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A-Level Biology > 23 Ecosystems > Flashcards

23 Ecosystems Flashcards

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1
Q

What is an ecosystem?

A

An ecosystem is all the interacting living organisms and the non living conditions in an area.

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2
Q

Which two type of factors affect ecosystems?

A

1) Biotic factors

2) Abiotic factors

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3
Q

What are biotic factors?

A
  • The living factors.

- E.g the size of the hedgehog population in an ecosystem.

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4
Q

What are non biotic factors?

A
  • The non-living or physical factors.

- E.g the amount of rain fall, annual temperature range of the ecosystem

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5
Q

Name 5 abiotic factors.

A

1) Light
2) Temperature
3) Water availability
4) Oxygen availability
5) Edhaphic (soil factors)

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6
Q

What does trophic level mean?

A

Each stage in a food chain

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7
Q

What is the first trophic level known as?

A

Producer- an organism that converts light energy into chemical energy by the process of photosynthesis.

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8
Q

What are consumers?

A

Organisms that obtain their energy by feeding on other organisms.

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9
Q

What is biomass?

A

Biomass is the mass of living material present in a particular place or in particular organisms.

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10
Q

What does ecological efficiency mean?

A

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

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11
Q

How much sunlight do producers convert into chemical energy?

A

1-3% of sunlight

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12
Q

Why is only a small percentage of sunlight converted into chemical energy?

A
  • Not all of solar energy available is used for photosynthesis, approximately 90% is reflected and some is unusable wavelength.
  • Other factors may limit photosynthesis e.g water availability
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13
Q

How can you calculate the energy available to the next trophic level?

A

Net production=gross production-respiratory losses

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14
Q

What percentage of biomass do consumers convert to their own organic tissue?

A

10%

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15
Q

Why is only a small percentage of biomass converted to consumers own tissue?

A

1) Not all of the biomass of an organism is eaten e.g plant roots or animal bones
2) Some energy is transferred to the environment as metabolic heat
3) Some parts of an organism are eaten but indigestible
4) Some energy is lost from the animal in excretory materials e.g urine

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16
Q

How can you calculate ecological efficiency?

A

(Energy or biomass available after transfer/energy or biomass available before transfer) *100

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17
Q

What is a decomposer?

A

An organism that feeds on and breaks down dead plant or animal matter and releasing nutrients available to photosynthetic producers in the ecosystem.

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18
Q

What are some examples of decomposers?

A

Microscopic fungi and bacteria

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19
Q

Why are decomposers saprotrophs?

A

Because they obtain their energy from dead or waste organic material.

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20
Q

What is a detritivore?

A

An organism which speeds up decay by breaking down detritus into smaller pieces.

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21
Q

What is the process of nitrogen fixation?

A

The conversion of nitrogen gas to ammonium compounds.

22
Q

What are some examples of nitrogen fixing bacteria?

A

Azotobacter and Rhizobacterium

23
Q

How do nitrogen fixing bacteria work?

A

They contain the enzyme nitrogenase, which combines atmospheric nitrogen with hydrogen to produce ammonia.

24
Q

What type of relationship is there with the plant and nitrogen fixing bacteria?

A

Symbiotic mutualistic relationship.

25
Q

Why is the relationship mutualistic?

A
  • The plant gains amino acids from Rhizobium

- The bacteria gain carbohydrates produced by the plant during photosynthesis, which they can use as an energy source.

26
Q

How does nitrification take place?

A

1) Nitrifying bacteria (nitrosomanas) oxidise ammonium compounds into nitrites.
2) Nitrobacter oxidise nitrites into nitrates.

27
Q

Where does nitrification take place?

A

in well-aerated soil

28
Q

What is denitrification?

A

The conversion of nitrates to nitrogen gas.

29
Q

In what conditions does denitrification occur?

A
  • In absence of oxygen e.g in waterlogged soils

So in ANAEROBIC CONDITIONS

30
Q

What is ammonification?

