Drugs in Medicine (Cambridge (CIE) IGCSE Biology)

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Microbiologists test strains of bacteria for antibiotic resistance.

They do this by soaking paper discs in antibiotics and placing them on bacteria growing in Petri dishes.

The paper discs in the centre of Petri dishes E and F in Fig. 1 have been soaked in penicillin. 

Fig. 1

State the type of microorganism that produces penicillin.

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State and explain the evidence from Fig. 1 that suggests that the bacteria in dish F are resistant to penicillin.

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(i)

Explain how bacteria become resistant to antibiotics and how humans can reduce the problem of antibiotic resistance. 

[6]

(ii)

Explain why viral infections cannot be treated with antibiotics.

[1]

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Some bacteria and viruses cause disease but many are useful to the biotechnology industry.

Explain why bacteria are useful in biotechnology.

Some scientists investigated the effect of two antibiotics (methicillin and penicillin) on the growth of two different bacteria.

They used filter paper discs soaked in antibiotic solution and placed the discs on two agar plates, one had been spread with bacteria A and the other with bacteria B.

The filter paper discs were prepared as follows:

1. Control

2. Penicillin

3. Methicillin

Fig. 1 shows the results from the investigation:

Fig. 1

Suggest what the paper disc might have been soaked in for the control.

Describe and explain the results in Fig. 1.

Predict and explain the appearance of a petri dish that is used to grow a strain of bacteria, Bacteria C, which possesses resistance to methicillin and penicillin.

DNA analysis of the three strains of bacteria (A, B and C) suggests an evolutionary link between them.

Bacteria C is thought to have evolved from one of the other two strains.

(i)

Suggest how bacteria C may have evolved from the other strains.

[1]

(ii)

Predict and explain whether Bacteria C is more likely to have evolved from Bacteria A or Bacteria B.

[2]

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Antibiotics have been widely used through the 20^th and 21^st centuries but are losing their effectiveness in medical and veterinary disease treatment. 

Table 1 shows some of the reasons.

Place a tick (✓) in the boxes that are genuine factors why antibiotics can lose their effectiveness in combatting medical and veterinary diseases. 

Table 1

Scientists developing new antibiotics sometimes find a molecule that does not kill the bacteria outright, but merely stops them from reproducing.

Explain why this is generally acceptable in the development of new antibiotics. 

Suggest why antibiotics tend to be effective against bacterial cells but not against animal cells.

A study in a large country analysed levels of three different antibiotics (A, B and C) in stream water leading towards and away from a large urban household waste dumpsite.

Prior to passing the dumpsite, the stream passes through a large urban township with limited sanitation. 

The levels of antibiotics are found in Table 1.

Table 1

Calculate the percentage increase of antibiotic B detected as the stream flows from the township and past the dumpsite. 

Suggest two ways in which antibiotics may have found their way into the water as shown in Table 1.

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Suggest two possible risks of antibiotics entering the environment such as in sewage and wastewater.