Plant Evolution Chapters 29 & 30

Main Points Evidence that land plants have evolved from green algae Disadvantages and advantages of life on land The major evolutionary characteristics of bryophytes and seedless vascular plants Plants have a unique life cycle termed alternation of generations with a gametophyte generation and a sporophyte generation The typical life cycle pattern of plants, as demonstrated by ferns The evolutionary significance of seeds and pollen as key adaptations to life on land The evolutionary significance of flowers and fruits in angiosperm reproduction

I. Land plants evolved from green algae A. Approximately 500 million yeas ago B. Enabled other life-forms to survive on land Advantages Challenges Increased sunlight (not filtered by water) Lack of water More carbon dioxide available Desiccation (drying out) Soil rich in nutrients Structural support against gravity Fewer predators

C. Alternation of generations 1. Composed of two multicellular stages Gametophyte – haploid, produces gametes Sporophyte – diploid, makes spores by meiosis

II. Bryophytes A. 3 phyla – mosses, liverworts, hornworts B. Non-vascular – no xylem or phloem 1. Must be small C. Gametophyte stage dominant 1. Require water for sperm to meet egg 2. Smallest, simplest sporophytes of all plant groups – must absorb water, sugar, nutrients from parental gametophytes

III. Seedless Vascular Plants A. Ferns, club mosses, horsetails B. Evolution of vascular tissue allowed plants to grow taller and gain more access to sunlight C. Still require a film of water for sperm to reach egg D. Diploid sporophyte stage dominant E. Formed forests of tall plants in the Carboniferous period, formed deposits of coal (now used as fuel)

Advantages over spores IV. Seed Plants A. Seeds – plant embryos packaged with a food supply in a protective coat Dispersed from parents by wind, animals, etc. Pollen - male gametophyte, contains 2 sperm nuclei, waterproof coating Advantages over spores Layers of protective tissue around embryo Contain a supply of stored energy Can wait for conditions to be good before germinating Sperm doesn’t require water to reach egg

B. Gymnosperms – naked seeds (no fruit, often cones) 1. Four phyla, largest is the conifers – pines, spruces, firs, and redwoods

C. Angiosperms – flowers and fruits About 90% of all plant species Flowers – specialized for sexual reproduction – improves the efficiency of pollination a. Don’t have to rely on wind, attract birds and insects which transfer pollen anthers (male parts) to carpels (female parts) of other flowers b. Grasses – don’t attract pollinators but produce huge quantities of wind-borne pollen

3. Fruits – mature ovaries Thicken as seeds develop from ovules after fertilization Help disperse seeds

4. Monocots and eudicots (dicots) a. Monocots – about 70,000 species, have one cotyledon in the seed, parallel leaf venation, flowering parts in multiples of 3 b. Eudicots – about 170,000 species, two cotyledons in seed, net leaf venation, flowering parts usually in multiples of 4s or 5s