3.5.4 Nutrient Cycles Flashcards
In which form do plants need nitrogen?
Most organisms can not use nitrogen gas so they must secure their nitrogen in its fixed form
What are the fixed forms of nitrogen?
Nitrate ions: NO3 (2- charge)
Ammonia: NH3
Ammonium: NH4 (+1 charge)
What are the four nitrogen processes? (No explanation)
Nitrogen fixation
Decomposition
Nitfrification
Dentrification
What is nitrogen fixation?
Forming fixed compounds from nitrogen gas
What is decomposition it terms of the nitrogen cycle?
The breaking down of compounds into ammonia
What is nitrification?
The oxidation of ammonia into nitrates
What is dentrification?
The reducing of nitrates into nitrogen gas
What is biological fixation?
Fixation by microbes
What is atmospheric fixation?
Fixation by lightning where the energy combines with oxygen
What is industrial fixation?
Fixing of nitrogen during the Haber process
What is Rhizobium?
A symbiotic bacteria which fixes nitrogen and takes sugars produced by the plant
Contains an enzyme called nitrogenase that converts nitrogen and hydrogen to ammonia
How do animals secure their nitrogen?
From plants through feeding
What is responsible for decomposition in the nitrogen cycle?
Microorganisms
What are the types of nitrifying bacteria?
Genus Nitrosomes: oxidises NH3 to nitrites
Genus Nitrobacter: oxidises nitrites to nitrates
Out of the phosphorous and nitrous cycles, which is faster?
Nitrous
What are the effects of a low concentration of phosphorous?
It reduces plant growth and slows soil microbial growth
Are soil microorganisms sinks or sources in terms of the phosphorous cycle?
They can act as both
How can fertiliser run-off damage local water sources?
Large amounts of phosphate lead to growth of algea Algea die quickly Decomposers break it down These microorganisms use a lot of oxygen Oxygen levels decrease in the water Other organisms die
How do animals absorb phosphates?
By eating plants or plant-eating animals
When animals die, phosphates return to the soil or oceans during decomposition
Then phosphorous ends up in sediments or rock formations
Seabirds eat phosphorous-containing fish
What is mineralisation?
When organic phosphorous compounds are mineralised by a wide range of organisms
What is assimilation?
When microorganisms assimilate phosphorous which enters in the composition of several macromolecules in the cell
Some microorganisms can store phosphorous in special granules
What is the solubility of phosphorous controlled by?
The pH and the presence of Ca / Mg / Fe / Al ions
What are natural fertilisers?
Materials derived from animal parts or residues
e.g. manure, seaweed and compost
What are artificial fertilisers?
Man - made fertilisers
Why are fertilisers needed?
To achieve the high crop yields demanded by developed worlds
What do fertilisers contain?
Minerals, such as nitrogen, potassium and phosphorous
What is the function of nitrogen in fertilisers?
Increases the plant’s capacity to produce new stems / flowers / fruit
Increases the speed of growth
What is the function of phosphorous in fertilisers?
Helps plants to produce oils and starch which is helpful for forming large and strong root systems
Helps the plant to develop chlorophyll which allows more photosynthesis
What is the function of potassium in fertilisers?
Aids in the building of protein
Fights off diseases
Essential for photosynthesis
How are artificial fertilisers different from natural fertilisers?
Artificial fertilisers add nutrients to the plant whereas natural fertilisers feed the microorganisms and the plant
What is groundwater contamination?
Nitrogen fertilisers break down into nitrates and easily travel through the soil
This creates an accumulative effect
This increases plant life which takes up a lot of oxygen and starves fish and crustaceans
What is the effect of repeated fertiliser on soil?
Reduces the fertility of the soil, making it barren after time
What is the process of eutrophication?
Excess nutrients enter waterways
Nutrients promote plant growth
An algae bloom occurs
Algae die and are decomposed by bacteria
The decomposition of algae requires oxygen
This causes a drop in oxygen levels
Therefore fish and other aquatic life die
What are acidifying processes?
The addition of nitrogen
Loss of nitrogen due to leaching or run - off
Production of organic acids from decaying matter
Removal of alkaline products such as hay
What is leeching?
The process of water carrying away soluble material when the upper layer of the soil does not absorb all the water
What happens when leaching removes too much nitrate from the soil?
The pH drops too far and becomes overly acidic
What does soil acidity alter?
Soil microbes
What is the effect of a high salt content in the soil?
It limits the ability of seeds to germinate so controlled leaching can reduce salt content
What is the process of acidification?
Acidification limits plant species
Which leads to weaker root systems
Which leads to erosion
The wind then removes more topsoil
