AP Biology, Chapter 29
Plant Diversity I: The Colonization of Land

SUMMARY
INTRODUCTION

AN OVERVIEW OF PLANT EVOLUTION
	Structural, chemical, and reproductive adaptations enabled plants to colonize land
		1. Summarize the terrestrial adaptations of plants.
			a. Apical meristems for longitudinal growth of subterranean and aerial organs
			b. Embryophytes: multicellular, dependent embryos retained by the female
			c. Alternation of generations with a dormant, resistant spore stage
			d. Waxy cuticle and gas exchange through stomata for water conservation
			e. Xylem and phloem for distribution of water+mineral and organic products
			f. Secondary biosynthetic products: tannins, lignins, sporopollenin
		2. Define and distinguish between the stages of the alternation of generations 
		reproductive cycle. Compare the life cycle of humans with alternation of generations.
			a. Stages
				i. Sporophyte: multicelluar diploid that performs meiosis
				ii. Haploid spores grow by mitosis into gametophyte
				iii. Gametophyte makes gametes
				iv. Gametes fuse to form diploid zygote
				v. Zygote divides by mitosis to form sporophyte
			b. Human haploids do not grow by mitosis into a multicellular organism
	The history of terrestrial adaptation is the key to modern plant diversity
		3. Describe the four great evolutionary episodes in the history of land plants.
			a. Ordovician, 475 mya
				i. Charophytes  land plants
				ii. Sporopollenin, jacketed gametangia, vascular tissue
			b. Early Devonian, 400 mya
				i.  ferns
				ii. Seedless vascular plants
			c. Late Devonian, 360 mya
				i.  gymnosperms
				ii. Seeds
			d. Cretaceous, 130 mya
				i.  angiosperms
				ii. Seeds protected in ovaries	
		4. Distinguish between the four main groups of land plants.
			a. Bryophytes
				i. Mosses and liverworts
				ii. Seedless and avascular with primitive tissues
			b. Pteridophytes
				i. Ferns, lycophytes, horsetails
				ii. Seedless with an independent gametophyte
			c. Gymnosperms
				i. Conifers, ginkgoes, cycads
				ii. Cone-bearing, seeds not enclosed in a flower or fruit
			d. Angiosperms
				i. Flowering plants
				ii. Seeds enclosed in fruit

THE ORIGIN OF PLANTS
	Plants probably evolved from green algae called charophytes
		5. Describe five shared derived homologies that link charophyceans and land plants.
			a. Homologous chloroplasts: pigments, stacked thylakoids, DNA sequence, # of 
			membranes
			b. Biochemical similarity: cell wall composition, peroxisomal enzymes
			c. Mitosis and cytokinesis
				i. Nuclear membrane disassembly
				ii. Spindle persists until cytokinesis
				iii. Cell plate for cytokinesis in some charophytes
			d. Similar sperm ultrastructure
			e. Genetic relationship: nuclear and rRNA sequences
	Alternation of generations in plants may have originated by delayed meiosis
		6. Describe a likely hypothesis for the origin of alternation of generations in plants.
			a. No multicellular alternation of generations in modern charophytes
				i. Multicellular form is haploid
				ii. Fertilization takes place on the haploid
				iii. Meiosis immediately follows
			b. Hypothesis
				i. Zygote divides by mitosis before meiosis
				ii. Advantage: more cells available for meiosis
	Adaptations to shallow water preadapted plants for living on land
		7. Explain how adaptations of charophycean algae to shallow water preadapted plants for 
		life on land.
			a. Sporopollenin protects spores
			b. Protective sheath on oogonium 
		8. Distinguish between the kingdoms Plantae, Streptophyta, and Viridiplantae. Note 
		which of these is used in the textbook. [6th edition]
			a. Plantae: land plants; embryophytes (used in the 6th edition)
			b. Streptophyta: embryophytes + charophyta
			c. Viridiplantae: embryophytes + charophyta + chlorophyta

