Question

Which structure is present in prokaryotes but absent in eukaryotes?

• A. \( \text{Mitochondria} \)
• B. \( \text{Ribosomes} \)
• C. \( \text{Nucleoid} \)
• D. \( \text{Golgi apparatus} \)

Hint:

Remember: "Pro" means before and "Karyon" means nucleus. Prokaryotes evolved before the membrane-bound nucleus appeared.

Answer 1

The Correct Option is C

Concept: The fundamental distinction between prokaryotic and eukaryotic cells lies in their internal organization.
• Eukaryotes possess a well-defined nucleus enclosed by a double membrane.
• Prokaryotes lack a membrane-bound nucleus and other membrane-bound organelles.

Step 1: Defining the Prokaryotic Genetic Region.
In prokaryotic cells, the genetic material (DNA) is not contained within a nuclear envelope. Instead, the DNA is located in an irregularly shaped region called the "Nucleoid." This region contains the single, circular chromosome and associated proteins.

Step 2: Comparison with Eukaryotic Structures.
Mitochondria and Golgi apparatus are membrane-bound organelles found only in eukaryotes. Ribosomes are present in both cell types, although they differ in size (70S vs 80S). Therefore, the nucleoid is the signature genetic region unique to prokaryotes. Final Answer: The structure present in prokaryotes but absent in eukaryotes is the Nucleoid.