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AQA A Level Biology flashcards > 5B - Energy Transfer and Nutrient Cycles > Flashcards

5B - Energy Transfer and Nutrient Cycles Flashcards

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1
Q

What does an ecosystem include?

A

All the organisms living in a particular area and all the abiotic conditions.

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2
Q

What are producers?

A

Organisms that make their own food through photosynthesis.

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3
Q

What do producers use the sugars produced in photosynthesis for?

A
  • Respiration -> Releasing energy for growth

* Making biological molecules (e.g. cellulose)

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4
Q

What is biomass?

A

The mass of living material in an organism (or the chemical energy stored).

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5
Q

Describe the order of a food chain.

A 
• Producer
• Primary consumer
• Secondary consumer
• Tertiary consumer
(• Decomposers)
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6
Q

How can biomass be measured?

A

Looking at:
• The dry mass (kg)
• The chemical energy stored (kJ)

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7
Q

What is dry mass?

A

The mass of an organism with the water removed.

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8
Q

How can dry mass (biomass) of an organism be measured?

A

1) Dry an organism at a low temperature in an oven
2) Weigh it regularly until the mass becomes constant (so all the water has been removed)
3) If needed, the result is scaled up to give the biomass of the total population or of the area being investigated
4) The mass of carbon is taken as about 50% of the dry mass

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9
Q

What are the units for dry mass per unit area?

A

kg/m2

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10
Q

What are the two ways dry mass may be quoted?

A
  • Dry mass of the total population
  • Dry mass of the area being investigated

NOTE: It may refer to the mass of carbon contained, not the total dry mass.

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11
Q

How much of dry mass is usually mass of carbon?

A

About 50%

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12
Q

How can the chemical energy (biomass) of an organism be measured?

A

1) Dry an organism at a low temperature in an oven
2) Weigh it regularly until the mass becomes constant (so all the water has been removed)
3) Burn the biomass in a calorimeter
4) The amount of heat given off tells you how much energy is in it

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13
Q

What are the units for chemical energy?

A

J (or kJ)

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14
Q

What is GPP?

A
  • Gross Primary Production

* The total amount of chemical energy converted from light energy by plants in a given area

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15
Q

What is R?

A
  • Respiratory loss

* The amount of the GPP lost to the environment as heat when plants respire

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16
Q

How much of GPP is lost as respiratory loss?

A

About 50%

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17
Q

What is NPP?

A
  • Net Primary Production
  • The remaining chemical energy from GPP that is not lost as respiratory losses. It is the energy available for growth and reproduction.
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18
Q

Give the equation relating GPP, NPP and R.

A

NPP = GPP - R

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19
Q

How is NPP stored?

A

As biomass.

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20
Q

How much of GPP is passed down to the next trophic level?

A

Just NPP.

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21
Q

What is primary productivity?

A

When primary production is expressed as a RATE, it is called this.

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22
Q

How is primary productivity usually expressed?

A
  • As a rate

* i.e. The total amount of chemical energy in a given area in a given time

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23
Q

What are the units for primary productivity?

A

kJ/ha/yr (or kJ/m2/yr)

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24
Q

What is the difference between primary production and primary productivity?

A
  • Primary production - Energy per area

* Primary productivity - Energy per area per time

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25
Q

The grass in an ecosystem has a gross primary productivity of 20,000 kJ/m2/yr. It loses 8,000 kJ/m2/yr as heat from respiration. What is the net primary productivity?

A

12,000 kJ/m2/yr

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26
Q

How much of a consumers’ food is transferred to the next trophic level?

A

About 10%

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27
Q

What are some reasons why not all biomass is passed between trophic levels?

A
  • Not all food is eaten (e.g bones)
  • Excretion
  • Respiration
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28
Q

What is the net production of a consumer?

A

The chemical energy stored in a consumers’ biomass that is available to the next trophic level.

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29
Q

What is the equation for net production of consumers?

A

N = I - (F + R)

Where:
N = Net production
I = Chemical energy in ingested food
F = Chemical energy lost in faeces and urine
R = Energy lost through respiration
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30
Q

What can the net production of consumers be called?

A

Secondary production

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31
Q

What is the difference between primary and secondary productivity?

A

Primary is in producers, while secondary is in consumers.

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32
Q

Rabbits receive 20,000 kJ/m2/yr and their net productivity is 2,000 kJ/m2/yr. What is the efficiency of energy transfer?