BRYOPHYTES
	The embryophyte adaptation evolved in bryophytes
		9. List and distinguish between the three phyla of bryophytes. Briefly describe the 
		members of each group, note their common names, and indicate which phylum 
		represented the earliest plants.
			a. Bryophyta
				i. Feathery with thin sporophyte stalks topped with sporangium
				ii. Commonly called mosses (ex. "peat")
			b. Hepatophyta
				i. Lobed with gemmae cups for asexual reproduction
				ii. Commonly called liverworts
			c. Anthocerophyta
				i. Sporophytes horn or spike-shaped
				ii. Commonly called hornworts (ex. Sphagnum)
				iii. These are most closely related to fully vascular plants
	The gametophyte is the dominant generation in the life cycle of bryophytes
		10. Describe the structure of the sporophyte and gametophyte stages of bryophytes. 			Explain why most bryophytes grow close to the ground.
			a. Sporophyte
				i. Thin stalk or spike tipped with sporangium
				ii. Grow up out of the archegonium after fertilization
			b. Gametophyte
				i. Dominant form
				ii. Green with small leaflike, stemlike, and rootlike (rhizoids) parts
				iii. Lacks well-developed vascular tissue and supporting tissue
				iv. Can't transport water very far 
		12. On a diagram the life cycle of a bryophyte, label the gametophyte and sporophyte 
		stages and the locations of gamete production, fertilization, and spore production.
			a. See 5th edition, page 553
	The three divisions of bryophytes are mosses, liverworts, and hornworts
		13. Describe the ecological and economic benefits of bryophytes.
			a. Form habitats of tiny animals
			b. Pioneer species; helps soil formation
			c. Store carbon
			d. Mined for fuel and for use as a soil amendment

THE ORIGIN OF VASCULAR PLANTS
	Introduction
	Additional terrestrial adaptations evolved as vascular plants descended from 
	bryophyte-like ancestors
		14. Describe the adaptations of vascular plants, including modifications of the life cycle 
		and modifications of the sporophyte, that have contributed to their success on land.
			a. Dominant sporophyte generation
			b. Modifications
				i. Branched sporophyte for producing more spores
				ii. Vascular tissue with chains of cells including xylem with lignified walls
	The branched sporophytes of vascular plants amplified the production of spores and 
	made more complex bodies possible

SEEDLESS VASCULAR PLANTS
	Introduction
	A sporophyte-dominant life cycle evolved in seedless vascular plants
		15. Distinguish between homosporous and heterosporous conditions.
			a. Homosporous: one type of spore, bisexual gametophyte (ex. ferns)
			b. Heterosporous: micro- (male) and mega- (female); separate gametophytes
		16. Explain why seedless vascular plants are most commonly found in damp habitats.
			a. Swimming sperm
			b. Fragile gametophytes 
	The three divisions of seedless vascular plants are lycophytes, horsetails, and ferns
		17. Compare the structures of lycophytes, pteridophytes, and sphenophytes.
			a. Lycophytes
				i. Large (40 m) woody trees in the fossil record
				ii. Currently prostrate hebaceous vines and epiphytes
				iii. Simple, microphyll leaves; sporangia on stalks
				iv. Separate gametophyte; non-photosynthetic; persistent, relies on 
				mycorrhizae
			b. Sphenophytes (horsetails)
				i. Once very diverse; fossil forms to 15 m
				ii. Reduced to 15 species; now found in swampy areas
				ii. Green jointed stems with tiny leaves
				iii. Stem tip cones harbor sporangia
			c. Pteridophytes
				i. Ferns, whisk ferns, and horsetails
				ii. Well-developed roots with lignified vascular tissue
				iii. Complex megaphyll leaves; sori are clusters of sporangia on leaf 
				bottoms
		18. Describe the production and dispersal of fern spores.
			a. Each sorus on the leaf bottom is a cluster of sporangia
			b. Springlike devices hurl spores
			c. Spores are small enough to be blown by the wind
		19. Describe the major life cycle differences between mosses and ferns.
			a. Ferns have a separate sporophyte stage
			b. Fern sporophyte is larger
			c. See fern life cycle, 5th edition, page 556
	Seedless vascular plants formed vast "coal forests" during the Carboniferous period
		20. Explain how coal is formed and note during which geologic period the most extensive 		coal beds were produced.
			a. Formation
				i. Anoxic swamps limited decay
				ii. Dead plants built up and were heated and compressed
			b. Geologic period: Carboniferous, 290-360 mya