Bacteria have an undefined nuclear region which lacks a nuclear membrane and contains only DNA without proteins. Such a region is called:
- A.Nucleosome
- B.Nucleus
- C.Nucleoprotein
- D.Nucleoid
Correct answer
Explanation
The correct answer is D, Nucleoid. A bacterium is a prokaryote, so its DNA lies in an irregular region called the nucleoid, with no nuclear membrane around it.
Prokaryotic cells such as bacteria have no membrane-bound organelles. Their genetic material is usually a single circular DNA molecule packed in one part of the cytoplasm, and this undefined region is the nucleoid. Eukaryotic cells, in contrast, keep their DNA inside a true nucleus bounded by a double nuclear envelope, with the DNA wound around histone proteins. Many bacteria also carry small extra rings of DNA called plasmids outside the nucleoid.
A is wrong: a nucleosome is a unit of eukaryotic chromatin, DNA wrapped around eight histone proteins.
B is wrong: a nucleus has a nuclear membrane, which bacteria lack.
C is wrong: a nucleoprotein is a complex of nucleic acid and protein, not a region of the cell.
Exam tip: prokaryote = nucleoid, no nuclear membrane, 70S ribosomes; eukaryote = true nucleus, 80S ribosomes.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
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