Chapter 30 The Evolution of Seed Plants

1. Chapter 30 The Evolution of Seed Plants Biology 102 Tri-County Technical College Pendleton, SC

2. Some Key Terms • Seed is fertilized, ripened ovule of gymnosperm or angiosperm • Seed consists of an embryo, food supply, and protective seed coat • Designed for dispersal by various means: • Wind • Animals • Water

3. Progressive Time Line • Several key adaptations were required in progression from nonseed to seed plants • Terrestrial habitat • Support, water supply (access/conservation), nutrients, and solving the “hanky-panky” problem • Size and dependency of generation • Bryophytes: dominant gametophyte with reduced sporophyte that is dependent of gametophyte

4. Progression, cont. • Ferns: dominant sporophyte with reduced gametophyte and both nutritionally independent of each other • Gymnosperms: dominant sporophyte and gametophyte reduced even further • Angiosperms: dominant sporophyte and even further reduced gametophyte • In seed plants, the gametophyte is nutritionally dependent on the sporophyte

5. Progression Visual

6. Homo versus Hetero • Homosporous plant produces single type spore that develops into gametophyte with both male and female reproductive organs • Heterosporous plant = 2 distinct spores with megaspore becoming larger, female gametophyte (mega) and microspore becoming smaller, male gametophyte (micro) • Bryophyta is homosporous; most ferns are homosporous (exceptions); seed plants (gymno/angio) always heterosporous

7. More on Spores • Spore (haploid reproductive structure) shed for dispersal by mosses and ferns • Seed plants retain megaspore and female gametophyte develops within megasporangia and depends on sporophyte for food and water • Microsporangium produces male gametophyte (pollen) which is distributed by wind, insect, bird, plant breeder, etc. • Pollen grain reaches appropriate surface, it develops further

8. OMG..more on sperm and egg • Mosses and ferns still dependent of moisture for sperm to swim to egg • Seed plants depend on pollen (male gametophyte) dispersal • Appropriate location, pollen grain grows pollen tube • Tip of tube penetrates megagametophyte, two sperm are released

9. Celebrate the Differences • Pollination is transfer of pollen to appropriate structure such as ovule, carpel, or pistil • Fertilization is union of sperm and egg to produce single cell called a zygote • Time for an Estesism….Yeehaw!!!! • Cone is axis bearing tight cluster of scales or leaves specialized for reproduction

10. Continue the Celebration • Flower is total reproductive structure of angiosperms • Dr. Richards: “modified leaf with carpels” • Fruit is ripened and mature ovary (or group of ovaries) • Sometimes applied to reproductive structures of other groups of plants

11. Celebration III • Naked seed describes ovules and seeds not protected by flower or fruit tissue • Covered seeds characteristic of the angiosperms • Ovary of flowering plant (with seeds it contains) develops into fruit after fertilization

12. Pine Life Cycle • Pollen grain falls onto ovulate cone and enters ovule through micropyle • Germinates in ovule, forms pollen tube that digests way through nucellus • Megaspore mother cell undergoes meiosis = 4 haploid megaspores (1 survives) • It grows and divides repeatedly by mitosis = immature female gametophyte

13. Pine Life Cycle, cont. • 2 or 3 archegonia (each with egg) develop within multicellular gametophyte • After 1 year, eggs ready for fertilization—2 sperm cells have developed and pollen tube has grown through nucellus to female gametophyte • Fertilization occurs when one sperm unites with egg nucleus • All eggs in ovule may be fertilized, but only ONE zygote develops into embryo (usually)

14. Pine Life Cycle, cont. • Pine embryo (new sporophyte) has rudimentary root and several embryonic leaves • Embedded in female gametophyte • Nourishes embryo until capable of photosynthesis • Ovule has developed into pine seed • Embryo (2N), food source (N), surrounding seed coat (2N) • Scales of ovulate cone separate (~another year) and winged seeds usually carried by wind to new location

15. Pine Life Cycle Visual

16. Pollen and Seed Cones • Multicellular gametophyte generation reduced and develops from haploid spores retained within sporangia • Male gametophyte is pollen grain (no anthridium) • Female gametophyte consists of multicellular nutritive tissue and an archegonium that develops within an ovule

17. Pollen and Seed Cones, cont. • Conifer life cycles are heterosporous • Male and female gametes develop from different types of spores produced by separate cones • Pollen cones have microsporangia • Cells undergo meiosis = haploid microspores • These small spores develop into pollen grains • pollen grains = male gametophyte (not quite true, but will do for this course)

18. Pollen and Seed Cones, cont. • Ovulate cones have megasporangia • Cells here undergo meiosis = large megaspores that develop into female gametophyte • Each ovule initially includes megasporangium (nucellus) enclosed in protective integuments • Has single opening called micropyle

19. XXX Rated Visual

20. It’s all about sex…

21. Perfect versus Imperfect • Flower containing both male and female reproductive parts called “perfect” • Has both megasporangia and microsporangia • Flower with ONLY megasporangia OR microsporangia called “imperfect” • Either stamens or carpels nonfunctional or absent in given flower

22. Monoecious/Dioecious • Monoecious means “one-house” • Megasporangiate & microsporangiate flowers occur on same plant (corn & beech) • In same flower or separate flowers • Dioecious means “two-houses” • Given plant produces flowers with stamens or flowers with carpels (pistils) but NEVER BOTH • Willows, date palms, and wacky-backy