Which one of the following structure is NOT found in prokaryotes ?
- A.Nuclear envelope
- B.Cell membrane
- C.Ribosome
- D.Cell wall
Correct answer
Explanation
The correct answer is A, Nuclear envelope. Prokaryotes have no true nucleus, so there is no membrane around their genetic material.
Prokaryotes are the simplest cells: bacteria and cyanobacteria (blue-green algae). Their single circular DNA lies loose in the cytoplasm in a region called the nucleoid, with no nuclear envelope and no nucleolus. They also lack membrane-bound organelles such as mitochondria, chloroplasts, the endoplasmic reticulum and the Golgi body. Eukaryotic cells of plants, animals, fungi and protists, by contrast, keep their DNA inside a double-membrane nuclear envelope. The very word prokaryote means "before the nucleus".
B is wrong: every living cell, prokaryotic or eukaryotic, is bounded by a cell membrane.
C is wrong: prokaryotes do have ribosomes, the smaller 70S type, to make proteins.
D is wrong: most bacteria have a rigid cell wall made of peptidoglycan.
Exam tip: prokaryote = no nuclear membrane, no membrane-bound organelles, 70S ribosomes; eukaryote = true nucleus and 80S ribosomes.
Practice Questions
View allA snowboard pulled up by a tow rope travels at the rate of 5 m/s up a mountain. If 3000 watt of power is used, what force was applied to it ?
- A.50 N
- B.100 N
- C.600 N
- D.15000 N
Show answer
Power equals force times velocity, so the force is 3,000 W divided by 5 m/s, which is 600 N. Power is the rate of doing work: P = W/t. Work is force times distance, W = F × d, so P = F × d/t, and since d/t is the…
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- B.energy only
- C.both material of the medium and energy
- D.none of the above
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- A.Conservation of energy
- B.Conservation of momentum
- C.Conservation of charge
- D.Conservation of mass
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- A.Ionization energy
- B.Electron affinity
- C.Electronegativity
- D.Atomic radius
Show answer
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- A.30 s
- B.2.1 s
- C.3.0 s
- D.4.1 s
Show answer
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