Chapter 30

1. Chapter 30 Plant Diversity II: The Evolution of Seed Plants

2. Plants are classified in 4 main divisions (aka phyla) according to whether or not they contain vascular tissue and whether or not they produce seeds, flowers, & fruits

3. All vascular seed plant lifecycles include a dominant sporophyte (2n) phase, an advantage for organisms exposed to unfiltered UV light. The sporophytes are much larger and long lasting that the gametophytes for all vascular plants. In the seeded vascular plants, the gametophytes are actually microscopic and contained within tissues of the parental sporophyte. Diploidy provides a survival advantage for organisms that rely on direct exposure to sunlight & its mutagenic UV radiation.

4. LE 30-2 Sporophyte (2n) Sporophyte (2n) Gametophyte (n) Seedless plant gametophytes are independent macroscopic organisms. Gametophytes of seed plants develop from microscopic spores inside the parent sporophytes. The 1n gametophytes are protected from UV radiation & herbivores and are less susceptible to desiccation. Gametophyte (n) Sporophyte dependent on gametophyte (mosses and other bryophytes) Large sporophyte and small, independent game-tophyte (ferns and other seedless vascular plants) Microscopic female gametophytes (n) in ovulate cones (dependent) Sporophyte (2n), the flowering plant (independent) Microscopic male gametophytes (n) in inside these parts of flowers (dependent) Microscopic male gametophytes (n) in pollen cones (dependent) Microscopic female gametophytes (n) in inside these parts of flowers (dependent) Sporophyte (2n), (independent) Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms)

5. Seed plants are heterosporous.♀ gametophytes produce ovules;♂gametophytes produce pollen. An ovule consists of a megasporangium (specialized parental 2n tissue analogous to an animal ovary), megaspore (1n) analogous to a female animal egg, and one or more protective integuments (layers of parental sporophyte 2n tissue surrounding & protecting megaspore or embyro) akin to the corpus luteum that surrounds the fertilized mammal egg. • Gymnosperm megaspores have one integument (form “naked” seeds) • Angiosperm megaspores usually have two integuments forming a seed coat)

6. Pollen and Production of Sperm • Microspores develop into pollen grains, which contain the male gametophytes • Pollination is the transfer of pollen to the part of a seed plant containing the ovules (a megaspore inside its integuments) • Pollen can be dispersed by air or animals, eliminating the water requirement for fertilization • If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule

7. Gymnosperm (conifer) embryos develop within ovules in the female cones. The embryo packaged with food inside 1 layer parental integument is called a naked seed. The Evolutionary Advantage of Seeds • A seed develops from the whole ovule • A seed contains the sporophyte embryo, along with its food supply, packaged in a protective coat Seed coat (derived from integument) Integument Female gametophyte (n) Spore wall Egg nucleus (n) Food supply (female gametophyte tissue) (n) Male gametophyte (within germinating pollen grain) (n) Discharged sperm nucleus (n) Megasporangium (2n) Embryo (2n) (new sporophyte) Pollen grain (n) Megaspore (n) Micropyle Unfertilized ovule Fertilized ovule Gymnosperm seed

8. LE 30-6_3 Key Haploid (n) Diploid (2n) Ovule Ovulate cone Megasporocyte (2n) Gymnosperm lifecycle Integument Longitudinal section of ovulate cone Micropyle Pollen cone Megasporangium Mature sporophyte (2n) Microsporocytes (2n) Germinating pollen grain Pollen grains (n) (containing male gametophytes) MEIOSIS MEIOSIS Surviving megaspore (n) Longitudinal section of pollen cone Sporophyll Microsporangium Seedling Germinating pollen grain Archegonium Integument Egg (n) Female gametophyte Seeds on surface of ovulate scale Germinating pollen grain (n) Food reserves (gametophyte tissue) (n) Seed coat (derived from parent sporophyte) (2n) Discharged sperm nucleus (n) Pollen tube Embryo (new sporophyte) (2n) FERTILIZATION Egg nucleus (n)

9. Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits • Angiosperms are flowering plants • These seed plants have reproductive structures called flowers and fruits • After their appearance 140 million years ago, the angiosperms underwent rapid adaptive radiation; today they are the most widespread and diverse of all plants • Angiosperm diversity reflects extensive co-evolution with animals, especially insects, the most diverse animals.

