2 (a) The human immunodeficiency virus (HIV) can cause AIDS - Edexcel - GCSE Biology - Question 2 - 2020 - Paper 1

The specific immune system employs various strategies to protect the body against disease:

1. Antibody Production: Once a pathogen is detected, the immune system activates B cells which produce antibodies. These antibodies bind to specific antigens present on the pathogens, neutralizing them or marking them for destruction by other immune cells.

2. T-cell Response: The immune system activates T cells, especially cytotoxic T cells, that directly kill infected cells. Helper T cells also play a role by coordinating the immune response and enhancing the action of B cells.

3. Memory Cells: After an infection is cleared, some B and T cells persist as memory cells. These cells provide long-term immunity by rapidly responding to subsequent exposures to the same pathogen.

To calculate the number of people diagnosed with measles in Belgium, follow these steps:

1. Substitution of Values: We know from Figure 1 that 21.00 people per million in Belgium were diagnosed with measles.

2. Calculation:

   ext{Number of people} = 21.00 imes 11.18 ext{ million} = 234.78 ext{ million}

3. Final Answer: Rounding this to three significant figures gives us 235.

Each country represented in Figure 1 has a different size population, which allows for comparisons to be made between countries. This distinction helps in understanding the prevalence of measles relative to the size of each population.

One factor that could affect the number of people diagnosed with measles is vaccination. Higher vaccination rates generally lead to lower incidences of measles, while lower rates can result in outbreaks, impacting the number of diagnosed cases.