Sexually transmitted infections — Cambridge IGCSE Biology
What an STI is, HIV and AIDS, how HIV is transmitted, and how the spread of STIs is controlled.
Revision notes
1 short note, in the order of the specification. Each one in short:
A sexually transmitted infection (STI) is an infection that is transmitted through sexual contact. HIV is a pathogen that causes an STI and may lead to AIDS. HIV spreads by sexual contact, blood-to-blood contact such as shared needles, and from mother to baby. Using condoms, not sharing needles and screening blood all help control its spread.
Exam questions
5 exam-style questions (11 marks), each with its mark scheme.
Answer the questionsFlashcards
4 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of reproduction on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
What is a sexually transmitted infection?
Show answer
An infection that is transmitted through sexual contact.
What may HIV infection lead to?
Show answer
AIDS.
Give two ways in which HIV can be transmitted.
Show answer
Any two from: sexual contact, sharing needles or contact with infected blood, from an infected mother to her baby.
How does a condom reduce the spread of STIs?
Show answer
It is a barrier that stops body fluids passing between partners.
Frequently asked questions
How is HIV transmitted?
HIV is transmitted in three main ways. It passes by sexual contact with an infected person, when body fluids pass from one person to the other. It passes by blood-to-blood contact, such as sharing needles used to inject drugs. It can also pass from an infected mother to her baby, across the placenta, during birth or in breast milk.
What is the difference between HIV and AIDS?
HIV is the virus, and AIDS is the condition that HIV infection may lead to. HIV, human immunodeficiency virus, is a pathogen that causes a sexually transmitted infection. It damages white blood cells of the immune system, so the body finds it harder to fight other infections. AIDS stands for acquired immune deficiency syndrome.
How can the spread of STIs be controlled?
The spread of STIs is controlled by using condoms, which act as a barrier so body fluids cannot pass between people. Other methods are not sharing needles, screening blood used for transfusions, testing and informing partners, having fewer sexual partners, and drug treatment, which reduces the amount of HIV in the body.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026