USA Biology Olympiad (USABO) Practice Exam

In a contamination scenario involving "swimmers itch," what cellular feature would you expect cyanobacteria to lack?

1. Cell wall

2. Nucleus

3. Nucleolus

4. Chloroplasts

The correct answer is: Nucleolus

In a contamination scenario involving "swimmer's itch," the expected cellular feature that cyanobacteria would lack is the nuclei. Cyanobacteria are classified as prokaryotes, which are characterized by the absence of a true nucleus. Instead of having a nucleus surrounded by a membrane, prokaryotic cells have their genetic material organized in a single circular chromosome located in a region called the nucleoid. The other cellular features listed are present in cyanobacteria. They possess a cell wall, which provides structure and protection, typical of bacterial cells. While cyanobacteria do not have chloroplasts as seen in eukaryotic plant cells, they are capable of photosynthesis due to the presence of thylakoid membranes where the photosynthetic pigments are located. This is an adaptation that allows them to capture light energy for photosynthesis effectively, indicating that they do not need separate organelles for those functions. Consequently, the lack of a nucleus is a definitive characteristic that distinguishes cyanobacteria from eukaryotic organisms.