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 against disease through a series of coordinated processes:

1. Recognition of Antigens: When pathogens enter the body, the immune system recognizes specific antigens (molecules on the pathogen's surface).

2. Activation of Immune Cells: T lymphocytes (T cells) are activated, which can directly kill infected cells or help B lymphocytes (B cells) to produce antibodies.

3. Production of Antibodies: B cells produce antibodies that bind to the pathogens, neutralizing them or marking them for destruction by other immune cells.

4. Memory Cell Formation: After an infection is cleared, some T and B cells become memory cells, allowing for a faster and stronger response if the same pathogen tries to invade again in the future.

To calculate the number of people diagnosed with measles in Belgium, we use the formula:

$ext{Number of people} = ext{Measles rate} imes ext{Population}$

Substituting the given values:
$ext{Number of people} = 21.00 imes 11.18 ext{ million}$
$= 234.78 ext{ million}$

Rounding to three significant figures, the answer is 235.

Having data from different countries is useful because:

1. Comparison of Health Policies: It allows for the comparison of healthcare policies and their effectiveness in managing diseases.
2. Understanding Disease Spread: It helps to analyze how diseases spread in various populations and the impact of prevention measures.

One factor that could affect the number of people diagnosed with measles is vaccination rates. Higher vaccination coverage in a country generally leads to lower incidence of measles.