AP Biology Spring 2011

 Outline evolutionary advances that converted marine algal ancestors into plants that could live on land  State the advances that converted primitive marsh plants into dry-land flowering plants  Use a diagram to illustrate the evolutionary trends in plants with specific reference to sporophyte and gametophyte dominance  Characterize mosses, seedless vascular plants, gymnosperms, and angiosperms  Discuss why angiosperms are most successful of all plants

 Green algae began invasion of land by plants 475 million years ago  Land conditions for plants improving › Water based photosynthesis was changing the atmosphere › Reduced amount of UV radiation

 Charophyte algae were evolving at the water’s edge  gave rise to plants  Charophytes : share common ancestor with all land plants  Rhyniophytes : first seedless vascular plants (Psilophyton)

 After the first invasion, 60 million years later, plants had radiated throughout the land  Seed fossils date back about 385 millions years  Angiosperms emerged around 145 million years ago and quickly (within 40 million years) became dominant land plants

 Life cycle of simple aquatic plants is dominated by the haploid gametophyte phase › Gametes of some green algae are all motile and of the same size › Others are differentiated into motile sperm and immotile eggs › A watery environment was necessary for gametes to meet each other

 Life cycle of complex land plants is dominated by the large, diploid sporophyte › Cells within the sporophyte undergo meiosis to give rise to the haploid spores › Spores develop into the gametophyte, which produces the gametes

 Over time, sporophytes, while developing extensive root and shoot systems, began holding onto spores and gametophytes › Protects and nourishes them

 Aboveground parts of plants became covered by a cuticle  Stomata became control points for water balance

 Underground parts of plants developed into root systems › Specialized for absorption of water and minerals through extensive cylindrical tubes

 Vascular tissue became increasingly extensive › Xylem : conducting water and minerals › Phloem : products of photosynthesis

 Extensive growth of stems and branches became possible due to strengthening of cell walls afforded by deposits of lignin

 Bryophytes and some vascular plants reproduce by releasing spores  Seed bearing vascular plants produce seeds and pollen › The male gametophytes- pollen grains- are released from the parent plant to be carried by whatever means to the female gametophyte › Seeds are immature sporphytes with a waterproof covering › Many seeds are adapted with a means of dispersal

 Bryophytes: include mosses, liverworts, hornworts › Not a monophyletic group

 No lignin in the stems  Most less than 20cm tall  Gametophyte is the largest part of the life cycle

 Cellular protective jacket surrounds sperm-producing and egg-producing parts of plant to prevent drying out  Sperm are flagellated, so water (or insects) are required for fertilization  Sporophytes remain attached to the gametophytes after fertilization  Bryophyte spores resistant to drought

 Liverworts : root-like rhizoids that attach to the ground and can reproduce asexually or sexually › Ex. Marchantia

 Hornworts : have pointy sporophyte that can survive after the gametophyte dies

 Mosses: › Egg and sperm develop in the gametangia at the shoot tips of the moss plants › After fertilization: zygote develops into a mature sporophyte, which consists of a sporangium in which spores develop › Compressed layers of dead mosses form peat bogs

 Most seedless vascular plant that flourished in the past are extinct

 Present day descendents: lycophytes, horsetails, ferns › Differ from bryophytes with respect to the sporophytes  Develop independently of the gametophyte  Have well developed vascular tissues  Are the larger, longer lived phase of the life cycle

 Although sporophytes of seedless vascular plants can live on land, their gametophytes cannot because they lack vascular tissues › Male gametes must have water to reach their eggs

 Lycophytes : once tree sized, now represented by small club mosses on the forest floor › Sporophyte has true roots, stems, and small leaves containing the vascular tissue › Strobili bear spores that germinate to form small, free living gametophytes  Group is closely tied to aquatic environment- sperm must swim to eggs

 Whisk ferns : not true ferns, shaped like whisk brooms with tiny reduced leaves  Sporophytes: have rhizomes that are short, branched, horizontal underground stems

 Ancient relatives of horsetails were treelike; only moderately sized Equisetum has survived › Plants are called sphenophytes and include scouring rushes › Sporophyte possess underground stems called rhyizomes › Scalelike leaves are arranged in whorls around the hollow, photosynthetic stem

 Spores are produced inside cone- shaped clusters of leaves at the shoot tip, called strobili

 Ferns : largest, most diverse group of seedless vascular plants › Mostly native to the tropics and are highly diverse in size

 Bear underground stems (rhizomes) and aerial leaves (fronds)  Sori : clusters of sporangia that release spores that develop into small heart- shape gametophytes  Some species of ferns live as epiphytes, aerial plants growing attached to tree branches or trunks Sori:

 Vast forests of lycophyte trees and horsetail plants existed in the Carboniferous  As sea level rose and fell, forest trees were submerged in sediments protected from decomposers

 First peat was formed, but increased pressure and heat produced coal  It has taken a remarkably short time for human technology to extract coal, one of nonrenewable fossil fuels, from the ground

 The most successful of the vascular plants are the seed-bearing species  Escaped dependency on water for fertilization, relying on air currents and insects

 Seed plants, gymnosperms, and angiosperms are the 3 main groups and differ from the seedless vascular plants in 3 ways

1. They produce microspores, which develop into pollen grains that carry the sperm to the female structures to accomplish pollination 2. They also produce megaspores, which develop into ovules and, at maturity, produce seeds › Each seed is a mature ovule consisting of the embryo sporophyte (egg cell plus sperm) plus seed coat

3. Compared to seedless vascular plants, these plants have thicker cuticles, stomata recessed below the surface of the leaf, and other competitive traits

 Humans have domesticated seed plants to be used as food supplies and for many other commercially important use