Question

Which of the following statements is correct about the plasma membrane?
a.It is a solid layer of protein that protects the content of a cell.
b.The plasma membrane of the bacterium has none of the same name components as the plasma membrane of an animal cell
c. It is a rigid and unmoving layer of phospholipid and protein.
d. It allows selected molecules to pass in and out of the cell.

Answer 1

Hint: The plasma membrane is the membrane which is present in the cells that separate the inside of the cells from the external environment. The plasma membrane consists of a lipid bilayer which is a semipermeable membrane.

Complete answer:
The plasma membrane is composed of lipids and proteins. The major lipids are phospholipids that are arranged in a bilayer. The lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner parts. The phospholipids membrane also contains cholesterol and it also contains protein and carbohydrate. The plasma membrane is selectively permeable to the ions and organic molecules and helps in the movement of substances in and out of the cells. It has a host of important properties which includes fluidity, transport etc.
The most important function of the plasma membrane is the transfer of molecules. The molecules can move across the membrane by the process known as passive transport.
Hence, the correct answer is d.

Note: The ratio of protein and lipids varies considerably in different cell types. In humans, the membrane of the erythrocyte has about 52% protein and about 40% lipids. The structure of the plasma membrane was proposed by Singer and Nicolson in 1972 and it was accepted as the fluid mosaic model.