Membranes are very important in the construction of organisms.\u00a0 Every membrane has the basic function of keeping\u00a0materials separate or else keeping them where they are.\u00a0\u00a0Every cell has a membrane surrounding (enveloping) it.\u00a0 Some people call it the cell membrane; others call it\u00a0the plasma membrane.<\/p>\n
The role of the cell membrane is sometimes described as protection – that it shelters the cell from its environment.\u00a0 To some extent you could argue that’s true, but really the cell membrane’s function is to control the movement of materials in and out of the cell.<\/p>\n
You can think of the cell as a factory.\u00a0 It has valuable things inside that need to be there.\u00a0 Some of those valuables are destined to leave, but only under\u00a0the correct\u00a0circumstances.\u00a0 Until the appropriate time of departure, those valuables must remain safe inside.<\/p>\n
The factory,\u00a0however, can’t just be locked up until someone comes to take delivery of the merchandise.\u00a0 New\u00a0supplies are arriving all the time, and\u00a0need to be taken in.\u00a0 However,\u00a0anything (and anyone)\u00a0not meant to be there is stopped at the door.<\/p>\n
A busy\u00a0factory probably has its doors open all\u00a0day, yet the movement of goods in and out of it is carefully controlled.\u00a0\u00a0Foremen watch the crews and the doors to make sure the right shipments leave at the right times.\u00a0 New shipments that arrive are confirmed before they are brought in.\u00a0 Securing the movement of the goods is a constant, involved process.<\/p>\n
With a cell, the conduction of goods in and out is much the same.\u00a0 Water, oxygen and carbon dioxide can pass through the cell membrane freely, but many\u00a0important molecules and ions\u00a0need to be allowed in – or even\u00a0brought in –\u00a0by the membrane.\u00a0 Otherwise, they can’t enter.\u00a0 With exiting, it’s the same situation.<\/p>\n
The cell “decides” what to let in\u00a0at any given instant based on what it needs to maintain the composition of its cytoplasm.\u00a0 The cytoplasm is the nonspecific, jelly-like “body” of the cell.\u00a0 It’s a complex mix of water, ions, proteins, lipids, sugars, and other biological compounds.\u00a0 Cytoplasm’s precise mix comprises the “living condition” of the cell.\u00a0 If the mix goes wrong, the cell dies.\u00a0 Cytoplasm can only be found in a living cell.<\/p>\n
Therefore, the cell membrane maintains the\u00a0“living” mix of the cytoplasm by controlling what enters and leaves the cell.\u00a0 It’s a function that may not sound specific at first, but\u00a0might be the most important of any the cell does.\u00a0 Just how<\/em> the cell membrane manages its role will be discussed in future posts.<\/p>\n