Which one of the following structures is not present in a prokaryotic cell ?
- (a)Cell wall
- (b)Ribosomes
- (c)Nucleus
- (d)Plasma membrane
Correct — C, Nucleus. A prokaryotic cell (such as a bacterium) has no true, membrane-bound nucleus. Its single circular DNA molecule lies free in the cytoplasm in a region called the nucleoid. Prokaryotes do have a cell wall, ribosomes (the 70S type) and a plasma membrane, so the one structure absent from them is the nucleus.
- (a)Cell wall — Prokaryotes such as bacteria do have a cell wall (peptidoglycan), so it is present, not absent.
- (b)Ribosomes — Prokaryotes contain ribosomes (70S) and use them for protein synthesis — they are present.
- (d)Plasma membrane — Every cell, including prokaryotes, is bounded by a plasma membrane; it is a universal feature, so it is present.
The defining difference between prokaryotic and eukaryotic cells is the nucleus. Eukaryotes keep their DNA inside a membrane-bound nucleus; prokaryotes do not — their genetic material sits in the cytoplasm as a nucleoid. Prokaryotes also lack other membrane-bound organelles such as mitochondria and the endoplasmic reticulum.
Cell wall, ribosomes and plasma membrane are all present in prokaryotes, so they are distractors. The only feature missing is the true nucleus — that is what makes a cell 'prokaryotic' (literally 'before the nucleus').
- Prokaryotes lack a true membrane-bound nucleus; their DNA lies in a nucleoid.
- They do possess a cell wall, plasma membrane and 70S ribosomes.
- They lack membrane-bound organelles (mitochondria, ER, Golgi).
- Bacteria and archaea are prokaryotes; plants, animals, fungi and protists are eukaryotes.
The only structure missing from a prokaryote is the nucleus — option (c).
- Thinking prokaryotes have no ribosomes — they do (70S).
- Assuming 'no nucleus' means 'no DNA' — the DNA is present, just not enclosed.
Asked directly ('which structure is not present in a prokaryotic cell') or via the nucleoid concept.
No directly related past PYQ was found.
- practice — not a real PYQ
In a prokaryotic cell, the region where the genetic material is located is called the
- (a)nucleolus
- (b)nucleoid
- (c)nucleosome
- (d)nucleus
Answer(b) nucleoid — the DNA lies free here, with no surrounding membrane.
- practice — not a real PYQ
Which of the following is found in both prokaryotic and eukaryotic cells?
- (a)Membrane-bound nucleus
- (b)Mitochondria
- (c)Ribosomes
- (d)Endoplasmic reticulum
Answer(c) Ribosomes — present in both, though of different sizes (70S vs 80S).