5.4 Nutrient cycles Flashcards
(97 cards)
1
Q
What is the nitrogen cycle important
A
Since animals and plants cannot obtain nitrogen through gas exchange
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
3
Q
What is nitrogen so essential
A
Needed for:
- Proteins
- ATP
- Nucleic acids
4
Q
What does nitrogen fixing mean
A
Converting nitrogen gas into a nitrogen containing compound
5
Q
Where does nitrogen fixing occur
A
In the root nodules
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
7
Q
What type of plants contain nitrogenase bacteria in their nodules
A
Legumes
8
Q
How is ammonia absorbed into the plant after being made at the nodules
A
In the form ammonium ions in water
9
Q
Once ammonium ions are in the plant what are they used for
A
Amino acids
ATP
Nucleic acids
10
Q
What 2 things can either happen to a plant during the nitrogen cycle
A
Either:
- Eaten by herbivores
- Death
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
12
Q
What microbe converts the dead organic matter into ammonia during the nitrogen cycle
A
Saprobiants
13
Q
What is the name of the process where dead organic matter is converted into ammonia
A
Ammonification
14
Q
During nitrification, what is ammonia firstly converted into
A
Nitrites , NO2-
15
Q
After ammonia has been converted into nitrites what are the nitrites then converted into
A
Nitrates, NO3-
16
Q
What type of bacteria converts ammonia into nitrites and nitrates
A
Nitrifying bacteria
17
Q
What is the name of the process by which nitrates are converted back into nitrogen gas
A
Denitrification
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
19
Q
What type of reaction is the convertion of nitrogen gas to ammonia
A
Reduction reaction
20
Q
How do nitrogen fixing bacteria respire
A
Aerobically
21
Q
How do saprobionts respire
A
Aerobically
22
Q
How do nitrifying bacteria respire
A
Aerobically
23
Q
How do denitrifying bacteria respire
A
Anaerobically
24
Q
How does nitrogen in the atmosphere get into proteins in plants
A
Nitrogen fixing
25
How does proteins in plants pass on their nitrogen to proteins in animals
Feeding
26
How does the proteins in animals become proteins in dead organic matter
Decomposition
27
How does proteins in animals become nitrogenous waste (urea)
Excretion
28
How does proteins in plants become proteins in dead organic matter
Decomposition
29
How does nitrogenous wastes (urea) become ammonia in the soil, and what does this
Ammonification by saprobiants
30
How does proteins in dead organic matter become ammonia in soil
Ammonification
31
How does ammonia in soil become nitrites in soil
Nitrification
32
How do nitrites in the soil become nitrates in the soil
Nitrification
33
How do nitrates in the soil enter proteins in plants
Absorption
34
How do nitrates in the soil re-enter the atmosphere
Denitrification
35
Why do plants need nitrogen
To manufacture proteins, nucleic acids and other nitrogen-containing compounds
36
Only few plants can use nitrogen gas directly, so what form of nitrogen do plants commonly use and how is it uptaken
Nitrate ions from soil that are absorbed by active transport by the roots
37
How do animals obtain nitrogen-containing compounds
By eating and digesting plants that have absorbed the nitrates
38
Are nitrate ions soluble
Yes
39
Are nitrate ions easily leached
Yes, they are easily leeched (wash) through the soil
40
In a natural ecosystem how are the nitrate concentrations restored after the nitrates have been leeched away beyond the reach of the roots
Largely by the recycling of nitrogen-containing compounds
41
In an agricultural ecosystem, how are the nitrate concentrations restored / increased
They are increased by adding fertilisers
42
In a natural ecosystem how are the nitrogen-containing compounds recycled
When plants and animals die, the process of decomposition begins, where microorganisms replenish the nitrate concentrations in the soil - releasing nitrate ions
43
What are the 4 stages in the nitrogen cycle
- Ammonification
- Nitrification
- Nitrogen fixing
- Denitrification
44
How do saprobiontic microorganisms convert nitrogen-containing compounds into ammonia
By feeding on faeces and dead organic matter - releasing ammonia
45
When ammonia is released by the saprobionts, what does it then form
Ammonium ions in the soil - when nitrogen returns to the non-living components of the ecosystem
46
During nitrification what are the 2 steps from ammonia ions to nitrate ions, stating what type of reaction it is
1. Oxidation of ammonium ions to nitrite ions
2. Oxidation of nitrite ions to nitrate ions
47
How do nitrifying bacteria obtain their energy
Using the energy released by the oxidation reactions converting ammonium ions to nitrate ions
48
Why do farmers need to keep soil structure light and well aerated by ploughing, and have a good drainage system
To create soil with air spaces so nitrifying bacteria can carry out the oxidation reactions with sufficient oxygen
49
What are the 2 types of microorganisms that carry out nitrogen fixation
- Free-living nitrogen-fixing bacteria
- Mutualistic nitrogen-fixing bacteria
50
How do free-living nitrogen-fixing bacteria fix nitrogen
By reducing gaseous nitrogen into ammonia
51
How do mutualistic nitrogen-fixing bacteria fix nitrogen
By living in root nodules of plants such as beans and peas
52
How is the relationship between nitrogen-fixing bacteria in the root nodules and the plant mutualistic
The plant receives nitrogen containing compounds and the bacteria receive carbon containing compounds
53
What condition is the soil usually in when there are more denitrifying bacteria than nitrifying
Waterlogged, low oxygen concentration
54
How could you identify plants that are growing in nitrogen poor soils
Light green with smaller leaves and stunted growth
55
