| Date | May 2016 | Marks available | 1 | Reference code | 16M.3.SL.TZ0.11 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Distinguish | Question number | 11 | Adapted from | N/A |
Question
Many people around the world wash themselves under a warm shower. This personal hygiene may expose individuals to harmful microorganisms such as Mycobacterium avium through inhalation of water droplets from the shower head and direct water contact. Samples taken from biofilms inside shower heads and municipal water sources were analysed. Proportions of other non-tuberculous mycobacteria (NTM) were also analysed. The results are shown in the pie charts.
List two properties of biofilms.
Distinguish between the data for shower head biofilms and municipal water sources.
Suggest reasons for biofilms developing inside shower heads.
Markscheme
They show emergent properties
They contain cooperative aggregates of microorganisms
The microorganisms cooperate through communication/quorum sensing
The microorganisms are highly resistant to antimicrobial agents
They adhere to a variety of surfaces
Formation/secretion of EPS/extracellular polymeric substances
Biofilms show a much higher percentage of M. avium than water
Accept inverse answer
Accept numerical answers
Conditions on the shower head favour bacterial growth
eg: moisture/temperature/nutrients
«Solid» surface on which to accumulate
Quorum reached
OR
critical concentration of signal molecules
Shower heads are seldom cleaned
Examiners report
Generally well answered showing good knowledge of biofilms.
Generally well answered showing good knowledge of biofilms.
Generally well answered showing good knowledge of biofilms.
