ecosystems Flashcards

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1
Q

How is phosphorus found in the phosphorus cycle?

A

Phosphorus is present in its mineral form as phosphate ions PO43- in sedimentary rock.

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2
Q

Outline the phosphorus cycle?

A
  1. Uplifting, weathering and erosion of rock causes phosphate ions to dissolve in water and soil, becoming available for plants, which absorb phosphate ions and incorporate them into their biomass
  2. Phosphate ions pass into animals who feed on the plant and are incorporated into organic molecules
  3. Excess phosphate ions are excreted in animal waste, dissolving and recycling phosphate ions into soil/water.
  4. When plants and animals die, they are broken down by saprobionts (bacteria or fungi), releasing phosphate ions into the water/soil.
  5. Some phosphate ions remain in inedible bones/shells of organisms which break down slowly by decomposition. They dissolve out of the rocks and are transported by streams and rivers into lakes/oceans where they precipitate and form sedimentary rock, completing the cycle.
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3
Q

4 stages of the nitrogen cycle?

A
  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
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4
Q

What is ammonification?

How is it carried out?

A
  1. Ammonification is where nitrogen compounds from dead organisms/waste are converted by (saprobionts) into ammonium ions in the soil.
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5
Q

What is Nitrification?

A

Nitrification is when nitrifying bacteria oxidise ammonium ions (with oxygen):

1) Oxidation of ammonium ions to nitrite ions NO2-
2) Oxidation of nitrite ions to nitrate ions NO3-

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6
Q

What is Nitrogen fixation?

A

Nitrogen fixation is 1st stage in the nitrogen cycle

1) nitrogen gas in the atmosphere is reduced to ammonia by:
1) Free nitrogen-fixing bacteria
2) Mutualistic nitrogen-fixing bacteria- in nodules on leguminous plant roots - obtain carbohydrates from plant + fix nitrogen and transform it into useable nitrogen-compounds for the plant.

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7
Q

What is Denitrification?

A

Denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria
They use nitrates in the soil to respire and produce nitrogen gas in anaerobic conditions eg. waterlogged soils
1) Lowering oxygen levels
2) Fewer aerobic nitrogen-fixing organisms
3) Increase in the number of anaerobic denitrifying bacteria
4) Convert nitrates into gaseous nitrogen which cannot be used in the plant.
5) Reduces the availability of nitrogen-containing compounds in the plant.

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8
Q

How are nitrate ions kept at a high level in natural ecosystems?

How are nitrate ions kept at a high level in agricultural ecosystems?

A

Nitrate concentration is kept high by constant recycling of nitrogen-containing compounds by saprobionts in ammonification.

In agricultural ecosystems, this is increased by the addition of fertilisers.

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9
Q

Outline the nutrient cycle.

A

The flow of nutrients within an ecosystem is cyclic

  1. Nutrient taken up by producers as (simple) inorganic molecules
  2. Producers incorporate nutrients into complex organic molecules.
  3. When the producer is eaten, nutrients are taken up by consumers
  4. Passes along the food chain
  5. When producers and consumers die, their complex molecules are broken down by saprobiontic microorganisms to release nutrients in their original, simple form.
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10
Q

What are the 2 stages of Nitrification?

A

Conversion of ammonium ions to nitrate ions in oxidation occurs in 2 stages with oxygen:

1) Oxidation of ammonium ions to nitrite ions NO2-
2) Oxidation of nitrite ions to nitrate ions NO3-

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11
Q

How can farmers use knowledge of the nitrogen cycle to increase productivity?

A

NITRIFICATION:

  • Nitrifying bacteria need oxygen, so soil should have many air spaces.
  • Soil should be aerated by ploughing
  • Light structure
  • Good drainage to prevent air spaces being filled with water.

DENITRIFICATION:
- soils should be aerated to prevent build-up of denitrifying bacteria in the soil.

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12
Q

What are PRODUCERS?

A

PRODUCERS:

  • photosynthetic organisms
  • synthesise organic compounds from atmospheric / aquatic carbon dioxide, sunlight, water and mineral ions into chemical energy.
  • sugars for respiratory substrates
  • other biological molecules which form the biomass of the plant.
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13
Q

What are SAPROBIONTS?

A

SAPROBIONTS:

  • fungi/bacteria
  • break down complex organic molecules in dead organisms into simple inorganic ones
  • recycle valuable minerals back into soil for reabsorption in plants.
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14
Q

What are CONSUMERS?

