Nutrient cycling
Students need to understand the key role that microorganisms play in the recycling of chemical elements within ecosystems. This encompasses the role of decomposers, such as saprobionts, and the roles of Nitrosomonas, Nitrobacter, Azotobacter and Rhizobiaa in the recycling of nitrogen. Students will need to describe the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification.
Linked to the nitrogen cycle students should be aware of the impact that the use of natural and artificial fertilisers can have. These are routinely used to replace the nitrates and phosphates lost by harvesting plants and removing livestock. There are environmental issues arising from the use of these fertilisers including leaching and eutrophication.
The importance of the carbon cycle should also be covered in this topic, with students being aware of factors that can affect the carbon cycle.
Some specifications also require students to demonstrate understanding of the recycling of other nutrients such as phosphorus.
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Measuring Carbon Cycling
This article from the Catalyst magazine focuses on how parts of carbon cycling, as it happens in forests, can be measured. Two of the processes used in this measure, flux towers and soil chambers, are described in the article.
Although measurement of the carbon cycle may not be identified within A level specifications, this article does provide useful background/around the subject reading at a suitable level.
The article itself is quite short, with one of the two pages devoted to photographs of the equipment used.
It would be possible to use this article as stimulus for a discussion on the limitations of either of these approaches or for devising equipment for specific purposes in biological measurement (what other examples can they name?) or the use of data loggers.
The other Catalyst article on carbon cycling in this list and this article would work well together. You could ask students to read, review and summarise each for homework/independent study.
Role of Bacteria in Nitrogen Cycle
In this investigation, students culture a free-living nitrogen-fixing bacterium (Azotobacter) from the soil. The protocol for this investigation is quite simple, but the understanding of why there is/isn't bacterial growth can be extended to ensure that it is suitable for A level students.