A

The conversion of nitrogen compounds in dead organic matter or waste into ammonium compounds by decomposers.

31
Q

Why are atmospheric carbon dioxide levels higher at night than during the day?

A
  • Photosynthesis only takes place in the light, and so during the day.
  • Photosynthesis removes carbon dioxide from the atmosphere.
  • Respiration is carried out by all living organisms throughout day and night, so it releases carbon dioxide at a relatively constant rate into atmosphere.
32
Q

Why have carbon dioxide levels increases significantly over the past 200 years?

A

Due to:

1) Combustion of fossil fuels- releases carbon dioxide back into the atmosphere
2) Deforestation- removes significant quantities of photosynthesising biomass from Earth. Therefore, less carbon dioxide is removed rom atmosphere.

33
Q

What is succession?

A

The progressive replacement of dominant type of species or community by another in an ecosystem, until a stable climax community is established.

34
Q

What are the two types of succession?

A

1) Primary succession

2) Secondary succession

35
Q

What is primary succession?

A
  • This occurs on an area of land that has been newly formed or exposed such as bare rock.
  • There is no soil or organic material present to begin with.
36
Q

What is secondary succession?

A

This occurs on areas of land where soil is present, but it contains no plant or animal species.
E.g bare earth that remains after a forest fire

37
Q

When does primary succession occur?

A
  • Volcanoes erupt, depositing lava- when lava cools and solidifies igneous rock is created.
  • Sand is blown by the wind or deposited by the sea to create new sand dunes
  • Slit and mud are deposited at river estuaries
  • Glaciers retreat depositing rubble and exposing rock.
38
Q

What is are seral stages?

A

The steps in succession.

39
Q

What are the main seral stages?

A
  • Pioneer community
  • Intermediate community
  • Climax community
40
Q

How does primary succession begin?

A
  • Primary succession begins by the colonisation of an inhospitable environment, by organisms known as pioneer species.
  • These species arrive as spores or seeds carried by the wind e.g algae and lichen
41
Q

What adaptations do pioneer species have to enable them to colonise this bare environment?

A
  • The ability of produce large quantities of seeds or spores, that are blown by the wind and deposited on new land
  • Seeds that germinate rapidly
  • The ability to photosynthesis to produce own energy
  • Tolerance to extreme environments
  • Ability of fix nitrogen from the atmosphere, which adds to the mineral content of the soil
42
Q

Describe what occurs in intermediate community.

A

1) The pioneer species die and decomposes, releasing organic products (humus) into the soil.
2) The soil becomes able to support the growth of new species of plant, known as secondary colonisers, as it contains minerals such as nitrates, and has the ability to retain water.
3) The secondary colonisers arrive as spores or seeds e.g mosses
4) As environmental conditions continue to improve, new species of plant arrive e.g ferns. These are known as tertiary colonisers.
5) At each stage rock continues to be eroded and mass of organic matter increases.
6) When organisms decompose, they contribute to a deeper more nutrient rich soil which retains more water.
7) This makes abiotic conditions more favourable initially for small flowering plants such as grasses, later shrubs and finally small trees.

43
Q

What occurs in climax community?

A
  • The final seral stage is called the climax community.

- The community is in a stable state and will show very little change over time.

44
Q

What is plagioclimax?

A

Plagioclimax is the final stage that is formed when succession is stopped artificially.

45
Q

Why does deflection succession occur?

A
  • Grazing and trampling of vegetation by domesticated animals
  • Removing existing vegetation to plant crops
  • Burning as a means of forest clearance
46
Q

What does distribution of organisms refer to?

A

Where organisms are found in organism

47
Q

What does abundance of organisms refer to?

A

Number of individuals of species present in an area at any given time.

48
Q

What increases number of individuals?

A

Immigration & births

49
Q

What decreases number of individuals?

A

Emigration and deaths

50
Q

How can you measure abundance?

A

In plants: Quadrats

In animals: Capture-recapture

A-Level Biology (41 decks)

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