1. After filtering a liquid plant extract, the scientists could see the virions using the light microscope.
2. After filtering a liquid plant extract, the disease was still transferred to a healthy plant.
3. After filtering a liquid plant extract, the virus cells multiplied.
4. After filtering a liquid plant extract, scientists were able to trace historical footprints.

1. Advances in technology provide historic evidence.
2. Biochemical and genetic information provide historic evidence.
3. Advances in technology provide new information for scientists.
4. Advances in technology have proven that viruses have a single common ancestor.

1. Measles is a DNA virus, and DNA viruses cause human diseases.
2. Dogs do not have glycoproteins.
3. The virus can’t attach to dog cells.
4. Dogs do not get RNA viruses.

The Baltimore classification system groups viruses according to how the mRNA is produced. When classified this way, the viruses in each group ________.

1. behave in a similar manner
2. look very similar
3. connect with living things
4. are based on the type of disease they cause

1. AZT blocks the enzyme called HIV protease, which the virus uses to reproduce itself.
2. AZT blocks the HIV integrase enzyme, which the virus uses to insert its viral DNA into the DNA of the host cell.
3. AZT prevents reverse transcriptase and HIV protease enzyme from functioning inside the body.
4. AZT prevents reverse transcriptase from making DNA from the viral RNA genome.

1. The lytic cycle can theoretically produce more virions as the viral genome takes over the host cell, resulting in the large-scale release of virions.
2. The lysogenic cycle can theoretically produce more virions as the reproductive cycle of viruses undergoing lysogeny is much faster than the reproductive cycle of viruses following lytic cycle.
3. The lysogenic cycle can theoretically produce more virions as the viral genome is incorporated into the host cell’s genome replicating along with the host cell.
4. The lytic cycle can theoretically produce more virions as the prophage following lysogenic cycle ultimately gets excised from the host cell’s genome and enter the lytic cycle.

1. The person is at risk of developing chickenpox. Chickenpox is the first infection with the virus before it enters latency in the host.
2. The person is at risk of developing shingles. Shingles is the first infection with the virus before it enters latency in the host.
3. The person is at risk of developing chickenpox. Chickenpox is the first infection with the virus that is already latent in the body.
4. The person is at risk of developing shingles. The virus enters the person and gets activated when a person with shingles comes in close contact.

1. The attachment step is the most critical, as infection cannot begin if virus does not attach to the host cell.
2. The replication step is the most critical as this step directs protein synthesis.
3. The assembly step is the most critical because new virions are assembled to infect cells.
4. The entry step is the most critical as nucleic acid of virus needs to enter the host cell naked, leaving the capsid outside.

For most people, the measles virus does not cause a serious illness. Symptoms include fever and a rash, but the symptoms are usually gone in about a week. However, for some, the measles virus can be much more serious. How can the measles virus cause a potentially fatal illness?

1. Measles can cause meningococcal disease, which causes severe headaches, seizures and in severe cases can be life-threatening.
2. Measles can cause variant Creutzfeldt-Jakob disease, which causes severe headaches, seizures and in severe cases can be life-threatening.
3. Measles can cause encephalitis/meningitis, which causes severe headaches, seizures and in severe cases can be life-threatening.
4. Measles can cause Legionnaires’ disease, which causes severe headaches, seizures and in severe cases can be life-threatening.

Why is immunization after being bitten by a rabid animal so effective and why aren’t people vaccinated for rabies like dogs and cats are?

1. It takes a month for the virus to travel from the site of the bite to the central nervous system. People are not vaccinated beforehand as routine vaccination of domestic animals makes it unlikely that humans will contract rabies from an animal bite.
2. It takes a week for the virus to travel from the site of the bite to the peripheral nervous system. People are not vaccinated beforehand as routine vaccination of domestic animals makes it unlikely that humans will contract rabies from an animal bite.
3. It takes a week for the virus to travel from the site of the bite to the central nervous system. People are not vaccinated beforehand as routine vaccination of domestic animals makes it unlikely that humans will contract rabies from an animal bite.
4. It takes a week for the virus to travel from the site of the bite to the central nervous system. People are not vaccinated beforehand, as routine vaccination of domestic animals makes it fully sure that humans will contract rabies from an animal bite.

1. As cats and dogs have different proteins than humans, the virus that causes colds in humans cannot find receptors in dogs and cats.
2. As cats and dogs have different receptors than humans, the virus that causes colds in humans cannot find receptors in dogs and cats.
3. As cats and dogs’ immune system attacks the virus unlike humans, so the virus that causes colds in humans cannot find receptors in dogs and cats.
4. As natural killer cells of cats and dogs attack the virus, the virus that causes colds in humans cannot find receptors in dogs and cats.

Prions are responsible for variant CJD (Creutzfeldt-Jakob Disease). How has this disease been documented to spread from human to human?

1. Surgery with instruments previously used in a patient with vCJD that were not adequately sterilized and contaminated pineal growth hormones taken from human pineal glands from infected cadavers.
2. Through human consumption of infected meat and contaminated pituitary growth hormones taken from human pituitary glands from infected cadavers.
3. Surgery with instruments previously used in a patient with vCJD that were not adequately sterilized and contaminated pituitary growth hormones taken from human pituitary glands from unwell individuals.
4. Surgery with instruments previously used in a patient with vCJD that were not adequately sterilized and contaminated pituitary growth hormones taken from human pituitary glands from infected cadavers.

1. They both replicate within a host cell and contain nucleic acids.
2. They both replicate within a host cell and do not contain nucleic acids.
3. They both replicate within a host cell and contain proteins.
4. They both replicate within a host cell and contain only RNA.

1. DNA or RNA, though present, is not transmitted when a prion causes infection.
2. The prion does not contain DNA or RNA.
3. Only parts of DNA or RNA are transmitted in a prion.
4. More of protein and less of DNA or RNA is transmitted.