Consider the following statements : I. No virus can survive in ocean waters. II. No virus can infect bacteria. III. No virus can change the cellular transcriptional activity in host cells. How many of the statements given above are correct?
- A.Only one
- B.Only two
- C.All the three
- D.None
Correct answer
Explanation
The correct answer is D, None. Each statement says "no virus can", and each is disproved by well-known viruses.
The oceans are full of viruses: a millilitre of seawater typically holds millions of virus particles, most of them infecting marine bacteria and algae, and by killing these microbes they play a large part in the ocean's carbon and nutrient cycles. Viruses that infect bacteria are so common that they have their own name, bacteriophages, and they are now studied as phage therapy against drug-resistant bacteria. Finally, every virus has to take over the host cell's machinery to copy itself, and many, such as HIV, influenza and cancer-causing viruses, switch the host's own genes on or off, changing its transcription.
A is wrong: not even one statement is correct.
B is wrong: two cannot be correct when all three are false.
C is wrong: all three statements are false.
Exam tip: marine viruses are the most abundant biological entities in the sea; bacteriophages infect bacteria; viruses reprogramme host transcription.
Practice Questions
View allWhich one of the following cell organelles contains DNA?
- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
Show answer
Mitochondria carry their own small, circular DNA and their own ribosomes. Mitochondria are the powerhouses of the cell, where aerobic respiration makes ATP.
Read the full explanation →Which set of vegetables is underground stem or modified stem of a plant?
- A.Potato, artichoke, round gourd
- B.Onion, garlic, carrot
- C.Potato, onion, garlic
- D.Potato, garlic, turnip
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All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.
Read the full explanation →A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :
- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
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A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.
Read the full explanation →A body floats in a liquid if the buoyant force is :
- A.equal to its weight.
- B.less than its weight.
- C.greater than its weight.
- D.zero.
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A floating body is in equilibrium, so the upward buoyant force exactly balances its weight. By Archimedes' principle, a body in a liquid is pushed up by a force equal to the weight of the liquid it displaces.
Read the full explanation →Which of the following are the different parts of a human brain ?
- A.Forefront brain, Standard brain and Hind brain
- B.Fore brain, Median brain and Rear brain
- C.Fore brain, Mid brain and Hind brain
- D.Precursor brain, Mean brain and Hind brain
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These are the three main divisions of the human brain. The fore brain is the largest part.
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