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INTRODUCTION TO PLANTS Plants evolved in terrestrial environments from a green algae ancestor which itself was presumably adapted to very shallow waters, ones prone to drying. Things in common: A. Both have chlorophylls A & B and carotenoids B. Both use starch as their primary carbohydrate food reserve. And both deposit it in the chloroplasts, not the cytoplasm as in other algal groups Chlorophyll a is a green pigment that absorbs red and blueviolet light. Chlorophyll b absorbs wavelengths in the blue and red-orange parts of the spectrum. All photoautotrophs contain carotenoids, which absorb blue-violet and blue-green wavelengths that are missed by the chlorophylls. They reflect wavelengths which are red, orange, and yellow. C. Cellulose is the principle component of the cell walls in plants. Likewise many green algae D. All true plants are oogamous. Some green algae are also oogamous. - one gamete is large and non-motile; one gamete is small and motile E. All true plants have an alternation of generations. So do many green algae- Why move onto the land? • Abundant and more consistent light for photosynthesis • More plentiful and freely circulating CO2 • lack of competition from other organisms • More surface area on leaves exposed to sun! Plant terrestrial adaptations "Living on land poses very different problems from living in the water. As plants have adapted to the terrestrial environment, complex bodies with extensive specialization of cells for different functions have evolved." These innovations include Waxy cuticle Stomata Vascular tissue Woody tissue (lignin) Pollen Seeds Development of the sporophyte as the dominant generation Flowers AND Fruit Challenges during Algae-to-Plant Transition Algae: Minerals absorbed from water Water from water Sunlight received within water Weight supported by water Sperm swim through water Spores swim through water Plants: Minerals / nutrients from soil Water from soil (susceptibility to desiccation) Sunlight received above soil (products require transport within plant) Weight not supported by air (requires internal supporting structure) air is less dense! Less water for sperm to swim through Less water for spores to swim through Lets imagine the first "plant" as an algae with most of its thallus "rooted" in the water, but with a portion lifted slightly above the water, or extending slightly past the shoreline, in a effort to better compete against its fellow algae found only at and below the water line Such an alga might not initially require a waxy cuticle (since water would always be available from the portion of the organism found below the water line), but might have given those individuals who first displayed such a cuticle above the water line less of a requirement for water. Thus the alga could move beyond the water therefore allowing slightly greater height and extension out over the shore Once a waxy cuticle was in place, diffusion of gasses could limit overall plant height (or spreading beyond the water), thereby selecting for small holes (stomata) in the waxy cuticle In an effort to better control moisture retention, it would be beneficial for the organism to selectively open and close the holes Such a algae could be essentially preadapted at this point to existing in the presence of less water, e.g., periodic desiccation due to fluctuating water levels At some point during the above sequence we essentially have seen the transition from status as a green alga to that of a moss WAXY CUTICLE • The transition from a watery environment to a terrestrial one most obviously involves an exposure to air • Air is drying (unless relative humidity is 100% • The cuticle prevents dessication •Stomata (singular, stoma) • The trouble with a waxy cuticle is that along with waterproofing comes air-proofing • Thus, the waxy cuticle prevents the diffusion of O2 and CO2 into and out of the plant, interfering with carbon fixing as well as cellular respiration • The innovation that solved this dilemma were small, opening and closing holes, called stomata, through which gasses can diffuse into and out of the plant Embryophyte • A new mode of reproduction was needed to solve the land issue – Nonaquatic environment – gametes produced in gametangia - - – Eggs fertilized with in female organ – Embryo retained in female ALTERNATION OF GENERATIONS • Haploid gametophyte produces and alternates with diploid sporophyte. • Sporophyte the produces gametophytes. These two types of plants are HETEROMORPHIC meaning they differ in structure. http://www.nova.edu/ocean/biol1060/plants.html GAMETOPHYTE Produces sperm and egg (hence, gamet-o-phyte) SPOROPHTYE Produces spores (hence spor-o-phyte) it is larger and more noticeable in all but bryophytes! SPOROPHYTE grows from GAMETOPHYTE! 4 major periods of plant evolution 1. Origin from aquatic ancestors (algae) called charophytes • • • 425 mya - Silurian period Cuticle Vascular tissue 2.Ferns – seedless • 400 mya Devonian 3.Origin of Seed • 360 mya end of Devonian 1.Gymnosperm – naked seed 2. Seed embryo packed w/ food and resistant coat 4. Flower plants with ovaries • 130 mya cretaceous 1. Angiosperm – angio means container TAXONOMY Based on vascular vs. nonvascular Divison Bryophyta – mosses, • nonvascular 2. Embryophytes that generally lack vascular tissue and require water for reproduction 2 adaptations made land possible 1. Waxy cuticle 2. Gametangia – protect developing gametes a. Antheridium – male gametangium b. Archegonium – produces single egg •Bryophytes are not free from aquatic habitat •Bryophytes lack woody tissue, thus •Gametophyte is dominant PTEROPHYTA • Carboniferous period forests loaded w/ ferns • Ferns have fronds which is a compound leaf • Fiddlehead uncurls as leaf grows Seed plants: • Coniferophyta (GYMNOSPERMS) – Earlier Fossil Record than Angiosperms – LACK enclosed chambers where seeds develop • Adaptations: – Leaves – cuticle • Male • female Seed plants: • Anthophyta – Used insects for pollination, – Specialized vascular tissue • Monocotyledone http://waynesword.palomar.edu/termfl2.htm DICOT – VASCULAR TISSUE IN AN “X” Draw these on your notes sheet SHALLOW WATER FIRST! A. Charophytes – B. Drying – C. Preadaptations for land: - waxy cuticle - protection of gametes - protection of developing embryos D. Thus land-life possible: - Sunlight unfiltered by water and algae Soil rich in minerals Absence of terrestrial herbivores III. Vascular Tissue Breakthrough • We talked about these on Tuesday! IV flower structure! A. Gametophytes retained in moist reproductive tissue of sporophyte generation B. POLLINATION – no longer need water for fertilization C. Seed replaces spore Use your book or the computer to label/define the flower parts! These are REALLY important! Problems with pollination and/or fertilization can cause fruit disorders such as "cat facing." If pollen is not evenly distributed on the stigma, all the ovules are not fertilized, preventing sections of the new fruit from developing Aggregate fruit Multiple fruit - • Look this last part up! How did animals and angiosperms coevolve?