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A-Level OCR Biology > Chapter 23 - Ecosystems > Flashcards

Chapter 23 - Ecosystems Flashcards

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1
Q

What is an ecosystem?

A

An ecosystem is made up of all the living organisms that interact with one another in defined area, and also the physical factors present in that region

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2
Q

What are abiotic factors of an ecosystem?

A

Abiotic factors are non-living/physical factors that affect an ecosystem

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3
Q

What are biotic factors of an ecosystem?

A

Biotic factors are living factors that affect an ecosystem. Often to do with competition.

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4
Q

Give two examples of biotic factors

A

Biotic- presence of organisms, the population size of organisms

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5
Q

Give two examples of abiotic factors

A

Abiotic- precipitation levels, temperature

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6
Q

What impact would a lack of light have on an ecosystem?

A

The lesser the light availability, the lesser the success of photosynthesis so the lesser the success of plants. As plants are the primary producers, a smaller number of primary producers would have a knock on effect for the entire ecosystem.

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7
Q

What effect would an increasing temperature would have on an ecosystem?

A

Changes in temperature will affect metabolic enzymes therefore metabolic activity of organisms.
Furthemore, changes in temperature can affect things like:
Migration
Hibernation
Plant leaf fall

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8
Q

What are three different types of soil?

A

Clay
Loam
Sandy

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9
Q

What are the properties of clay soil?

A

Fine particles, easily waterlogged and forms clumps when wet

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10
Q

What are the properties of loam soil?

A

Different sized particles, retains water but does not become water-logged

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11
Q

What are the properties of sandy soil?

A

Coarse well separated particles, allows free draining (does not retain water), and is easily eroded

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12
Q

Why would the type of soil affect an ecosystem?

A

Different types of soil would react differently to abiotic factors like water levels, which would have a direct impact on plant life, and as plants are the foundation of ecosystems, this would impact the entire ecosystem.

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13
Q

What does changes in abiotic factors affect the most and why?

A

Plants, as they convert abiotic factors like sunlight and water into energy (through photosynthesis), as well as get nutrients from abiotic factors like soil. Hence their livelihood almost entirely depends on abiotic factors

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14
Q

What are autotrophs?

A

Organisms that are capable of self-nourishment by using inorganic materials as a source of nutrients and using photosynthesis or chemosynthesis as a source of energy

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15
Q

What are heterotrophs?

A

Organisms that are not capable of self-nourishment, so have to source and eat food in order to gain chemical energy.

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16
Q

What are autotrophs also referred to as?

A

Producers

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17
Q

What are heterotrophs also referred to as?

A

Consumers

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18
Q

What are the different trophic levels?

A 
(Sometimes) quaternary consumer
Tertiary consumer
Secondary consumer
Primary consumer
Producer
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19
Q

What is biomass?

A

The mass of living material present in particular areas or organisms (i.e. all the cells and tissues)

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20
Q

Why must the dry mass of organisms be calculated instead of the overall mass?

A

Varying amounts of water in organisms will cause unreliable results

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21
Q

What are two problems with measuring dry mass?

A
  • The organism must be killed
  • To minimise destruction of organisms, only a small sample is taken, but this may not be representative of the entire population
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22
Q

What is biomass measured in?

A

Grams per square metre for land

Grams per cubic metre for water

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23
Q

What is the energy at each trophic level measured in?

A

kJ per square metre per year

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24
Q

Why is energy measured on a yearly basis?

A

To allow for changes in photosynthetic production and consumer feeding patterns throughout the year

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25
Q

Why is there a limited number of trophic levels?

A

As there would be insufficient biomass to pass on to subsequent organisms

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26
Q

What are pyramids of numbers?

A

Each level is a trophic level.

The size of each level represents the abundance of organisms within that trophic level.

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27
Q

What are pyramids of biomass?

A

Each level is a trophic level or a particular group of organisms.
The size of each level represents the biomass of that group.
The size of each level essentially always decreases as you go up the pyramid

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28
Q

What is the exception to the trend in pyramids of biomass?

A

Marine biomass pyramids tend to be inverted at the bottom.
This is because phytoplankton are the primary producer - phytoplankton have a v small mass (they are microscopic) so the biomass is smaller than that of the next trophic level.

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29
Q

How can biomass and energy be equated?

A

As organic compounds, which make up biomass, are a store of energy, energy can be equated to biomass. However when animals consume food, only a small proportion ingested is converted into new tissue (biomass).

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30
Q

What is ecological efficiency?

A

The efficiency with which biomass or energy is transferred from one trophic level to the next

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31
Q

What factors limit ecological efficiency at producer level?

