Question

The latest model for plasma membrane is
A) Lamellar model
B) Unit membrane model
C) Fluid mosaic model
D) Molecular lipid model

Answer 1

Hint:The outer covering of the cell is known as plasma membrane. It is also known as cell membrane and it separates the inner cell components from the exterior environment.

Complete answer:
Before we find the correct option, let us first know a little more about plasma membrane.
The plasma membrane as mentioned earlier is the outer layer of the cell. It is made up of lipids, carbohydrates, and proteins.

Option a: The lamellar model also known as the “Sandwich model.” It was proposed in 1935 by two scientists Davson and Danielli. As per this model, the plasma membrane is a trilaminar layer, i.e. on both the sides it is bounded by a lipid layer. There were many issues with the model one of them being that they assumed that all membranes were of uniform thickness, which we now know isn't true. Therefore, this is the incorrect option.

Option b: The unit membrane model was proposed by Robertson. As per this, the plasma membrane is a lipid bilayer and it is surrounded by proteins on either side. The proteins present in the inner and outer side differ. The model was rejected as the temperatures at which the membrane solidified did not match with the data expected under the proposed model. Therefore, this is the incorrect option.

Option c: Fluid mosaic model is the latest accepted model of plasma membrane. It was proposed in 1972 by Nicolson and Singer. According to this model, in the lipid layer the protein molecules are embedded.

The lipid bilayer is responsible for providing elasticity and fluidity to the membrane. There are small amounts of carbohydrates found in the membrane. This is the most accepted model of plasma membrane. Therefore, this is the correct option.

Option d: The molecular lipid model is also known as pauci molecular model. As per this model, the lipid bilayer lies in between two layers of globular proteins. The plasma membrane is both trilaminar and lipoproteins. There were many issues with the model, and it was not accepted. Therefore, this is the incorrect option.

Thus, the correct option is (c) Fluid mosaic model.

Note:Plasma membrane has various functions like-
>It acts as a physical barrier.
>It is selectively permeable.
>It helps in cell signalling.