Question

How does the cell membrane change over time?

Answer 1

Hint: The detailed structure of cell membrane was accepted only after the invention of the electron microscope. Meanwhile, chemical studies were performed on the cell membrane, mostly in human red blood cells, which helped the scientists to deduce the possible structure of plasma membrane.

Complete answer:
The studies proved that the cell membrane is a composition of lipids which are arranged in a bilayer. Also, the lipids are arranged penetrating the membrane such that the polar head is towards the outer side and the hydrophobic tail is towards the inner part. This ensures us that the nonpolar tail of the saturated hydrocarbons should be situated as, that it should be protected from the aqueous environment.
On further biochemical investigation it was clearly revealed that the cell membranes also possess protein and carbohydrate along with presence of lipids. The amount of protein and lipid present varies in different cell types.
An improved model of the structure of cell membrane was proposed by Singer and Nicolson which was widely accepted and named as the fluid mosaic model. According to this, the quasi -fluid nature of lipid supports lateral movement of proteins within the overall bilayer. The ability to move inside the membrane is measured as its fluidity. Before anything we should know the most important functions of the plasma membrane. They are as follows:
-It has the ability that it can transport molecules across it.
-It’s one of the most significant properties is that it is selectively permeable to some molecules present on either side of it.
-Many molecules can move briefly across the membrane without any requirement of energy; this characteristic property is called the passive transport.
 This involves the movement from higher concentration to the lower.
-Water can also be allowed to move across this membrane from higher to lower concentration. Movement of water by diffusion is called osmosis.
During the processes taking place in the cell, the cell gradually loses its integrity and here we can conclude that the cell membrane finally changes.

Note: Depending on the ease of extraction, membrane proteins can be classified as integral or peripheral. Peripheral proteins are partially or completely buried in the membrane.
The fluid nature of the membrane is an important factor for the functions like cell growth, formation of intercellular junctions, secretion, endocytosis and cell division. Hence the fluid mosaic model has made the study very easy.