ecosystems Flashcards
How is phosphorus found in the phosphorus cycle?
Phosphorus is present in its mineral form as phosphate ions PO43- in sedimentary rock.
Outline the phosphorus cycle?
- 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
- Phosphate ions pass into animals who feed on the plant and are incorporated into organic molecules
- Excess phosphate ions are excreted in animal waste, dissolving and recycling phosphate ions into soil/water.
- When plants and animals die, they are broken down by saprobionts (bacteria or fungi), releasing phosphate ions into the water/soil.
- 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.
4 stages of the nitrogen cycle?
- Nitrogen fixation
- Ammonification
- Nitrification
- Denitrification
What is ammonification?
How is it carried out?
- Ammonification is where nitrogen compounds from dead organisms/waste are converted by (saprobionts) into ammonium ions in the soil.
What is Nitrification?
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-
What is Nitrogen fixation?
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.
What is Denitrification?
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.
How are nitrate ions kept at a high level in natural ecosystems?
How are nitrate ions kept at a high level in agricultural ecosystems?
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.
Outline the nutrient cycle.
The flow of nutrients within an ecosystem is cyclic
- Nutrient taken up by producers as (simple) inorganic molecules
- Producers incorporate nutrients into complex organic molecules.
- When the producer is eaten, nutrients are taken up by consumers
- Passes along the food chain
- When producers and consumers die, their complex molecules are broken down by saprobiontic microorganisms to release nutrients in their original, simple form.
What are the 2 stages of Nitrification?
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-
How can farmers use knowledge of the nitrogen cycle to increase productivity?
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.
What are PRODUCERS?
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.
What are SAPROBIONTS?
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.
What are CONSUMERS?
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.
What is biomass?
Why is ‘biomass’ unreliable?
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.
Why is most of the Sun’s energy not converted by producers?
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.
What is gross primary production?
Gross primary production (GPP) - the total quantity of chemical energy stored in plant biomass in a given area
Why is the energy transferred to primary consumers less than transferred to producers?
- 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
Why does the energy stored at each trophic level decrease?
- 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.
What is the net production of consumers (N)?
Net production = chemical energy in ingested food - (chemical energy lost to environment in waste + respiratory losses)
