Definition
Cells are the smallest, coherent units from which organs and tissues are built. Each cell is surrounded by a cell membrane, a barrier consisting of a special double layer of fat particles, the so-called lipid double layer. Lipid bilayers can be imagined as two fat films lying on top of each other, which cannot separate due to their chemical properties and thus form a very stable unit. Cell membranes fulfill many different functions: They are used for communication, protection and as a control station for cells.
Which different cell membranes are there?
Not only the cell itself is surrounded by a membrane, but also the cell organelles. Cell organelles are small areas within the cell that are delimited by membranes, each of which has its own task. They differ in their proteins, which are embedded in the membranes and act as transporters for substances to be transported across the membrane.
The inner mitochondrial membrane represents a special form of the cell membrane. Mitochondria are organelles that are important for the energy production of the cell. They were only subsequently incorporated into the human cell in the course of evolution.
Therefore they have two lipid bilayer membranes. The outer one is the classical human membrane, the inner one the membrane specific for the mitochondrium. It contains cardiolipin, a fatty acid that is built into the fat film and is found only in the inner membrane and no other.
In the human body, therefore, only cells that are surrounded by a cell membrane are found. However, there are also cells, such as bacteria for example, which are additionally surrounded by a cell wall. The terms cell wall and cell membrane can therefore not be used synonymously.
Cell walls are significantly thicker and additionally stabilize the cell membrane. In the human body, cell walls are not necessary because many individual cells can form strong associations. Bacteria, on the other hand, are unicellular organisms, i.e. they consist of only one single cell, which would be significantly weaker without the cell wall.