| Date | November 2010 | Marks available | 2 | Reference code | 10N.3.SL.TZ0.13 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Discuss | Question number | 13 | 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. D. strigosa is shown as a shaded gradient indicating a strong bias towards spawning in the early portion of this window.
State the range of the time of spawning for the male M. cavernosa.
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.
Markscheme
from 60 to 105 minutes (post-sunset) / 45 minutes
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;
Examiners report
Almost everyone correctly identified the range of spawning requested.
Few candidates were able to clearly express that the tight time frame of spawning of males and females of a species increased the possibility of fertilization. Many mentioned predators and carried this on into part (c) rather than looking at fertilization.
Many candidates gained 1 mark for suggesting that different spawning windows for different species avoided interspecific fertilization but few were able to get a second mark. Some were able to state that such cross-fertilization was usually non-productive.
Many received full marks.
