Question 19N.3.hl.TZ0.25
| Date | November 2019 | Marks available | [Maximum mark: 7] | Reference code | 19N.3.hl.TZ0.25 |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Discuss, Explain, Outline, Suggest | Question number | 25 | Adapted from | N/A |
The discovery of penicillins contributed to the development of antibiotics.
Explain how the beta-lactam ring is responsible for the antibiotic properties of penicillin. Refer to section 37 of the data booklet.
[3]
ring is «sterically» strained
OR
angles of 90° instead of 109.5/109/120° angles
OR
angles smaller than 109.5/109/120°/tetrahedral/trigonal planar/triangular planar angle ✔
ring breaks up/opens/reacts «easily»
OR
amido/amide group «in ring» is «highly» reactive ✔
«irreversibly» binds/bonds to enzyme/transpeptidase
OR
inhibits enzyme/transpeptidase «in bacteria» that produces cell walls
OR
prevents cross-linking of «bacterial» cell walls ✔
NOTE: Accept arguments using correct descriptions of hybridization for M1.
Do not accept "breaks/binds to cell walls" – a reference to the enzyme is needed for alternatives 1 and 2 for M3.
Do not accept "cell membrane" for "cell wall".
Outline the impact of antibiotic waste on the environment.
[1]
«leads to bacterial» resistance «to antibiotics»
OR
destroys useful/beneficial bacteria
OR
useful/beneficial/less harmful bacteria replaced with «more» harmful bacteria ✔
NOTE: Accept “affects/disturbs micro-ecosystems”.
Suggest a concern about the disposal of solvents from drug manufacturing.
[1]
Any one of:
«most are» toxic «to living organisms»
OR
incomplete combustion/incineration can produce toxic products/dioxins/phosgene
OR
carcinogenic/can cause cancer ✔
NOTE: Do not accept “harmful to the environment”.
accumulate in groundwater
OR
have limited biodegradability ✔
NOTE: Do not accept just “pollutes water”.
cost of disposal ✔
NOTE: Do not accept “hazard of disposal”.
NOTE: Accept “ozone depletion” only if there is some reference to chlorinated solvents.
Discuss two difficulties, apart from socio-economic factors, associated with finding a cure for AIDS.
[2]
Any two of:
HIV difficult to detect/remains dormant ✔
HIV mutates rapidly/quickly ✔
HIV replicates rapidly/quickly ✔
HIV destroys «T-»helper cells/white blood cells/lymphocytes
OR
HIV attacks immune system ✔
HIV has several «significantly different» strains/subtypes ✔
NOTE: Accept “virus” for “HIV”.
Do not accept “AIDS mutates” without mention of the HIV/virus.
Penalize the use of “AIDS” for “HIV” once only.
Accept “HIV metabolism linked to that of host cell” OR “drugs harm host cell as well as HIV”.