Biology 1010 Lecture Notes

Unit 3. Multicellular organisms

These notes were last updated Ocotober 24, 2001

Some key words, phrases, and ideas :

  1. Life in the Proterozoic
    1. status of life during the early Proterozoic
    2. origins of multicellularity
      1. what is multicellularity
      2. features of multicellular animals
        1. colonial aggregates to specialized tissues to specialized organs
        2. symmetry; cephalization and sensory systems
        3. skeletal/muscular systems
        4. digestive systems
        5. coeloms and pseudocoeloms
        6. protostomes and deuterostomes
          1. protostomes: mouth develops from the blastopore, spiral and determinate cleavage, coleom develops from a split in the mesoderm
          2. deuterostomes: anus develops from the blastopore (mouth develops later), radial and indeterminate cleavage, coelom develops from the digestive system
      3. early evolution of multicellular animals
        1. porifera (sponges)
          1. sessile filter-feeders (flagellate cells similar in shape to some types of zooflagellates)
          2. primitive organization without well-defined tissues and organs
          3. structural framework of spicules/spongin
        2. cnidarians (jelly fish and corals)
          1. radial symmetry
          2. well-developed tissues but no organs
          3. beginnings of a digestive system and neuromuscular system
          4. cnidocytes with nematocysts
          5. polyp and medusa stages
          6. some colonial forms
        3. flatworms (turbellarians)
          1. bilateral symmetry--cephalization
          2. three basic tissues plus true organs
            1. digestive system
            2. eyespots and nervous system
            3. excretory system
        4. rotifers and nematodes
          1. bilateral, some with good cephalization
          2. three basic tissues plus true organs
            1. one-way digestive system
            2. ventral nerve cord and a ring-type brain
          3. pseudocoelom
          4. determinate development
        5. protostomes lineages
          1. mollusks (gastropods and cephalopods)
            1. body plan: visceral mass, mantle and mantle cavity, foot
            2. most with radula
            3. three important groups
              1. cephalopods -- foot divided into tentacles with suckers; well-developed nervous system
              2. gastropods -- body twists during development; spiral shells
              3. bivalves -- right and left shells
          2. annelids (segmented worms, including leeches)
          3. onychophorans (segmented worms with primitive appendages)
          4. marine arthropods (trilobites, chelicerates, crustaceans)
            1. common features include a jointed exoskeleton, segmented body with usually with some degree of specialization, complex nervous systems often with compound eyes
            2. three important aquatic lineages
              1. trilobites (extinct group with a lobed body)
              2. chelicerates (horseshoe crabs and arachnids (spiders, scorpions, ticks, and mites))
                1. usually body divided into cephalothorax and abdomen
                2. first pair of appendages are chelicerae, second pair are pedipalps; these are followed by multiple pairs of walking legs
                3. breathe through book gills or book lungs
              3. crustaceans (crabs, copepods, cladocerans, barnacles, isopods (pill bugs), and amphipods)
                1. body divided into cephalothorax and abdomen
                2. appendages are biramous (with two branches)
                3. first two pairs of appendages are antennae, the next three are modified for chewing (mandibles and maxillae)
        6. deuterostome lineages
          1. echinoderms (starfish and sea urchins)
            1. secondary 5-fold radial symmetry
            2. unique tube feet
            3. carbonate plates just below the skin
          2. protochordates (arrow worms and acorn worms)
            1. arrow worms -- torpedo-like body with a tail extending past the anus; common predators in the plankton
            2. acorn worms -- proboscis (trunk or nose) for gathering food and a worm-like body; common benthic animals, some around the deep-sea vents; key features for us include
              1. pharyngeal gill slits
              2. hollow dorsal nerve cord
              3. rudimentary cartilaginous skeleton
          3. chordates
            1. defining characteristics
              1. pharyngeal gill slits
              2. tail extending past the anus
              3. hollow dorsal nerve cord
              4. dorsal notochord
            2. major lineages
              1. urochordates (tunicates and the like)
              2. cephalochordates (lancelets)
              3. vertebrates
  2. Life in the Paleozoic (545 to 245 million years ago)
    1. early Paleozoic
      1. Cambrian seas--dominated by trilobites and brachiopods, with primitive molluscs and echinoderms common; chordates are poorly represented in the fossil record (ends 505 million years ago)
      2. Ordovician seas--trilobites and ammonites common as are starfish, corals, gastropods, and bivalves (
    2. rise of the vertebrates
      1. armored agnathan fish--dominant vertebrates in the Ordovician and most of the Silurian; with armor plates, but no jaws or vertebrae (use notochord)
      2. placoderm (jawed) fish--rose to dominance among the vertebrates in the Silurian; armored, with jaws derived from gills, and a partially calcified skeleton
      3. modern fishes--chondrichthyes (sharks and rays) and osteichthyes (bony fish)
        1. arose from placoderms during the Devonian
        2. sharks are marine organisms with gill slits, fixed fins, torpedo shape, cartilaginous endoskeleton,and no swim bladder
