<Li> Many eukaryotic cells are ciliated with primary cilia . Primary cilia play important roles in chemosensation, mechanosensation, and thermosensation . Cilia may thus be "viewed as a sensory cellular antennae that coordinates a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation ." </Li> <Li> Motile cells of eukaryotes can move using motile cilia or flagella . Motile cells are absent in conifers and flowering plants . Eukaryotic flagella are less complex than those of prokaryotes . </Li> <P> All cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, regulates what moves in and out (selectively permeable), and maintains the electric potential of the cell . Inside the membrane, the cytoplasm takes up most of the cell's volume . All cells (except red blood cells which lack a cell nucleus and most organelles to accommodate maximum space for hemoglobin) possess DNA, the hereditary material of genes, and RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery . There are also other kinds of biomolecules in cells . This article lists these primary components of the cell, then briefly describes their function . </P> <P> The cell membrane, or plasma membrane, is a biological membrane that surrounds the cytoplasm of a cell . In animals, the plasma membrane is the outer boundary of the cell, while in plants and prokaryotes it is usually covered by a cell wall . This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids, which are amphiphilic (partly hydrophobic and partly hydrophilic). Hence, the layer is called a phospholipid bilayer, or sometimes a fluid mosaic membrane . Embedded within this membrane is a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell . The membrane is said to be' semi-permeable', in that it can either let a substance (molecule or ion) pass through freely, pass through to a limited extent or not pass through at all . Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones . </P>

What are the main functions of each of the cell component
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