Question

When plants/animals are infected with viruses, they may produce an antiviral substance that is capable of inhibiting the multiplication of viruses. Identify the correct name of the substance.
A. Virion
B. Antivirion
C. Antigen
D. Interferon

Answer 1

Hint: When a pathogen enters the body of a living organism, the immune system of the host starts its defence mechanism against the pathogen. The pathogen may be killed or stopped from replicating depending on their nature.

Complete answer:
Virus is an infectious agent, which needs living cells in a host organism to multiply. They infect all life forms including animals, plants, bacteria, archaea etc. After infecting an organism, they survive and produce thousands of identical copies of itself in the host cells. Once the immune system identifies the virus, it starts responding by producing cytokines, interferons or antibodies. The cytokines combat the virus-infected cells by inducing apoptosis or by killing the cell with cytotoxic factors. Interferons respond by preventing the replication of viruses. The antibodies produced by the host system kills the virus even before it infects the cells through phagocytosis.

Thus, the antiviral substance produced by the infected plants/animals that inhibits the multiplication of viruses is (D) interferon.

Note:
The other options might look plausible but they have a different meaning. As mentioned earlier, viruses can survive only inside the host body. But when they are outside the body, they exist in complete form with DNA/RNA enclosed in capsid (protein coat) and an envelope of lipids. This form of virus is called virion. Antivirion, also known as virucide, kills the virions in the surrounding and are not intended to be used inside the body. They differ from anti-virus, which only prevents the proliferation of viruses inside the body. Antigen is a protein molecule on the surface of the pathogen which when recognised by the immune system elicits immune response.