Plant Diversity II The Evolution of Seed Plants

SEEDS! Seeds are plant embryos packaged with a food supply in a protective coat

Evolution of Plants

Five Reproductive Adaptations Reduction of the gametophyte: shift from haploid to diploid condition female gametophyte and embryo depend on sporophyte protection against drought Protects the delicate antheridia and archegonia Increasing reproductive success Heterospory Production of two types of spores Megaspores – female gametophyte – eggs Microspores – male gametophyte - sperm

Five Reproductive Adaptations Ovules: production of eggs Megasporangium, megaspore plus protective tissue = ovule Increases protection of the egg and developing zygote Increases reproductive fitness Evolution of pollen Male gametophyte = pollen grain Contain two sperm nuclei Waterproof coat for transfer by wind Remember before – water was required for fertilization THIS IS A KEY ADAPTATION

Five Reproductive Adaptations Seeds Advantages over spores Multicellular Layers of protective material Supply of stored energy means seed can WAIT for good germination conditions Stored energy supplements early growth of the embryo

Gymnosperms (bare naked) Cone-bearing plants Lack enclosed chambers (ovaries) for seeds Ovules and seeds develop on specialized leaves called sporophylls Ginkgo, cycads, and conifers All are “evergreens” Needle-shaped leaves Vascular tissue refinement: tracheids~ water conducting and supportive element of xylem

Reproduction in Gymnosperms

Reproductive Cycle

Gymnosperm Life Cycle Sporophyte produce gametophytes inside of cones Pollen cone (male) produces microspore via meiosis Ovulate cone (female) produces megaspores via meiosis Fertilization pollen grains discharge sperm into egg

Angiosperms – Flowers and Fruits Seed plants that produce the reproductive structures called flowers and fruits. 90% of all plant species “Flowering plants” Anthophyta

The Flower defining structure of angiosperms Reproductive structure: pollen transfer; specialized shoot with modified leaves Sepals: enclose flower before it opens - protection Petals: attract pollinators Stamens: male, produce microspores in the anther that develops the pollen grain Carpels: female, produce megaspores - stigma, style, ovary, ovules

Fruits Fruits are the mature ovaries of the plant The wall of the ovary thickens to become the fruit. The purpose of fruit is to disperse the seeds

Monocots and Eudicots Angiosperms are divided into two groups Monocots ~70,000 species One cotyledon in the seed Parallel leaf veins Flowering parts in multiples of three

Monocots and Eudicots Angiosperms are divided into two groups Eudicots ~170,000 species Two cotyledon in the seed Net leaf veins Flowing parts in multiples of fours or fives

Angiosperm life cycle