Exam questions · Biology · Health and Communicable Disease
How Communicable Diseases Spread
- 7 exam questions
- 22 marks
- 8 quick checks
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1 Name [4 marks]
Name the four types of pathogen that cause communicable diseases.
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Model answer
Viruses, bacteria, protists and fungi.
Mark scheme
- Viruses — 1 mark
- Bacteria — 1 mark
- Protists — 1 mark
- Fungi — 1 mark
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2 Describe [3 marks]
Describe three ways in which a communicable disease can be spread from one person to another.
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Model answer
Pathogens can pass by direct contact, such as through blood or sexual contact. They can be breathed in as droplets that are released when an infected person coughs or sneezes. They can be spread in contaminated food or water that is swallowed.
Mark scheme
- Direct contact (touch, blood or body fluids) — 1 mark
- In the air in droplets from coughs and sneezes — 1 mark
- In contaminated water or food that is taken in (accept vectors) — 1 mark
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3 Explain [3 marks]
Malaria is caused by a protist. Explain how the disease is spread from one person to another.
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Model answer
The protist is carried by a vector, which is the female Anopheles mosquito. The mosquito feeds on the blood of an infected person and takes up the protist. When it bites another person, it passes the protist into that person's blood, so that the disease is spread. The mosquito is not harmed by the protist.
Mark scheme
- The mosquito is a vector that carries the pathogen — 1 mark
- It takes up the protist when it feeds on an infected person — 1 mark
- It passes it into the blood of another person when it bites — 1 mark
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4 Explain [3 marks]
After flooding in a town, there is an outbreak of cholera. Explain how the flooding may have caused the outbreak.
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Model answer
The flood water can mix sewage with the supply of drinking water, so that the water is contaminated with the bacteria that cause cholera. People who drink the water take the bacteria into their gut. The bacteria reproduce and release toxins, which cause the disease, and it spreads rapidly to many people who use the same water.
Mark scheme
- Sewage mixes with the drinking water, so it contains the cholera bacteria — 1 mark
- People who drink the water take in the bacteria — 1 mark
- The disease spreads quickly, because many people use the same supply — 1 mark
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5 Describe [3 marks]
Tobacco mosaic virus infects tobacco plants. Describe two ways in which a plant virus can be spread from one plant to another.
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Model answer
The virus can be passed in the sap on the hands or tools of workers who touch an infected plant and then a healthy plant. It can also be carried by insects, such as aphids, that feed on an infected plant and then on healthy plants. It can also pass by direct contact between leaves.
Mark scheme
- Spread by contact with infected plants or sap, on hands or tools — 1 mark
- Spread by insect vectors such as aphids — 1 mark
- Development of one of the methods, such as that the vector feeds on the sap — 1 mark
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6 Calculate [3 marks]
A single bacterium divides once every 30 minutes. Calculate the number of bacteria that could be produced from a single bacterium after 4 hours. Give your answer in standard form.
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Model answer
4 hours is 240 minutes, and \(240 \div 30 = 8\) divisions. The number of bacteria is \(2^8 = 256\), which is \(2.56 \times 10^2\) in standard form.
Mark scheme
- 8 divisions — 1 mark
- \(2^8 = 256\) — 1 mark
- \(2.56 \times 10^2\) — 1 mark
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7 Calculate [3 marks]
Source: A town has a population of 40 000. A random sample of 500 people was tested for an infection, and 30 of the people had the infection. Estimate the number of people in the town who have the infection, and give one reason why the estimate may not be accurate.
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Model answer
\(\frac{30}{500} = 0.06\), and \(0.06 \times 40\,000 = 2400\) people. The estimate may not be accurate because the sample is small and may not be representative of the whole town.
Mark scheme
- \(30 \div 500 = 0.06\) — 1 mark
- 2400 people — 1 mark
- A reason, such as that the sample may not be representative or is small — 1 mark
Quick check
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1
Which type of pathogen has hyphae and spores?
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C: Fungi
Fungi are made of threads called hyphae and they reproduce by spores.
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2
How does the flu virus spread?
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A: In droplets in the air
Droplets from coughs and sneezes contain the virus and are breathed in by other people.
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3
What is a vector?
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D: An organism that carries a pathogen between hosts
A vector carries a pathogen from one host to another without being affected by it.
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4
Which disease is spread in contaminated drinking water?
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B: Cholera
Cholera is caused by bacteria that spread in water contaminated with sewage.
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5
How do the spores of barley powdery mildew mainly spread?
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C: On the wind
Fungal spores are very light and are carried on the wind.
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6
Which of these protists causes malaria?
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A: A single-celled organism with a nucleus
Malaria is caused by a protist, carried by Anopheles mosquitoes.
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7
One bacterium divides every 20 minutes. How many bacteria are there after 2 hours?
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D: 64
2 hours is 6 divisions, and 2 to the power 6 is 64.
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8
In a sample of 100 people, 8 have a disease. About how many in a population of 5 000 would have it?
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B: 400
8 divided by 100 is 0.08, and 0.08 multiplied by 5 000 is 400.