        3. bony fish started as fresh water organisms with gill opening, moveable fins, variable shape, bony endoskeleton, and with a swim bladder (why?)
    3. movement to land (late Silurian early Devonian--about 400 million years ago)
      1. requirements
        1. resistance to or protection from drying out
        2. resistance to or protection from ultraviolet light
        3. support structures
        4. some way to bring gametes together
        5. temperature regulation
      2. early colonizers
        1. algae and fungi
        2. spore plants
          1. eggs and zygotes protected in archegonium
          2. improvements in water relations in sporophyte
            1. stomata
            2. vascular tissue (also useful for support)
          3. difficulties with fertilization (bring sperm to the egg)
        3. uniramian arthropods (millipedes and centipedes, insects)
          1. exoskeleton for support, movement, protection from drying and UV
          2. many breathe through trachea (internal)
          3. many use internal fertilization
          4. many primitive forms eat microorganisms (bacteria, fungi, algae) already present
        4. chelicerates
          1. exoskeleton for support, movement, protection from drying out and UV
          2. enclosed book gills to make book lungs
          3. many use internal fertilization
          4. probably ate uniramians
        5. amphibians
          1. endoskeleton from support and movement
          2. breathe through modified swim bladder (lungs), supplement in some cases with skin breathing
          3. early forms retained scaly exterior (similar to early fish) providing some protection from drying and UV
          4. fertilization still external, eggs unprotected, therefore eggs laid in water, juveniles spend some time in water (tadpoles)
      3. origins of seed plants
        1. some spore plants developed separate male and female gametophytes (micro- and macrogametophytes)
        2. some of these were provided with protective structures composed of sporophyte tissue
        3. pollen grains (with a much reduced male gametophyte) and ovules (with a female gametophyte) eventually evolved from these; seeds are mature ovules with a developing sporophyte embryo inside (for a total of three generations)
        4. the evolution of seeds and improvements in the water relations of the sporophyte allowed them to spread into drier areas
      4. origins of amniote eggs
        1. amniote eggs--new type of vertebrate egg with four basic membranes: amnion (amniotic sac) containing amniotic fluid (a pool for the embryo to develop in); yolk sac providing nourishment; allantois for waste; chorion associated with shell formation
        2. organisms with amniote eggs and internal fertilization were no longer tied to pools of water for reproduction; this lead to another period of adaptive radiation in vertebrates
        3. important amniote lineages
          1. thecodonts and archosaurs
          2. pelycosaurs and therapsids
          3. ichthyosaurs and plesiosaurs
          4. lizards and snakes
          5. turtles
    4. by the end of the Paleozoic
      1. seas full of sharks and fish, modern-looking invertebrates, algae
      2. land covered in spore plants with growing numbers of seed plants; insects and arachnids common, vertebrate life dominated by therapsids (Dimetrodon)
  3. Terrestrial life in the Mesozoic (245 to 65 million years ago)
    1. status of life at the beginning of the Mesozoic
    2. dinosaurs, birds, and mammals
      1. the question of warm-bloodedness
        1. advantages and disadvantages
        2. tests for warm-bloodness
        3. were dinosaurs warm-blooded
      2. evolution of mammals
        1. basic features: mammary glands, hair, external ears
        2. origins
    3. flowering plants
      1. new structures
        1. ovaries, carpels, and pistils; fruits
        2. stamens with anthers
        3. sepals and petals
      2. connections with pollination
    4. status of life at the end of the Mesozoic
  4. Terrestrial life in the Cenozoic
    1. status of life at the beginning of the Cenozoic
    2. rise and adaptive radiation of the mammals
    3. origins of humans
      1. earliest primates small, tree-dwelling, nocturnal, insect-eaters with with grasping fingers and toes, binocular vision; split into two lineages, the prosimians (lemurs and tarsiers) and the anthropoids
      2. anthropoids (monkey-like primates) are mostly diurnal, mostly plant-eaters, with relatively large brains; most form complex social groups; split into two lineages about 30 million years ago, the old world monkeys and the new world monkeys
      3. hominoids split from the old world monkeys about 25 million years ago; modern representatives include orangutans, gibbons, chimps, and gorillas
      4. hominids split from the hominoids about 8 million years ago in Africa; basic change--bipedal
        1. genus Australopithecus--bipedal, brains about 500 cc; many species
        2. genus Homo--first appearance about 2.5 million years ago; distinguished by slightly larger brains (700 cc) and primitive tools
          1. the number of early species is somewhat controversial, might include Homo habilis, Homo rudolfensis, and Homo ergaster, might all be representatives of one species, Homo habilis
          2. Homo erectus first appeared about 1.5 million years ago; distinguished by larger brain (1000 cc), more advanced tools, definite social groupings; spread from Africa throughout the Old World
          3. Homo sapiens first appeared between 0.5 and 0.2 million years ago; marked by still larger brain size (1450 cc) and cosntantly improving tools; spread from Africa throughout world starting about 0.1 million years ago, reaching the New World about 0.01 million years ago; may soon spread to other planets in the solar system

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