In eukaryotic cells, the region within a cell membrane that surrounds the nucleus; it contains organelles, which carry out energy production, metabolism, and protein synthesis.

• A. Endoplasmic reticulum
• B. Cytoplasm
• C. Nucleus
• D. Ribosome

Answer: (B)

The region inside the plasma membrane that surrounds the nucleus is the cytoplasm. Cytoplasm includes the cytosol (the fluid part) and all the organelles suspended in it. These components carry out energy production, metabolism, and protein synthesis—mitochondria generate energy, various enzymes in the cytosol handle metabolic processes, and ribosomes (free-floating or attached to the endoplasmic reticulum) carry out protein synthesis. The endoplasmic reticulum is one of the organelles contained in the cytoplasm, not the region itself, and the nucleus is enclosed within its own membrane but resides inside this cytoplasmic space.