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AQA A level Biology > 5.4 Nutrient cycles > Flashcards

5.4 Nutrient cycles Flashcards

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1
Q

What is the nitrogen cycle important

A

Since animals and plants cannot obtain nitrogen through gas exchange

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2
Q

What can’t animals and plants obtain nitrogen through gas exchange

A

Since nitrogen gas contains a triple bond so it requires a lot of energy to break

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3
Q

What is nitrogen so essential

A

Needed for:
- Proteins
- ATP
- Nucleic acids

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4
Q

What does nitrogen fixing mean

A

Converting nitrogen gas into a nitrogen containing compound

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5
Q

Where does nitrogen fixing occur

A

In the root nodules

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6
Q

Why does nitrogen fixing happen in the root nodules

A

Because there are bacteria in the nodules called nitrogenase are able to convert nitrogen gas into ammonium or nitrates

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7
Q

What type of plants contain nitrogenase bacteria in their nodules

A

Legumes

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8
Q

How is ammonia absorbed into the plant after being made at the nodules

A

In the form ammonium ions in water

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9
Q

Once ammonium ions are in the plant what are they used for

A

Amino acids
ATP
Nucleic acids

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10
Q

What 2 things can either happen to a plant during the nitrogen cycle

A

Either:
- Eaten by herbivores
- Death

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11
Q

Once a herbivore has eaten a plant how does the nitrogen get put back into the nitrogen cycle , 2 ways

A
  • By death of the animal
  • By excretion of urine
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12
Q

What microbe converts the dead organic matter into ammonia during the nitrogen cycle

A

Saprobiants

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13
Q

What is the name of the process where dead organic matter is converted into ammonia

A

Ammonification

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14
Q

During nitrification, what is ammonia firstly converted into

A

Nitrites , NO2-

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15
Q

After ammonia has been converted into nitrites what are the nitrites then converted into

A

Nitrates, NO3-

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16
Q

What type of bacteria converts ammonia into nitrites and nitrates

A

Nitrifying bacteria

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17
Q

What is the name of the process by which nitrates are converted back into nitrogen gas

A

Denitrification

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18
Q

If nitrates aren’t denitrified back into nitrogen gas, how else go they rejoin the nitrogen cycle

A

By absorption through the soil and into plants

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19
Q

What type of reaction is the convertion of nitrogen gas to ammonia

A

Reduction reaction

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20
Q

How do nitrogen fixing bacteria respire

A

Aerobically

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21
Q

How do saprobionts respire

A

Aerobically

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22
Q

How do nitrifying bacteria respire

A

Aerobically

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23
Q

How do denitrifying bacteria respire

A

Anaerobically

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24
Q

How does nitrogen in the atmosphere get into proteins in plants

A

Nitrogen fixing

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25
Q

How does proteins in plants pass on their nitrogen to proteins in animals

A

Feeding

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26
Q

How does the proteins in animals become proteins in dead organic matter

A

Decomposition

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27
Q

How does proteins in animals become nitrogenous waste (urea)

A

Excretion

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28
Q

How does proteins in plants become proteins in dead organic matter

A

Decomposition

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29
Q

How does nitrogenous wastes (urea) become ammonia in the soil, and what does this

A

Ammonification by saprobiants

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30
Q

How does proteins in dead organic matter become ammonia in soil

A

Ammonification

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31
Q

How does ammonia in soil become nitrites in soil

A

Nitrification

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32
Q

How do nitrites in the soil become nitrates in the soil

A

Nitrification

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33
Q

How do nitrates in the soil enter proteins in plants

A

Absorption

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34
Q

How do nitrates in the soil re-enter the atmosphere

A

Denitrification

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35
Q

Why do plants need nitrogen

A

To manufacture proteins, nucleic acids and other nitrogen-containing compounds

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36
Q

Only few plants can use nitrogen gas directly, so what form of nitrogen do plants commonly use and how is it uptaken

A

Nitrate ions from soil that are absorbed by active transport by the roots

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37
Q

How do animals obtain nitrogen-containing compounds

A

By eating and digesting plants that have absorbed the nitrates

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38
Q

Are nitrate ions soluble

A

Yes

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39
Q

Are nitrate ions easily leached

A

Yes, they are easily leeched (wash) through the soil

40
Q

In a natural ecosystem how are the nitrate concentrations restored after the nitrates have been leeched away beyond the reach of the roots

A

Largely by the recycling of nitrogen-containing compounds

41
Q

In an agricultural ecosystem, how are the nitrate concentrations restored / increased

