CIE A Level Biology Topic 10: Infectious Diseases Exam Questions

About CIE A Level Biology Topic 10: Infectious Diseases

Infectious diseases in the Cambridge 9700 syllabus looks at named diseases, the pathogens that cause them, how they are transmitted and how their spread can be controlled. You need to know cholera, malaria, tuberculosis and HIV/AIDS in detail, including the biological, social and economic factors that affect control. The topic then covers how antibiotics such as penicillin work, why they are ineffective against viruses, and how antibiotic resistance develops and spreads by natural selection. It links forward to immunity in Topic 11 and to selection and evolution at A Level. Questions often give data on disease incidence and ask you to evaluate control methods.

What you need to know

• Cholera Caused by the bacterium Vibrio cholerae; spread by food or water contaminated with faeces. Control: clean water supply, sewage treatment and good hygiene.
• Malaria Caused by Plasmodium species (protoctists); transmitted by female Anopheles mosquitoes. Control: insecticide-treated nets, spraying, draining standing water and antimalarial drugs; resistance in both mosquitoes and Plasmodium makes control difficult.
• Tuberculosis Caused by Mycobacterium tuberculosis and Mycobacterium bovis; spread by airborne droplets and, for M. bovis, unpasteurised milk. Control: BCG vaccination, contact tracing and long courses of several antibiotics.
• HIV/AIDS HIV is a retrovirus spread by sexual intercourse, infected blood and from mother to child. Control: condoms, screening blood, not sharing needles and antiretroviral drugs.
• Antibiotics Penicillin inhibits enzymes that build cross-links in bacterial cell walls, so walls weaken and cells burst by osmosis. Antibiotics do not affect viruses, which lack cell walls and their own metabolism.
• Antibiotic resistance Random mutations give some bacteria resistance; antibiotic use selects for them, and resistance genes can spread on plasmids. Reduce resistance by completing courses and limiting unnecessary prescribing.

Common mistakes in Topic 10: Infectious Diseases

• Saying bacteria become resistant because they get used to the antibiotic; resistance comes from random mutations that are then selected for.
• Stating that the mosquito causes malaria; the pathogen is Plasmodium and the mosquito is the vector.
• Writing that antibiotics can treat HIV; antibiotics do not work on viruses, and antiretroviral drugs are used.
• Confusing infectious disease with non-infectious disease; infectious diseases are caused by pathogens and can be transmitted.
• Giving only biological control measures when asked about social and economic factors such as poverty, crowded housing and access to healthcare.

Try three Topic 10: Infectious Diseases exam-style questions