capsule & disperse spores • Also reproduce asexually from gemmae (small bundles of cells that bounce out of cups when hit by rainwater) • Campbell, Figure 29.8

16. Division Anthocerophyta • Hornworts • Resemble liverworts but sporophyte is horn-shaped • Photosynthetic cells have one large single chloroplast • Campbell, Figure 29.9

17. Adaptation to land • Antheridium produces flagellated sperm • Archegonium produces a single egg • Fertilization occurs within the archegonium • Zygote develops into an embryo within the archegonium (embryophytecondition)

18. Ancestral aquatic habitat evident… • Water required for reproduction • Flagellated sperm cells swim from the antheridium to the archegonium • Vascular tissue is absent • Water is distributed throughout the plant by the relatively slow process of diffusion, capillary action, cytoplasmic streaming

19. Six terrestrial adaptations: 1) Regional specialization of the plant body: • subterranean roots that absorb water & minerals from the soil • aerial shoot system of stems & leaves to make food

20. Terrestrial adaptations: 2) Structural support • support is provided by lignin embedded into the cellulose matrix of cell walls

21. Terrestrial adaptations: • Vascular systems evolved: • XYLEM – complex tissue that conducts water & minerals from the roots to the rest of the plant; composed of dead, tube-shaped cells that form a microscopic water-pipe system • PHLOEM – conducts sugars, amino acids, etc. throughout the plant; composed of living cells arranged in tubules

22. Terrestrial adaptations: • 4)Pollen– pollination eliminated the need for water to transport gametes • 5) Seeds • 6) Increased dominance of the diploid sporophyte

23. Vascular plants display two distinct reproductive strategies: • Homosporous plants produce one type of spore • Each spore develops into a bisexual gametophyte with both antheridia and archegonia • Heterosporous plants produce two kinds of spores: • Megaspores develop into female gametophytes possessing archegonia • Microspores develop into male gametophytes possessing antheridia

24. Comparison Single Eggs Homosporous type of Bisexual Sporophyte spore gametophyte Sperm Female Megaspore Gametophyte Eggs Heterosporous Sporophyte Microspore Male Sperm Gametophyte

25. Seedless vascular plants: primitive tracheophytes • Division Psilophyta - whisk ferns • Division Lycophyta - club mosses • Division Sphenophyta - horsetails • Division Pterophyta - ferns

26. Division Lycophyta • Club mosses (Fig. 29.12) • Sporangia are borne on sporophylls – leaves specialized for reproduction • In some sporoangia, sporophylls are clustered at branch tips into club-shaped strobili – hence the name club moss • Spores develop into inconspicuous gametophytes that are nurtured by symbiotic fungi. • Most are homosporous. (Selaginella is heterosporous.)

27. Division Sphenophyta • (Fig. 29.13) Equisetum • Common in Northern Hemisphere in damp locations • Homosporous • Gametophyte is only a few mm • Gametophyte is free-living & photosynthetic

28. Division Pterophyta: FERNS • 12,000 existing species • most ferns have fronds • homosporous • sori on underside of leaf with annulus to catapult spores into the air • prothallus (gametophyte) requires water

29. Figure 29.11 Life Cycle of a Fern

30. “Coal forests” • During the Carboniferous period, the landscape was dominated by extensive swamp forests: club mosses, whisk ferns, horsetails were gigantic plants • Organic rubble of the seedless plants accumulated as peat(Figure 29.14) • When later covered by sea and sediment, heat & pressure transformed the peat into coal