Question
The worm Branchiobdella italica lives on the external surface of the freshwater crayfish Austropotamobius pallipes. A study was carried out in a river in central Liguria, north-western Italy, of the range of sizes of B. italica found on adult A. pallipes.
a. Describe the body length frequency of the B. italica worms collected in this study. [1]
b. The relationship between A. pallipes and B. italica is mutualistic.
A. pallipes feeds on algae and another worm, B. exodonta, lives inside A. pallipes as a parasite. State the trophic level of B. exodonta in this food chain. [1]
c. Distinguish between mutualism and parasitism, providing another example of mutualism and another example of parasitism. [2]
▶️Answer/Explanation
Markscheme
a. higher frequency of medium length worms
b. shows normal distribution
c. lower frequency at extremes
secondary consumer / third trophic level
a. in parasitism only one organism benefits whereas in mutualism both benefit
b. example for both parasitism AND mutualism
Do not allow B. italica or B. exodonta as examples.
eg parasitic: human tapeworms AND mutualism: bacteria in human digestive tract
Question
b. Define indicator species. [1]
c. Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant. [3]
e. Determine whether islands are open or closed ecosystems. [1]
▶️Answer/Explanation
Markscheme
organism that is present/absent when specific environmental conditions exist
OR
organism used to assess a specific environmental condition
a. example eg: DDT / mercury / cadmium
b. substance accumulates in «fat» tissue/not excreted «when consumed»
c. contaminated organisms consumed «in large quantities» by higher level consumers
d. pollutant becomes more concentrated at each higher trophic level / through the food chain
e. some pollutants are more likely to be biomagnified «accumulate in fat tissue»
OR
some organisms are more likely to be affected by biomagnification than others
OR
biomagnification not the same at each trophic level
Only [2] if verified example not given.
closed because islands do not exchange matter/nutrients with surroundings
OR
open because islands do exchange matter/nutrients with surroundings