Which cellular component is found in plant cells, animal cells, and bacterial cells?

• A. Nuclei
• B. Ribosomes
• C. Mitochondria
• D. Chloroplasts

Answer: (B)

Ribosomes are the protein-synthesis machines that every cell needs to make proteins. They read genetic instructions and assemble amino acids into polypeptide chains, which are essential for all cellular functions. In bacteria, ribosomes are the smaller 70S type, while in plant and animal cells, ribosomes in the cytosol and on the rough endoplasmic reticulum are the larger 80S type. Even within plant and animal cells, the organelles mitochondria and chloroplasts contain their own ribosomes (70S), reflecting their bacterial origins. This universal presence across plant, animal, and bacterial cells makes ribosomes the correct choice.

Nuclei are only in eukaryotic cells (plants and animals) and are not present in bacteria. Mitochondria are characteristic of many eukaryotic cells but not bacteria. Chloroplasts are found in plant (and some algae) cells but not in animal cells or most bacteria.