Read Parasites by Cost and Life Cycle
Parasites gain resources at a host’s expense and often show specialised life-cycle and reproductive traits.
Parasitism is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Recognise adaptations
Common trends include reduced unnecessary sensory or locomotory structures and high reproductive potential. Some species evolve mimicry or attachment adaptations; these are not universal.
Use more than one host
A parasite may use an intermediate host to develop or transmit before reaching its definitive host. The intermediate host can facilitate completion of the parasite’s life cycle.
Interpret parasite–host evidence carefully
A positive scatter-plot association between parasite burden and host behaviour is evidence of correlation, not by itself causation or host benefit. Differential predation or survival can also change which hosts remain available for observation.
Keep parasite correlations cautious
More brain cysts correlate with more time spent near the water surface, but correlation alone does not prove that parasites cause surfacing. Predation can remove heavily infected large fish and create survivorship bias in the observed sample. The source supports B and D, not a causal claim. Choose B and D.
OlympIQ exam lens
- ✓Parasite benefits; host is harmed.
- ✓High reproduction is common; high locomotion is not universal.
- ✓Intermediate hosts support life-cycle stages.
- ✓Separate association from causal mechanism.
- ✓Consider survivorship and sampling effects when interpreting infection data.
- ✓Parasite-burden correlations require causal and survivorship alternatives to be considered.
A life-cycle host is not necessarily the parasite’s final reproductive host.
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