| Date | November 2010 | Marks available | 2 | Reference code | 10N.3.HL.TZ0.4 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Discuss | Question number | 4 | Adapted from | N/A |
Question
Corals can be male, female or hermaphrodite (both male and female) and the release of their gametes is called spawning. Data was collected to study the spawning behaviour in the Gulf of Mexico of three genera of coral: Montastraea, Stephanocoenia and Diploria. The spawning behaviour is expressed in minutes post-sunset. Peak spawning windows are shown as grey bars and the range as black bars.
Suggest why it may be advantageous for each species of coral to spawn within a tight time frame.
Discuss the significance of different spawning windows for different species.
Scientists hypothesized that the release of the male gamete triggers a chemical signal for females to release their eggs. Discuss this hypothesis.
The spawning window of D. strigosa is shown as a shaded gradient indicating a strong bias towards spawning in the early portion of the window. Suggest a reason for the spawning behaviour of D. strigosa.
Define the term innate behaviour.
Markscheme
to increase the possibilities of fertilization
a. to avoid interspecific/cross-fertilization;
b. cross-fertilization usually not successful/non-productive;
c. some overlap of species spawning occurs so temporal separation is not completely successful;
d. example of overlap (e.g. D. strigosa overlaps with M. cavernosa/M. franksi);
a. females always spawned after males suggesting hypothesis correct;
b. for example in M. cavernosa or S. intercepta;
c. difficult to tell for hermaphrodites;
d. chemical analysis of water should be undertaken after males spawned / other chemical signals / further evidence required to support cause and effect;
a. the spawning of D. strigosa is influenced by male M. cavernosa;
b. the spawning of D. strigosa is influenced by the release of M. franksi;
c. D. strigosa spawning diminishes due to the appearance (spawning) of M. franksi;
d. light intensity determined;
innate behaviour develops independently of the environmental context / not learned/ stereotyped / inherited / genetic pre-disposition
Do not accept instinct.
Examiners report
Some candidates had a hard time recognizing the importance of the timing of spawning to fertilization in part (b).
Some candidates had a hard time recognizing the importance of the timing of spawning to fertilization in part (b), or to avoiding cross-breeding in part (c) and instead related it to the presence of predators.
In part (d), many candidates discussed the hypothesis, not in relationship to the data but rather to the potential causes of a possible chemical signal.
Most candidates performed well in the data analysis with (e) being the best discriminator of the better candidates.
