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Zoology Questions.doc

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University of Guelph
ZOO 2700
Andreas Heyland

Zoology Questions 11. What are some intracellular specialized structures possessed by protists and what are their functions? What structures in multicellular animals are they analogous to? • The protist kingdom includes protozoans and algae. (Two groups of fungi with similar characteristics to protozoans, myxomycetes and oomycetes, have been classified as protists.) • Unicellular protozoans and algae are unicellular eukaryotes. The pluricellular algae are eukaryotes of simple structure too. It is believed that protists are phylogenetic ancestors of living beings of the other eukariotic kingdoms (fungi, animals and plants). • The basic difference between protozoans and algae is the fact that protozoans are heterotrophs while algae are photosynthetic autotrophs. • Protozoans are unicellular beings with some similar characteristics to animal cells. • In comparison to pluricellular organisms protozoans are more proximal to the animal kingdom than to plants: they are heterotrophs, they have a rudimentary locomotion system (amoeboid movements, cilia, flagella), they do not have cell wall, some species present structures that resemble structures of a primitive digestive system, with cytostome (mouth) and cytopyge (anus), specialized in digestion and excretion. • The evolutionary hypothesis that animal cells have come from differentiation of protozoans is strong. • Protozoans are eukaryotic cells so they have organelles and structures common to this kind of cell: endoplasmic reticula, Golgi apparatus, digestive vesicles, ribosomes, mitochondria, nucleus with genetic material, karyotheca, etc. All these elements are found dispersed throughout the cytoplasm. Protozoans do not have cell walls. • Protozoans from the mastigophora group (like trichomonas) have flagella and others, others from the ciliated group (like paramecium) have cilia. • All protozoans, as eukaryotes, have nucleus. Some species, like the paramecium, have two nuclei: the macronucleus and the micronucleus. 12. What are the two major cytoskeletal filaments in eukaryotic cells? • Eukaryotic cells contain three main kinds of cytoskeletal filaments, which are microfilaments, intermediate filaments, and microtubules. The cytoskeleton provides the cell with structure and shape, and by excluding macromolecules from some of the cytosol it adds to the level of macromolecular crowding in this compartment.[3] Cytoskeletal elements interact extensively and intimately with cellular membranes.[4] Microfilaments (actin filaments) • These are the thinnest filaments of the cytoskeleton. They are composed of linear polymers of actin subunits, and generate force by elongation at one end of the filament coupled with shrinkage at the other, causing net movement of the intervening strand. They also act as tracks for the movement of myosin molecules that attach to the microfilament and "walk" along them. Actin structures are controlled by the Rho family of small GTP-binding proteins such as Rho itself for contractile acto- myosin filaments ("stress fibers"), Rac for lamellipodia and Cdc42 for filopodia. Intermediate filaments • These filaments, around 10 nanometers in diameter, are more stable (strongly bound) than actin filaments, and heterogeneous constituents of the cytoskeleton. Like acti
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