Nutrient cycles

Question 1

Name the general stages of the phosphorous cycle

Answer 1

1) Weathering
2) Runoff
3) Assimilation
4) Decomposition
5) Uplift

Question 2

What happens during weathering and runoff?

Answer 2

Phosphate compounds from sedimentary rocks leach into surface water and soil

Question 3

Explain the significance of phosphorus to living organisms

Answer 3

• Plants convert inorganic phosphate into biological molecules e.g. DNA, ATP, NADP.
• Phosphorus is passed to consumers via feeding

Question 4

What happens during uplift?

Answer 4

Sedimentary layers from oceans (formed by the bodies of aquatic organisms) are brought up to land over many years

Question 5

How does mining affect the phosphorus cycle?

Answer 5

Speeds up uplift

Question 6

Name the 4 main stages of the nitrogen cycle

Answer 6

1) Nitrogen fixation
2) Ammonification
3) Nitrification
4) Denitrification

Question 7

What happens during atmospheric fixation of nitrogen?

Answer 7

1) High energy of lightning breaks N2 into N
2) N reacts with oxygen to form NO2-
3) NO2- dissolves in water to form NO3-

Question 8

Outline the role of bacteria in nitrogen fixation

Answer 8

• Mutualistic nitrogen-fixing bacteria in nodules of legumes & free-living bacteria in soil
• Use the enzyme nitrogenase to reduce gaseous nitrogen into ammonia

Question 9

Outline the role of bacteria in ammonification

Answer 9

1) Saprobionts feed on and decompose organic waste containing nitrogen (e.g. urea, proteins, nucleic acids)
2) NH3 released
3) NH3 dissolves in water in soil to form NH4+

Question 10

Outline the role of bacteria in nitrification

Answer 10

2-step process carried out by saprobionts in aerobic conditions

• 2NH4+ + 3O2 > 2NO2- + 2H20 + 4H+
• 2NO2 + O2 > 2NO3-

Question 11

Outline the role of bacteria in denitrification

Answer 11

Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen

Question 12

Explain the significance of nitrogen to living organisms

Answer 12

Plant roots uptake nitrates via active transport use them to make biological compounds e,g:

• Amino acids
• NAD/NADP
• Nucleic acids

Question 13

Outline the role of mycorrhizae

Answer 13

Mutualistic relationship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions

Question 14

Give 3 benefits of planting a different crop on the same field each year

Answer 14

• Nitrogen-fixing crops e.g. legumes make soil more fertile by increasing soil nitrate content.
• Different crops have different pathogens.
• Different crops use different proportions of certain ions