IGCSE · Practice questions · Sexually transmitted infections

Block the route, stop the spread.

Six original Cambridge-style questions on sexually transmitted infections, HIV and AIDS, routes of transmission and control measures, including interpreting data.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Route, then barrier.

STI: an infection transmitted through sexual contact.
HIV is a virus that causes an STI; infection may lead to AIDS.
Routes: unprotected sex, shared needles, infected blood, mother to baby.
Control: condoms, fewer partners, testing and treatment, clean needles, screening blood, education.

Recall

[2 marks]

State what is meant by a sexually transmitted infection and name the virus that causes one.

An infection that is transmitted through sexual contact. ✓
HIV (human immunodeficiency virus). ✓

Recall

[3 marks]

Describe three ways in which HIV can be transmitted.

Unprotected sexual contact with an infected person. ✓
Sharing needles (e.g. among drug users) or transfusion of infected blood. ✓
From an infected mother to her baby across the placenta, during birth or in breast milk. ✓

Explain

[2 marks]

Explain the link between HIV and AIDS.

HIV infects and destroys lymphocytes, so over time the immune system is weakened. ✓
The person may then develop AIDS and catch other infections that the body cannot fight. ✓

Explain

[4 marks]

Explain how four different measures can control the spread of STIs such as HIV.

Using condoms: a barrier that prevents exchange of body fluids during sex. ✓
Having fewer sexual partners: reduces the number of contacts through which infection can pass. ✓
Testing and treatment (with contact tracing): infected people know their status, are treated and can protect partners; treatment lowers the virus level. ✓
Not sharing needles / screening donated blood / education (any one, with explanation). ✓

Data

[3 marks]

A computer model of 70 people started with 3 infected. After 10 years, 41 were infected with no control measures and 9 were infected when condoms and clean needles were used.

(a) Calculate the percentage of people infected after 10 years in each case. (b) Explain why the control measures had this effect.

(a) No measures: 41 ÷ 70 × 100 = 58.6% (59%). With measures: 9 ÷ 70 × 100 = 12.9% (13%). ✓
(b) Condoms act as a barrier, so fewer infections pass on through sexual contact. ✓
Clean needles stop the virus spreading through blood between people who inject drugs. ✓

Explain

[2 marks]

A person with an HIV infection is given antibiotics by mistake. Explain why the antibiotics will not cure the infection.

HIV is a virus. ✓
Antibiotics act on bacteria and do not affect viruses (viruses have no cell structures for antibiotics to target). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.