13 ecosystems and energy Flashcards
How is phosphorus found in the phosphorus cycle?
- 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/soil, becoming available for plants.
- plants absorb phosphate ions and incorporate them into biomass
- Phosphate ions pass to animals who feed on the plant and are incorporated into organic molecules
- Excess phosphate ions are excreted in waste, dissolving and recycling into soil/water.
- When plants/animals die - broken down by saprobionts, releasing phosphate ions into water/soil.
- Some phosphate ions remain in inedible bones/shells of organisms which break down slowly by decomposition. They dissolve out of rocks and are transported by streams into oceans where they precipitate and form sedimentary rock, completing cycle.
4 stages of the nitrogen cycle?
- Nitrogen fixation
- Ammonification
- Nitrification
- Denitrification
What is ammonification?
How is it carried out?
nitrogen compounds from dead organisms /waste converted by saprobionts into ammonium ions in soil.
What is Nitrification?
when nitrifying bacteria oxidise ammonium ions
to nitrite ions NO2-
then to nitrate ions NO3-
What is Nitrogen fixation?
1st stage in nitrogen cycle
1) nitrogen gas is reduced to ammonia by:
1) Free nitrogen-fixing bacteria
2) Mutualistic nitrogen-fixing bacteria in nodules on leguminous plant roots (fix nitrogen/ transform to useable nitrogen-compounds)
What is Denitrification?
1) Anaerobic conditions decrease oxygen levels
2) Less aerobic nitrifying/more anaerobic
4) Denitrifying bacteria use nitrates in soil as a respiratory substrate, converting nitrates to nitrogen gas - cannot be used in the plant.
5) Reduces availability of nitrogen-containing compounds in 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?
- constant recycling of nitrogen-containing compounds by saprobionts
- addition of fertilisers.
Outline the nutrient cycle.
- Nutrient taken up by producers as (simple) inorganic molecules
- Producers synthesise complex organic molecules.
- When producer is eaten, nutrients taken up by consumers
- Passes along food chain
- When producers and consumers die, complex molecules are broken down by saprobiontic microorganisms to release nutrients in original, simple form.
How can farmers use knowledge of the nitrogen cycle to increase productivity?
(DE) NITRIFICATION:
- Nitrifying bacteria need oxygen, so soil should have many air spaces.
- aerated by ploughing
- Light structure
- Good drainage to prevent air spaces being filled with water.
What are PRODUCERS?
- photosynthetic organisms
- synthesise organic compounds from atmospheric / aquatic carbon dioxide, sunlight, water and mineral ions into chemical energy.
- sugars for respiration
- other biological molecules which form the biomass of the plant.
What are SAPROBIONTS?
- fungi/bacteria
- break down complex organic molecules in dead organisms into simple inorganic ones
- recycle minerals back into soil - reabsorption.
What are CONSUMERS?
- consumers obtain energy by eating biomass of other organisms
- those that eat producers are herbivorous (primary)
- those that eat primary = secondary carnivores etc.
- some 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:
- 90% is reflected back or absorbed into atmosphere by clouds/ dust
- 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 stopping energy being converted.
