Bacterial diseases — AQA GCSE Combined Science
Test yourself on Bacterial diseases with AQA GCSE practice questions.
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Bacterial diseases explained
Salmonella bacteria cause food poisoning when ingested in contaminated food or food prepared in unhygienic conditions.
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The bacteria and the toxins they secrete trigger fever, abdominal cramps, vomiting and diarrhoea. In the UK, poultry are vaccinated against salmonella to reduce the spread of infection to humans. For example, a person may eat undercooked chicken that carries salmonella; the bacteria multiply in the gut and release toxins that irritate the digestive system, producing the symptoms. Vaccinating poultry interrupts this transmission route by reducing the number of infected birds entering the food chain. Understanding this cycle helps explain how hygiene, cooking and vaccination work together to control bacterial disease.
Gonorrhoea is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.
Gonorrhoea is a sexually transmitted disease caused by a bacterium. Symptoms include a thick yellow or green discharge from the vagina or penis and pain on urinating. It is spread by sexual contact. Penicillin once treated gonorrhoea easily, but many resistant strains have appeared, so some antibiotics no longer work. Spread can be controlled by treatment with antibiotics or by using a barrier method of contraception such as a condom. For example, using a condom during sexual contact reduces the transfer of the bacterium between partners, while prompt antibiotic treatment can cure the infection and reduce onward transmission. The rise of resistant strains shows why completing prescribed treatment and reducing transmission are important.
Your focus
- Describe how salmonella food poisoning is spread by bacteria ingested in food or on food prepared in unhygienic conditions.
- Explain how vaccination of poultry in the UK helps control the spread of salmonella.
- Identify fever, abdominal cramps, vomiting and diarrhoea as symptoms caused by salmonella bacteria and the toxins they secrete.
Show all 6 objectives
- Describe the symptoms of gonorrhoea as a thick yellow or green discharge from the vagina or penis and pain on urinating.
- Explain that gonorrhoea is caused by a bacterium, spread by sexual contact, and was easily treated with penicillin until resistant strains appeared.
- Describe how the spread of gonorrhoea can be controlled by antibiotics or by using a barrier method of contraception such as a condom.
Bacterial diseases exam tips
Marking Points
- Salmonella is a bacterium that causes food poisoning.
- Transmission occurs by ingesting contaminated food or food prepared in unhygienic conditions.
- Symptoms include fever, abdominal cramps, vomiting and diarrhoea.
- Symptoms are caused by the bacteria and the toxins they secrete.
- In the UK, poultry are vaccinated against salmonella to control the spread.
- Vaccination reduces the number of infected poultry, lowering the risk of contaminated food reaching consumers.
- Gonorrhoea is a sexually transmitted disease (STD) caused by a bacterium.
- Symptoms include a thick yellow or green discharge from the vagina or penis and pain on urinating.
- Gonorrhoea is spread by sexual contact.
- It was easily treated with the antibiotic penicillin until many resistant strains appeared.
- Spread can be controlled by treatment with antibiotics.
- Spread can be controlled by the use of a barrier method of contraception such as a condom.
Examiner Tips
- 💡When asked how salmonella is spread, name both routes: ingestion of contaminated food and food prepared in unhygienic conditions.
- 💡If asked why poultry are vaccinated, link vaccination to reducing the spread of salmonella to humans through the food chain.
- 💡When describing symptoms, include fever, abdominal cramps, vomiting and diarrhoea, and state that toxins secreted by the bacteria contribute to these symptoms.
- 💡Use the term 'toxins' accurately; do not write 'poisons' unless you also explain that toxins are substances produced by the bacteria.
- 💡When describing gonorrhoea, state that it is a sexually transmitted disease caused by a bacterium and spread by sexual contact.
- 💡If asked about treatment, mention that penicillin was once effective but resistant strains have appeared, so antibiotics are used to control spread.
- 💡When explaining control, give both antibiotic treatment and barrier contraception such as a condom.
- 💡Use the phrase 'thick yellow or green discharge' accurately, and link pain on urinating to the infection.
Common Mistakes
- Thinking that salmonella is a virus: correct this by stating it is a bacterium and that bacterial diseases can be treated with antibiotics, although antibiotics are not always used for mild food poisoning.
- Believing that symptoms are caused only by the bacteria themselves: correct this by explaining that the bacteria secrete toxins, and both the bacteria and toxins cause fever, cramps, vomiting and diarrhoea.
- Confusing vaccination of poultry with treatment of humans: correct this by clarifying that poultry are vaccinated to prevent them carrying and spreading salmonella, which reduces human infection.
- Assuming that food poisoning is always caused by poor personal hygiene: correct this by noting that contaminated food, undercooking and cross-contamination can also spread salmonella.
- Thinking gonorrhoea is caused by a virus: correct this by stating it is caused by a bacterium, which is why antibiotics can be used for treatment.
- Believing penicillin still always treats gonorrhoea easily: correct this by explaining that many resistant strains have appeared, so penicillin is no longer always effective.
- Confusing control methods with symptoms: correct this by separating symptoms (discharge and pain on urinating) from control measures (antibiotics and barrier contraception).
- Assuming any barrier method is equally effective: correct this by specifying a condom as the example given, and explain that it reduces sexual contact transmission.