Question

What would have happened? If plasma membrane had not been selectively permeable.

Answer 1

Cell membrane is also known as plasma membrane. The plasma membrane is a bilayer of lipid composition. Lipid is nothing but fat. Lipid structures which separate the contents of cell compartments and the outer environment. Lipid separates the matrix and the organelles. The plasma membrane, also known to be the cell surface membrane or plasmalemma. It is a phospholipid bilayer.

Complete answer:
As we all knew that plasma membrane is selectively permeable, and selectively permeable means it only allows specific content or molecules which are friendly to the cell and which do not harm the cell content in any way like- killing the organelles, groping its regular functions or any kind of infections.
If a plasma membrane would not be selectively permeable, which is its nature, then, the foreign particles will enter the cells and they can harm the balance between the cell content and the outside environment. Such molecules can be toxins which can either kill the cell or harm it.
If a cell loses its plasma membrane, the outer components flood into the cell and the wall no longer will be there to exchange material from surroundings by diffusion or osmosis as plasma membrane acts as a mechanical barrier. Hence, the protoplasmic material will vanish and the cell will eventually die.
A plasma membrane is said to be a semipermeable membrane because it allows certain molecules but not all to pass or enter into the cell. It regulates the movement of materials in and out of the cell and also facilitates the electrical signaling between them. Plasma membrane has functions like it serves the purpose of passing nutrients and flow of ions into and out of the cells. Plasma membrane also interacts with other cells' boundaries and surfaces.

Note:
The plasma membrane had other different types of proteins such as- the embedded proteins they function as gated channels transports the movement of compounds across the membrane. They act as neurotransmitters. The peripheral membrane proteins do provide mechanical and structural support to the membrane. The last type of proteins are glycan anchor proteins. GPI is present in the neuronal membrane.