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Date May 2017 Marks available 1 Reference code 17M.3.HL.TZ2.7
Level Higher level Paper Paper 3 Time zone Time zone 2
Command term State Question number 7 Adapted from N/A

Question

The shore crab (Carcinus maenas) preys on mussels (Mytilus edulis). M. edulis vary in size. The frequency distribution of the numbers of each length of M. edulis eaten by a population of C. maenas per day is shown in the graph.

State the most common length of M. edulis eaten by the C. maenas population.

[1]
a.

Suggest reasons for the length you stated in (a) being the most common length of M. edulis that C. maenas eat.

[3]
b.

Markscheme

17.5 mm OR 15 mm to 20 mm

a.

a. larger mussels too much effort to open OWTTE
OR
best ratio between effort and energy return 

b. smaller mussels means more individuals have to be eaten for the same return on effort 

c. greater time/predator exposure spent during foraging to obtain required daily energy 

d. it «may be» the most common size available
OR
«correct mussel» size favoured by natural selection 

e. the claws are best adapted to prey on mussels of this size

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Additional higher level topics) » A.6 Ethology
Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Additional higher level topics)
Option A: Neurobiology and behaviour

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