Advanced Placement (AP) Biology Practice Exam

What characteristic distinguishes prokaryotic cells from eukaryotic cells?

1. Presence of a nucleus

2. Presence of ribosomes

3. Size and shape

4. Presence of membrane-bound organelles

The correct answer is: Presence of a nucleus

The presence of a nucleus is a defining characteristic that distinguishes prokaryotic cells from eukaryotic cells. Prokaryotic cells, such as bacteria, lack a true nucleus; instead, their genetic material is located in a nucleoid region that is not surrounded by a membrane. This fundamental difference in cellular organization is critical to the classification of life forms. Eukaryotic cells, which include those of plants, animals, fungi, and protists, possess a well-defined nucleus that houses their DNA within a nuclear membrane. This distinction is significant because it affects various cellular processes, such as gene expression, replication, and the overall complexity of the organism. The other options mentioned do not accurately serve as distinguishing characteristics between prokaryotic and eukaryotic cells. For instance, both types of cells contain ribosomes, although they differ in size and composition. While size and shape can vary between individual cells, they are not definitive traits that separate the two categories. Similarly, eukaryotic cells have membrane-bound organelles, while prokaryotic cells do not, but the presence of the nucleus remains the more pivotal distinguishing feature.