The intense rose color in the cytoplasm is most likely due to which cellular structure?

• A. Mitochondria
• B. Golgi apparatus
• C. Rough Endoplasmic Reticulum
• D. Nucleus

Answer: (C)

Intense rose (eosinophilic) staining of the cytoplasm points to a high protein content produced by ribosome-rich organelles. The rough endoplasmic reticulum is studded with ribosomes and is the main site of synthesis for many secreted and membrane proteins. When a cell is actively producing proteins, its cytoplasm becomes densely packed with rough ER and newly made proteins, which bind eosin strongly and give a pronounced pink color under routine stains. The nucleus typically stains basophilic due to DNA/RNA, the Golgi apparatus tends to be less intensely stained, and mitochondria, while contributing to cytoplasmic staining, do not alone dictate this level of pinkness. Therefore, the rose-colored cytoplasm most likely reflects abundant rough endoplasmic reticulum.