Question

The basic unit of the plasma membrane is
A. Cellulose and Carbohydrate
B. Protein and Phospholipid
C. Protein and Cellulose
D. Protein and Carbohydrate

Answer 1

Hint: Plasma membrane or cell membrane is made up of lipid bilayer and proteins that are embedded on that bilayer. There are two types of proteins that are generally found on the plasma membrane – integral membrane protein and peripheral protein.

Complete answer: Plasma membrane consists of phospholipid and proteins mainly.
Phospholipids form the basic structure of a cell membrane and form a lipid bilayer in which protein is embedded.
The phosphate head of the phospholipids is polar or hydrophilic and the two fatty acid tails are non-polar or hydrophobic. Proteins that are present on the plasma membrane are important for transporting substances across the membrane.
Peripheral and integral proteins that are embedded within the phospholipid bilayer carry out the specific functions of the cell membrane – such as selective transport of molecules across the cell and cell-cell recognition.

The main two features of phospholipid bilayers that are important for the membrane to function are –
1. The structure of phospholipid bilayer acts as membranes as a barrier between two aqueous compartments and
2. The phospholipids are viscous fluids, and the fatty acid chains of the phospholipids have one or more double bonds that make kink (s) into the fatty acid chains and maintain the fluidity of the plasma membrane.

So, the correct answer is option B. protein and phospholipid.

Note: There are two fatty acid chains present in the phospholipids which form a bilayer. But if one chain is removed, it will form a circular structure – called the micelle and it has fluidity than the bilayer.