Key Differences Between Eukaryotes and Prokaryotes

Subject : Biology

Question:

Which of the following characteristics distinguishes eukaryotes from prokaryotes?

A. Eukaryotes engage in sexual reproduction.

B. Eukaryotes have a defined nucleus.

C. Eukaryotes have membrane-bound organelles.

D. Eukaryotes have complex internal structures.

Expert Verified Solution:

The correct answer is B. Eukaryotes have a defined nucleus.

Eukaryotes and prokaryotes are the two primary categories of cells that define life on Earth, and understanding the differences between them is crucial for understanding biology.

Detailed Explanation:

Eukaryotes are organisms whose cells contain a well-defined, membrane-bound nucleus. This is the most fundamental feature that distinguishes them from prokaryotes, which do not have a true nucleus. Instead, prokaryotic cells, such as bacteria and archaea, have their genetic material free-floating in the cytoplasm, forming a region called the nucleoid but not enclosed by a membrane.

In eukaryotes, the nucleus serves as the control center of the cell. It contains the cell’s DNA (genetic material) and is separated from the cytoplasm by a double membrane called the nuclear envelope. This structure helps to regulate the flow of information and molecules between the nucleus and the rest of the cell.

Other characteristics that distinguish eukaryotes from prokaryotes, although important, are not as definitive as the presence of the nucleus:

Sexual Reproduction (Option A): While many eukaryotes engage in sexual reproduction (such as animals and plants), this is not a defining characteristic. Some eukaryotes, like certain fungi or protists, reproduce asexually. Moreover, some prokaryotes also have methods of genetic exchange (like conjugation), although they don’t engage in sexual reproduction in the same sense.

Membrane-bound Organelles (Option C): Another feature of eukaryotic cells is the presence of membrane-bound organelles, such as mitochondria, chloroplasts, and the endoplasmic reticulum. These structures carry out specific functions within the cell. In contrast, prokaryotes lack these organelles, performing similar functions in different ways. While this is a significant difference, the nucleus remains the most definitive feature separating eukaryotes from prokaryotes.

Complex Internal Structures (Option D): Eukaryotic cells are generally more complex, having cytoskeletons and a wide range of internal structures that allow them to maintain shape, transport materials, and divide in more intricate ways. However, the complexity of their internal structure is still secondary to the fact that they have a true nucleus, which is their most distinguishing feature.