Question

Which of the following structures is present only in prokaryotic cells?

• A. Mitochondria
• B. Nucleus
• C. Nucleoid
• D. Endoplasmic reticulum

Hint:

Remember the basic difference: \[ \boxed{\text{Prokaryotes} \rightarrow \text{Nucleoid}} \] \[ \boxed{\text{Eukaryotes} \rightarrow \text{True Nucleus}} \] The nucleoid is not enclosed by a nuclear membrane, making it the defining genetic structure of prokaryotic cells.

Answer 1

The Correct Option is C

Concept: Prokaryotic cells are simple, unicellular organisms that lack membrane-bound organelles. Their genetic material is not enclosed within a nuclear membrane but is located in a region known as the nucleoid. This feature distinguishes prokaryotic cells from eukaryotic cells.
• Prokaryotes include bacteria and archaea.
• They lack a true nucleus and membrane-bound organelles.
• Their DNA is usually circular and lies freely in the cytoplasm within the nucleoid region.
• Eukaryotic cells possess a membrane-bound nucleus and organelles such as mitochondria and endoplasmic reticulum.

Step 1: Understand the nucleoid.
The nucleoid is an irregularly shaped region in the cytoplasm where the bacterial chromosome is located. Unlike the nucleus of eukaryotic cells, it is:
• Not surrounded by a nuclear membrane.
• Contains the genetic material (DNA).
• Unique to prokaryotic cells. \[ \boxed{\text{Prokaryotic Cell} \rightarrow \text{Nucleoid (No Nuclear Membrane)}} \]

Step 2: Eliminate the incorrect options.

• Mitochondria are membrane-bound organelles found only in eukaryotes.
• The nucleus is present only in eukaryotic cells.
• Endoplasmic reticulum is also a membrane-bound organelle found only in eukaryotes.
• The nucleoid is characteristic of prokaryotic cells.

Step 3: Choose the correct option.
Hence, \[ \boxed{Option (C) is the correct answer. \]