CIE iGCSE Co-Ordinated Science B10. Diseases and immunity Exam Style Questions Paper 4
Question
(a) The total number of new HIV infections in the world is monitored. The results are shown in Fig. 1.1.
(i) Calculate the percentage decrease in the number of new HIV infections between 2000 and 2010 as shown in Fig. 1.1.
▶️Answer/Explanation
Answer: 31%
Explanation: The number of new HIV infections in 2000 was 3.2 million, and in 2010, it was 2.2 million. The decrease is 3.2 – 2.2 = 1.0 million. The percentage decrease is calculated as (1.0 / 3.2) × 100 = 31.25%, which rounds to 31%.
(ii) Suggest three reasons for the decrease in the number of new HIV infections.
▶️Answer/Explanation
Answer: 1. Discovery of routes of transmission
2. Increased use of barrier contraception
3. Screening of blood transfusions
Explanation: The decrease in HIV infections can be attributed to better understanding of how the virus spreads, increased use of protective measures like condoms, and improved screening of blood donations to prevent transmission.
(b) HIV is a virus that targets white blood cells.
(i) State two functions of white blood cells.
▶️Answer/Explanation
Answer: 1. Phagocytosis
2. Antibody production
Explanation: White blood cells play a crucial role in the immune system by engulfing and destroying pathogens (phagocytosis) and producing antibodies to neutralize harmful substances.
(ii) White blood cells are one component of blood. State two other main components of blood.
▶️Answer/Explanation
Answer:
1. Red blood cells
2. Plasma
Explanation: Blood is composed of red blood cells, which transport oxygen, and plasma, the liquid component that carries cells and nutrients throughout the body.
(c) State the name of the barrier that protects the fetus from toxins in the mother’s blood.
▶️Answer/Explanation
Answer: Placenta
Explanation: The placenta acts as a barrier between the mother and fetus, allowing the exchange of nutrients and oxygen while protecting the fetus from harmful substances in the mother’s blood.