Which cellular structure is NOT found in all cells (i.e., is present in eukaryotes but absent in prokaryotes)?

• A. Plasma membrane
• B. Ribosomes
• C. Cytoplasm
• D. Nucleus

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the difference between prokaryotic and eukaryotic cells. Prokaryotic cells are simpler and lack membrane-bound organelles, while eukaryotic cells have complex structures including membrane-bound organelles.
2. Step 2: Identify the cellular structures listed: plasma membrane, ribosomes, cytoplasm, and nucleus. Consider which of these are common to both prokaryotes and eukaryotes.
3. Step 3: Recall that the plasma membrane, ribosomes, and cytoplasm are found in all cells because they are essential for basic cell functions such as protection, protein synthesis, and the internal environment.
4. Step 4: Recognize that the nucleus is a membrane-bound organelle that contains the cell's genetic material and is characteristic of eukaryotic cells only; it is absent in prokaryotic cells.
5. Step 5: Conclude that the nucleus is the cellular structure not found in all cells, specifically present in eukaryotes but absent in prokaryotes.