Why is nitrogen in the atmosphere not directly available to plants
Since the N2 has a triple bond making it very stable since it's hard to break the bonds
56
How does deforestation affect the nitrogen cycle
- Nitrates will be leeched out of the soil
- Soil erosion, so reducing soil quality
57
How does crop rotation improve soil fertility
It increases the fertility if it includes legueous plants
58
Livestock farming creates large volumes of animal waste. How would this affect the nitrogen cycle
More dead organic matter so greater concentration of ammonia in soil so more nitrates available
59
What would happen if a farmer used too much fertiliser, what adverse affects can this have on the environment
Washed into rivers, eutrophication and leeching into surrounding water bodies
60
Why are animals not essential to the nitrogen cycle
They only contribute to the dead organic matter
61
How does harvesting of crops affect the nitrogen cycle
It reduces the soils fertility
62
Why is it necessary for farmers to plough their fields
To minimise the denitrifying bacteria so more nitrogen compounds remain in the soil
63
Explain how grass, non-legume, obtains the nitrogen it needs
Nitrates or ammonium ions
64
Name 3 biological molecules that contain phosphorus
- ATP
- Phospholipids
- Nucleic acids
65
In the carbon and nitrogen cycle the main reservoir of each element is in the atmosphere, what is the main reservoir of phophorus
In mineral form rather than in the atmosphere
66
In what form does phosphorus exist in
Phosphate ions , PO4^3-
67
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
Geographical uplifting
68
What processes help the phosphate ions within the sedimentary rock be dissolved
Weathering and erosion
69
How to the phosphate ions get into animals from the rocks
The ions are dissolved meaning they can be absorbed by plants and animals then feed on the plants
70
In animals what happens to excess phosphate ions
They are excreted and may accumulate in waste materials
71
When plants or animals die what happens to the phosphate
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
What happens to the phosphate ions released after decomposition or ions that very dissolved out of rocks but not absorbed
They're transported by streams and rivers into lakes and oceans where they form sedimentary rocks thus completing the cycle
73
What are the roles of mycorrhizae in nutrient cycles
- 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
How does mycorrhizae acting like a sponge benefit the plant
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
How does mycorrhiza play a part in the nutrient cycles, particularly the phosphate cycle
It improves the uptake of relatively scarce ions
76
What type of relationship is between mycorrhizae and the plant
Mutualistic
77
Why is the relationship between mycorrhizae and the plant mutualistic
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
Why do farmers add fertilisers to their fields
To increase the mineral ions concentrations in the soil
79
Why are fertilisers necessary for farmers to use to keep up the high demand for crops
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
Why does harvesting mean that the farmer will need to use fertilisers
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
What are the 2 types of fertilisers
- Natural (organic) fertilisers
- Artificial (inorganic) fertilisers
82
What does natural/ organic fertiliser consist of
Dead and decaying remains of plants and animals as well as animal wastes such as manure and bone meal
83
How are artificial/ inorganic fertilisers made
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
In artificial/ inorganic fertiliser there are almost always compounds containing what 3 elements
- Nitrogen
- Phosphorus
- Potassium
85
Explain why fertilisers are needed in an argicultural ecosystem
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
Suggest a reason why, after a certain point, the addition of more fertiliser no longer improves the productivity of a crop
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
Distinguish between natural and artificial fertilisers
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
What are 2 advantages of using natural fertilisers
- There's a gradual release of minerals ions
- Decreases likelihood of leeching
89
What are the advantages of using artificial fertilisers
- 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
What are the 2 main benefits of using fertilisers
- Replaces mineral ions removed in harvest
- Increases crop productivity
91
What are 3 disadvantages of using fertilisers
- Reduces species diversity
- Leaching
- Eutrophication
92
What is the role of saprobionts in decomposition
They convert dead organic matter into mineral ions as a result of extracellular digestion, releasing mineral ions
93
What is the role of mycorrhizae
To increase the surface area of the plants roots for absorption of water and mineral ions
94
Use of artificial fertilisers can cause eutrophication, explain how
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
Explain why applying high concentrations of nitrate to the soil can cause crops to wilt
Water potential in soil is decreased so water moves out by osmosis
96
Explain why leguminous plants can grow in soils with low concentrations of nitrate ions
Bacteria reduces the nitrogen gas into ammonia and then ammonium ions can be absorbed
97
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction
requires 16 molecules of ATP for each molecule of nitrogen that is reduced.
When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit.
Explain how. (2 marks)
1. Less/no ATP/energy required/used
OR
More ATP/energy available;
2. ATP/energy can be used for
growth/synthesis/replication
OR
Lower (rate of) respiration required
OR
ATP for phosphorylation;
