BISC 120 MIDTERM #3 - BISC 120 MIDTERM #3 How Plants...

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BISC 120 MIDTERM #3 How Plants Colonized the Land: From Algal Protists to Flowering Plants Red/green algae closely related to land plants - 1 bya, heterotrophic protist acquired cyanobacterial endosymbiont - Archaeplastida: supergroup used to classify, includes red/green algae, land plants - Red algae: o Accessory pigment phycoerythrin masking green of chlorophyll o Greenish red in shallow waters, almost black in deep waters o Accessory pigments allow absorption of blue/green light, penetrates far into water o Multicellular; largest are seaweed, cell walls of coralline algae hardened by CaCO 3 ; branching + encrusting - Green algae: grass-green chloroplasts; related to land plants; unicellular, colonial, multicellular; have two main groups o Chlorophytes: Mainly live in fresh water, some marine/terrestrial; some in damp soil, as symbionts in lichens or snow Three mechanisms making them more complex/larger Forming colonies of individual cells (filamentous masses) o Hollow ball whose wall composed of biflagellated cells embedded in gelatinous matrix; cells connected by cytoplasm; large colonies release small ‘daughter’ colonies Forming true multicellular bodies by cell division and differentiation Repeated division of nuclei with no cytoplasmic division o Caulerpa; branched filaments w/o cross-walls; ‘supercell’ Charophytes: close relatives of embryophtye (land) plants Freshwater dwelling, branched multicellular algae that stay at water surface; cylindrical, whorled branches with 6-16 branchlets around each node Share certain key traits with plants: o Rings of cellulose-synthesizing proteins (not linearly arranged) o Peroxisome enzymes (minimize loss of organic product) o Structure of flagellated sperm o Formation of phragmoplast (forms between nuclei in cell division; becomes new cell wall) o Presence of sporopollenin-like polymer (prevents exposed zygotes from aerial dessication) o Sequence similarities (nuclear/chloroplast gene sequences, not descendants but relatives; three possible ‘plant’ kingdoms - Why first plants want to live above the waterline? o Advantages: more sunlight, CO 2 , more nutrients, fewer herbivores/parasites o Disadvantages: scarcity of water, gravity (diminished support); desiccation
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o Derived traits of plants Alternation of generations and multicellular, dependent embryos Gametophyte (haploid) produces gametes (haploid) by mitosis Fusion of gametes makes sporophytes (diploid), producing spores (haploid) by meiosis Diploid embryo retained within tissue of female gametophyte Nutrients transferred from parent to embryo via placental transfer cells Land plants (embryophytes) b/c of dependency on parent embryo Walled spores produced in sporangia Sporophyte produces spores in sporangia Diploid cells (sporocytes) undergo meiosis to make haploid spores Spore walls contain sporopollenin, makes them resistant Multicellular gametangia
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This note was uploaded on 11/18/2011 for the course BISC 120Lg taught by Professor 11:00-01:50pm during the Spring '06 term at USC.

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BISC 120 MIDTERM #3 - BISC 120 MIDTERM #3 How Plants...

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