A
  • Some wavelengths of light are not absorbed
  • Some light is transmitted through or reflected off the leaf
  • Energy is used in respiration and photosynthetic reactions
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32
Q

What is net production of a producer?

A

Net production = gross production - respiratory losses

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33
Q

What factors limit ecological efficiency at consumer level?

A
  • Not all of the biomass of an organism is consumed (e.g. bones and roots)
  • Some parts of an organism are eaten but indigestible so leave as waste
  • Energy is transferred to the environment as heat, as a result of movement and respiration
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34
Q

What is the formula for ecological efficiency?

A

Ecological efficiency = energy or biomass available after transfer / energy or biomass available before transfer

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35
Q

What is net production of a consumer?

A

Net production = gross productivity - (respiratory losses + energy lost in urine + faeces)

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36
Q

Give 2 problems of pyramid of numbers

A
  • Oversimplified

- Doesn’t to into consideration the size of organisms (e.g. a single oak tree could provide energy for many organisms)

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37
Q

Give 2 problems of pyramid of biomass

A
  • Measuring dry mass involves killing the organism

- They only measure biomass of one specific time point

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38
Q

What is the advantage of pyramids of energy?

A
  • Measured over a year period, so takes into account variation over the year (e.g. different photosynthetic periods)
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39
Q

What is a problem with pyramids of energy?

A
  • Data must be collected over a large time period (can be difficult)
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40
Q

Give 4 human methods to increase productivity of energy transfer

A

Herbicides
Fungicides
Insecticides
Fertiliser

41
Q

How do herbicides increase productivity of energy transfer?

A

Kill weeds - less competition - more energy available for crop growth

42
Q

How do fungicides increase productivity of energy transfer?

A

Kill fungi - more energy available for crop to grow as opposed to fighting infection

43
Q

How do pesticides increase productivity of energy transfer?

A

Less biomass lost - more biomass that can pass to next trophic level

44
Q

How do fertilisers increase productivity of energy transfer?

A

Putting in nutrients into soil - more growth - growth not restricted as nutrients not a limiting factor

45
Q

What can animals do to increase productivity of energy transfer?

A
  • Stay warm
  • Reduce movement
  • Eat a high energy diet
46
Q

What is the relationship between complexity of food chains and biomass lost?

A

The more complex the food chain (i.e. the greater the number of trophic levels), the more biomass and energy that is lost

47
Q

What are decomposers?

A

Organisms that feed on and break down dead organic matter into inorganic compounds. Decomposers are saprotrophs

48
Q

What is saprobiotic nutrition?

A

Where decomposers secrete enzymes that externally break down complex dead or waste organic molecules into simpler soluble molecules. The decomposers then absorb these simpler molecules to obtain energy.

49
Q

What is released during saprobiotic nutrition?

A

Through saprobiotic nutrition, inorganic compound and elements are released into the environment from the decomposers

50
Q

What are detritivores?

A

Organisms that help speed up the decay process by feed on detritus (dead and decaying material). They break the detritus down into smaller pieces of organic material

51
Q

What is the effect of detritivores breaking the detritus down into smaller pieces?

A

Increases the surface area for the decomposers to work on

52
Q

What is the main difference between decomposers/saprotrophs and detritivores?

A

Decomposers secrete enzymes that digest dead material externally, whereas detritivores digest internally

53
Q

Why do animals and plants need nitrogen?

A

Because it is an essential element of amino acids (and so proteins) and DNA

54
Q

How do animals obtain nitrogen?

A

In the food they eat

55
Q

How do plants obtain nitrogen?

A

From the environment

56
Q

Where can plants not obtain nitrogen from?

A

The atmosphere- plants cannot take up nitrogen gas (N2). The nitrogen must be combined with other elements like oxygen or hydrogen in order to be taken up by plants

57
Q

What is nitrogen fixation?

A

The combination of nitrogen with hydrogen to produce ammonia (NH3), which can be absorbed and used by plants

58
Q

What is the role of bacteria in nitrogen fixation?

A

Nitrogen-fixing bacteria contain enzymes that combine the hydrogen and nitrogen to form ammonia

59
Q

What is the name of the bacterial enzyme used in nitrogen fixation?

A

Nitrogenase

60
Q

What are the two types of nitrogen-fixing bacteria with example of each?

A
  • Free-living soil bacterium (e.g. Azotobacter)

- Bacteria found in the root nodules of the plant which have a symbiotic mutualistic relationship (e.g. Rhizobium)

61
Q

What does a symbiotic mutualistic relationship mean with regard to nitrogen-fixing bacterium and plants?

A

It is mutually beneficial:

  • the plant gains NH3 produced by the bacteria to be used as a source for nitrogen to be used in amino acids and DNA
  • the bacterium gains carbohydrates produced by the plant to be used as an energy source
62
Q

What is nitrification?

