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

The specific immune system defends the body through two main processes: humoral immunity and cell-mediated immunity.

1. Humoral Immunity: This involves B cells that produce antibodies specific to pathogens. When a pathogen is detected, B cells are activated and differentiate into plasma cells that secrete antibodies. These antibodies bind to the pathogens, neutralizing them and marking them for destruction by other immune cells.

2. Cell-Mediated Immunity: This process involves T cells, specifically cytotoxic T lymphocytes, that recognize and destroy infected cells. Helper T cells play a role in activating B cells and enhancing the immune response.

Additionally, memory cells are formed after infection, allowing for a quicker and more effective response upon re-exposure to the same pathogen.

To calculate the number of people in Belgium diagnosed with measles:

1. Identify the measles diagnosis rate for Belgium from Figure 1, which is 21.00 per million.

2. Calculate the total number of people diagnosed with measles:

   $ext{Number of people diagnosed} = 21.00 imes 11.18$

3. Performing the calculation:

   $ext{Number of people diagnosed} = 234.78$

4. Rounding to three significant figures gives:

   $235$

Comparing disease data between countries is easier because each country has a different size population, which allows for adjustments in statistics to ensure fairness in comparisons. Additionally, this approach helps identify trends or outbreaks that may be localized or widespread.

Factors that may affect the number of diagnosed measles cases include:

1. Vaccination Rates: Higher vaccination coverage leads to lower incidences of measles.
2. Reporting and Diagnosis Systems: Countries with efficient reporting systems may diagnose more cases.
3. Access to Quality Healthcare: Better healthcare access results in more cases being identified.
4. Environmental Factors: Local conditions, such as population density and proximity to outbreaks, can influence spread.