Cell The Unit Of Life

The endoplasmic reticulum is shortly abbreviated as ER. It is a type of organelle in eukaryotic cells. The structure of ER is composed of the interconnected network of flattened and membrane-enclosed sacs or tube-like structures. These structures are known as cisternae. There are two regions of the ER. Smooth ER and rough ER are classified on the basis of absence and presence of ribosomes on the surface of the ER respectively.

Step 1: Understanding the Concept: The plasma membrane is a dynamic, semi-permeable lipid bilayer that acts as the boundary of the cell and mediates cellular interactions.
Step 2: Key Formula or Approach: Review the functional repertoire of the plasma membrane versus the internal organelles of a cell.
Step 3: Detailed Explanation: The plasma membrane serves several critical functions at the cell surface.
It facilitates the bulk intake of materials via vesicular invagination, known as Endocytosis (Option 1).
It contains specialized proteins that link adjacent cells together, resulting in the Formation of intercellular junctions like tight junctions and desmosomes (Option 2).
It is actively involved in exocytosis, which facilitates the Secretion of cellular products into the extracellular space (Option 3).
However, DNA synthesis (replication) is a highly regulated genetic process that occurs strictly within the intracellular compartment—specifically inside the nucleus in eukaryotes, or within the nucleoid region of the cytoplasm in prokaryotes. The plasma membrane is entirely uninvolved in the biochemical synthesis of DNA.
Step 4: Final Answer: DNA synthesis is not a function of the plasma membrane.