A

10%

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33
Q

What is the difference between a food chain and food web?

A
  • Food chain -> Shows simple lines of energy transfer.

* Food web -> Shows how lots of food chains overlap.

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34
Q

What is each stage in a food chain called?

A

Trophic level

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35
Q

What are decomposers?

A

Organisms that break down dead or undigested material, allowing nutrients to be recycled.

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36
Q

What are the two main ways in which farming practices increase the efficiency of energy transfer?

A

1) Reducing the energy lost to other organisms (e.g. pests)

2) Reducing the energy lost through respiration

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37
Q

How can farmers increase efficiency of energy transfers by reducing energy lost to other organisms?

A 
Simplifying food webs by removing pests by:
CHEMICAL PESTICIDES
• Insecticides
• Herbicides
BIOLOGICAL AGENTS
• Parasites
• Pathogenic bacteria and viruses
INTEGRATED SYSTEMS (both chemical and biological)
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38
Q

How do insecticides help to increase the efficiency of energy transfers?

A
  • They kill insect pests that eat and damage crops

* So less biomass is lost and the NPP is greater

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39
Q

How do herbicides help to increase the efficiency of energy transfers?

A
  • They kill weeds, which removes competition and removes the habitat and food source of insect pests
  • So more biomass is grown and less is lost, so the NPP is greater
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40
Q

How do parasites help to increase the efficiency of energy transfers?

A
  • They live in or lay their eggs on a pest insect, which kills it or reduces its ability to function
  • So less biomass is lost to pests and the NPP is greater
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41
Q

How do pathogenic bacteria and viruses help to increase the efficiency of energy transfers?

A
  • They kill insect pests that eat and damage crops

* So less biomass is lost and the NPP is greater

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42
Q

How can farmers increase efficiency of energy transfers by reducing energy lost by respiration?

A
  • Restricting the movement of animals

* Building pens indoors and keeping them warm

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43
Q

What are the pros and cons of factory farming?

A

PROS
• More food can be produced in a shorter space of time, often at a lower cost
CONS
• Raises ethical issues

44
Q

What is a natural ecosystem?

A

One that hasn’t been changed by human activity.

45
Q

What happens when human activity enters a natural ecosystem?

A

It can disrupt the cycling of nutrients.

46
Q

What is the technical name for decomposers?

A

Saprobionts

47
Q

What are saprobionts?

A

A type of decomposer that feed on the remains of dead plants and animals, and on their waste products.

48
Q

How are saprobionts useful in food webs?

A

They break down dead and waste matter, allowing important chemical elements to be recycled.

49
Q

How do saprobionts work?

A

EXTRACELLULAR DIGESTION
• Secrete enzymes and digest food externally
• Then absorb the nutrients they need

50
Q

What does extracellular digestion involve?

A

Breaking down organic molecules into inorganic ions.

51
Q

What is saprobiotic nutrition?

A

Obtaining nutrients from dead organic matter using extracellular digestion.

52
Q

What is the name for symbiotic relationships between fungi and roots of plants?

A

Mycorrhizae

53
Q

What are mycorrhizae?

A

Symbiotic relationships between some fungi and roots of plants.

54
Q

What are mycorrhizae between?

A

Some fungi and roots of plants

55
Q

Describe how mycorrhizae work.

A
  • Fungi are made up of long, thin strands called hyphae, which connect to the plant roots
  • Hyphae increase surface area from the plant’s root system, helping them absorb ions that are scarce and water
  • In turn, the fungi obtain organic compounds from the plants, such as glucose
56
Q

What do plants gain from mycorrhizae?

A

Increased surface area for absorption of:
• Ions
• Water

57
Q

What do fungi gain from mycorrhizae?

A

Organic compounds, such as glucose, from the plant

58
Q

What is nitrogen needed for in plants and animals?

A

To make:
• Proteins
• Nucleic acids (DNA and RNA)

59
Q

How much of the atmosphere is nitrogen gas?

A

78%

60
Q

Why can’t nitrogen from the atmosphere be used by plants and bacteria directly?

A

It is very reactive.

61
Q

What does the nitrogen cycle show?

A

How nitrogen is converted into a usable form and then passed on between different living organisms and the non-living environment.

62
Q

What are the 4 stages of the nitrogen cycle?

