| Date | May 2010 | Marks available | 1 | Reference code | 10M.3.SL.TZ1.23 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | State | Question number | 23 | Adapted from | N/A |
Question
Below is a diagram of the nitrogen cycle.
Indicate the processes occurring at A and B.
A: ..................................................................
B: ..................................................................
Draw an arrow to indicate where in the cycle Azotobacter plays a role.
State the role of Nitrobacter in this cycle.
Outline the consequences of releasing nitrate fertilizer into rivers.
Markscheme
Both required for [1].
A: denitrification
B: putrification/decay/decomposition
arrow pointing from nitrogen in atmosphere to ammonium compounds
nitrification / converts nitrite to nitrate
adding nitrates causes increase in growth of phytoplankton/algal blooms;
decomposition (of increased biomass/dead plants/animals) uses up more oxygen;
can result in death of other aquatic organisms due to lack of oxygen;
plant/algal biomass increases causing turbidity of water;
Examiners report
Understanding of the nitrogen cycle is not good, and few candidates answered these questions correctly.
Understanding of the nitrogen cycle is not good, and few candidates answered these questions correctly.
Understanding of the nitrogen cycle is not good, and few candidates answered these questions correctly.
The majority were able to discuss changes in the level of algae and the lack of oxygen, so most achieved one or two marks.
