Plant Evolution

Adaptations Cuticle alternation of generations specialized tissues

Cuticle Waxy coating on surfaces resists drying out stomata exist to allow necessary gas exchange

Alternation of generations Plants live part of their life in a haploid stage and part in a diploid stage haploid portion is called the gametophyte generation because it produces the reproductive cells diploid portion called sporophyte generation because it produces spores

Alternation continued... The gametophyte plant produces male and female sex organs (male and female gametangium) eggs are fertilized by sperm to form a zygote embryo development (seed) occurs within the female gametangium (see fig 23-1 on p 421, 23-5 on p 426 and 23-8 on p 430)

Specialized tissues Other than bryophytes all other plants have vascular tissues xylem - conducts water and minerals phloem - conducts food

Bryophytes Only nonvascular plants (mosses, liverworts) no ability to internally transport water and materials require moist environment live in colonies, has rhizoids to anchor it important in soil formation Rhizoids do not act like roots since they have no vascular tissues Bryophytes are the only plant with a dominant gametophyte generation, that is the plant you see is in a haploid form! The gametphyte is born at the top of the plant, there may be separate sexes that is male and femal plants or male and femal may be found on the same plant in other species. The male sperm are carried to the female by flowing water. The diploid zygote grows into a mutilcellur embryo and matures into a sprorphyte, a diploid plant. The sporophyte plant grows out of the top of the female gametophyte. The sporophyte remains attached and gets nutrition from the femal plant.. At maturity the sporophyte turns brown. It has a foot, a seta (stalk) and a capsule within which meiosis occurs to form the haploid spores. At maturity the capsule opens the haploid spores are released and if they fall on sutiable ground grow into a gametophyte

Ferns Seedless, flowerless, vascular plants have xylem and phloem has alternation of generation, the common familiar leafy plant is the sporophyte generation has a rhizome and leaves

Ferns II Spore production occurs on places on the fronds, sporangia are formed in which meiosis occurs to form spores. Spores are often born in clusters called sori spores are released and if they germinate will grow into the gametophytes method of fertilization is primitive like bryophytes

Ferns Whisk ferns - extinct, no roots, no leaves but did have vascular system above and below ground! Horsetails - roots, rhizomes and vertical stems

Heterospory Homospory - one type of spore produced by bryophytes and many ferns Heterospory - some ferns have two types of spores produced microspores (male gametophytes) and macrospores (female gametophytes) the development of heterospory leads two the two most successful kinds of plants

Gymnosperms Vascular, seed bearing, flowerless plants means “naked seed” largest division is conifers - woody cone bearing gymnosperms leaves are called needles most have male and female parts on same plant. Reproductive parts in cone.

Gymnosperm reproduction Microspores and macrospores formed in separate cones Male cones smaller than female, on lower branches meiosis in male cone produces a male gametophyte, also called a pollen grain carried by air current to female gametophyte

Angiosperms Flowering, vascular plants most successful plants fertilization in flowering plants called double fertilization 2 sperm involved - 1 fertilizes the egg, the other fuses with 2 cells in female gametophyte to form endosperm

2 classes of Angiosperms Monocots - mostly herbaceous, long, narrow leaves, parallel veination, flower parts occur in threes, single cotyledon (embryonic leaf), endosperm present in seed vascular bundles scattered

2 classes of Angiosperms Dicotyledons - herbaceous or woody, leaves variable in shape, netted veination, flower parts occur in 4 and 5, 2 cotyledons, endosperm usually absent in mature seed vascular bundles arranged in a circle

Plant Evolution Bryophytes - no roots, leaves or stems, no vascular system, simple reproduction relying on water, gametophyte (haploid) dominant generation Ferns - first vascular system, rhizomes (horizontal stems), fronds, sporophyte (diploid) dominant generation

Plant Evolution Gymnosperms - first leaves (needles), vascular system, stems and roots, naked seeds Angiosperms - vascular system more organized, leaves, ability to shed leaves, seed provided with nutritive tissues, flowers, more sophisticated reproductive methods