| Date | May 2013 | Marks available | 3 | Reference code | 13M.3.SL.TZ1.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Analyse | Question number | 19 | Adapted from | N/A |
Question
Scientists studied the characteristics of plant species growing in front of the progressively receding Rutor glacier in Italy. As the ice recedes plants are able to colonize the exposed ground. In a study of primary succession, scientists sampled plants from three areas exposed during different time periods. The data is shown in the following triangle graph.
Each species is represented by a number and positioned according to its degree of competitiveness (the ability to exclude other species), stress-tolerance (the ability to use nutrients efficiently) and ruderalism (the ability to develop rapidly to avoid disturbance).
Stages of succession were classified according to the time the ground had been exposed: early succession (species occurring in ground exposed for less than 68 years), mid-succession (species found in ground exposed between 69 and 181 years) and late-succession (species found in ground exposed for more than 181 years).
State the most ruderal species.
Species number 4 has a ruderalism value of 29. State the stress-tolerance value and competitiveness value of this species.
Stress-tolerance value: ......................
Competitiveness value: ......................
Analyse the change of species over time.
Markscheme
early succession species/examples of species /(numerical species numbers)/9
stress-tolerance value: 34 (Accept answers between 33 and 35)
competitiveness value: 38 (Accept answers between 37 and 39)
a. high ruderalism and (slightly higher) competitiveness in early succession;
b. (as time goes / succession stages advance) stress-tolerance increases;
c. competitiveness decreases;
d. ruderalism decreases/is more variable;
e. competitiveness least important factor / stress-tolerance most important factor;
f. exceptions for all categories;
Examiners report
This option was attempted by many candidates. The data was more challenging for some than in previous years but candidates on the whole responded well to it.
(a) (i) almost all answers were correct
This option was attempted by many candidates. The data was more challenging for some than in previous years but candidates on the whole responded well to it.
(i) almost all answers were correct, though (ii) proved more difficult.
This option was attempted by many candidates. The data was more challenging for some than in previous years but candidates on the whole responded well to it.
For (b) candidates were able to list, but few were able to analyse as required by the question stem.
