Explanation
- A
1 and 2 only
Viruses that infect bacteria (bacteriophages) and fungi (mycoviruses) are real, but plant viruses are equally well established. Stopping at 1 and 2 therefore omits a correct host group.
- B
3 only
Plants alone would ignore bacteriophages and fungal viruses. 3 only is incomplete.
- C
1 and 3 only
Bacteria and plants without fungi would omit mycoviruses, which infect fungi. 1 and 3 only is therefore not the key.
- D
1, 2 and 3
Viruses are obligate intracellular parasites and can infect bacteria, fungi and plants (as well as animals and protozoa). Bacteriophages, mycoviruses and classic plant viruses such as tobacco mosaic virus illustrate all three. Hence 1, 2 and 3 is the official key.
Summary. Official key is (d) 1, 2 and 3. A virus needs a living host cell; the host may be a prokaryote or a eukaryote. Bacteriophages infect bacteria; many RNA/DNA viruses infect fungi; plants suffer mosaic, leaf-curl and other viral diseases. There is no biological bar that confines viruses to animals only. All three listed groups can be infected.
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