Microbiology and pathogensEdexcel A-Level Biology B: Topic test

20 questions, 54 marks

Edexcel A-Level Biology B

Microbiology and pathogens topic test

Total 54 marks

Name

Class

Date

1
A student monitors the growth of a bacterial culture in nutrient broth at 37 °C. Every 30 minutes she removes a small sample from the flask and measures its turbidity with a colorimeter.
(a)
Why does the turbidity of the culture increase as the bacteria grow?
[1 mark]
AMore cells scatter more of the light passing through the broth.
BEach cell becomes larger and absorbs more light as the culture ages.
CThe broth cools and becomes cloudy.
DThe bacteria release a coloured pigment as soon as they divide.
(b)
The student passes the neck of the flask through a Bunsen flame each time she removes the bung. What is the main reason for this?
[1 mark]
ATo kill the bacteria already in the broth
BTo create an upward air current that prevents microorganisms in the air entering the flask
CTo raise the temperature of the broth to 37 °C
DTo increase the oxygen concentration in the broth
(c)
Explain why turbidity readings would give a higher value for the number of bacteria than a viable count when the culture is in the death phase.
[2 marks]
Total for question 1: 4 marks
2
A teenager develops a fever, low blood pressure and a widespread rash after wearing a tampon for much longer than recommended. Staphylococcus aureus is growing in the tampon but is not found in her blood. A doctor explains that bacteria such as Salmonella also harm the body, but through endotoxins rather than exotoxins.
(a)
What name is given to a toxin that is secreted into the surroundings by living Staphylococcus aureus bacteria?
[1 mark]
AEndotoxin
BAntigen
CExotoxin
DAntibody
(b)
Which statement about the endotoxins of Salmonella is correct?
[1 mark]
AThey are secreted by living bacteria as soluble proteins.
BThey are made only by bacteria that invade the host's cells.
CThey are enzymes made by the host's cells in response to infection.
DThey are components of the bacterial cell wall that are released when the cells break down.
(c)
Explain how the teenager has symptoms throughout her body even though the bacteria are found only in the tampon.
[2 marks]
Total for question 2: 4 marks
3
Patients with tuberculosis must take a combination of three or four different antibiotics for at least six months. Some patients feel better after a few weeks and stop taking the tablets.
(a)
Explain how patients stopping treatment early can lead to the spread of antibiotic-resistant bacteria.
[3 marks]
(b)
Explain why taking a combination of antibiotics reduces the chance that resistant bacteria will develop.
[4 marks]
Total for question 3: 7 marks
4
An elderly man is given a seasonal influenza vaccine in October. In January he is exposed to an influenza virus with the same surface antigens as the vaccine, and he does not become ill. His granddaughter, who was not vaccinated, is infected by the same virus. She develops influenza and recovers after a week.
(a)
Explain why the man did not become ill in January.
[6 marks]
(b)
Describe how the granddaughter's immune system eliminated the virus during her first infection.
[6 marks]
Total for question 4: 12 marks
5
In 1999 a new race of the stem rust fungus, Puccinia graminis, appeared in Uganda. Its spores are carried long distances by the wind, and it can infect wheat varieties that were resistant to earlier races. Wheat in many regions is grown as a single genetically uniform variety.
(a)
How is the stem rust fungus mainly spread between wheat fields?
[1 mark]
ABy mosquitoes that feed on the wheat
BBy droplets released when infected plants cough
CBy contaminated drinking water
DBy spores carried on the wind
(b)
Which statement describes the pathogenic effect of stem rust on wheat?
[1 mark]
ABacterial exotoxins block photosynthesis in the leaves.
BFungal hyphae grow into the stem tissues and absorb nutrients, which reduces the yield of grain.
CA virus takes over the plant cells and replicates inside them.
DSpores block the stomata so that gas exchange stops and the plant dies at once.
(c)
Suggest why the new race spreads rapidly through regions where only one variety of wheat is grown.
[2 marks]
Total for question 5: 4 marks
6
In a region of West Africa where malaria is endemic, a trial releases large numbers of sterile male Anopheles mosquitoes to reduce the mosquito population. The research team publishes its results in a scientific journal before the national health service decides whether to adopt the method.
(a)
What does it mean to say that malaria is endemic in the region?
[1 mark]
AThe disease is constantly present in the population
BThe disease has spread to many countries at once
CThe disease is present only in epidemic outbreaks
DThe disease affects only the mosquito population
(b)
What is the role of the scientific community in validating the trial?
[1 mark]
AChoosing the method with the lowest cost
BMaking sure all residents agree to take part
CScrutinising the methods and data, for example by peer review, and repeating the work
DPreventing results being published before a decision is made
(c)
Suggest two social or economic implications for the region if this method controls malaria successfully.
[2 marks]
Total for question 6: 4 marks
7
In a town of 12 000 people a vaccine is offered against a viral disease. The vaccine makes 90% of the people who receive it immune. In one year 80% of the population are vaccinated. Babies under six months are too young to be vaccinated.
(a)
Calculate the percentage of the town's population that became immune as a result of the vaccination.
[3 marks]
(b)
Explain how the vaccination programme can protect the babies, and explain one problem that arises if a growing proportion of parents choose not to vaccinate their children.
[4 marks]
Total for question 7: 7 marks
8
A hospital infection control team finds methicillin-resistant Staphylococcus aureus (MRSA) on the bed rails of a ward. Patients with open wounds are at risk. The team swabs the rails, grows the bacteria on agar plates and later reviews the hospital's antibiotic prescribing and hand-hygiene policy.
(a)
Describe how the team could isolate a single species of bacterium from the mixed sample on the swab using streak plating, using aseptic technique and working safely.
[6 marks]
(b)
Explain how antibiotic resistance in Staphylococcus aureus has developed and spread in hospitals, and why it is difficult to control.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).