| Date | November 2010 | Marks available | 3 | Reference code | 10N.3.SL.TZ0.2 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 2 | Adapted from | N/A |
Question
Outline the function of the appetite control centre in the brain.
Outline the implications for the health of a person who has a BMI of 16 kg m–2.
Describe a primary succession in a named type of habitat.
Markscheme
a. causes sensation of being full/having eaten too much (when receives messages);
b. stimulated by hormones (insulin, CCK) produced by pancreas/small intestine after eating;
c. stretch receptors in stomach after eating;
d. hormones (leptin) produced by adipose tissue in response to fat storage;
e. send message to appetite control centre in brain;
BMI of 16 (kg m-2) is underweight so there is a health risk;
underweight so may be taking in insufficient nutrients;
a. named type of habitat; (e.g. land left after lava flow/glacier retreat / sand dune)
b. primary succession occurs on bare/lifeless substrate;
c. organisms move into an area and change its nature/pioneers colonize;
d. pioneers are simple autotrophs; (e.g. lichens grow first)
e. break down substrate; (e.g. to form organic soil)
f. leads to an eventual climax ecosystem; (e.g. forest)
g. stages in the succession follow a set sequence;
Award [2 max] if no named type of habitat given or if example is of secondary succession such as after a forest fire.
Examiners report
Many candidates were able to get 2 out of the 3 available marks for stating that the appetite control centre causes a sensation of being full and then stating one message sent to the centre after eating. Stretch receptors were often incorrectly stated as being in the small intestine or pancreas and few added that leptin was produced in response to fat storage by adipose tissue.
This question asked candidates to outline the implication of the given BMI. Therefore more was expected than simply stating that the person would be underweight.
The descriptions of primary succession were not clear or detailed enough. Few used the words pioneer or climax community. Many incorrectly referred to the first plants as mosses rather than lichens. Despite this, the generous mark scheme allowed many to gain 2 marks.
