Question 1: Define a virus and describe its basic structure.

Answer: A virus is a tiny infectious agent that consists of genetic material (DNA or RNA) enclosed within a protein coat called a capsid. It has no cellular structure and cannot reproduce on its own.

Question 2: Explain how a virus infects a host cell and replicates.

Answer: A virus attaches to a specific receptor on the surface of a host cell, injects its genetic material into the cell, hijacks the cell's machinery to produce new virus particles, and then causes the cell to burst, releasing the new viruses.

Question 1: A virus has a replication cycle of 8 hours. How many new viruses will be produced after 48 hours, starting from one virus? Show your working.

Answer: Number of cycles = 48 hours / 8 hours = 6 cycles. Total viruses = 2^6 = 64. Starting from 1 virus, total = 64 viruses after 48 hours.

Question 2: Calculate the surface area of a spherical virus with a diameter of 100 nm. Use the formula for the surface area of a sphere: 4πr^2. Provide your answer in square nanometers (nm^2).

Answer: Radius r = 50 nm; Surface area = 4 × π × (50)^2 ≈ 4 × 3.1416 × 2500 ≈ 31,416 nm^2.

Question 1: Design a basic experiment to test whether a virus can infect a particular type of cell. Outline the main steps and safety precautions.

Answer: First, obtain a culture of the target cells and a sample containing the virus. In a sterile environment, expose the cells to the virus sample. Include controls without the virus. Observe for signs of infection such as cell death or changes. Safety precautions include working in a biosafety cabinet, wearing protective clothing, and sterilising waste. Dispose of infected materials according to biosafety protocols.

Question 1: A study reports that a certain virus causes 70% of infected individuals to develop symptoms within 3 days. In a sample of 150 infected individuals, how many are expected to show symptoms within this period? Explain your reasoning.

Answer: Expected number = 70% of 150 = 0.70 × 150 = 105 individuals. This is based on the reported percentage of symptomatic cases within 3 days.

Question 1: Describe the main differences between viruses and bacteria in terms of structure and reproduction.

Answer: Viruses are much smaller than bacteria, have no cellular structure, and consist of genetic material enclosed in a protein coat. They cannot reproduce independently and require a host cell. Bacteria are single-celled organisms with a cell wall, membrane, cytoplasm, and genetic material, and they can reproduce independently through cell division.

Question 2: Multiple Choice: Which of the following is NOT a characteristic of viruses? A) They can reproduce independently. B) They consist of genetic material and protein coat. C) They require a host cell to reproduce. D) They are smaller than bacteria.

Answer: A) They can reproduce independently.

Question 1: Explain how viruses are used in the development of vaccines and give an example of a vaccine that uses a virus as a vector.

Answer: Viruses are modified to carry harmless genetic material from other pathogens to stimulate an immune response without causing disease. An example is the use of adenoviruses in some COVID-19 vaccines as vectors to deliver genetic instructions to cells.