The bacteria that fought back
354 words over 35 numbered lines, then 6 parts worth 13 marks (Modular Unit 2 (4WBI2) style, 12–13 marks). Read the article, answer each part, then open its mark scheme and set your mark.
Illustrative article written for Scholar Lab, not a Pearson text. The biology is real; the studies, people and figures are invented or rounded for practice.
The bacteria that fought back
When penicillin was first used in the 1940s, it seemed like a miracle.
Infections that had killed people for centuries, such as pneumonia and
infected wounds, could suddenly be cured in a few days. Within a few
years, however, doctors noticed that some bacteria were no longer
killed by the drug. Today, infections that do not respond to
antibiotics kill more than a million people every year.
Antibiotics kill bacteria or stop them from growing, but they have no
effect on viruses. Bacteria reproduce very quickly, and every time a
bacterium divides its DNA is copied. Occasionally a mistake is made,
producing a mutation. Most mutations have no effect, but a few give a
bacterium resistance to an antibiotic, for example by producing an
enzyme that breaks the drug down.
When a patient takes an antibiotic, the bacteria that are not
resistant die. Any resistant bacteria survive and reproduce, and they
pass the resistance allele on to their offspring. After a few days,
almost all of the bacteria in the infection may be resistant. This is
why patients are told to finish the whole course of antibiotics, even
if they feel better.
Hospitals are a particular risk, because many patients are already
weak and many antibiotics are used. Bacteria can spread from patient
to patient on the hands of staff, on equipment and on door handles. In
an illustrative hospital study, washing hands with alcohol gel between
patients reduced infections with one resistant bacterium from 48 cases
a year to 18.
Farming adds to the problem. In some countries, antibiotics are added
to the food of healthy chickens and pigs to make them grow faster.
Resistant bacteria from the animals can reach people through meat that
has not been cooked properly, or through water polluted with animal
waste.
Very few new antibiotics have been discovered since the 1980s.
Scientists are now searching for them in unusual places, such as soil
from caves, the mucus on fish skin and bacteria that live on insects.
Others are testing viruses that infect only bacteria. Meanwhile,
doctors are trying to prescribe antibiotics only when they are really
needed.
Read the article. Use the information in the article and your own knowledge to answer the questions. The lines in brackets show where to look; select them to highlight the text.
Use the information in the article and your own knowledge to answer the questions. The lines in brackets show you where to look; select them to highlight the text.
State what is meant by the term mutation.
(1)A patient with a cold asks a doctor for antibiotics. Explain why the doctor refuses.
(2)Explain how a population of bacteria becomes resistant to an antibiotic.
(4)Calculate the percentage decrease in infections after hand washing was introduced. Give your answer to one decimal place.
(2)Suggest why adding antibiotics to the food of healthy animals increases the number of resistant bacteria.
(2)Scientists collect bacteria from cave soil. Describe how they could find out whether these bacteria produce a substance that kills other bacteria.
(2)Total for this question: 13 marks
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