| Date | November 2011 | Marks available | 1 | Reference code | 11N.3.HL.TZ0.7 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Calculate | Question number | 7 | Adapted from | N/A |
Question
Removal of toxic heavy metals from industrial waste water is essential in order to control environmental pollution. Industrial waste water near Yanbu City, Saudi Arabia was found to contain 19 species of microorganisms that could tolerate heavy metals. The accumulation of cadmium ions in the most common of these microorganisms, Aspergillus fumigatus, was investigated.
The graph below shows the effect of pH on the ability of A. fumigatus to absorb cadmium ions from an aqueous solution.
Describe the cadmium ion uptake by A. fumigatus at pH 6.
Calculate the difference in cadmium ion uptake between pH 4 and pH 5 at 60 minutes.
..........................%
Discuss the use of A. fumigatus for the removal of cadmium ions in polluted waters.
The investigation found that both living and dead A. fumigatus cells were able to absorb cadmium ions. Suggest an advantage of using dead A. fumigatus cells.
Markscheme
rapid initial uptake (to approximately 75 % uptake);
rate of uptake slows and plateaus (at approximately 85 % uptake after 90 minutes);
only 90 % of cadmium ions absorbed (however long the contact time) / reaches maximum at 120 min;
64 (%) (allow responses in the range of 62 to 66 %)
can remove almost 100 %/98 % cadmium ions at pH 5 therefore very efficient;
A. fumigatus able to remove cadmium ions at pH values tested;
removal of cadmium ions more efficient at higher pH/weak acid;
strongly acidic/very low pH may inhibit/reduce uptake of cadmium ions by A. fumigatus;
pollution causing acidification of water may make removal more difficult;
A. fumigatus common therefore may be convenient/easy to use / OWTTE;
cadmium is not actually removed as it may pass along food chains / be released when A. fumigatus dies / unknown impact on environment;
easier to store/collect/transport dead/dried material;
prevents overgrowth of A. fumigatus;
reduce BOD and allow other organisms to use more resources/live in water;
Examiners report
Well answered in general.
Well answered in general although many candidates failed to calculate the difference in cadmium ion uptake.
Little use of the data available. Only 2 of the mark scheme choices seen in answers.
Mostly well answered.
