nitrogen cycle

Question 1

1. nitrogen fixation:

Answer 1

• Atmospheric nitrogen gas is converted into nitrogen-containing compounds such as ammonia, which forms ammonium ions (in solution) that can then be used by plants
• carried out by nitrogen fixing bacteria and lightening

Question 2

2. ammonification:

Answer 2

• Nitrogen compounds in waste products (e.g. urine and faeces) and dead organisms are converted into ammonia by saprobionts (a type of decomposer including some fungi and bacteria)
• This ammonia forms ammonium ions in the soil

Question 3

3. nitrification:

Answer 3

• The ammonium ions in the soil are converted by nitrifying bacteria into nitrogen compounds that can be used by plants, known as nitrates
• Initially, nitrifying bacteria convert ammonium ions into nitrites
• Different nitrifying bacteria then convert these nitrites into nitrates

Question 4

4. denitrification:

Answer 4

• Denitrifying bacteria use nitrates in the soil during respiration
• This process produces nitrogen gas, which returns to the atmosphere
• This process occurs in anaerobic conditions (when there is little or no oxygen available, such as in waterlogged soil)