A

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

63
Q

How does nitrogen from the atmosphere get taken up by plants and animals?

A
  • It must be in the form of nitrogen compounds (e.g. nitrates).
  • Plants absorb nitrates from the soil.
  • Animals can only take in nitrogen by consuming other organisms.
64
Q

Describe nitrogen fixation.

A
  • When nitrogen gas in the atmosphere is turned into nitrogen-containing compounds by bacteria such as Rhizobium.
  • They turn nitrogen into ammonia, which goes on to form ammonium in solution that can be used by plants.
  • Rhizobium are found inside root nodules (growths on the roots) of leguminous plants.
  • This is mutualistic -> Bacteria provide plants with nitrogen compounds and the plant provides them with carbohydrates.

• Atmospheric nitrogen -> Ammonia -> Ammonium -> Nitrogen compounds in plants

65
Q

Give an example of a nitrogen-fixing bacteria.

A

Rhizobium

66
Q

Where is Rhizobium (a nitrogen-fixing bacteria) found?

A

In root nodules (growths on the roots) of leguminous plants

67
Q

Give some examples of leguminous plants.

A
  • Peas
  • Beans
  • Clover
68
Q

What does nitrogen fixation convert from and to?

A

Atmospheric nitrogen -> Ammonia -> Ammonium -> Nitrogen compounds in plants

69
Q

How do nitrogen compounds reach animals?

A

Through feeding on plants and animals that contain nitrogen containing compounds.

70
Q

Describe ammonification.

A
  • Saprobionts turn nitrogen compounds from dead organisms and waste into ammonia, which then form ammonium ions.
  • Nitrogen compounds in plants -> Ammonia -> Ammonium ions
71
Q

What carries out ammonification?

A

Saprobionts (decomposers)

72
Q

What does ammonification convert from and to?

A

Nitrogen compounds in plants -> Ammonia -> Ammonium ions

73
Q

Describe nitrification.

A

• When ammonium ions in the soil are changed into nitrites and then nitrates that can then be used by plants.
FIRST STEP
• Nitrosomonas change ammonium ions into nitrites
SECOND STEP
• Nitrobacter change nitrites into nitrates

• Ammonium ions -> Nitrites -> Nitrates

74
Q

Give an example of nitrifying bacteria.

A
  • Nitrosomonas (ammonium ions -> nitrates)

* Nitrobacter (nitrites -> nitrates)

75
Q

What does nitrification convert from and to?

A

Ammonium ions -> Nitrites -> Nitrates

76
Q

Describe denitrification.

A
  • Denitrifying bacteria convert nitrates in the soil into nitrogen gas (by using the nitrates in respiration and releasing nitrogen gas)
  • This happens under anaerobic conditions

• Nitrates -> Atmospheric nitrogen

77
Q

How do denitrifying bacteria work?

A

The use nitrates in the soil to respire, which releases nitrogen gas into the atmosphere.

78
Q

Under what conditions do denitrifying bacteria work?

A

Anaerobic e.g. in waterlogged soils

79
Q

How else can nitrogen get into an ecosystem?

A
  • Lightning -> Fixes atmospheric nitrogen

* Artificial fertilisers -> Produced from atmospheric nitrogen on an industrial scale in the Haber process

80
Q

Do you need to learn the name of the different microorganisms in the nitrogen cycle?

A

No

81
Q

Name all of the microorganisms involved in the nitrogen cycle.

A
  • Nitrogen fixing bacteria
  • Saprobionts (bacteria, fungi, etc.) in ammonification
  • Nitrifying bacteria
  • Denitrifying bacteria
82
Q

Remember to practise drawing out the full diagram for the nitrogen cycle.

A

Pg 132 of revision guide.

83
Q

Describe the whole nitrogen cycle.

