Question 1: Define a virus and explain how it differs from bacteria.

Answer: A virus is a microscopic infectious agent that requires a host cell to reproduce, consisting of genetic material (DNA or RNA) enclosed in a protein coat. Unlike bacteria, viruses are not cells and cannot carry out metabolic processes on their own.

Question 2: Describe the basic mechanism by which viruses infect host cells.

Answer: Viruses infect host cells by attaching to specific receptors on the cell surface, then injecting their genetic material into the cell. This hijacks the cell's machinery to produce new virus particles, which are then released to infect other cells.

Question 3: Explain why viruses are considered obligate parasites.

Answer: Viruses are considered obligate parasites because they cannot reproduce or carry out metabolic processes without invading a host cell.

Question 1: A virus infects 1,000 cells in a culture. If each infected cell produces 10,000 new viruses during its lifecycle, how many viruses are produced in total?

Answer: 10000000

Question 2: Calculate the infection rate per hour if 200 new infections are recorded over a 4-hour period in a population of 10,000 susceptible individuals.

Answer: 50

Question 1: Describe a safe method to investigate the effect of a disinfectant on virus particles in a laboratory setting.

Answer: Use a virus sample in a controlled environment, apply the disinfectant, and then test for remaining infectivity using cell cultures or PCR. Wear appropriate PPE, work in a biosafety cabinet, and dispose of materials following safety protocols.

Question 2: Identify two variables that must be controlled in an experiment testing the effectiveness of antiviral drugs.

Answer: Concentration of the virus, exposure time, temperature, and type of cell used for testing.

Question 1: A study recorded the number of virus particles in a sample over a 24-hour period: 100, 500, 2000, 8000, 32000. Describe the trend observed and suggest a possible biological explanation.

Answer: The data shows an exponential increase in virus particles over time, indicating rapid replication. This suggests the virus is actively infecting cells and reproducing quickly, leading to a sharp rise in virus quantity.

Question 2: Based on the data provided, estimate the fold increase in virus particles from 0 to 24 hours.

Answer: 320 times (from 100 to 32000).

Question 1: Explain how vaccines can help prevent viral infections. (6 marks)

Answer: Vaccines introduce a harmless part of the virus, such as a protein or inactivated virus, to the immune system. This stimulates the production of antibodies and memory cells, enabling the body to recognise and fight the virus quickly if encountered again, thereby preventing infection.

Question 2: Which of the following is NOT a characteristic of viruses? A) They have genetic material (DNA or RNA) B) They can reproduce independently C) They require a host cell to reproduce D) They are smaller than bacteria

Answer: B

Question 1: Describe how understanding virus replication has contributed to the development of antiviral medicines.

Answer: Knowledge of virus replication cycles has enabled scientists to identify stages where drugs can inhibit viral processes, such as blocking enzyme functions or preventing viral entry into cells, leading to effective antiviral medicines.

Question 2: Discuss the importance of vaccination programs in controlling viral outbreaks in populations.

Answer: Vaccination programs help establish herd immunity by reducing the number of susceptible individuals, thereby limiting the spread of the virus. This is crucial in controlling outbreaks, protecting vulnerable groups, and reducing the overall disease burden in society.