Cell Envelope MCQ - Practice Questions with Answers

The outer covering of protoplasm of the bacterial cell is called the cell envelope. It includes 3 parts i.e glycocalyx, cell wall and cell membrane. 
Glycocalyx-  

• Outermost mucilage layer of cell envelope that consists of non-cellulosic polysaccharide with or without proteins. 
• If glycocalyx is loose and smooth, it is called the slime layer however if it is thick and tough, it is called a capsule.
• Glycocalyx helps in the prevention of desiccation, protection from phagocytes, toxic chemicals, drugs and viruses. It is also involved in attachment, immunogenicity and virulence. 

 Cell wall- 

• Rigid solid covering present between plasma membrane and glycocalyx.
• The cell wall is made up of peptidoglycan.
• Peptidoglycan is a polysaccharide made of two glucose derivatives N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), alternated in long chains. The chains are cross-linked to one another by means of four amino acids i.e. L-alanine, D-glutamine, L-lysine or meso-diaminopimelic acid (DPA), and D-alanine.
• On the basis of the structure of the cell wall, bacteria can be Gram positive or Gram negative 
• The cell wall provides structural support to the cell, maintaining the shape of the cell and it also protects the cell. 

Plasma membrane- 

• The innermost layer of the cell envelope. It is selectively permeable i.e. allows the transfer of few molecules only. 
• It is made up of phospholipid bilayer. Chemically, the bacterial cell membrane is similar to the eukaryotic cell membrane.
• The bacterial membrane is metabolically active and has a role in respiration and synthesis of lipids and cell wall components.