What is the structure of rough endoplasmic reticulum characterized by?

The rough endoplasmic reticulum is characterized by its rough appearance due to the presence of ribosomes on its cytoplasmic surface. These ribosomes are the sites of protein synthesis, and their adherence gives the rough endoplasmic reticulum its distinctive texture, differentiating it from the smooth endoplasmic reticulum, which lacks ribosomes and has a smooth surface.

This rough surface is critical for the function of the rough endoplasmic reticulum, which is primarily involved in the synthesis and processing of proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle. The presence of ribosomes enables the rough endoplasmic reticulum to produce large quantities of proteins efficiently, highlighting its role in the overall cellular function and metabolism.

As for other options, while smooth endoplasmic reticulum has a smooth surface and ribosomes are notably absent there, such features do not pertain to the rough endoplasmic reticulum. Additionally, the rough endoplasmic reticulum is not involved in photosynthesis, which is primarily a function of chloroplasts in plant cells.