Practise how penicillin disrupts bacterial cell walls, why antibiotics cannot target viruses, and how resistance evolves and can be limited in populations.
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?
Gram-positive bacteria because the peptidoglycan layer is exposed to penicillin directly
Gram-positive bacteria because it has a thinner layer surrounding the cell membrane overall
Gram-negative bacteria because the thin peptidoglycan layer can be broken down faster
Gram-negative bacteria because there is more periplasm available, which gives a weaker structure
Which statement correctly explains why viruses are unaffected by penicillin?
Penicillin only affects host cell metabolism.
Penicillin only binds with 70 S ribosomes.
Penicillin only blocks mRNA synthesis in prokaryotes.
Penicillin only blocks peptidoglycan synthesis.
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.
1, 2 and 3
1 and 2 only
1 and 3 only
2 and 3 only