AEMCA Practice Exam 2025 - Free Practice Questions and Study Guide for Advanced Emergency Medical Care Assistant Certification.

The rough endoplasmic reticulum (RER) is primarily responsible for the synthesis and transport of proteins within the cell. It is studded with ribosomes on its cytoplasmic surface, giving it a "rough" appearance. These ribosomes translate mRNA into polypeptide chains, which enter the RER for folding, processing, and transport. The RER also plays a crucial role in synthesizing membrane proteins and secretory proteins, effectively facilitating their movement to various locations within the cell or exporting them outside the cell.

In contrast, lysosomes are involved primarily in digestion and waste removal, breaking down macromolecules, old cell parts, and microorganisms. The cytoplasm serves as the medium for chemical reactions and houses organelles but does not actively transport materials like the RER. The cell membrane regulates what enters and exits the cell but isn’t involved in the internal transport of materials. Therefore, the rough endoplasmic reticulum stands out as the key structure for intracellular transport of proteins, marking it as the correct option.