Question 1: Define a virus in your own words.

Answer: A virus is a tiny infectious agent that requires a host cell to reproduce and can cause disease.

Question 2: Describe the basic structure of a virus, including its key components.

Answer: A virus consists of genetic material (DNA or RNA) enclosed within a protein coat called a capsid; some viruses also have a lipid envelope.

Question 1: Explain the process by which a virus infects a host cell and reproduces.

Answer: Viruses attach to a specific receptor on the host cell surface, inject their genetic material into the cell, hijack the cell's machinery to replicate viral components, assemble new viruses, and then cause the cell to burst, releasing new viruses.

Question 2: What is the term used to describe the process when a virus becomes inactive in the host cell and does not cause disease immediately?

Answer: Lysogeny or latent phase.

Question 1: List two differences between viruses and bacteria.

Answer: Viruses are acellular and require a host to reproduce, whereas bacteria are cellular organisms capable of independent life. Additionally, viruses are generally smaller than bacteria.

Question 2: Are antibiotics effective against viruses? Explain your answer.

Answer: No, antibiotics are not effective against viruses because viruses lack the cellular structures bacteria have, and antibiotics target bacterial processes.

Question 1: A virus infects a cell and produces 100 new viruses every hour. How many viruses will be produced after 4 hours, assuming no immune response or other limiting factors? Show your working.

Answer: Initial virus count = 1; after 1 hour = 100; after 2 hours = 100^2; after 3 hours = 100^3; after 4 hours = 100^4. Therefore, total viruses = 100^4 = 100,000,000.

Question 1: Describe a safe laboratory procedure for studying viruses without risk of infection.

Answer: Use of sealed containment facilities (biosafety cabinets), wearing protective clothing, sterilising equipment, and working with attenuated or inactivated viruses to prevent infection.

Question 1: A study shows that a certain virus infects 50% of individuals exposed to it within 24 hours. If 200 people are exposed, how many are expected to become infected? Show your calculation.

Answer: Expected number infected = 50% of 200 = 0.5 × 200 = 100 people.

Question 1: Explain how vaccination helps protect individuals and the wider community from viral infections. Include the concepts of herd immunity and immune response in your answer.

Answer: Vaccination introduces a harmless form of the virus or its components into the body, stimulating the immune system to produce antibodies. This prepares the immune system to respond quickly if exposed to the actual virus. Widespread vaccination reduces the number of susceptible individuals, thereby establishing herd immunity, which protects those who cannot be vaccinated. This overall reduction in virus transmission helps control outbreaks and prevents epidemics.

Question 1: Describe one way in which viruses have influenced the development of modern medicine or technology.

Answer: Viruses have been used as vectors in gene therapy to deliver healthy genes into patients' cells, helping treat genetic disorders.