A

1) NITROGEN FIXATION
• Nitrogen gas in the atmosphere is turned into nitrogen-containing compounds by bacteria such as Rhizobium.
• They turn nitrogen into ammonia, which goes on to form ammonium in solution that can be used by plants.
• Rhizobium are found inside root nodules (growths on the roots) of leguminous plants.
(• Atmospheric nitrogen -> Ammonia -> Ammonium -> Nitrogen compounds in plants)
2) AMMONIFICATION
• Saprobionts turn nitrogen compounds from dead organisms and waste into ammonia, which then form ammonium ions.
(• Nitrogen compounds in plants -> Ammonia -> Ammonium ions)
3) NITRIFICATION
• When ammonium ions in the soil are changed into nitrites and then nitrates that can then be used by plants.
(• Ammonium ions -> Nitrites -> Nitrates)
4) DENITRIFICATION
• Denitrifying bacteria convert nitrates in the soil into nitrogen gas (by using the nitrates in respiration and releasing nitrogen gas)
• This happens under anaerobic conditions
(• Nitrates -> Atmospheric nitrogen)

84
Q

What do plants and animals need phosphorus for?

A

To produce biological molecules such as:
• Phospholipids
• DNA
• ATP

85
Q

How is phosphorus found in rocks and in oceans?

A

As phosphate ions.

86
Q

How can plants and other producers use phosphate ions?

A

They can be assimilated (absorbed and then used to make more complex molecules) from water in soil.

87
Q

What is the formula for phosphate ions?

A

PO4 3-

88
Q

What is assimilation?

A

When ions are absorbed by plants so they can be used to make more complex molecules.

89
Q

Describe the phosphorus cycle.

A

1) Phosphate ions in rocks are released into soil by weathering.
2) Phosphate ions are taken into plants through the roots (mycorrhizae help with this).
3) Phosphate ions transferred through the food chain (as animals eat plants and other animals)
4) Phosphate ions are lost in waste products from animals.
5) Saprobionts break down organic compounds when plants and animals die and their waste, releasing phosphate ions into the soil
6) Weathering of rocks ALSO releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, such as algae, and passed along the food chain to birds.
7) Waste products from sea birds are known as guano. It returns a significant amount of phosphate ions to soil.

90
Q

Is the phosphorus cycle one cycle?

A

No, it is kind of 2 cycles -> one in the water and one on land.

91
Q

What is guano?

A

Sea bird waste

92
Q

What is guano used for and why?

A

It is often used as a natural fertiliser, since it has a high proportion of phosphate ions.

93
Q

Remember to practise drawing out the phosphorus cycle.

A

Pg 133 of revision guide

94
Q

How are nutrients lost from fields?

A
  • Harvesting crop.
  • Removing animals or animal products.

It removes the minerals that these have taken up from the soil. They cannot decompose there or release waste products, so the minerals are not returned to the soil.

95
Q

What are fertilisers used for?

A

Replacing lost ions (e.g. phosphates or nitrates) from soil, which means more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer.

96
Q

What are the two types of fertiliser?

A
  • Natural

* Artificial

97
Q

What are artificial fertilisers?

A
  • Inorganic

* Contain pure chemicals (e.g. ammonium nitrate) as powders or pellets

98
Q

What are natural fertilisers?

A
  • Organic

* Include manure, composted vegetables, crop residues and sewage sludge

99
Q

What are the issues with fertilisers?

A
  • Leaching -> Eutrophication

* Crops and other plants to die if there is too much of a particular nutrient

100
Q

What is leaching?

A

When water-soluble compounds in the soil are washed away e.g. by rain. It is often into nearby ponds and rivers.

101
Q

When is leaching most likely to occur?

A

When fertiliser is applied just before heavy rainfall.

102
Q

What type of fertiliser leads to more leaching and why?

A
  • Artificial fertilisers -> Inorganic ions are relatively soluble -> More likely to cause leaching
  • Natural fertilisers -> Nitrogen and phosphorus are contained in organic molecules that need to be decomposed by microorganisms before the nutrients can be used by plants -> Decomposition is gradual, so the release is slow -> Less likely to cause leaching
103
Q

Which nutrient in artificial fertilisers is likely to cause more leaching and why? (Nitrates or phosphates)

A

Nitrates, because they are more soluble.

104
Q

What can leaching lead to?

A

Eutrophication

105
Q

Describe the process of eutrophication.

A

1) Mineral ions leached from fertilised fields stimulate the rapid growth of algae in ponds and rivers.
2) Large amounts of algae block light from reaching the plants below.
3) The plants are unable to photosynthesise and eventually die.
4) Bacteria feed on the dead plant matter, which causes their number to grow. Their aerobic respiration reduces the oxygen concentration of the water.
5) Fish and other aquatic organisms die because there isn’t enough dissolved oxygen.

AQA A Level Biology flashcards (19 decks)

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