Each year, there are 462 000 deaths from malaria in children under 5 years old globally.
Insecticide-treated nets could prevent 50% of malaria cases and reduce deaths of children under 5 years old by 18%.
How many children could be saved by using insecticide-treated nets?
▶️ Answer/Explanation
Ans: B
Calculate 18% of 462,000: \( 0.18 \times 462,000 = 83,160 \). The nets could save 83,160 children (B), as the reduction applies to the total deaths, not just preventable cases.
Antibiotic-resistant strains of Mycobacterium tuberculosis are a major problem when treating TB.
A new antibiotic, teixobactin, could be very effective at killing M. tuberculosis with only a small risk that the bacteria will evolve teixobactin resistance.
Penicillin and similar antibiotics bind to a single protein, but teixobactin binds to two lipids that are needed for the formation of the bacterial cell wall. Teixobactin binds to regions of the two lipids that do not vary across many different species of bacteria.
Which statements help to explain why the use of teixobactin is thought to be less likely to lead to the evolution of antibiotic resistance than the use of many other antibiotics, such as penicillin?
▶️ Answer/Explanation
Ans: C
Statement 1 is correct because teixobactin targets two lipids, requiring multiple mutations for resistance, unlike penicillin (single protein target). Statement 3 is correct as conserved lipid structures across species indicate evolutionary constraints, making resistance less likely. Statement 2 is incorrect because while lipids are not directly encoded by DNA, their synthesis depends on enzymes (proteins) that can mutate, indirectly affecting lipid structure.
Bacteria may be classified according to differences in cell wall structure. The differences are shown by using the Gram stain.
The diagram shows part of a Gram-positive bacterium and part of a Gram-negative bacterium, drawn to the same scale.
The antibiotic penicillin kills bacteria by inhibiting the synthesis of the cell walls during bacterial cell growth.
Which type of bacteria will be killed by penicillin more easily and why?
▶️ Answer/Explanation
Ans: A
Gram-positive bacteria (option A) are more susceptible to penicillin because their thick peptidoglycan layer is directly exposed to the antibiotic. In Gram-negative bacteria, the outer membrane acts as a protective barrier, making the peptidoglycan layer less accessible to penicillin. The thickness of the peptidoglycan layer in Gram-positive bacteria (20-80nm) compared to Gram-negative (2-7nm) provides more target sites for penicillin’s action.
Scientists investigated the effect of increasing concentrations of an antibiotic on the development of antibiotic resistance in bacteria.
The scientists grew four groups of bacteria and added a different concentration of antibiotic to each group. The number of resistant bacteria and the total population of bacteria were measured at intervals for 24 hours for each group.
The graphs show the results.
Which statements are correct conclusions that can be made from the results of this investigation?
(1) Increasing the concentration of antibiotic decreases the population of non-resistant bacteria at the end of 24 hours.
(2) The proportion of antibiotic-resistant bacteria increases with increasing concentrations of antibiotics.
(3) Increasing the concentration of antibiotic always increases the number of resistant bacteria.
(A) 1, 2 and 3
(B) 1 and 2 only
(C) 1 and 3 only
(D) 2 and 3 only
▶️ Answer/Explanation
Ans: B
Statement (1) is correct: The graphs show that higher antibiotic concentrations reduce the total bacterial population (mostly non-resistant bacteria). Statement (2) is correct: The proportion of resistant bacteria (relative to the total population) increases with antibiotic concentration due to selective pressure. Statement (3) is incorrect: While resistance proportion rises, the absolute number of resistant bacteria does not always increase (e.g., at the highest concentration, resistant counts may plateau or decline). Thus, only 1 and 2 are valid conclusions.