In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The gradients of the other ions are most likely accounted for by

Cell membranes are considered organelles because they are important for the maintenance of the cell's structure, function, and survival.  Here are some functions of cell membranes: Barrier: The plasma membrane acts as a barrier between the cell's interior and its environment. It allows the entry and exit of molecules through a process called permeability. Transport: Membranes play an important role in both active and passive transport. Pump proteins use energy to transport molecules across the cell membrane. Attachment: The cell membrane participates in attachment. Signaling: The cell... Show more

Cell membranes are considered organelles because they are important for the maintenance of the cell's structure, function, and survival. 

Here are some functions of cell membranes:
Barrier: The plasma membrane acts as a barrier between the cell's interior and its environment. It allows the entry and exit of molecules through a process called permeability.
Transport: Membranes play an important role in both active and passive transport. Pump proteins use energy to transport molecules across the cell membrane.
Attachment: The cell membrane participates in attachment.
Signaling: The cell membrane participates in signaling.
Homeostasis: The cell membrane aids in maintaining homeostasis in the cell.
Fluidity: The cell membrane is capable of maintaining membrane fluidity at different temperatures.
Structure: Membrane proteins provide stability and structure to the cell membrane. 

Cell membranes are composed of two layers of lipids (phospholipids) and cholesterols distributed between the layers. Glycolipids are an integral part of the outer layer of the membrane. Glycolipids help to maintain the fluidity and flexibility of the cell membrane, which is important for the movement of molecules in and out of the cell.

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