What are the basic internal structures of cells?

• A. Organelles
• B. Inclusions
• C. Ribosomes
• D. Nucleolus

Answer: (A)

Organelles are the basic internal structures of cells, each enclosed by a membrane (in most cases) and dedicated to a specific task—like the nucleus housing DNA and directing activity, mitochondria generating ATP, and the endoplasmic reticulum and Golgi apparatus processing and shipping proteins. Inclusions are storage materials such as glycogen or lipid droplets that don’t form membrane-bound compartments with active roles, so they aren’t considered true organelles. The nucleolus is a specialized region inside the nucleus where ribosomal RNA is made and ribosomes begin to assemble; it isn’t a separate organelle. Ribosomes, the protein-synthesis machines, can be free in the cytoplasm or attached to the rough ER, but they are components within the organelle-system rather than the broad category itself. So, the best term for the internal cellular components is organelles.