Outline how antibiotic resistance in bacteria can arise in response to environmental change.

Outline the principle of immunity.

Discuss the benefits and dangers of vaccination.

antibiotic resistance can be inherited;
alleles for resistance can be passed from one cell to another by exchange of plasmids/conjugation;
some varieties are more resistant than others;
bacteria reproduce very rapidly and have high mutation rate;
evolution can occur rapidly;
increased exposure to antibiotics is the environmental change that selects for resistant varieties;
for example, in hospitals / animal feed / inappropriate prescriptions / not finishing prescriptions;
bacteria without resistance die / resistant bacteria survive and pass on genes to next generation;
results in change in genetic makeup of population;

immunity is the ability of an organism to resist infection;
due to presence of (specific) antibodies;
immunity can be active or passive;
passive due to receiving antibodies from external sources/across placenta/from breast milk/injection;
active results from facing an infection directly/through vaccination;
pathogen/foreign cell invades body;
leads to clonal selection/formation of B memory cells;
B-cells produce specific antibodies;
if same pathogen enters body again memory cells activated/stimulated to divide;
antibodies produced faster and in greater amounts;

Benefits: [4 max]
immunity results
can limit pandemics/epidemics/spread of (infectious) diseases;
diseases can be eradicated/smallpox eliminated;
reduces mortality/deaths due to disease;
can protect vulnerable groups/young/old/with other conditions;
decrease crippling effects of diseases (such as polio);
decreased health care costs;

Dangers: [4 max]
may produce (mild) symptoms of the disease;
human error in preparation/storage/administration of vaccine;
individual may react badly to vaccine / defective immune system / hypersensitive/allergic reaction;
immunity may not be life-long/booster required;
possible toxic effects of mercury-based preservatives/thimerosal;

Most candidates scored few marks, failing to mention gene transmission in bacteria, variation, or widespread use of antibiotics as the environmental change.

Surprisingly few candidates could define immunity well. Some detailed accounts of how immunity is gained were given, but failure to describe accurately what happens if the same pathogen enters again or the different types of immunity meant that many candidates gained a low score.

Vague, rambling accounts about T and B cells were provided quite often. There was too much detail on the sequence of events leading to the development of memory cells (named as T or B) and less on how this resulted in immunity. Antibodies and antigens were sometimes confused.

Candidates were generally better at giving the benefits rather than the dangers, but few candidates could give four of both. Misunderstanding about vaccinations was common which is quite a worry for candidates who have been through an advanced biology course. Many mentioned autism without substantiation.