AQA GCSE Biology 4.3.1 Communicable Diseases Exam Questions

About AQA GCSE Biology 4.3.1 Communicable Diseases

Communicable diseases is the main part of AQA Infection and response, examined on Paper 1. You need to know how bacteria, viruses, fungi and protists cause disease and spread, and learn the named examples on the specification: measles, HIV, tobacco mosaic virus, salmonella, gonorrhoea, rose black spot and malaria. The section also covers non-specific defences, how white blood cells respond, vaccination, antibiotics and painkillers, and how new drugs are discovered and tested. Examiners often ask how spread can be reduced, how vaccination prevents illness, why antibiotics do not work on viruses, and how clinical trials are designed.

What you need to know

• Pathogens and spread Pathogens are microorganisms that cause infectious disease. Bacteria may produce toxins that damage tissues; viruses live and reproduce inside cells, causing damage. Pathogens spread by direct contact, by water or by air, and spread can be reduced by hygiene, isolating infected individuals, destroying vectors and vaccination.
• Viral diseases Measles: fever and red skin rash, spread by inhalation of droplets, prevented by vaccination. HIV: flu-like illness at first, controlled with antiretroviral drugs, attacks immune cells and can lead to AIDS; spread by sexual contact or exchange of body fluids. Tobacco mosaic virus: mosaic pattern of discolouration on leaves, reducing photosynthesis.
• Bacterial, fungal and protist diseases Salmonella causes food poisoning (fever, cramps, vomiting, diarrhoea); UK poultry are vaccinated. Gonorrhoea is a sexually transmitted disease with thick yellow or green discharge and pain on urinating, treated with antibiotics, though many strains are resistant to penicillin. Rose black spot is a fungus causing purple or black spots on leaves. Malaria is caused by a protist carried by mosquitoes (vectors) and causes recurrent fever.
• Non-specific human defences The skin, hairs and mucus in the nose, cilia and mucus in the trachea and bronchi, and hydrochloric acid in the stomach help stop pathogens entering or surviving in the body.
• White blood cells White blood cells defend the body by phagocytosis, by producing antibodies specific to the antigens on a pathogen, and by producing antitoxins that neutralise toxins.
• Vaccination A vaccine contains small quantities of dead or inactive pathogen. White blood cells produce antibodies, so if the real pathogen enters later, antibodies are produced rapidly and the person does not become ill. If a large proportion of a population is vaccinated, spread is reduced.
• Drugs and drug development Antibiotics such as penicillin kill bacteria inside the body but not viruses; painkillers treat symptoms only. Digitalis comes from foxgloves, aspirin from willow, and penicillin was discovered by Alexander Fleming from Penicillium mould. New drugs are tested for toxicity, efficacy and dose in preclinical tests on cells, tissues and live animals, then in clinical trials on healthy volunteers and patients, often double blind with a placebo.

Common mistakes in 4.3.1 Communicable Diseases

• Saying antibiotics kill viruses. Antibiotics only work on bacteria; viral diseases are treated with antivirals or by easing symptoms.
• Saying white blood cells 'eat' pathogens without naming the process. Use the term phagocytosis and say the pathogen is engulfed and digested.
• Saying vaccines contain antibodies. Vaccines contain dead or inactive pathogens (antigens) that stimulate white blood cells to make antibodies.
• Saying antibodies kill any pathogen. Antibodies are specific to one antigen.
• Describing a double blind trial as one where patients do not know what they take. In a double blind trial neither the patients nor the doctors know who has the drug and who has the placebo.

Try three 4.3.1 Communicable Diseases exam-style questions