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Bio1020, Diversity of Life: February 10.docx

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University of Lethbridge
BIOL 1020
Robert Laird

February 10, 2014 – Biology Cytoplasmic streaming is direction, move towards needs without a nervous system. Protists: Summary • Massive biodiversity • Massive diversity of form and function • Role as primary producers (25% of world’s photosynthesis) • Role as mutualists (allows termites to digest wood) • Role as parasites (ex. Malaria) • Most roles probably unknown Multicellular eukaryotes: Evolution of mutlicellularity (Chapters 13,25) • Molecular clocks using DNA sequences suggest that multicellularity first emerged ~1.5 billion years ago. (know this by radio carbon dating) • Less than ½ of the time of life on Earth • Since then, it has evolved independently many (ca. 25?) times • Evolutionary enigma – why would NS favor evolution of multicellularity? • What took so long to develop multicellularity? o Snowball Earth hypothesis:  Sever ice ages 750 to 580 million years ago  Most landmasses and most oceans were ice-covered  Life probably existed mostly in extreme environments (deep-sea volcanic vents, right next to the equator) o Problems with the cellular cooperation and complexity • Advantages of Multicellularity o Larger size  Larger size is often advantageous but… (need more nutrients, more visible to predators)  Cells are limited by rates of diffusion • e.g., O2, nutrients o Tissue specialization  Different tissues can perform different tasks o Better buffer from environment (ability to survive harsher environments) o Some multicellular species can regenerate lost organs/tissues (just injured they can heal, regenerate lost tails (reptiles)) o Protection/separation of reproductive systems o Improved foraging and movement (Fig. 53.20) Read the figure o Other advantages? Less likely to be affected by predation • Unicellularity -> Multicellularity o How?  Symbiosis  Internal division of multinucleate protists  Coloniality (e.g. Volvox) Group of cells coming together. (Most favored hypothesis) Intro to life cycles and life cycle variation • The sequence of stages in the reproductive his
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