36 NCEA Style Question: Biological Clocks in Animals

Fiddler crabs live on tidal mudflats. They feed on detritus in the mud at low tide, and return to their burrow at high tide to rest. The diagram below shows the actogram for a fiddler crab's activity in a laboratory. The crab was kept in constant light.

1. (a) Identify the two biological rhythms shown by the crab:

(b) Identify the origin of the biological rhythms:

2. Explain the pattern seen in the actogram. Predict the continued activity of the crab in the lab in relation to the high tide at the beach of collection:

3. Discuss the role of biological rhythms in animals, using the fiddler crab as an example. Include the origins of biological rhythms, the importance of zeitgebers, and the importance of accurate timing. You may use extra paper if required:

Days 1 2 3 4 5 6 7 8 9 10 11 12 Simplified actogram for fiddler crab

0 6 12 18 24 High tide at beach of collection

Time of day (hours) Times crab was active