Nutrient Cycles Flashcards
Describe the Nitrogen cycle.
Nitrogen fixation
- Atmospheric nitrogen gas is converted into nitrogen-containing compounds
- This is carried out by nitrogen-fixing bacteria such as Rhizobium
- The bacteria convert nitrogen into ammonia, which forms ammonium ions
- These nitrogen-fixing bacteria are found inside the root nodules of leguminous plants such as peas, beans and clover
- The bacteria have a symbiotic relationship with these plants - the bacteria provide the plants with nitrogen-containing compounds and the plants provide the bacteria with organic compounds such as carbohydrates
Ammonification
- Nitrogen compounds in waste products and dead organisms are converted into ammonia by saprobionts
- This ammonia forms ammonium ions in the soil
Nitrification
- The ammonium ions in the soil are converted by nitrifying bacteria into nitrogen compounds that can be used by plants, known as nitrates
1. Nitrifying bacteria such as Nitrosomonas convert ammonium ions into nitrites
2. Different nitrifying bacteria such as Nitrobacter then convert these nitrites into nitrates
Denitrification
- Denitrifying bacteria use nitrates in the soil during respiration
- This process produces nitrogen gas, which returns to the atmosphere
- This process occurs in anaerobic conditions (such as in waterlogged soil)
Describe the Nitrogen Cycle
-
Nitrogen fixation:
- Atmospheric nitrogen gas is converted into nitrogen-containing compounds so it can be absorbed by plants
- this is done by:
nitrogen- fixing bacteria that naturally occurs in the soil, convert nitrogen into ammonium
- directly in a pant through plant nodules as they contain bacteria that can covert nitrogen gas–> ammonium gas OR nitrate
ONLY FOR LEGIMUNUOS PLANTS -
Nitrification:
- convert ammonium–> Nitrites by nitrifying bacteria.
- convert nitrites into nitrates by nitrifying bacteria -
Assimilation:
- nitrates in the coil are absorbed into the plant by active transport & then assimilated to be used for amino acids, ATP, DNA -
Ammonification
- animals eats the plants =nitrates get into animals
- animals decompose= nitrogen containing molecules (ATP, DNA, proteins) are broken down and digested by saprobionts -
Denitrification
- denitrifying bacteria convert nitrates back into nitrogen gas in the atmosphere
NITROGEN IS LOST
- this will only occur if not enough O2 in soil / if soil is water logged
Describe the Phosphorous cycle.
- Phosphorus in rocks is slowly released into the soil and into water sources in the form of phosphate ions (PO₄³⁻) by the process of weathering
- Phosphate ions are taken up from the soil by plants through their roots or absorbed from water by algae
- Phosphate ions are transferred to consumers during feeding
- Phosphate ions in waste products and dead organisms are released into the soil or water during decomposition by saprobionts
- The phosphate ions can be taken up and used once again by producers or may be trapped in sediments that, over very long geological time periods may turn into phosphorus-containing rock once again
What are the roles of microorganisms in recycling minerals?
Saprobionts → decompose waste + dead matter via extracellular digestion, so inorganic ions available to other organisms
Nitrogen-fixing bacteria → convert Nitrogen gas into nitrogen containing compounds (e.g. ammonia which can be turned into ammonium ions)
Nitrifying → converts ammonia to nitrites, nitrites to nitrates
Mycorrhizal → increases SA to optimise water + mineral ion absorption
Why are fertilisers used?
Fertilisers can be used to add important mineral ions, such as ions of nitrogen, phosphorus and potassium, back into the soil.
What are natural fertilisers?
Natural fertilisers are made up of organic matter in the form of the dead and decomposing remains of organisms and waste products.
- not very concentrated
- large amounts needed
- released over long periods of time
What are artificial fertilisers?
Artificial fertilisers are made up of inorganic matter in the form of powders or pellets that contain pure chemical compounds.
- concentrated
- smaller amounts needed
What are the environmental issues caused by fertilisers?
Leaching → Eutrophication
Describe the process of eutrophication.
- Excessive nutrients from fertilisers run-off from the land to the water → this causes algal bloom
- This blocks sunlight so aquatic plants below the surface die as they are unable to photosynthesise
3.The algae also start to die when competition for nutrients becomes too intense - Decomposing bacteria feed on the dead organic matter and also increase in number, as they respire aerobically, these bacteria use up the dissolved oxygen in the water
- As a result, the amount of dissolved oxygen in the water rapidly decreases, so aquatic organisms such as fish and insects may be unable to survive
Advantages of fertilisers (natural)
Cheaper & often free if farmer owns animals.
Disadvantage of fertilisers (natural)
The exact minerals & proportions can’t be controlled.
Advantage of fertilisers (artificial)
They’re chemicals created to contain exact products, therefore meet the needs for crops
Disadvantage of fertilisers (artificial)
Can cause leaching & are more expensive.