10. Flowers • The flower is an angiosperm structure specialized for sexual reproduction • A flower is a specialized shoot with up to four types of modified leaves: • Sepals, which enclose the flower • Petals, which are brightly colored and attract pollinators • Stamens, which produce pollen • Carpels, which produce ovules

11. LE 30-7 Stigma Carpel Stamen Anther Style Filament Ovary Petal Sepal Ovule Receptacle

12. Fruits • A fruit typically consists of a mature ovary but can also include other flower parts • Fruits protect seeds and aid in their dispersal • Various fruit adaptations help disperse seeds • Seeds can be carried by wind, water, or animals to new locations

13. LE 30-9 Wings enable maple fruits to be easily carried by the wind. Seeds within berries and other edible fruits are often dispersed in animal feces. The barbs of cockleburs facilitate seed dispersal by allowing these fruits to hitchhike on animals.

14. The Angiosperm Life Cycle • In the angiosperm life cycle, double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule • One sperm fertilizes the egg, while the other combines with two nuclei in the central cell of the female gametophyte and initiates development of a 3n food-storing endosperm • The endosperm nourishes the developing embryo

15. LE 30-10c Key Haploid (n) Diploid (2n) Microsporangium Anther Microsporocytes (2n) Mature flower on sporophyte plant (2n) MEIOSIS Microspore (n) Generative cell Ovule with megasporangium (2n) Tube cell Male gametophyte (in pollen grain) Ovary Pollen grains Germinating seed MEIOSIS Stigma Pollen tube Megasporangium (n) Sperm Embryo (2n) Surviving megaspore (n) Endosperm (food supply) (3n) Seed Pollen tube Seed coat (2n) Style Antipodal cells Female gametophyte (embryo sac) Pollen tube Polar nuclei Synergids Eggs (n) Sperm (n) Zygote (2n) Nucleus of developing endosperm (3n) Eggs nucleus (n) FERTILIZATION Discharged sperm nuclei (n)

16. Angiosperm Diversity • The two main groups of angiosperms are monocots and eudicots (aka dicots) • Remembering that the monocots are generally simpler or less organized will help you remember the characteristics.

17. LE 30-12ba • Cotyledon: seed leaf • Monocots store most of food in endosperm (3n)m, but dicots (eudicots) store most in the two cotyledons MONOCOTS EUDICOTS Orchid (Lemboglossum rossii) California poppy (Eschscholzia california) Eudicot Characteristics Monocot Characteristics Embryos Two cotyledons One cotyledon

18. LE 30-12bb MONOCOTS EUDICOTS Pyrenean oak (Quercus pyrenaica) Leaf venation Veins usually netlike Veins usually parallel Stems Pygmy date palm (Phoenix roebelenii) Vascular tissue usually arranged in ring Vascular tissue scattered

19. LE 30-12bc MONOCOTS EUDICOTS Lily (Lilium “Enchantment”) Roots Dog rose (Rosa canina), a wild rose Taproot (main root) usually present Root system usually fibrous (no main root)

20. LE 30-12bd MONOCOTS EUDICOTS Barley (Hordeum vulgare), a grass Pea (Lathyrusner vosus, Lord Anson’s blue pea), a legume Pollen Pollen grain with one opening Pollen grain with three openings Flowers Anther Zucchini (Cucurbita Pepo), female (left), and male flowers Floral organs usually in multiples of three Floral organs usually in multiples of four or five Stigma Ovary Filament

21. Evolutionary Links Between Angiosperms and Animals Pollination of flowers &transport of seeds by animals are two important mutualistic relationships in terrestrial ecosystems Evidence for co-evolution of plants & their pollinators/seed dispersers is match between flower shape and nectar collecting body parts or fruits & food choices.

22. Even though the angiosperms arose only about 140 million years ago, they are the most diverse and abundant of earth’s plants. Why? • Pollen (male gametes, akin to sperm) are carried far from the parent sporophytes by animals • Seeds (sporophyte embryos) can be carried far from parent sporophytes by animals or wind/water • So opportunities for self-fertilization or close relative fertilization is lower than in the bryophytes & pterophytes (sperm don’t swim too far) or gymnosperms (pollen don’t fly as far & cones often fall directly under the parent sporophyte)

23. Concept 30.4: Human welfare depends greatly on seed plants • No group of plants is more important to human survival than seed plants • Plants are key sources of food, fuel, wood products, and medicine • Our reliance on seed plants makes preservation of plant diversity critical

24. A botanist discovers a new species of plant with a dominant sporophyte, chlorophyll a and b, and a cell wall made of cellulose. In assigning this plant to a division, all of the following would provide useful information except whether or not the plant has ____ • endosperm. • seeds. • flagellated sperm. • flowers. • starch.