| Date | May 2013 | Marks available | 1 | Reference code | 13M.2.HL.TZ1.4 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Define | Question number | 4 | Adapted from | N/A |
Question
Distinguish between autotrophs and heterotrophs.
Define saprotroph.
State an external feature that is different in:
Cnidaria and Mollusca.
State an external feature that is different in:
Mollusca and Annelida.
Markscheme
autotrophs make their own food/organic molecules/organic matter and heterotrophs feed on/obtain their food/organic molecules from other organisms;
autotrophs use/require inorganic molecules/CO2 and heterotrophs require (complex) organic molecules;
an organism that lives on/in non-living/dead (organic) matter and secretes digestive enzymes/digestive juices into it / OWTTE
Cnidaria have radial symmetry while Mollusca have bilateral symmetry;
Cnidaria have tentacles/nematocysts/stinging cells while Mollusca do not;
Mollusca (may) have a (hard) shell while Cnidaria do not;
Mollusca have a mouth and anus while Cnidaria have only one opening;
Mollusca have a muscular/large foot while Cnidaria do not;
other valid external difference;
Annelida are segmented while Mollusca are not (visibly segmented);
Annelida may have bristles/chetae/chaetae while Mollusca do not;
Mollusca (may) have a (hard) shell while Annelida do not;
Mollusca have a muscular/large foot while Annelida do not;
other valid external difference;
Examiners report
Nearly all candidates knew something about autotrophs and heterotrophs but answers tended to be too loose to score many marks. A common error was to suggest that plants make energy.
Fewer than half of candidates were able to state what a saprotroph is. Answers had to make it clear that saprotrophs feed on dead organic matter by external digestion, to exclude detritivores that ingest dead matter.
Candidates were evenly divided between those who had no idea of the external features of Cnidaria, Annelida and Mollusca, those who knew some of their features but failed to score marks because they did not give both sides of the comparison and those who gave correct and full comparisons.
Candidates were evenly divided between those who had no idea of the external features of Cnidaria, Annelida and Mollusca, those who knew some of their features but failed to score marks because they did not give both sides of the comparison and those who gave correct and full comparisons.
