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The cytoplasm comprises cytosol (the gel-like substance enclosed within the cell membrane) and the organelles – the cell's internal sub-structures. All of the contents of the cells of prokaryote organisms (such as bacteria, which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm. The cytoplasm is about 80% water and usually colorless. It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways including glycolysis, and processes such as cell division. The concentrated inner area is called the endoplasm and the outer layer is called the cell cortex or the ectoplasm. Movement of calcium ions in and out of the cytoplasm is thought to be a signaling activity for metabolic processes.〔C. Michael Hogan. 2010. (''Calcium''. eds. A.Jorgensen, C. Cleveland. Encyclopedia of Earth ). National Council for Science and the Environment.〕 In plants, movements of the cytoplasm around vacuoles are known as cytoplasmic streaming. ==Physical nature of cytoplasm== The physical properties of the cytoplasm have been contested in recent years. It remains uncertain how the varied components of the cytoplasm interact to allow movement of particles and organelles while maintaining the cell’s structure. The flow of cytoplasmic components plays an important role in many cellular functions which are dependent on the permeability of the cytoplasm.〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3519356/〕 An obvious example of such function is cell signalling, a process which is dependent on the manner in which signaling molecules are allowed to diffuse across the cell.〔http://www.sciencedirect.com/science/article/pii/S000634950474312X〕 While small signaling molecules like calcium ions are able to diffuse with ease, larger molecules and subcellular structures often require aid in moving through the cytoplasm.〔http://www.cell.com/abstract/S0092-8674%2813%2901479-7〕 The irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cytoplasm」の詳細全文を読む スポンサード リンク
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