A

CONSUMERS:

  • consumers obtain energy by eating biomass of other organisms
  • those that eat producers are herbivorous primary consumers.
  • those that eat primary consumers are seconday- tertiary etc. and are carnivorous.
  • some of these biological molecules are used as respiratory substrates by consumers.
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15
Q

What is biomass?

Why is ‘biomass’ unreliable?

A

Biomass is the total mass of living material in a specific area at a given time.

The raw mass is easy to obtain, but varying amounts of water makes it unreliable.

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16
Q

Why is most of the Sun’s energy not converted by producers?

A

Most of the Sun’s energy isn’t converted because:
- Over 90% is reflected back into space by clouds/dust or absorbed by the atmosphere

  • Not all wavelengths of light can be absorbed and used in photosynthesis
  • Light may not fall on a chlorophyll molecule
  • Might be a limiting factor of photosynthesis e.g. CO2 stopping the energy being converted.
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17
Q

What is gross primary production?

A

Gross primary production (GPP) - the total quantity of chemical energy stored in plant biomass in a given area

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18
Q

Why is the energy transferred to primary consumers less than transferred to producers?

A
  • up to 50% of the chemical energy in producers is used in respiration, reducing the amount of chemical energy stored.
  • remaining chemical energy stored in plant biomass after environmental respiratory losses is called - Net primary production (NPP)
    Net production = gross production - respiratory losses
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19
Q

Why does the energy stored at each trophic level decrease?

A
  • Some of the organism isn’t eaten eg. bones
  • Some parts are consumed but not digested, so are lost in faeces
  • Some energy is lost in excretory materials, e.g. urine
  • Energy lost as heat from respiration and directly from the body to the environment.
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20
Q

What is the net production of consumers (N)?

A

Net production = chemical energy in ingested food - (chemical energy lost to environment in waste + respiratory losses)

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21
Q

Why do most food chains only have 4 or 5 trophic levels?

A

Because the energy transfer between trophic levels is inefficient.

  • insufficient energy to support a large population
  • total mass of organisms in a particular place (biomass) is less at higher trophic levels
  • total amount of energy stored is less at each level
22
Q

What is Productivity?

A
  • Productivity is the rate at which something is produced (plants are producers) over a given time in a given area kJ m-2 (year-1)
23
Q

What is Net Productivity?

A

Net Productivity = Gross Productivity - Respiratory Losses

24
Q

What is ecology?

A

ECOLOGY: the study of inter-relationships between organisms and their environment, including both biotic and abiotic factors.

25
Q

What is an ecosystem?

A

ECOSYSTEM = dynamic system of interactions between communities of organisms and the abiotic factors of their environment. An ecosystem can support a particular size population - the carrying capacity.

26
Q

What is a habitat?

A

HABITAT = where an organism lives. Species occupy ‘niches’ due to specific biotic/abiotic adaptations.

27
Q

What is a population?

A

POPULATION = all the organisms of one species occupying the same habitat at the same time.

28
Q

What is a community?

A

COMMUNITY = all populations of different species living/interacting in the same habitat at the same time.

29
Q

What is the carrying capacity?

A

CARRYING CAPACITY = the max population size that can be maintained over time in a particular habitat (determined by certain limiting factors)

30
Q

What is an ecological niche?

A

ECOLOGICAL NICHE = where an organism lives and how it fits into its environment (its role). Every species occupies a different niche, including biotic and abiotic interactions within its habitat eg. what it eats, what it is eaten by.

31
Q

How is population size limited by temperature?

A

Temperature - different optimums for different species.

Low temperatures slow enzyme activity, reducing the metabolic rate of the organism.

Above optimum, enzymes denature, reducing carrying capacity.

For mammals…The further organisms from the optimum temperature, the slower their growth rate.
Lower temperature lowers metabolic rate. As mammals produce heat in respiration, low temperatures use more energy to maintain a constant body temp so less energy is used for growth.

32
Q

How is population size limited by light?

A

Light - ultimate source of energy for ecosystems.

If light intensity is greater, more energy is used to create spores/seeds in plants, so they reproduce quicker.

Or, competition as organisms block each other’s light sources.

33
Q

How is population size limited by pH?

A

pH - affects enzymes (rate/denaturation. If organisms live within the correct pH, they have larger populations.

34
Q

How is population size limited by water/humidity?

A

Water and humidity - humidity affects transpiration in plants and evaporation rate from animals.

35
Q

How is population size limited by Interspecific competition?

A

Interspecific competition is between members of different species where one has a competitive advantage to increase the population size of their species and diminish the population size of another.

The competitive exclusion principle: states that when two species compete for limited resources, the one that uses resources most effectively will eliminate the other.