A

They are increased by adding fertilisers

42
Q

In a natural ecosystem how are the nitrogen-containing compounds recycled

A

When plants and animals die, the process of decomposition begins, where microorganisms replenish the nitrate concentrations in the soil - releasing nitrate ions

43
Q

What are the 4 stages in the nitrogen cycle

A
  • Ammonification
  • Nitrification
  • Nitrogen fixing
  • Denitrification
44
Q

How do saprobiontic microorganisms convert nitrogen-containing compounds into ammonia

A

By feeding on faeces and dead organic matter - releasing ammonia

45
Q

When ammonia is released by the saprobionts, what does it then form

A

Ammonium ions in the soil - when nitrogen returns to the non-living components of the ecosystem

46
Q

During nitrification what are the 2 steps from ammonia ions to nitrate ions, stating what type of reaction it is

A
  1. Oxidation of ammonium ions to nitrite ions
  2. Oxidation of nitrite ions to nitrate ions
47
Q

How do nitrifying bacteria obtain their energy

A

Using the energy released by the oxidation reactions converting ammonium ions to nitrate ions

48
Q

Why do farmers need to keep soil structure light and well aerated by ploughing, and have a good drainage system

A

To create soil with air spaces so nitrifying bacteria can carry out the oxidation reactions with sufficient oxygen

49
Q

What are the 2 types of microorganisms that carry out nitrogen fixation

A
  • Free-living nitrogen-fixing bacteria
  • Mutualistic nitrogen-fixing bacteria
50
Q

How do free-living nitrogen-fixing bacteria fix nitrogen

A

By reducing gaseous nitrogen into ammonia

51
Q

How do mutualistic nitrogen-fixing bacteria fix nitrogen

A

By living in root nodules of plants such as beans and peas

52
Q

How is the relationship between nitrogen-fixing bacteria in the root nodules and the plant mutualistic

A

The plant receives nitrogen containing compounds and the bacteria receive carbon containing compounds

53
Q

What condition is the soil usually in when there are more denitrifying bacteria than nitrifying

A

Waterlogged, low oxygen concentration

54
Q

How could you identify plants that are growing in nitrogen poor soils

A

Light green with smaller leaves and stunted growth

55
Q

Why is nitrogen in the atmosphere not directly available to plants

A

Since the N2 has a triple bond making it very stable since it’s hard to break the bonds

56
Q

How does deforestation affect the nitrogen cycle

A
  • Nitrates will be leeched out of the soil
  • Soil erosion, so reducing soil quality
57
Q

How does crop rotation improve soil fertility

A

It increases the fertility if it includes legueous plants

58
Q

Livestock farming creates large volumes of animal waste. How would this affect the nitrogen cycle

A

More dead organic matter so greater concentration of ammonia in soil so more nitrates available

59
Q

What would happen if a farmer used too much fertiliser, what adverse affects can this have on the environment

A

Washed into rivers, eutrophication and leeching into surrounding water bodies

60
Q

Why are animals not essential to the nitrogen cycle

A

They only contribute to the dead organic matter

61
Q

How does harvesting of crops affect the nitrogen cycle

A

It reduces the soils fertility

62
Q

Why is it necessary for farmers to plough their fields

A

To minimise the denitrifying bacteria so more nitrogen compounds remain in the soil

63
Q

Explain how grass, non-legume, obtains the nitrogen it needs

A

Nitrates or ammonium ions

64
Q

Name 3 biological molecules that contain phosphorus

A
  • ATP
  • Phospholipids
  • Nucleic acids
65
Q

In the carbon and nitrogen cycle the main reservoir of each element is in the atmosphere, what is the main reservoir of phophorus

A

In mineral form rather than in the atmosphere

66
Q

In what form does phosphorus exist in

A

Phosphate ions , PO4^3-

67
Q

What is the name of the process by which the sedimentary rocks containing phosphate ions are brought to the surface after being under the sea

A

Geographical uplifting

68
Q

What processes help the phosphate ions within the sedimentary rock be dissolved

A

Weathering and erosion

69
Q

How to the phosphate ions get into animals from the rocks

A

The ions are dissolved meaning they can be absorbed by plants and animals then feed on the plants

70
Q

In animals what happens to excess phosphate ions

A

They are excreted and may accumulate in waste materials

71
Q

When plants or animals die what happens to the phosphate

A

Certain bacteria and fungi break down the dead organic matter releasing the phosphate ions into the water or soil, however some of the ions remain in parts of the animal such as bones or shells that are very slow to breakdown

72
Q

What happens to the phosphate ions released after decomposition or ions that very dissolved out of rocks but not absorbed

