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A Level 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 a defined area.

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2
Q

What is a biotic factor?

A

The living factors. Eg competition.

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3
Q

What is an abiotic factor?

A

Non living or physical factors. Eg temperature range or rainfall levels.

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4
Q

What are the key examples of abiotic factors?

A 
Light
Temperature
Water availability 
Oxygen availability 
Edaphic (soil) factors
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5
Q

What is the first trophic level?

A

Producer

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6
Q

What is a producer?

A

An organism that converts light energy into chemical energy by the process of photosynthesis.

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7
Q

What is a primary consumer?

A

The consumer that eats the producer.

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8
Q

Why do food chains rarely have more than 4 trophic levels?

A

Because there is not sufficient biomass and stored energy left to support any further organisms.

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9
Q

How do you calculate biomass at each trophic level?

A

Multiply the biomass present in each organism by the total number of organisms at that trophic level.

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10
Q

What is a disadvantage of using a pyramid of biomass?

A

They only represent the biomass at a given time, it does not take into account seasonal changes.

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11
Q

How do you find the dry mass of an organism?

A

Organisms must be killed first, then they must be placed in an oven at 80 degrees C until all water has evaporated.

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12
Q

How can you be sure all water has evaporated when finding a dry mass?

A

When you get at least 2 identical mass readings.

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13
Q

How can you minimise destruction when finding dry mass?

A

A small sample is taken. However this small sample may not be representative of the population as a whole.

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14
Q

What is biomass measured in?

A

Grams per square metre

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15
Q

Why do trophic levels lose biomass?

A

Because biomass consists of all the cells and tissues of the organisms present including carbs and other carbon compounds. Carbon compounds store energy so these can be equated to energy content.when animals eat, only a small proportion of the food is converted to new tissues: only this tissue can be transferred to next trophic level.

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16
Q

What is energy available at each trophic level measured in?

A

Kilojoules per metre squared per year. This allows for changes in photosynthesis and feeding patterns throughout the year.

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17
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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18
Q

Why do producers only concert 1-3% of sunlight into chemical energy and biomass?

A
  • not all solar energy is used for photosynthesis, 90% is reflected
  • other factors limit photosynthesis eg. Water availability
  • a proportion of energy is ‘lost’, as it is used for photosynthetic reactions.
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19
Q

What is gross production?

A

The solar energy that plants convert to organic matter.

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20
Q

What is net production?

A

The energy available to the next trophic level.

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21
Q

How to calculate net production?

A

Net production = gross production - respiratory losses

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22
Q

Why do consumers at each trophic level convert 10% maximum of the biomass in their food to their own tissue?

A
  • not all the biomass of an organism can be eaten eg animal bones.
  • some energy is transferred to the environment at metabolic heat, as a result of movement and respiration.
  • some parts of animal are eaten but indigestible so they’re egested as faeces
  • some energy is lost from the animal in excretory materials such as urine.
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23
Q

How to calculate the efficiency of an energy transfer?

A

Ecological efficiency = energy or biomass available after transfer / energy or biomass available before transfer x 100

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24
Q

How can human activities manipulate biomass through ecosystems?

A

Agriculture involves manipulating the environment to favour plant species. Plants and animals are provided with their ideal abiotic conditions they need to thrive.

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25
Q

In a natural ecosystem, what trophic level would human occupy?

A

Human would occupy the second, third or fourth trophic level.

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26
Q

What kind of food chains does agriculture create?

A

Simple food chains.

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27
Q

What is decomposition?

A

A chemical process by which a compound is broken down into smaller molecules, or its constituent elements.

28
Q

What is a decomposer?

A

An organism that feeds on and breaks down dead plant or animal matter turning organic compounds into inorganic ones.

29
Q

Why are decomposers saprotrophs?

A

Because they obtain their energy from dead or waste organic material (saprobiotic nutrition).

30
Q

What are detritivores and why are they important?

A

Detritivores speed up the decay process by feeding on detritus - dead and decaying material. They break it down into smaller pieces increasing the surface area for the decomposers to work on.

31
Q

Examples of detritivores?

A

Woodlice and earthworms.

32
Q

What is nitrogen fixation?

A

Combining atmospheric nitrogen with hydrogen to produce ammonia.

33
Q

What are the 2 nitrogen fixing bacteria? What enzyme is present?

A

Azotobacter and Rhizobium.

Nitrogenase

34
Q

Which bacteria is a free living soil bacterium?

A

Azotobacter

35
Q

Where do rhizobium bacteria live?

A

Inside root nodules of leguminous plants such as peas beans and clover

36
Q

How do the nitrogen fixing bacteria have a symbiotic mutualistic relationship with the plant?

