Question

Which of the following is NOT a difference that would allow one to distinguish between a prokaryotic and a eukaryotic cell? A. Ribosomal subunit weight B. Presence or absence of the nucleus C. Presence or absence of the cell wall D. Membrane-bound versus no membrane-bound organelles

Short answer

Option C: Presence or absence of the cell wall

Step-by-step solution

Understand the Question

We need to identify which characteristic does NOT distinguish between prokaryotic and eukaryotic cells.

Examine Option A: Ribosomal subunit weight

Prokaryotic cells have 70S ribosomes, and eukaryotic cells have 80S ribosomes. This is a distinguishable difference.

Examine Option B: Presence or absence of the nucleus

Prokaryotic cells do not have a nucleus, while eukaryotic cells have a nucleus. This is a distinguishable difference.

Examine Option C: Presence or absence of the cell wall

Both prokaryotic and eukaryotic cells can have a cell wall (e.g., plant cells and bacteria). Thus, this is NOT a distinctive characteristic.

Examine Option D: Membrane-bound versus no membrane-bound organelles

Prokaryotic cells lack membrane-bound organelles, whereas eukaryotic cells have them. This is a distinguishable difference.

Conclusion

The only option that does not clearly distinguish between prokaryotic and eukaryotic cells is the presence or absence of the cell wall (Option C).

Key concepts

Ribosomal Subunit Weight

Ribosomes are the molecular machines responsible for protein synthesis in all living cells. However, they differ between prokaryotic and eukaryotic cells. Prokaryotic cells have 70S ribosomes, composed of 50S and 30S subunits. Eukaryotic cells have 80S ribosomes, composed of 60S and 40S subunits.
The 'S' in these numbers stands for Svedberg units, a measure of how fast particles sediment in a centrifuge.
These differences in ribosomal subunit weight are significant enough to help distinguish between the two cell types.
Prokaryotic ribosomes are generally smaller and less complex than eukaryotic ribosomes.
This difference is particularly important in antibiotic treatments. Some antibiotics target bacterial ribosomes without affecting human ribosomes.

Nuclear Presence

One of the key differences between prokaryotic and eukaryotic cells is the presence of a nucleus. Eukaryotic cells have a well-defined nucleus that contains their genetic material (DNA).
This nucleus is surrounded by a double membrane called the nuclear envelope. In contrast, prokaryotic cells do not have a nucleus.
Their genetic material is located in a region called the nucleoid, which is not enclosed by a membrane.
The presence of a nucleus allows eukaryotic cells to have a more complex regulatory mechanism for gene expression.
This complexity enables the specialization of different cell types in multicellular organisms.
In prokaryotes, the simpler nucleoid region means their gene regulation and cell functions are less complex than those of eukaryotes.

Cell Wall Presence

The presence or absence of a cell wall is not a distinguishing feature between prokaryotic and eukaryotic cells. Some prokaryotes, like bacteria, have cell walls made of peptidoglycan.
Some eukaryotes, like plant cells, also have cell walls, but these are made of cellulose. Differences in cell wall composition are significant but do not help us broadly distinguish between prokaryotes and eukaryotes.
Additionally, animal cells (which are eukaryotic) do not have cell walls at all.
This means that the presence of a cell wall cannot universally differentiate prokaryotic cells from eukaryotic cells.
However, the composition and function of these cell walls are critical in other contexts, such as plant structure and bacterial protection.

Membrane-Bound Organelles

Eukaryotic cells contain many membrane-bound organelles that compartmentalize the cell and perform specialized functions. Examples include the mitochondria, endoplasmic reticulum, and Golgi apparatus.
These organelles enable complex cellular processes to occur in isolated environments, leading to greater efficiency and regulation.
For example, mitochondria are known as the powerhouses of the cell because they generate ATP through cellular respiration.
In contrast, prokaryotic cells lack membrane-bound organelles. Their cellular processes occur in the cytoplasm or along the cell membrane.
This absence of compartmentalization means that prokaryotic cells generally have simpler and more direct pathways for metabolic activities.