A

They’re transported by streams and rivers into lakes and oceans where they form sedimentary rocks thus completing the cycle

73
Q

What are the roles of mycorrhizae in nutrient cycles

A
  • Act like extensions of the root system and vastly increase the surface area for the absorption of water and minerals
  • It also acts as a sponge and so holds water and minerals in the neighbourhood of the roots
74
Q

How does mycorrhizae acting like a sponge benefit the plant

A

It holds water and minerals in the neighbourhood of the roots and enables the plant to better resist drought and to take up inorganic ions more readily

75
Q

How does mycorrhiza play a part in the nutrient cycles, particularly the phosphate cycle

A

It improves the uptake of relatively scarce ions

76
Q

What type of relationship is between mycorrhizae and the plant

A

Mutualistic

77
Q

Why is the relationship between mycorrhizae and the plant mutualistic

A

The plant benefits from improved water and mineral ion uptake while the mycorrhiza receives organic compounds such as sugars and amino acids from the plant

78
Q

Why do farmers add fertilisers to their fields

A

To increase the mineral ions concentrations in the soil

79
Q

Why are fertilisers necessary for farmers to use to keep up the high demand for crops

A

Because food production is intensive since its concentrated on specific areas of land that are repeatedly used - this leads to large demand on the soil since mineral ions are continually taken up by the crops so the minerals are being removed from the soil

80
Q

Why does harvesting mean that the farmer will need to use fertilisers

A

Since normally the plants/ animals will die and become dead organic matter however when harvested the organisms are removed before they die so that area will have fallen concentrations of many minerals

81
Q

What are the 2 types of fertilisers

A
  • Natural (organic) fertilisers
  • Artificial (inorganic) fertilisers
82
Q

What does natural/ organic fertiliser consist of

A

Dead and decaying remains of plants and animals as well as animal wastes such as manure and bone meal

83
Q

How are artificial/ inorganic fertilisers made

A

They’re mined from rocks and deposits and then converted into different forms and blended together to give the appropriate balance of minerals for a particular crop

84
Q

In artificial/ inorganic fertiliser there are almost always compounds containing what 3 elements

A
  • Nitrogen
  • Phosphorus
  • Potassium
85
Q

Explain why fertilisers are needed in an argicultural ecosystem

A

Crops are grown repeatedly and intensively in the same area of land. Mineral ions are taken up by the crops, which are transported and consumed away from the land. The mineral ions they contain are not returned to the same area of land and so the levels in the soil are reduced, which can limit the rate of photosynthesis. Fertilisers need to be applied to replace them if photosynthesis/ productivity is to be maintained

86
Q

Suggest a reason why, after a certain point, the addition of more fertiliser no longer improves the productivity of a crop

A

Some other factor is limiting photosynthesis, e.g. light, carbon dioxide, and only the addition of this factor will increase photosynthesis and hence productivity

87
Q

Distinguish between natural and artificial fertilisers

A

Natural fertilisers are organic and come from living organisms in the form of dead remains, urine or faeces. Whereas artificial fertilisers are inorganic and are mixed from rocks and deposits

88
Q

What are 2 advantages of using natural fertilisers

A
  • There’s a gradual release of minerals ions
  • Decreases likelihood of leeching
89
Q

What are the advantages of using artificial fertilisers

A
  • They provide a more concentrated source of minerals
  • A lower volume is needed compared to natural fertilisers resulting in lower costs
  • Can be blended in known composition
90
Q

What are the 2 main benefits of using fertilisers

A
  • Replaces mineral ions removed in harvest
  • Increases crop productivity
91
Q

What are 3 disadvantages of using fertilisers

A
  • Reduces species diversity
  • Leaching
  • Eutrophication
92
Q

What is the role of saprobionts in decomposition

A

They convert dead organic matter into mineral ions as a result of extracellular digestion, releasing mineral ions

93
Q

What is the role of mycorrhizae

A

To increase the surface area of the plants roots for absorption of water and mineral ions

94
Q

Use of artificial fertilisers can cause eutrophication, explain how

A

Nutrients leaching into water body which increase algal growth so decrease light which decreases photosynthesis, so less oxygen in the water so more death

95
Q

Explain why applying high concentrations of nitrate to the soil can cause crops to wilt

A

Water potential in soil is decreased so water moves out by osmosis

96
Q

Explain why leguminous plants can grow in soils with low concentrations of nitrate ions

A

Bacteria reduces the nitrogen gas into ammonia and then ammonium ions can be absorbed

AQA A level Biology (32 decks)

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