Lec11 Algae

Information about Lec11 Algae

Published on January 1, 2008

Author: Mertice

Source: authorstream.com

Content

Lecture 11: Algae, Bryophytes and Ferns:  Lecture 11: Algae, Bryophytes and Ferns Kingdom Protista: Algae Red algae, diatoms, kelps, dinoflagellates, green algae Significance of algae to humans Kingdom Plantae: moving onto land Features and challenges for living on land Bryophytes Ferns ALGAE:  ALGAE Algae belong to the Kingdom Protista Algae are eukaryotes (cells have organelles) Algae are mostly photosynthetic, like plants: Have 4 kinds of photosynthetic pigments Many accessory pigments – blue, red, brown, gold Require moist environments because they lack a waxy cuticle (remember: cuticle prevents water loss in terrestrial plants) General features of Algae:  General features of Algae Can be microscopic or macroscopic: size ranges from bacteria size to 50 meters long! Lack vascular (conducting) tissues – No xylem or phloem No true roots, stems or leaves Modes of sexual reproduction: Both sexual and asexual Algae illustrate the importance of photosynthesis to the Earth’s ecology! Diversity of Algae:  Diversity of Algae There are millions of algal species, but we’ll focus in these five groups: Diatoms Dinoflagellates Red Algae Kelps or Brown Algae Green algae 1. Diatoms:  1. Diatoms Diatoms: Division Bacillariophyta Large group of algae (many unidentified). Relatively recently evolved group Habitat: Diatoms live in cool oceans Structure: mostly unicellular, have silica in their cell walls Diatoms:  Diatoms Very important for aquatic food chains: they provide phytoplankton sun Phytoplankton  Zooplankton  small fish  larger fish mollusks whales Can reproduce asexually for many generations, then sexually 3. Red Algae:  3. Red Algae Red algae: Division Rhodophyta (4000 species) Are some of the oldest eukaryotic organisms on earth (2 billion year old fossils) Abound in tropical, warm waters Act as food and habitat for many marine species Structure: from thin films to complex filamentous membranes Why are Red algae red?:  Why are Red algae red? Accessory pigments! Phycobilins mask the Chlorophyll a – thus they look red. Due to these accessory pigments, red algae can photosynthesize in deeper waters (at different light wavelengths). Red algae:  Red algae Commercial uses: Carrageenan used for making ice cream, jellies, syrups, breads. Also for lotions, toothpaste, pharmaceutical jellies. Agar for growing bacteria and fungi for research purposes. As food. 4. Kelps or Brown Algae:  4. Kelps or Brown Algae Kelps: Division Phaeophyta Closely related to diatoms, also a recent group… but look very different from diatoms! Habitat: rocky coasts in temperate zones or open seas (cold waters) Structure: multicellular only Holdfast, stipe, blade, air bladder Up to 50 meters long 5. Green Algae:  5. Green Algae Division: Chlorophyta Largest and most diverse group of algae Habitat: found mostly in fresh waters and on land. Float in rivers, lakes, reservoirs, creeks. Can also live on rocks, trees, soil Green algae:  Green algae Sea lettuce (Ulva) lives in salt waters along the coast. Structure of green algae: from Single cells (Micrasterias) Filaments Colonies (Volvox) Thalli (leaf-like shape) Green algae:  Green algae Terrestrial plants arose from a green algal ancestor Both have the same photosynthetic pigments (Chlorophyll a and b). Some green algae have a cell wall made of cellulose Cells divide similarly Benefits of Algae:  Benefits of Algae Beneficial algae: They are the base of the aquatic food chain – photosynthetic organisms Lichens: algae and fungi symbiosis Also serve as shelters: Kelps form underwater forests; red alga form reefs Harmful algae:  Harmful algae Excessive growth of algae causes: Clogging of water ways, streams, filters… makes the water taste bad. Can be toxic to animals “Red tides” caused by dinoflagellates Commercial uses of algae:  Commercial uses of algae Algin – a thickening agent for food processing (brown algae) Carrageenan – foods, puddings, ice cream, toothpaste (red algae) Iodine (brown algae) Agar – for growth media used in research (red algae) As food – red and brown algae As plant fertilizers Diatomaceous earth: used for filtering water, insulating, soundproofing Kingdom Plantae:  Kingdom Plantae When moving from water to land, both plants and animals faced the same challenges, but evolved different ways to deal with them Plants evolved from algae:  Plants evolved from algae Algae cannot survive on land (only in moist environments) Plants had to adapt (evolve) characteristics that would allow them to survive and live on dry land Cooksonia is the earliest known land plant (fossil) It’s non-vascular and similar to today’s bryophytes Ancestor of plants: Green Algae:  Ancestor of plants: Green Algae The ancestor of land plants was probably a green alga: something like modern Coleochaete 1. They both have same photosynthetic pigments (Chlorophyll a & b, carotenes, etc.) 2. Both use starch to store photosynthetic products 3. Both have cellulose in their wall 4. Both have ‘alternation of generations’… 5. Both form a cell plate during cell division Kingdom Plantae:  Kingdom Plantae Evolutionary tree of plants From primitive advanced traits Bryophytes Green alga ancestor Ferns Gymnosperms Angiosperms Vascular  Seeds  Terrestrial  Flowers Living on land:  Living on land Several environmental challenges had to be met by early plants in order to live on land… A. OBTAINING ENOUGH WATER Plants evolved roots to anchor the plant Roots to absorb water and dissolved minerals B. PREVENTING WATER LOSS:  B. PREVENTING WATER LOSS Plants evolved a cuticle – waxy layer Evolution of multicellular gametangia (sex organs) – helped protect gametes from drying out. Evolution of a resistant coat on spores that prevents drying out