Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B15.5 — Sexually transmitted infections (Part (a))
• Topic B9.4 — Blood (Part (b))
• Topic B15.4 — Sexual reproduction in humans (Part (c))
(a)(i) 31%
Reading from Fig. 1.1: infections in 2000 \( = 3.2 \) million, in 2010 \( = 2.2 \) million.
Decrease \( = 3.2 – 2.2 = 1.0 \) million.
Percentage decrease \( = \dfrac{1.0}{3.2} \times 100 = 31\% \).
(a)(ii) Any three from:
Discovery of routes of transmission.
Increased use of barrier contraception / abstinence.
Screening of blood transfusions.
Reduced drug use / use of clean needles.
Monitoring / testing / screening for HIV.
Increased education / awareness.
(b)(i) Phagocytosis; antibody production.
White blood cells defend the body by engulfing pathogens (phagocytosis).
They also produce antibodies that neutralise pathogens or toxins.
(b)(ii) Red blood cells; plasma (also accept platelets).
Blood is made up of red blood cells, white blood cells, platelets, and plasma.
Red blood cells carry oxygen, and plasma is the liquid that transports cells and dissolved substances.
(c) Placenta
The placenta separates the mother’s and fetus’s blood supplies.
It allows exchange of nutrients, oxygen, and waste while acting as a barrier to many toxins and pathogens.
