Question

What is the permeability of a cell?

Answer 1

Hint: The cell membrane surrounds the cytoplasm of the cell and gives the boundary and shape to the structure of the cell. Various substances and molecules have to cross this membrane in order to enter into or move out of the cell. This is made up of phospholipid and is a bilayered structure.

Complete answer:
The cell membrane around the cell plays a role in harboring the cytoskeleton to give shape to the cell, and in attaching to the extracellular matrix and other cells to grasp them together in order to form tissues. Various species of fungi, bacteria, most archaea, and plants have a cell wall also, which provides mechanical support to the cell and prevents the passage of larger molecules across it.
Permeability of a cell membrane refers to the ease with which a molecule or a substance can pass through the cell membrane. It is the rate at which the passive diffusion occurs across the membrane. Transporting molecules through the cell membrane is one of the chief functions of the cell membrane. The cell membrane is selectively permeable, i.e. they permit only certain molecules to enter and leave the cell. It is an important characteristic to maintain the integrity of the cell.
The permeability of molecules across the cell membrane rely upon the polarity, charge and the size of molecules. Neutral molecules can cross the cell membrane without needing any energy with the help of passive transport, whereas polar molecules are not able to cross the nonpolar lipid bilayer and are in need of carrier proteins for their transport, i.e. facilitated transport. Molecules are transported from higher concentration to lower concentration i.e., along the concentration gradient in passive transport and do not require energy, e.g. simple diffusion and facilitated diffusion.
The cell membrane is able to control what enters and exits the cell, thus facilitating the transport of materials needed for survival. The movement of substances through the membrane can be either "passive", occurring without the use of cellular energy, or "active", requiring the cell to spend energy in the form of ATP in transporting it. The membrane also helps to maintain the cell potential. The cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell recruits a number of transport mechanisms that include biological membranes.

Note:
The cell membrane has different lipid and protein compositions in different types of cells and may therefore have specific names for certain cell types. This includes Sarcolemma present in Muscle cells. Oolemma in the cell membrane of the oocyte. Axolemma in the plasma membrane on the axons of the nerve cells.