Which of the following is an example of prokaryotic cells?

Correct — D. A prokaryotic cell has no membrane-bound nucleus. Its DNA lies free in the cytoplasm in a region called the nucleoid, and it has no mitochondria, plastids, endoplasmic reticulum or Golgi body.

Bacteria are the textbook example: a single circular DNA molecule, 70S ribosomes, a cell wall, often a plasmid, and a size of a few micrometres.

The other three organisms are single-celled but eukaryotic — each keeps its DNA inside a true nuclear membrane → option (d).

Why the others are wrong

• (a)
  Plasmodium — Plasmodium, the malaria parasite, is a protozoan and therefore a eukaryote with a proper nucleus. Being microscopic and parasitic does not make a cell prokaryotic.
• (b)
  Yeast — Yeast is a fungus, and all fungi are eukaryotes. Yeast is in fact the standard laboratory eukaryote for genetics, precisely because it has a normal nucleus.
• (c)
  Leishmania — Leishmania, which causes kala-azar, is a flagellate protozoan. Like Plasmodium it is unicellular but nucleated, so it sits on the eukaryotic side.

The prokaryote-eukaryote split is the first division in cell biology.

Prokaryotes — bacteria, cyanobacteria, mycoplasma, archaebacteria — have a nucleoid instead of a nucleus, 70S ribosomes, and no membrane-bound organelles.

Eukaryotes — protists, fungi, plants and animals — have a nuclear membrane, 80S cytoplasmic ribosomes and organelles that divide labour inside the cell. Being one-celled says nothing either way, which is the trap the three wrong options are built on.

Key facts

• Prokaryotic cells have no nuclear membrane and carry their genetic material in a nucleoid region.
• Bacteria, cyanobacteria and mycoplasma are prokaryotes, grouped in Kingdom Monera.
• Prokaryotic ribosomes are 70S while eukaryotic cytoplasmic ribosomes are 80S.
• Protozoa such as Plasmodium and Leishmania are eukaryotes despite being single-celled.

Common traps

• Equating single-celled with prokaryotic, which misplaces every protozoan.
• Calling yeast a bacterium because it is used in fermentation.
• Forgetting that cyanobacteria, once called blue-green algae, are prokaryotes.

No directly related past PYQ was found.