Drugs in Medicine (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

Extended Tier Only

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

Extended Tier Only

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]

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:

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 (C), which possesses resistance to methicillin and penicillin.

Extended Tier Only

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

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

State the name of the genetic change that allows new strains of bacteria to evolve from other strains.

[1]

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

[2]

Extended Tier Only

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

Place a tick (✓) in the boxes that explain why antibiotics can lose their effectiveness in combatting disease.

Table 1

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

Suggest why these molecules might be effective in the treatment of bacterial infection.

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 site.

Prior to passing the site the stream passes through a large urban area 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 how antibiotics may have entered the water, as shown in Table 1.

Extended Tier Only

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