A

The process by which ammonium compounds (NH3 or NH4+) are converted into nitrogen containing molecules that can be used by plants

63
Q

What type of reaction is nitrification and what does this mean for where it occurs?

A

It is an oxidation reaction, meaning it only occurs in well-aerated soil

64
Q

How do producers take carbon in from the atmosphere?

A

CO2 used in photosynthesis

65
Q

How do producers release carbon into the atmosphere?

A

From respiration

66
Q

How do consumers take carbon from producers?

A

Feeding

67
Q

How do consumers release carbon into the atmosphere?

A

From respiration

68
Q

How do decomposers get carbon from consumers or producers?

A

They decompose dead organisms

69
Q

How do decomposers release carbon back into the atmosphere?

A

Through decomposition

70
Q

What happens to carbon in dead organisms when decomposition cannot occur?

A

Carbon will be trapped and become fossil fuel

71
Q

How do fossil fuels release carbon back into the atmosphere?

A

Through combustion

72
Q

When are carbon dioxide levels higher throughout the day and why?

A

CO2 levels are higher at night because photosynthesis does not occur without light

73
Q

When are carbon dioxide levels lower throughout the year and why?

A

CO2 levels are lower during summer because more photosynthesis is occurring

74
Q

What is succession?

A

The process by which an ecosystem changes over time. It takes place in a number of steps

75
Q

What are the steps known as in succession?

A

Seral stages

76
Q

What happens at each seral stage?

A

Key species change the abiotic factors, to make them more suitable for subsequent species.

77
Q

Where does primary succession occur?

A

It occurs on newly formed or newly exposed land (e.g. erupted volcano matter or sea levels dropping)

78
Q

What does primary succession begin with?

A

No soil or organic matter

79
Q

When does secondary succession occur?

A

When the area has been cleared of all plants, however, there has been little/no disruption to the soil (e.g. land effected by forest fire or deforestation)

80
Q

What are the seral stages of primary succession?

A 
Pioneer community
Secondary colonisers
Tertiary colonisers
Scrubland
Climax community
81
Q

What are 2 examples of pioneer species in primary succession?

A

Lichens

Marram grass

82
Q

What are the adaptions of lichens that allows them to be pioneer species?

A

They are able to colonise bare rock, by secreting acid that breaks down the rock to release minerals

83
Q

What are the adaptions of marram grass that allows it to be a pioneer species?

A

They are able to colonise sand, as they have long roots which can reach water

84
Q

What must pioneer species be able to do?

A

Survive in extreme conditions

85
Q

What 3 seral stages make up the intermediate community?

A

Secondary colonisers
Tertiary colonisers
Shrubland

86
Q

What happens after pioneer species (e.g. lichens) die?

A

Decomposers break down the organic matter, releasing nutrients onto the land.

87
Q

What is formed from the decomposing of pioneer species?

A

A basic soil is formed, which is capable of retaining some water

88
Q

What is the basic soil known as?

A

Humus

89
Q

What happens during the intermediate community seral stages?

A

The secondary coloniser grows, then dies and decomposes, releasing more nutrients.
The tertiary coloniser grows, then dies and decomposes and so on.
After each stage the abiotic factors continue to improve (e.g. the soil becomes increasingly nutrient rich). This allows for more and more complex and advanced species to develop.

90
Q

What are dominant species?

A

The species at each seral stage that is doing the outcompeting i.e. the one that is succeeding. It is different at each stage

91
Q

How does biodiversity change throughout succession?

A

Biodiversity tends to increase as succession takes place, however it tends to peak in the intermediate community then decrease, as the dominant species of the climax community out-competes other species resulting in their elimination

92
Q

What is the relationship between species dominance and biodiversity?

A

The more successful the dominant species, the less the biodiversity in a given ecosystem

93
Q

What is the difference between primary and secondary succession?

A

In secondary succession, soil is already present, meaning pioneer species tends to be larger and the process is faster.

94
Q

How does animal succession work?

A

It works alongside plant succession. It begins with primary consumers like insects, which are able to consume and shelter in the mosses and lichens. As the abiotic and biotic factors improve, more complex animals will colonise.

95
Q

Why does animal succession take longer?

A

They must migrate into the new area, and will only migrate when the biotic factors are favourable

96
Q

What is the final stage known as when succession is stopped artificially?

A

The plagioclimax

97
Q

What is an example of deflected succession?

A

Grazing and trampling of vegetation by livestock; results in large areas remaining as grassland. This would make the grassland the plagioclimax

98
Q

What is the climax community?

A

The final seral stage, in which the community is at a stable state.

A-Level OCR Biology (21 decks)

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