AP Biology, Chapter 30
Plant Diversity II: The Evolution of Seed Plants

SUMMARY
INTRODUCTION

OVERVIEW OF REPRODUCTIVE ADAPTATIONS OF SEED PLANTS
	Introduction
		1. Describe the adaptive significance of the three most important reproductive 
		adaptations of seed plants for life on land.
	The gametophytes of seed plants became even more reduced than the gametophytes 
	of seedless vascular plants
			a. Dominant diploid sporophyte
				i. Sunlight causes more mutations for organisms in air
				ii. Diploidy represents a spare set of alleles
			b. Why have a multicellular gametophyte at all?
				i. Haploids with harmful recessive mutations die
				ii. Gametophytes in seed plants are nurtured by maternal tissues
	In seed plants, the seed replaced the spore as the main means of dispersing offspring
			a. Seeds are multicellular and much more complex
				i. Protects embryo
				ii. Has food supply for early development
				iii. Smaller surface to volume ratio
			b. Seeds develop from ovules
				i. Megaspore is surrounded by the nucellus
				ii. Entire structure is covered by the integuments
				iii. Megaspore develops into the female gametophyte
				iv. After fertilization the zygote divides to form the embryo
				v. Female gametophyte forms the food supply
				vi. Integuments form the seed coat
			c. Seeds can have unique dispersal strategies
	Pollen became the vehicles for sperm cells in seed plants
			a. Microsporangium  microspore  pollen grain
			b. Pollen is airborne; most seed plant sperm lack flagella

GYMNOSPERMS
	Introduction
	The Mesozoic era was the age of gymnosperms
		2. Relate the climate changes of the Mesozoic era to the success of gymnosperms during 
		that time.
			a. Formation of Pangaea
			b. Drier conditions, much less coastline
			c. Seeds are better adapted for surviving dry conditions
			d. Mechanisms requiring swimming sperm were selected against
	The four divisions of extant gymnosperms are the cycads, the ginkgo, the 
	gnetophytes, and the conifers
		3. List and distinguish among the four phyla of gymnosperms.
			a. Cycadophyta
				i. Cone-like cluster of sporophylls 
				ii. "Palms"
				ii. Symbiotic nitrogen-fixing cyanophyte
			b. Ginkgophyta
				i. One species remains; common street tree
				ii. Fan-like leaves, deciduous
			c. Gnetophyta
				i. Non-clade?
				ii. Xylem most like that in flowering plants
				iii. Weltwitschia, Ephedra
			d. Coniferophyta
				i. The most common gymnosperms
				ii. Seeds found between the leaves of cones
				iii. Most are evergreen; includes largest, tallest, oldest 
				iv. Conifers: pine, fir, cedar, hemlock, cypress, Sequoia 
	The life cycle of the pine demonstrates the key reproductive adaptations of seed 
	plants
		4. Describe the life history of a pine and indicate which structures are part of the 
		gametophyte generation and which are part of the sporophyte generation.
			a. Sporophyte
				i. Dominant form
				ii. Has separate male and female cones with sporangia
			b. Gametophytes
				i. Male cones make microspores that become pollen
				ii. Ovulate (female) cones make megaspores than become ovules
			c. Pollination and development
				i. Pollen lands inside the micropyle
				ii. Germinates; pollen tube delivers sperm
				iii. Each ovule develops into a winged seed
			d. Seeds dispersed mainly by the wind, also scattered by animals

