How Diseases Spread and Are Prevented

1. 1 State [2 marks]

   State how (a) cholera and (b) tuberculosis are spread.

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   Model answer

   (a) Cholera is spread in water that has been contaminated by sewage. (b) Tuberculosis is spread in droplets in the air, when an infected person coughs or sneezes.

   Mark scheme

   • Cholera: water — 1 mark
   • TB: airborne droplets — 1 mark
2. 2 Define [2 marks]

   Define the term vector, and give an example.

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   Model answer

   A vector is an organism that carries a pathogen from one host to another. An example is the Anopheles mosquito, which carries malaria.

   Mark scheme

   • Carries a pathogen between hosts — 1 mark
   • Example — 1 mark
3. 3 Describe [3 marks]

   Describe three ways in which the spread of malaria can be reduced.

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   Model answer

   Any three from: sleeping under insecticide-treated mosquito nets; spraying insecticide; draining standing water where mosquitoes breed; using repellents; taking anti-malarial drugs; treating infected people quickly.

   Mark scheme

   • First method — 1 mark
   • Second method — 1 mark
   • Third method — 1 mark
4. 4 Explain [3 marks]

   Explain how providing a safe supply of drinking water reduces the spread of cholera.

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   Model answer

   Cholera bacteria are spread in water that is contaminated by sewage. A safe supply of water, which is treated or protected from sewage, does not contain the bacteria. People who drink it do not take in the bacteria, so they do not get infected.

   Mark scheme

   • Cholera spread in contaminated water — 1 mark
   • Safe water free from bacteria — 1 mark
   • People do not take in the bacteria — 1 mark
5. 5 Calculate [3 marks]

   After an area was sprayed with insecticide, the number of malaria cases fell from 1200 to 420 per year. Calculate the percentage reduction in cases.

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   Model answer

   The fall is 1200 − 420 = 780. The percentage reduction is 780 ÷ 1200 × 100 = 65%.

   Mark scheme

   • Fall of 780 — 1 mark
   • Divides by 1200, times 100 — 1 mark
   • 65% — 1 mark
6. 6 Evaluate [6 marks]

   Evaluate the use of mosquito nets and insecticide spraying to reduce the spread of malaria.

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   Model answer

   Insecticide-treated nets are cheap and simple, and they protect people while they sleep, which is when the mosquitoes bite. They also kill the mosquitoes that land on them. However, they only protect people when used properly, and do not protect them during the day. Spraying insecticide kills large numbers of mosquitoes and can protect a whole community. But it must be repeated, can be costly, harms other insects and the environment, and the mosquitoes may become resistant. Overall, nets are the most cost-effective, and the best results come from using several methods, such as nets, drainage and rapid treatment, together.

   Mark scheme

   • Nets: cheap and protect while sleeping — 1 mark
   • Nets: limitation (proper use, not during day) — 1 mark
   • Spraying kills many mosquitoes — 1 mark
   • Spraying: cost, environment or resistance — 1 mark
   • Combination of methods — 1 mark
   • A reasoned conclusion — 1 mark

Quick check

1. 1

   How is cholera spread?

   1. AIn contaminated water
   2. BIn droplets from a cough
   3. CBy mosquito bites
   4. DBy airborne spores
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   A: In contaminated water

   Cholera spreads in water that is contaminated by sewage.

2. 2

   How is tuberculosis spread?

   1. AIn water
   2. BBy mosquitoes
   3. CIn droplets in the air
   4. DBy sexual contact
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   C: In droplets in the air

   TB bacteria are carried in droplets that are coughed or sneezed out, and breathed in by others.

3. 3

   Which organism is the vector of malaria?

   1. AThe flea
   2. BThe Anopheles mosquito
   3. CThe housefly
   4. DThe rat
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   B: The Anopheles mosquito

   The female Anopheles mosquito carries the Plasmodium protist.

4. 4

   Which measure helps to prevent cholera?

   1. AMosquito nets
   2. BCutting down trees
   3. CFace masks
   4. DTreating sewage and providing clean water
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   D: Treating sewage and providing clean water

   Clean water and sewage treatment keep the bacteria out of drinking water.

5. 5

   Which measure helps to prevent malaria?

   1. ASleeping under a mosquito net
   2. BBoiling food
   3. CUsing a mask
   4. DWashing hands
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   A: Sleeping under a mosquito net

   Mosquito nets stop the vector from biting people.

6. 6

   How is ash dieback spread over long distances?

   1. ABy mosquito bites
   2. BBy drinking water
   3. CBy airborne spores and imported trees
   4. DBy animals' faeces
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   C: By airborne spores and imported trees

   The fungus makes spores which are carried by the wind, and it also spreads on imported trees.

7. 7

   Why does draining standing water reduce malaria?

   1. AIt kills Plasmodium
   2. BMosquitoes breed there
   3. CIt cleans the air
   4. DIt treats the sick
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   B: Mosquitoes breed there

   Mosquitoes lay their eggs in standing water, so there are fewer mosquitoes.

8. 8

   Cases of a disease fall from 500 to 200. What is the percentage reduction?

   1. A30%
   2. B40%
   3. C50%
   4. D60%
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   D: 60%

   The fall is 300, and \(300 \div 500 \times 100 = 60\%\).

9. 9

   John Snow removed the handle of a water pump in 1854. What did this show?

   1. ACholera was spread through water
   2. BCholera was spread through the air
   3. CThe pump was made of poison
   4. DCholera was caused by mosquitoes
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   A: Cholera was spread through water

   The outbreak of cholera declined, which showed that the disease was spread in the water supply.