I have been under the thinking that cell membrane and cell wall can be used either ways and that there is no difference between the two at all. But then I realized as I read through different kinds of cells, that there is a difference between a cell wall and a cell membrane. As much as, they are one of the main distinguishing feature between defining a eukaryotic cell and a prokaryotic cell. So then what is a cell wall? A cell wall is what is found in plant You do not have access to view this node. The cell wall is an outer covering that provides a rigid support so that the content of the plant cells do not leak out. It provides protection as well as strength to the cell as well as letting fluids passing through. Where as a cell membrane is what is found in animal You do not have access to view this node. The cell membrane is also known as plasmalemma, provides a layer of protection to hold the cell contents in and plays an important role in the transport of molecules back and forth from the cell to its surroundings. It is sempermeable and conducts ions, proteins and other substance required to transport for the functioning of a You do not have access to view this node. Being one of the organelles of the cell it provides help with maintaining cell adhesion and ion conductivity.
Plasmalemma finds various uses in different living organisms. For example in sea urchin eggs, it is present as the vitelline membrane covering hyaline plasma layer. On fertilization, vitelline membrane becomes thick and gets converted into fertilization membrane and is present separately from the plasma membrane that is located beneath. It forms the outermost part or membrane in amoeba and also contains various filamentous structures. Plasmalemma is present in the cytoplasm of plants as the external membrane. In the course of osmotic stress when laid in hypertonic salt solution, plant cells proceeds for plasmolysis and here the plasmalemma gets separated from the cell wall cellulose present inside the You do not have access to view this node.
The plasmalemma structure is also termed as fluid mosaic as it is a network of both lipids and proteins. The lipids and proteins are present in varying proportions of 1:1 - 1:3. These lipids are dotted with proteins and are found to stick to the membrane or form a bridge spanning from outside to the inside. . The plasmalemma is around 10 nanometers thick. While some of the proteins help in the structural function others are enzymes, carriers or transporters which is the only for some molecules to pass through. The proteins that help with carbohydrates are called glycoproteins. The lipids are again of different types. Lipids such as phospoholipids, phytoesterols, sulfolipids are present in the viscous cell membrane. The proteins seem to be held in the interphase between the water and lipid molecules and seem to be in a constant flux.
Semipermeability is the defining characteristics of plasmalemma and allows the movement of only particular or selected molecules in and out of the cell. The plasmalemma has specialized functions in different organisms. It is covered with a layer of thinly structured phospholipids along with protein molecules. It is present in every biological cell and serves the part of dividing the inner atmosphere of the cell from the outer atmosphere. The plasmalemma surface is composed of proteins that are known to perform various functions such as acceptance of nutrients or even giving anchor to the flagellum. Because of the semi permeable nature of the membrane, there is selective transportation of molecules across the plasmalemma. Lipophilic molecules such as the smaller sodium ions can pass through. Other molecules which can pass the semi permeable layer are O2, N2, H2O, benzene, glycerol, urea and CO2. Molecules that cannot pass through this layer are glucose, sucrose, H+ , Na+ , HCO3 , K+Ca2+ , Cl- , Mg2+.
The permeability of plasmalemma is dependent upon its composition to a large extent. The protein and phospholipid part play a major role in this selective permeability.
The factors that determine it are:
The plasma membrane has a key role in restricting or allowing the specific molecules through its cell membrane. One of the important functions is ion conductivity. It pumps in the molecules into the cell and also pumps out the unwanted toxins out of the You do not have access to view this node. The transport that occurs without spending any energy by the cell is passive transport process while the transport which needs energy for these processes is termed as active transport processes.