| Date | May 2016 | Marks available | 2 | Reference code | 16M.3.HL.TZ0.14 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | List | Question number | 14 | Adapted from | N/A |
Question
Where high amounts of ammonium ions are present in agricultural areas, gaseous ammonia can be released into the atmosphere. This ammonia can dissolve and be carried across distances and then be deposited through precipitation. In a study of the effects of deposition of ammonium in a forest, soil samples were taken starting at the forest edge next to an open field and moving toward the centre of the forest.
Outline the procedure that was most likely used by the researchers to decide where to take the samples.
List two sources of the ammonium in the forest soils apart from deposition in rainfall.
Suggest one reason for ammonium levels in the interior of the forest being lower than the soil ammonium close to the edge.
Markscheme
Line transect
OR
a line is identified and individual walks the line
Decision on where to start and end the line/transect
Samples taken every 20m/at regular intervals
Activity of soil microorganisms/ammonification/nitrogen fixation
Urine/feces/other nitrogenous waste
Dead organisms
Fertilizers «on edge of forest»
Greater distance from an open field where they are applying fertilizer
More ammonium absorbed/recycled
Less ammonium in rain reaches soil/trapped in treetops
Examiners report
Identification of the procedure seemed like an easy question but in fact few candidates were correctly able to indicate that a transect was used and that using the graph as a guide, samples were probably taken at 20m intervals. Many tried to show how a random number generator would have been used instead.
Many were able to score 2 marks for listing sources of ammonium in the soil. However, some confused pesticides with fertilizers.
This was a discriminating question with only some able to suggest a reason for lower ammonium levels in the forest interior. The ‘forest edge’ seemed to lead some candidates incorrectly into a discussion of the edge effect.
