The Nitrogen Cycle

Question 1

Why do organisms need nitrogen?

Answer 1

It is necessary for making proteins for growth

(It has to be turned into nitrates before plants can use it)

Question 2

List the four different types of bacteria involved in the nitrogen cycle.

Answer 2

• Decomposers
• Nitrifying bacteria
• Denitrifying bacteria
• Nitrogen-fixing bacteria

Question 3

Explain the role of decomposers in the nitrogen cycle.

Answer 3

• Decompose proteins and urea, turning them into ammonia which forms ions that can be used by plants
• This also returns nitrogen to soil

(Bacteria and fungi in soil)

Question 4

Explain the role of nitrifying bacteria in the nitrogen cycle.

Answer 4

Turn ammonia into nitrites and then nitrates

(Found in soil)

Question 5

Explain the role of denitrifying bacteria in the nitrogen cycle.

Answer 5

Turn nitrates back into nitrogen gas

(Typically found in waterlogged soil)

Question 6

Explain the role of nitrogen-fixing bacteria in the nitrogen cycle.

Answer 6

Turn nitrogen gas from the atmosphere into ammonia, which forms ammonium ions

(Some live in soil, or in root nodules of plants, e.g. peas, beans)

Question 7

Explain the role of lightning in the nitrogen cycle.

Answer 7

• It turns nitrogen gas in the air into nitrates in the soil which plants can use
• There’s so much energy in a bolt of lightning that it’s enough to make nitrogen react with oxygen in the air to give nitrates

Question 8

Explain how crop rotation can increase the amount of nitrates in the soil.

Answer 8

• This is where different crops are grown each year in a cycle
• The cycle usually includes a nitrogen-fixing crop (e.g. peas, beans), which helps to put nitrates back into soil for another crop to use the next year

Question 9

Explain how the use of fertilisers can increase the amount of nitrates in the soil.

Answer 9

Spreading animal manure or compost on fields recycles nutrients left in plant and animal waste and returns them to soil through decomposition