Which feature is shared by both prokaryotic cells (such as bacteria) and eukaryotic cells (such as plant and animal cells)?

Introduction:
Cells are broadly classified into prokaryotic and eukaryotic types. Prokaryotes include bacteria and archaea, while eukaryotes include plants, animals, fungi and protists. Many exam questions test your understanding of what these two cell types have in common and what distinguishes them. This question asks you to identify a feature shared by both prokaryotic and eukaryotic cells from among several possibilities involving the nucleus and organelles.

Given Data / Assumptions:
- The comparison is between prokaryotic and eukaryotic cells. - Options mention nucleus, DNA, nuclear membrane and membrane bound organelles. - We assume standard textbook definitions of these cell types. - The question is about shared features, not differences.

Concept / Approach:
Both prokaryotic and eukaryotic cells use DNA as their genetic material. In prokaryotes, DNA is located in a nucleoid region and is not enclosed by a membrane, while in eukaryotes, DNA is organised into chromosomes inside a membrane bound nucleus. Prokaryotes lack a true nucleus and membrane bound organelles such as mitochondria and chloroplasts, which are characteristic of eukaryotic cells. Therefore, the presence of DNA as the genetic material is the key feature shared by both, whereas a nucleus, nuclear membrane and complex organelles are eukaryotic features only.

Step-by-Step Solution:
Step 1: Recall that the main difference between prokaryotes and eukaryotes is that eukaryotes have a nucleus and organelles, while prokaryotes do not. Step 2: Recognise that both cell types must store genetic information somewhere to control cell functions and heredity. Step 3: Understand that in both types, this genetic information is encoded in DNA molecules. Step 4: Note that in prokaryotes, the DNA is typically a circular chromosome in the cytoplasm, whereas in eukaryotes it is linear and enclosed in a nucleus. Step 5: Check each option and see that only the presence of DNA fits both cell types. Step 6: Confirm that a true nucleus, nuclear membrane and membrane bound organelles are found only in eukaryotic cells.

Verification / Alternative check:
Cell biology texts describe prokaryotic cells as lacking a nucleus and membrane bound organelles but still having a DNA containing region called the nucleoid. They emphasise that the genetic material is DNA, often with plasmids as additional DNA rings. Eukaryotic cells are described as having a nucleus with a nuclear envelope, along with organelles such as mitochondria, endoplasmic reticulum and Golgi apparatus. Both cell types also share basic features like plasma membrane and ribosomes, but the question focuses specifically on the options given, where DNA is the clear common feature mentioned.

Why Other Options Are Wrong:
A true membrane bound nucleus: Present only in eukaryotic cells; prokaryotic cells have a nucleoid without a surrounding membrane. A nuclear membrane enclosing chromosomes: Again, a eukaryotic feature; prokaryotes lack this membrane bound compartment. Membrane bound organelles such as mitochondria: Found in eukaryotes; prokaryotes do not have mitochondria or similar organelles.

Common Pitfalls:
Some students misinterpret the term nucleus and assume all cells must have one because they all have DNA. They also sometimes confuse ribosomes or plasma membrane features with organelles. To avoid this, remember that prokaryotes are simpler, with DNA freely placed in the cytoplasm, and lack membrane bound internal compartments. The safest common feature to choose here is the presence of DNA as the genetic material in both prokaryotic and eukaryotic cells.

Final Answer:
A key feature shared by both prokaryotic and eukaryotic cells is the Presence of DNA as the genetic material.