BIO1130 - Cambrian and Ordovician Periods

BIO1130 - Cambrian and Ordovician Periods - fer in...

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“Tube-within-tube” body plan ffer in protostomes and Deuterostomes. are: s system & Brain lies on ventral side of body v ous system and Brain lies on dorsal side of body Cambrian and Ordovician Periods Near – End Proterozoic: (2 Billion Years as Single Celled Protists) - Explosion of unicellular life (some bigger than others) - Continental land masses arising from ocean near end of Proterozoic - Massive flourishing of invertebrates o Consumed carbon dioxide, therefore carbon dioxide levels decrease Why Did it take 3 Billion years for multicellular life to originate? - Something changed in the ancient oceans (filled with bacteria, single celled protists, etc.) Snowball Earth : (2 or 3 cycles had occurred during earth’s lifetime) - Earth was completely covered by ice and snow - No primary productivity during this time period o Underneath ocean, still getting volcanic gases, sulphur gases Hydrothermal vents : extremophiles (low oxygen environments) - Impossible for multi-cellular life to begin Slushball Earth : (more likely theory) - Near equator, there is a slushy, icy things o Allows some of the aerobic protists and bacteria to form and survive - Earth was frozen over however, near the equator it was much warmer allowing more forms of life to form there Doushantuo Fossils: (found in China) - Spherical in shape - Looks like zygote - The thought is that these fossils represent fossilized embryos o Are they evidence of multicellular life, or just bacterial aggregates? We don’t know - Prior to Cambrian Ediacaran Fossils: (found in New Found Land) - Predate the Cambrian - Experiments in multi-cellular life before Cambrian (Only a hypothesis. .) - Fossilized sponges (evidence that sponges DID exist): o Sponges – filtration of water to trap protists, archae, bacteria ect. (because the ocean was of food) o Colonial Choanoflagellates are the types of organisms that are seen in Ediacaran Fossils Very first multicellular organisms that are trapping food Ectoderm: - Outermost layer forms external covering and nervous system Mesoderm: - Middle layer form muscles of body wall and other structures between gut and external coverin Germ Layers Endoderm: - Innermost layer forms lining of gut (some organisms, respiratory organs) Ediacaran Period : - Choanocyte: o Uses a single Flagellum (animal – like) When it beats (spiral), it propels water away from the sponge Water passes series of microvilli (acts as filter) Phagocytosis (to feed – like an animal) o Collar cells of sponges (individual cells) - Colonial Choanoflagellates: (Group of Choanocytes working together) o Said to be the first ‘experiments’ of multicellularity
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Cambrian and Ordovician Periods o Cluster of cells on a single stalk (sessile) o Thought to be the ancestor of animals because: Molecular and morphological data of choanoflagellates Ex. Many similarities between choanoflagellates and collar cells of sponges (Choanocytes) Nucleic acid sequencing also supports this hypothesis
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BIO1130 - Cambrian and Ordovician Periods - fer in...

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