C.6 The nitrogen and phosphorus cycles Flashcards
What is the nitrogen cycle?
The biogeochemical cycle where nitrogen is converted into various chemical forms
What is unable to be used by plants and animals?
Nitrogen
What does chemoautotrophic bacteria convert nitrogen into?
Compounds that can be assimilated by plants and animals
What are the four components of the nitrogen cycle?
Nitrogen fixation
Ammonification
Nitrification
Dénitrification
What is the first stage of the nitrogen cycle?
Nitrogen fixation
What is nitrogen fixation?
The conversion of inert nitrogen gas into ammonia
What catalyses the conversion of nitrogen into ammonia?
The enzyme nitrogenase
What produces nitrogenase?
Nitrogen-fixing bacteria in the soil
When does ammonia become ammonium?
When mixed with water
What does Rhizobium supply ammonia to plants in exchange for?
Carbohydrates
How can ammonia be produced from organic sources of nitrogen?
When broken down by decomposers
In ammonification, what happens as a plant or animal decays?
Saprotrophs will decompose organic materials to produce ammonia
What does ammonification release?
Ammonium ions into the soil which can be absorbed by plants
What is nitrification?
The conversion of ammonium ions into nitrites and nitrates by nitrifying bacteria in the soil
What converts ammonium ions into nitrites?
Nitrosomonas
What do nitrobacters convert?
The nitrites into nitrates
What do nitrosomonas and nitrobacter reactions require?
Oxygen
If the reaction needs oxygen, what must the soil be?
Well aerated to ensure a rich supply of nitrites and nitrates
Why do nitrates and nitrites function as a predominant source of nitrogen for plants?
As they are easier for plants to assimilate
What is dentrification?
A chemical reduction process that converts nitrates into nitrogen gas
What carries out dentrification?
Denitrifying bacteria
When does denitrification occur?
In the absence of oxygen
What can be used instead of oxygen as an electron acceptor during cellular respiration?
Nitrates
When will nitrates be used during cellular respiration instead of oxygen?
In oxygen poor condition
What is reduced when nitrates are used instead of oxygen?
The availability of nitrates to plants
When does waterlogging occur?
When the soil becomes inundated with water through flooding or irrigation with poor drainage
How does waterlogging impact the nitrogen cycle?
By reducing the levels of nitrates and nitrites in the soil
Through which process does waterlogged soil lose nitrates and nitrites?
Denitrification and leaching
Where will there be a build up of water when rainfall exceeds evaporation?
Within porous soil
What happens as water drains downwards through the soil?
Soluble minerals are removed with it
What does continual leaching do to the upper layers of soil?
Impoverishes them
What does the continual leaching do to the lower bedrock?
Concentrates dissolved minerals in the lower bedrock
Where is leaching most common?
In highly porous soils
Where is leaching least common?
In textured soils
What does a reduction in nitrogen availability within the soil mean for plants?
That they are unable to access sufficient quantities of nitrogen from the soil via their roots
How are insectivorous plants able to obtain nitrogen in low nutrient environments?
By feeding on invertebrates
What is an example of an insectivorous plant?
Venus fly trap
What happens when the insect is trapped in the plant?
Digestive enzymes are released that allow it to absorb nutrients from the insect
How are insectivorous plants baited to attract insects?
By nectar
What does the phosphorus cycle show?
How different forms of phosphorus are transitioned within the environment
What do certain rocks contain high levels of?
Phosphate
Where can the phosphate released from rocks end up?
Into the soil and water
How do rocks that contain phosphate lose it to the soil and water?
Chemical weathering
Why do organisms require phosphates?
To synthesise nucleic acids, membranes and ATP
When are phosphates returned to the soil?
Upon the decomposition of plant and animal remains
What does the phosphorous cycle not include?
A gaseous component
Why is the rate of turnover in the phosphorus cycle much lower than other cycles?
Because it doesn’t have a gaseous component
What are the two rates which are slower due to the fact there is no gaseous component in the phosphorus cycle?
Rate or turnover and replenishment
How can phosphates be removed from the lithosphere?
Via mining
What can phosphates be converted into?
Phosphate based fertilisers
Why is turning phosphate into fertilisers good?
It allows phosphates that otherwise remain inaccessible in buried rock to become available for plant use
Why are fertilisers good for plants?
It increases their productivity by increasing plant access to phosphate
What happens to the phosphates that comprise part of the plants biomass when the crops are harvested?
They are lost from the phosphorus cycle
What does using fertiliser in one site cause in another?
The depletion of phosphorus reserves
What is the continued production of phosphate based fertilisers depleting?
Global phosphorus reserves
What is contradictory about the demand for fertiliser but turnover in the phosphorus cycle?
Demand for fertiliser is high but turnover in the phosphorus cycle is low
What are phosphate minerals classed as?
Non-renewable resource
When is it predicted for phosphates to become severely restricted?
Within 50 - 100 years
What is the problem with the possible future restriction of phosphates?
It would greatly limit the crop yield
What is eutophication?
The enrichment of an ecosystem with chemical nutrients
In eutrophication, how can nutrients be introduced?
Via leaching from soil by rainfall or released as part of sewage
Where is eutrophication common?
Around agriculture lands where using fertilisers are prevalent
What happens when there is an increase in nutrient supplies within waterways?
An algal bloom occurs but then they die. There is an increase in decomposers which results in increased oxygen demand by bacteria. Saprotrophs consume all available oxygen cleaning out the water supply. It also reduces oxygen production by seaweed
What will stress the survival of marine organisms in eutrophication?
The reduced oxygen production of seaweeds
What can eutrophication potentially lead to within the ecosystem?
A reduction in biodiversity
What is the bulk of soil made up of?
A mixture of organic matter, rock and mineral particles
What does the relative proportion of components of soil determine?
Soil type
What can soil testing kits be used to identify ?
Nutrients
Soil ph
texture
water content
How do soil testing kits test for nutrients?
Chemical reagents produce colour changes when testing for N, P and K
How do soil testing kits test for soil pH?
Colour changes can be used to identify the acidity or alkalinity of a soil sample
How can soil testing kits test for texture?
Soil can be separated into layers according to particle size
How can soil testing kits test for water content?
Electrical meters can determine water quantities based on the soils capacity to transmit an electrical current
Why do gardeners and farmers need to test their soil for the different components?
To determine the viability of the soil for planting purposes
Why do nitrates and nitrites function as a predominant source of nitrogen for plants?
