Which of the following is NOT a subcellular structure found in both plant and animal cells?

The correct answer is B. Chloroplasts. Both plant and animal cells contain the structures A. Nucleus, C. Mitochondria, D. Endoplasmic reticulum, and E. Golgi apparatus. However, only plant cells contain chloroplasts, which are responsible for photosynthesis and the synthesis of organic molecules from inorganic precursors using light energy. Therefore, B. Chloroplasts is the incorrect answer because it is found only in plant cells, not animal cells.