Nutrient Cycles Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Name the general stages in the phosphorus cycle.

A
  1. Weathering
  2. Runoff
  3. Assimilation
  4. Decomposition
  5. Uplift
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is the phosphorus cycle a slow process?

A
  • phosphorus has no gas phase, so there is no atmospheric cycle
  • most phosphorus is stored as phosphate ions in rocks.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What happens during weathering and runoff?

A

Phosphate compounds from sedimentary rock leach into surface water and soil.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Explain the significance of phosphorus to living organisms.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What happens during uplift?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does mining affect the phosphorus cycle?

A

Speeds up uplift

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Name the 4 main stages of the nitrogen cycle.

A
  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why can’t organisms use nitrogen directly from the atmosphere?

A

N2 is very stable due to strong covalent triple bond.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens during atmospheric fixation of nitrogen?

A
  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 (-)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Outline the role of bacteria in nitrogen fixation.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Outline the role of bacteria in ammonification

A
  1. Saprobionts feed on and decompose organic waste containing nitrogen (e.g. urea, proteins etc)
  2. NH3 released.
  3. NH3 dissolves in water in soil to form NH4 (+)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Outline the role of bacteria in nitrification.

A

2-step process carried out by saprobionts in aerobic conditions:
2NH4 (+) + 3O2 —> 2NO2 (-) + 2H2O + 4H(+)
2NO2 (-) + O2 —> 2NO3 (-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Outline the role of bacteria in denitrification.

A

Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain the significance of nitrogen to living organisms.

A

Plant roots uptake nitrates via active transport & use them to make biological compounds e.g.
1. Amino acids
NAD/NADP
3. Nucleic acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Outline the role of mycorrhizae.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

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

A
  1. Nitrogen-fixing crops e.g. legumes make soil more fertile by increasing soil nitrate content
  2. Different crops have different pathogens
  3. Different crops use different proportions of certain ions
17
Q

Name the two categories of fertiliser and state the purpose of using fertiliser.

A
  • Organic: decaying organic matter & animal waste
  • Inorganic: minerals from rocks, usually containing nitrogen, phosphorus, potassium
  • To increase gross productivity for higher yield
18
Q

At a certain point, using more fertiliser no longer increases crop yield. Why?

A

A factor unrelated to the conc of mineral ions limits the rate of photosynthesis, the rate of growth cannot increase any further.

19
Q

Outline 2 main environmental issues caused by the use of fertilisers.

A
  1. Leaching: nitrates dissolve in rainwater and ‘runoff’ into water sources
  2. Eutrophication: water source becomes putrid as a result of agal bloom
20
Q

What happens during eutrophication?

A
  1. Aquatic plants grow exponentially since nitrate level is no longer a limiting factor
  2. Agal bloom on water surface prevents light from reaching the bottom and plants die
  3. Oxygen levels decrease as population of aerobic saprobionts increases to decay dead matter, so fish die
  4. Anaerobic organisms reproduce exponentially and produce toxic waste which makes water putrid
21
Q

How can the risk of eutrophication be reduced?

A
  • sewage treatment marshes on farms
  • pumping nutrient-enriched sediment out of water
  • using phosphate-free detergents