Therefore, no 2 species are capable of occupying the same niche because the resources competed for are limiting. (eat different food)

36
Q

How is population size limited by Intraspecific competition?

A

Intraspecific competition is between members of the same species for limited resources such as food, water, breeding sites etc.
The limited availability of resources determines population size because there will be more or less competition.
1) Pop increases when resources plentiful
2) As pop size increases, more competition over limited resources (food)
3) Resources are limiting, so organisms cannot survive and the population declines
4) Smaller pops reduce competition for resources so more available for growth and reproduction, so population grows again.

37
Q

How is population size limited by predator - prey relationships?

A

Effect of predator - prey relationship on population size
1. Predators eat prey, reducing the population of prey
2. With fewer prey available, predators are in
greater competition with each another for the prey
that are left
3. Predator population decreases due to intraspecific
competition wherein some predators may not be
able to catch enough prey for their survival and
reproduction.
4. With fewer predators, fewer prey are consumed,
So prey population increases as they survive
longer and reproduce more
5. More prey, so predator population also increases because there is more food available
6. Repeats

38
Q

Why is it difficult to ‘prove’ that population decrease is due to competition?

A
  • Correlations do not mean causation (another 3rd extraneous variable may have been unaccounted for)
  • Many other factors influence population size (abiotic)
39
Q

What is succession?

A

Succession = changes in the abiotic factors of a community over time due to the species present.

40
Q

What is a Pioneer Species?

A

Pioneer Species = a species that can colonise bare rock/ hostile environments.

41
Q

What is a Climax community?

A

Climax community is a stable community where there is no further succession and the final community is formed. There are often dominant animal and plant species.

42
Q

Adaptations of pioneer species?

A
  • tolerance to extreme conditions
  • ability to fix nitrogen from the air
  • photosynthesise light.
  • easily disperse seeds over vast distances
  • rapid germination of seeds
43
Q

What is the climax community limited by?

A

Competition (interspecific or intraspecific)
Nutrient availability and water availability in the soil
Number of producers providing energy for food chain
Light intensity increasing rate of photosynthesis
Disease killing species members
Predation
Space for nesting/shelter

44
Q

What is the climax community limited by?

A
  • Competition (interspecific or intraspecific)
  • Nutrient and water availability in the soil
  • Number of producers providing energy for food chain
  • Light intensity increasing rate of photosynthesis
  • Disease killing species members
  • Predation
  • Space for nesting/shelter
45
Q

Why is a climax community more stable than a pioneer community?

A
  • More species present increasing biomass
  • More complex food webs due to high species diversity, so predators have greater variety of prey
  • Change in one species has little effect on others as if a food source dies, an alternative food source will be relied upon
46
Q

Explain how changes in species composition occurs in succession.

A
  • species present change habitat eg. soil
  • other species able to colonise
  • new species better competitors
  • out-compete existing species
47
Q

5 Common features of succession?

A
  1. Abiotic environment less hostile as soil forms to retain water, nutrients are more plentiful and plants shelter from the wind.
  2. Greater no. and variety of habitats/niches
  3. Increased biodiversity as more varied species occupy more varied habitats
    Decreases as climax community is reached because of interspecific competition, where dominant species out-competes other species for light/minerals/space, leading to their elimination from the community
  4. Increased complexity of food webs as increased biodiversity = more food sources
  5. Increased biomass
48
Q

How does succession occur in ecosystems?

A
  1. Few adapted pioneer species colonise an inhospitable environment (bare rock)
  2. Pioneer species die and decompose, releasing nutrients which fertilise soil and produce a thick layer
  3. Change abiotic environment- less hostile
  4. More niches / habitats
  5. Enables other species to colonise
  6. Increases species biodiversity
  7. Stability of the population increases
  8. Climax community is reached
49
Q

How does succession occur in ecosystems?

A
  1. Few adapted pioneer species colonise an inhospitable environment (bare rock)
  2. Pioneer species die and decompose, releasing nutrients which fertilise soil and produce a thick layer
  3. Change abiotic environment- less hostile
  4. More niches / habitats
  5. Enables other species to colonise
  6. Increases species biodiversity
  7. Stability of population increases
  8. Climax community reached
50
Q

What is productivity measured in?

A

Kilojoules of energy per square meter per year (kJ/m2/year-1)

51
Q

How do humans increase productivity?

A
  • Animals are harvested young, when most of their energy is used for growth
  • hormones and steroids are used to increase growth
  • selective breeding of breeds with higher growth rates/ more desirable breeds
  • animals treated with antibiotics to prevent loss of energy due to fighting pathogens
  • limiting movement reduces energy loss due to heat and muscle contraction, maximising the mass