Multiple Choice Question The cell envelope is defined as O the plasma membrane and any slime layer than may be present the plasma membrane and peptidoglycan layers the plasma membrane and all layers external to it the outermost layer covering a cell

The correct answer is: **the plasma membrane and all layers external to it** **Explanation:** The **cell envelope** refers to the complete set of structures that surround the cell membrane in a cell, particularly in bacteria. This includes: 1. **Plasma Membrane:** The fundamental lipid bilayer that controls the movement of substances in and out of the cell. 2. **Cell Wall:** Provides structural support and protection. In bacteria, this is often composed of peptidoglycan. 3. **Outer Membrane (in Gram-negative bacteria):** An additional lipid bilayer that lies outside the peptidoglycan layer. 4. **Capsule or Slime Layer:** These are external layers that can provide protection against desiccation and help in adherence to surfaces. Given the options: - **Option 1:** Only mentions the plasma membrane and slime layer, which is incomplete. - **Option 2:** Focuses on the plasma membrane and peptidoglycan layers but may exclude other external structures like the outer membrane in Gram-negative bacteria. - **Option 3:** **Correct** as it encompasses the plasma membrane and all external layers, providing a comprehensive definition. - **Option 4:** Only refers to the outermost layer, neglecting the plasma membrane and other intermediate structures. **Therefore, the most accurate definition of the cell envelope is the plasma membrane and all layers external to it.**