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

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

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

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

Progression Visual

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

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

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

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

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

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

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

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)

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

Pine Life Cycle Visual

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

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)

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

XXX Rated Visual

It’s all about sex…

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

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