A
  • Plants gain amino acids from Rhizobium which are produced by fixing nitrogen gas in the air into ammonia in the bacteria.
  • The bacteria gain carbohydrates produced by the plant during photosynthesis, which they use as an energy source.
37
Q

What is nitrification?

A

The process by which ammonium compounds in the soil are converted into nitrogen containing molecules that can be used by plants.

38
Q

What are the 2 steps of nitrification?

A
  • Nitrifying bacteria (eg nitrosomonas) oxidise ammonium compounds into nitrites (NO2-)
  • Nitrobacter oxidise nitrites into nitrates (NO3-)

Nitrate ions are highly soluble so this is the main way that nitrogen enters a plant.

39
Q

What is denitrification?

A

In the absence of oxygen, for example in water logged soils, denitrifying bacteria convert nitrates in the soil back into nitrogen gas.

40
Q

What is ammonification?

A

The process by which decomposers convert nitrogen- containing molecules in dead organisms, faeces and urine into ammonium compounds.

41
Q

5 stages of the carbon cycle?

A 
Photosynthesis 
Respiration 
Combustion 
Decomposition
Feeding
42
Q

What causes fluctuations in the carbon cycle?

A

Time of day - photosynthesis takes place during the day only, respiration occurs all the time, CO2 levels higher at night.

Time of year - more CO2 in winter as there is less photosynthesis.

43
Q

Why have co2 levels increases significantly in the last 200 years?

A

Combustion of fossil fuels.

Deforestation.

44
Q

What is primary succession?

A

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.

45
Q

What is secondary succession?

A

Occurs on areas of land where soil is present but it contains no plant or animal species. An example would be the bare earth that remains after a forest fire.

46
Q

When does primary succession occur?

A

When:

  • volcanoes erupt
  • sand is blown by wind or deposited by sea
  • silt and mud exposed on river estuaries
  • glaciers retreat exposing rock
47
Q

What is a pioneer community?

A

Colonisation of an inhospitable environment by organisms such as pioneer species. First seral stage. Arrive by spores or seeds carried by wind.

48
Q

Adaptations of pioneer species?

A

Ability to produce large quantities of seeds or spores.
Seeds that germinate rapidly
Ability to photosynthesise to produce own energy
Tolerance to extreme environments
Ability to fix nitrogen from the atmosphere to add to mineral content of soil.

49
Q

Example of secondary coloniser community?

A

Moss

50
Q

Why can a soil support secondary colonisers after the pioneer community?

A

Because the soil now contains minerals and nitrates and can retain some water.

51
Q

How are tertiary colonisers adapted to their function?

A

Waxy cuticle that protects them against water loss

52
Q

Intermediate community?

A

Small flowering plants
Grasses
Small shrubs

53
Q

What is a climate community?

A

The community is at a stable state, little change over time. Normally a few dominant plant and animal species. Biodiversity decreases due to dominant species out-competing pioneer or other species.

54
Q

Explain animal succession?

A

Primary consumers such as insects and worms colonise first, they consume and shelter in the mosses and lichens present. Must move in from neighbouring areas. Secondary consumers arrive when suitable food source has been established. Larger organisms will colonise when biotic conditions are favourable.

55
Q

What is deflected succession?

A

Human activities can halt the natural flow of succession and prevent the ecosystem from reaching a climax community. Caused by agriculture.

56
Q

What factors cause deflected succession?

A

Grazing and trampling of vegetation by domesticated animals
Removing existing vegetation to plant crops.
Burning as a means of forest clearance.

57
Q

How would you normally measure distribution of organisms within an ecosystem?

A

Belt transects or line transect

58
Q

What will increase the abundance of the number of individuals present in an ecosystem?

A

Immigration and births

59
Q

Why may the abundance of organisms decrease?

A

Emigration and deaths

60
Q

How to measure plant species abundance?

A

Quadrats randomly placed. Count individual plant species within quadrat

61
Q

Calculation for estimated plant species abundance?

A

Estimated number in population (m-2)= number of individuals in species / area of sample in m2

62
Q

What technique is used to measure abundance in animal species?

A

Capture - mark - release - recapture

63
Q

Animal estimated population size calculation?

A

(Number of individuals in first sample x number of individuals in second sample) / number of recaptured marked individuals

64
Q

What does a diversity index of 1 mean?

A

Infinite biodiversity

65
Q

What are the 3 main soil types?

A

Clay - fine particles, easily waterlogged, and forms clumps when wet.

Loam - different sized particles, retains water but does not become water logged

Sandy - coarse, well separated particles that allow free draining, Sandy soil does not retain water and is easily eroded.

66
Q

What do the letters stand for in Simpson’s Diversity Index?

D N n

A

D = diversity index

N = number of organisms in the ecosystem

n = number of individuals of each species

A Level Biology (22 decks)

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