The nitrogen cycle involves a range of reactions and microorganisms.

Which process usually occurs under anaerobic conditions?

A farmer grows a different crop in a field each year for three years. In the fourth year the farmer plants a leguminous crop and then ploughs this into the soil. The next year the rotation starts again.

Which microorganisms will increase by the time the rotation starts again?

1 - denitrifying bacteria

2 - nitrifying bacteria

3 - nitrogen-fixing bacteria

4 - decomposing bacteria

Which soil would have the smallest number of denitrifying bacteria?

Decomposition of organic matter can cause the concentration of ammonia to rise in a fish tank. High concentrations of ammonia in the tank are toxic to fish. Bacteria may be added to remove the ammonia.

Which type of bacteria should be added?

Which processes are essential in making nitrogen in dead plant material available to growing plants?

1 - ammonification

2 - deamination

3 - nitrification

4 - nitrogen fixation

In organic matter, macromolecules containing nitrogen are broken down by decomposers. The decomposers are also respiring aerobically.

Which molecules will be released?

1 - carbon dioxide

2 - ammonium ions

3 - nitrate ions

In an ecosystem, at which stage is most energy lost?

An insect consumes 180 J of plant material.

Of this, 95 J of energy is passed out in the insect’s faeces and 58 J is used for respiration.

Which percentage of the energy, in the original plant material taken in by the insect, is converted into biomass?

The diagram shows the flow of energy through a food chain. Figures are in kJ m^-2 year^-1.

What percentage of light energy is available to the herbivore?

Why does the application of nitrate fertilisers cause an increase in crop production?