C. GETTING ENOUGH ENERGY:  C. GETTING ENOUGH ENERGY In land, plants obtained enough sunlight for photosynthesis Different strategies for obtaining light: Growing taller and above other plants – plants began to evolve support cells Others had to adapt to lower light intensities D. Photosynthesis/water dilemma:  D. Photosynthesis/water dilemma Problems – plants need pores for gas exchange for photosynthesis, but open pores (stomata) allow water to leave (95% water taken is lost) Solution – stomata open during the day (for photosynthesis gas exchange) and close during the night (to allow plant to recover from water loss) E. MULTICELLULARITY:  E. MULTICELLULARITY Evolved in algae Advantages: root better, protect gametes, grow tall to obtain sunshine Disadvantage: getting water to all cells Plants evolved vascular tissues, xylem and phloem F. SEXUAL REPRODUCTION:  F. SEXUAL REPRODUCTION Algae have motile gametes and single sex organs Land plants developed air-borne dissemination of desiccation-resistant stage Land plants developed multicellular sex organs Sexual reproduction gives plants genetic variability – enable them to adapt better to their environments G. LIFE CYCLE:  G. LIFE CYCLE Algae, water dependent life cycle  water independent life cycle in land plants Plants developed dryness-resistant gametophytes (spores) or zygotes (seeds) Smaller size primitive  larger size plants Dominant gametophyte stage (n)  dominant sporophyte stage (2n) Life cycles: animals vs. plants:  Life cycles: animals vs. plants Animals like humans, live in the 2n stage. Dominant 2n stage Single celled gametes are 1n 2 n = 46 1 n = 23 (meiosis) Plant life cycle: alternation of generations:  Plant life cycle: alternation of generations Plants spend part of their life cycle in the haploid (1 n) stage, and part in the diploid (2 n) stage – both stages are multicellular Sporophyte generation (2n) Gametophyte generation (1n) Slide31:  Plants display an alternation of haploid and diploid phases in their life cycle. (see text and image on page 139 in the textbook “Plants and Society”) BRYOPHYTES:  BRYOPHYTES Bryophytes include mosses, liverworts Non-vascular plants, i.e. they don’t have xylem or phloem Advancements over algae: cuticle, multicellular gametangia, stomata Habitat: they require moist environment for active growth and sexual reproduction Bryophyte life cycle:  Bryophyte life cycle Exhibit alternation of generations: they have a gametophyte and sporophyte generation (See text image on pg. 140 please) Bryophytes:  Bryophytes Gametophyte generation (1n) is dominant Has green “leafy stems” and root-like structures called rhizoids, for anchoring (not true roots!) Have stomata and cuticle Bryophytes lack vascular tissue – do not have xylem or phloem. This absence of vascular tissue prevents bryophytes from having true roots, stems or leaves. Also, lack of conducting tissue limits their size. Bryophyte reproduction:  Bryophyte reproduction Gametophyte plant produces multicellular sex organs: Archegonia – produces eggs (female) Antheridia – produces motile sperm (male) Outer layers protects and prevents drying Motile sperm must swim to archegonia. Bryophyte reproduction:  Bryophyte reproduction Sporophyte occurs after egg is fertilized by sperm (2 n) Sporophyte grows in the archegonium of the gametophyte plant – it’s dependent on it Mature sporophyte consists of: Foot (point of attachment) Seta (stalk) Capsule (spore case) Bryophytes:  Bryophytes Sporocytes within the Sporophyte undergo meiosis to produce a single kind of haploid spore If spore lands on suitable place, it will germinate into a protonema, the initial stage of the gametophyte plant. Bryophyte significance:  Bryophyte significance Bryophytes are small and inconspicuous, but important part of the biosphere Food for mammals, birds Important to prevent soil erosion along streams Commercially – peat moss (Sphagnum) is used as fuel, soil conditioner, by florists FERNS:  FERNS An important group of plants – 10,000 species exist Ferns have developed vascular tissue Habitat: Moist tropics, woodlands, streambanks Also exhibit Alternation of Generations, but… The diploid Sporophyte generation is dominant (larger and more visible) The haploid Gametophyte is small & short lived. Fern life cycle: dominant sporophyte:  Fern life cycle: dominant sporophyte Sporophyte generation (diploid) is dominant, larger Sporophyte has well developed vascular system (xylem, phloem) (See image on page 141 of the textbook please) Fern sporophyte morphology:  Fern sporophyte morphology Fern sporophyte has fronds (leaves) Young fronds are called fiddleheads They also have an underground horizontal stem called the rhizome True roots arise from the rhizome Fronds:  Fronds Ferns have complex leaves called fronds, for photosynthesis and reproduction Under the fronds, spores are produced in sporangia in clusters called sori (sorus = singular) In sporangia, meiosis occurs producing haploid spores Fern Gametophyte generation (1n):  Fern Gametophyte generation (1n) Single spore grows into the gametophyte plant Heart-shaped called prothallus, very small. Archegonia and antheridia produced in prothallus Female gametophytes produce a chemical that induces spores to produce male gametophytes around it Fern gametophyte :  Fern gametophyte Antheridium produces motile sperm that swim to the archegonia’s egg – fusion occurs and the diploid sporophyte generation begins Zygote develops into a new embryo – that eventually grows into mature sporophyte Significance of ferns:  Significance of ferns Ecologically important: Hold and form soil to prevent erosion As food – fern fiddleheads eaten in Hawaii, Japan, Philippines – very nutritious and delicious! As ornamental plants Coal formation from ancient ferns

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