The figure shows a doctor examining a patient with tuberculosis. The patient stopped taking antibiotics after three days because they felt better. Some bact...
Question 1 Report
The figure shows a doctor examining a patient with tuberculosis. The patient stopped taking antibiotics after three days because they felt better. Some bacterial cells remained in the lungs. The doctor explains that finishing the prescribed course reduces the chance that resistant bacteria will form a large population. Bacteria divide rapidly when conditions in the body are suitable.
Table 1 shows bacteria in samples from the patient.
| Sample time | Susceptible cells | Resistant cells |
|---|---|---|
| Before treatment | 1200 | 8 |
| After 3 days | 55 | 6 |
(a) Describe the effect of treatment on susceptible cells. [1]
(b) What could happen to the six resistant cells if treatment stops? [1]
(c) Explain why taking the full course can slow the evolution of resistance. [3]
Fig. 1 shows a mosquito net treated with insecticide. In a village, some mosquitoes have an inherited resistance allele. Mosquitoes that land on an untreated net can pass through gaps less often than those landing on a treated net, but the insecticide kills susceptible mosquitoes. Health workers count mosquitoes caught indoors before nets are distributed and two years later.
Table 1 gives the percentage of mosquitoes surviving a standard insecticide test.
| Time | Mosquitoes tested | Survived (%) |
|---|---|---|
| Before nets | 200 | 4 |
| Two years later | 200 | 27 |
(a) Describe the change in survival percentage. [1]
(b) Give one advantage of using a net as well as insecticide. [1]
(c) Explain why insecticide-treated nets may become less effective over time. [3]
Answer Details
Tuberculosis treatment
(a) The number of susceptible cells decreased from 1200 to 55. [1]
(b) If treatment stops, the six resistant cells may reproduce or divide, producing a larger resistant population. [1]
(c) Continued treatment kills more susceptible bacteria. [1] It reduces the number of bacteria left to reproduce. [1] Therefore, fewer resistant bacteria survive and pass resistance alleles on, slowing the evolution of resistance. [1]
Insecticide-treated nets
(a) Survival increased from 4% before nets to 27% two years later. [1]
(b) The net provides a physical barrier and reduces bites even if mosquitoes are resistant to insecticide. [1]
(c) Resistant mosquitoes survive insecticide exposure. [1] They reproduce and pass resistance alleles to offspring. [1] The proportion of resistant mosquitoes rises, so fewer mosquitoes are killed and the nets become less effective. [1]
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