Nitrogen Cycle

Question 1

Describe the role of bacteria in nitrogen fixation.

Answer 1

• nitrogen fixing bacteria release enzymes which reduce nitrogen gas into ammonia
• ammonia then dissolves in water to produce ammonium ions

Question 2

Describe the role of bacteria in nitrification.

Answer 2

• nitrifying bacteria release enzymes that oxidise ammonium ions into nitrites
• another type of nitrifying bacteria release other enzymes which further oxidise nitrites into nitrates

Question 3

Describe the role of bacteria in denitrification.

Answer 3

• denitrifying bacteria release enzymes which reduce nitrates back into nitrogen gas
• these bacteria are anaerobes so denitrification only occurs in anaerobic conditions

Question 4

Describe the role of plant roots in the nitrogen cycle.

Answer 4

1. Absorb ammonium ions and nitrates by active transport
2. Ions are used to make:
   
   • amino acids for proteins
   • DNA/RNA nucleotides ( bases are nitrogenous)
   • adenine for ATP production

Question 5

Describe the role of animals in the nitrogen cycle.

Answer 5

1. Animals eat plants so digest and absorb the amino acids from proteins to from new animal proteins
2. Protein that hasn’t been digested is egested and urea is excreted through urine which both contain nitrogen containing molecules

Question 6

Describe the process of ammonification in the nitrogen cycle.

Answer 6

1. Proteins in dead organisms and faeces are hydrolysed by saprobionts
2. Saprobionts release enzymes onto dead organic matter and hydrolyse proteins and absorb the amino acids by facilitated diffusion to make their own proteins
3. Excess amino acids are deaminated to releases ammonium ions which are excreted into the soil
4. Ammonia can be dissolves in water to produces ammonium ions which can then be converted into nitrites then nitrates then into nitrogen gas.