Why it is important to reduce friction in moveable joints

Smooth cartilage prevents friction as the bones move against one another. in freely moveable joints, the entire joint is enclosed inside a membrane filled with lubricating synovial fluid, which helps to provide extra cushioning against impact.

thymine. in rna, thymine is replace by uracil

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

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