Question 1: Define the term 'antigen' and explain its role in the immune response.

Answer: An antigen is a substance that triggers an immune response, usually a protein on the surface of pathogens, which stimulates the production of antibodies.

Question 2: Describe the main function of white blood cells in defending the body against pathogens.

Answer: White blood cells identify, attack, and destroy pathogens through processes such as phagocytosis and antibody production.

Question 3: Explain how vaccination helps to protect individuals and populations from infectious diseases.

Answer: Vaccination introduces a harmless form of a pathogen or its antigens to stimulate the immune system to produce memory cells, providing immunity against future infections.

Question 1: A vaccine produces an average of 10^5 antibody molecules per millilitre of blood. If a person's blood contains 5 litres of blood, how many antibody molecules are present in total?

Answer: 5 x 10^5 x 10^5 = 5 x 10^10 antibody molecules

Question 2: Calculate the percentage increase in antibody production if a booster shot increases antibody levels from 2 x 10^5 to 8 x 10^5 per millilitre.

Answer: [(8 x 10^5 - 2 x 10^5) / 2 x 10^5] x 100 = 300%

Question 1: Design a simple experiment to test the effectiveness of a new vaccine against a specific pathogen. Describe the key variables, control measures, and safety precautions.

Answer: Students should outline that they will have at least two groups: vaccinated and unvaccinated (control). Variables include vaccine dosage and timing. Controls should include placebo injections. Safety precautions include wearing protective clothing, sterilising equipment, and proper disposal of biological waste. The experiment involves exposing both groups to the pathogen and observing the immune response or infection rates.

Question 1: A study shows that after vaccination, 95% of participants developed detectable antibody levels within two weeks, while only 20% of unvaccinated individuals showed similar levels. What does this data suggest about the vaccine's effectiveness?

Answer: The data suggests that the vaccine is highly effective in stimulating an immune response, with a significant increase in antibody production among vaccinated individuals.

Question 1: Describe the process by which the human body recognises and responds to a new pathogen, including the roles of antigens and memory cells. (6 marks)

Answer: The body recognises a new pathogen through its antigens, which are identified by white blood cells. These cells produce specific antibodies that bind to the antigens, neutralising the pathogen. Some white blood cells become memory cells, which remain in the bloodstream and enable a faster, stronger response if the same pathogen infects the body again. This process forms the basis of immunity.

Question 1: Explain how the development of mRNA vaccines, such as those for COVID-19, utilises knowledge of human defence systems.

Answer: mRNA vaccines use a piece of genetic material to instruct cells to produce a pathogen's antigen, triggering an immune response and memory cell formation, which provides immunity without exposing the person to the live pathogen.