ANGIOSPERMS (FLOWERING PLANTS)
	Introduction
		5. Distinguish between monocots, dicots, and eudicots.
			a. Monocots
				i. A clade as supported by molecular data
				ii. Traditional characters: single seed leaf, parallel venation, flower parts 
				in 3s
				ii. Includes grasses, lilies, yuccas, orchids, palms
			b. Dicots
				i. Not monophyletic
				ii. Traditional characters: two seed leaves, branched venation, flower 
				parts in 4s and 5s
			c. Eudicots [6th edition]
				i. A clade as supported by molecular data
				ii. Traditional dicot characteristics
				iii. Includes roses, legumes, sunflowers, buttercups, oaks, maples
			d. New clades based on molecular data [6th edition]
				i. Water lilies
				ii. Star anise (original source of shikimic acid for Tamifu)
				iii. Amborella, most primitive angiosperm (oldest clade)
	Terrestrial adaptation continued wit the refinement of vascular tissue in angiosperms
		6. Contrast the xylems of the conifers and angiosperms.
			a. Conifers (and Amborella) have tapering, chained tracheids
			b. Most angiosperms have end-to-end vessel elements
			c. Angiosperms also have tracheids modified as supporting fibers
	The flower is the defining reproductive adaptation of angiosperms
		7. Identify the following floral structures and describe a function for each:
			a. Sepals: green modified leaves surrounding and protecting the petals		
			b. Petals: colored modified leaves in animals-pollinated flowers		
			c. Stamens: male reproductive organs, produce pollen		
			d. Carpels: female reproductive organs, produce ovules
			e. Filament: stalk of the stamen, holds up the anther
			f. Anther: stamen sac where pollen is produced
			g. Stigma: sticky tip of the carpel, captures pollen
			h. Style: stalk of the carpel connecting the stigma and ovary
			i. Ovary: base of the carpel, contains ovules, develops into fruit
	Fruits help disperse the seeds of angiosperms
		8. Define "fruit" and explain how fruits are modified in ways that help disperse seeds.
			a. Fruit is the developed mature ovary, protects and disperses seeds
			b. Examples of modifications
				i. Many fibers for catching the wind
				ii. Hooks for attaching to fur
				iii. Sweet flesh to entice animals
			c. Seeds in fruit have made angiosperms the dominant plants on Earth
	The life cycle of an angiosperm is a highly refined version of the alternation of 
	generations common to all plants
		9. Describe the essential features of the generalized life cycle of an angiosperm and the 
		development of the male and female gametophyte.
			a. Anthers produce microspores that develop into pollen
			b. Ovules produce megaspores that form embryo sacs
			c. Pollen lands on stigma, pollen tube grows down the style
			d. Pollen tube penetrates micropyle, delivers nuclei to embryo sac
			e. One sperm nucleus + egg nucleus gives zygote  embryo
			f. 2nd sperm nucleus + 2 embryo sac nuclei  3n endosperm food supply
			g. Seed is embryo and food supply in developed ovule wall 
		10. Explain the process and function of double fertilization.
			a. Pollen delivers two nuclei
			b. One sperm nucleus + egg nucleus gives zygote  embryo
			c. 2nd sperm nucleus + 2 embryo sac nuclei  3n endosperm food supply
	The radiation of angiosperms marks the transition from the Mesozoic era to the 
	Cenozoic era
	Angiosperms and animals have shaped one another's evolution
		11. Explain how animals may have influenced the evolution of terrestrial plants and vice 
		versa.
			a. Coevolution: responsive adaptation in ecologically connected species
			b. Examples
				i. Seeds and spores eaten on the ground  get taller
				ii. Seeds up off the ground  increase mobility
				iii. Extreme case: one pollinator  one plant species
	Agriculture is based almost entirely on angiosperms
		12. Describe the significance of angiosperms to human agriculture.
			a. All of our fruit and vegetable crops are angiosperms
			b. And we rely on their symbionts and pollinators
PLANTS AND HUMAN WELFARE
		13. Describe the apparent impact of terrestrial plants on Earth's atmosphere and 
		therefore climate.
			a. Highest CO2 was 0.7% about 500 mya
			b. Appearance of land plants is coincident with reduction
				i. Some stored after photosynthesis
				ii. Some reacted with minerals released by root action
			c. Less CO2, less global warming
			d. Down to current levels, 0.03%, 325 mya: Carboniferous
			e. Permian extinction/Pangaea formation bumped it back up to 0.2%
				i. Seed plants appeared
				ii. Steadily went down to current levels 
		14. Describe the importance of plant diversity.
			a. Source of alleles for crop improvement
			b. Unknown useful secondary products like medicines
			c. Model systems for material science