Effectors - Effectors:Respondingtostimuli Skeletalelements...

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Effectors: Responding to stimuli Skeletal elements  and muscles are  necessary for mobility  or to perform work
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    Microbes Motility of micro-organisms accomplished  by organelles (cilia, flagella) or cytoplasmic  streaming (pseudopodia) Viscous nature of aquatic media provides  resistance against which work (i.e.  movement) can be accomplished
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    Cilia vs flagella Both generate force by the sequential creation and breaking of linkages  (crossbridges) between adjacent proteins.  Requires ATP.  Same basic process  applies to how muscles can shorten!
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    Cytoplasmic streaming Cytoplasmic “skeletal” elements provide rigidity (which can be altered)  allowing cells to change shape.  Actin is a cytoskeletal element found in  all cells, and also plays a key role in muscle function. 
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    Larger critters Water provides an excellent  supporting medium for larger  soft-bodied animals, such as  jelly fish But in the absence of water…
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    Skeletons provide support Hydrostatic skeletons  operate on the non- compressibility of a liquid (i.e. water) Exoskeletons  are hard parts encasing the body.   Includes segmented “armor” of arthropods (made  of chitin) as well as calcareous shells of molluscs  Endoskeletons  are hard supporting structures  buried within the soft parts (e.g. bones).  
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    (a) Body segments at the head and just in front of the rear are short and thick (longitudinal muscles contracted; circular muscles relaxed) and anchored to the ground by bristles. The other segments are thin and elongated (circular muscles contracted; longitudinal muscles relaxed.) (b) The head has moved forward because circular muscles in the head segments have contracted. Segments behind the head and at the rear are now thick and anchored, thus preventing the worm from slipping backward. (c) The head segments are thick again and anchored in their new positions. The rear segments have released their
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Effectors - Effectors:Respondingtostimuli Skeletalelements...

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