Nutrient cycles Flashcards
State a feature of all nutrient cycles
-They contain microorganisms such as bacteria and fungi
-Many of the microorganisms are saprobionts
What is a saprobiont?
-A microorganism such as bacteria or fungi that decompose dead plant and animal material
-this returns nutrients to the soil
What is meant by the term ‘extracellular digestion’
-saprobionts secrete enzymes
-this digests dead animal and plant material
-they absorb the nutrients they require
-also known as saprobiotic nutrition
What are ‘mycorrhizae’?
-fungal associations
-between plant roots and beneficial fungi
-this is a symbiotic relationship
What is the role of ‘mycorrhizae’?
-The fungi are composed of long, thin strands known as hyphae
-these connect to the plant roots and increase the SA
-this allows for greater water and mineral absorption
Explain how the presence of mycorrhizae results in a symbiotic (mutualistic) relationship
-The store of water and mineral ions in the mycorrhizae can be used by the plant in times of drought
-The fungi obtain organic compounds such as carbohydrates from the plant
State the percentage of the atmosphere that is composed of nitrogen
78%
State why nitrogen is essential for plants and animals
-For growth
As it is needed to create:
-Amino acids/ proteins
-Nucleic acids (DNA and RNA)
-ATP
Explain why plants are unable to absorb atmospheric nitrogen
-Atmospheric nitrogen is unreactive
-Require bacteria to convert it into nitrogen-containing compounds
State the four processes involved in the nitrogen cycle
- Nitrogen fixation
- Ammonification
- Nitrification
- Denitrification
Describe the process of nitrogen fixation
-Nitrogen-fixing bacteria such as Rhizobium break the triple bond between two nitrogen atoms in atmospheric nitrogen
-They convert this nitrogen into ammonium ions
State an example of nitrogen-fixing bacteria
Rhizobium
Where are nitrogen-fixing bacteria found?
-Free living in the soil
-In the root nodules of leguminous plants e.g. clover (symbiotic relationship)
Describe the process of ammonification
-Saprobionts decompose proteins, urea and DNA
-from animal waste into ammonium ions
Describe the process of nitrification
-Nitrifying bacteria convert ammonium ions to nitrate and nitrite ions
-A two-stage oxidation reaction
Describe the process of denitrification
-Anaerobic denitrifying bacteria converts nitrates in the soil back to atmospheric nitrogen gas
-Anaerobic denitrifying bacteria use nitrates from the soil to respire and they produce atmospheric nitrogen
Why is phosphorus essential for plants an animals?
To create:
-DNA
-RNA
-ATP
-Phospholipid bilayers
Where is phosphorus found?
-In rocks
-Dissolved in oceans
-In the form of phosphate ions (PO4^3-)
Phosphate ions that is dissolved in water and in soil is assimilated by plants. What does the term ‘assimilated’ mean?
-Plants absorb the phosphate
-use the phosphorus to make more complex biological molecules
Describe the phosphorus cycle
- Weathering of rocks releases phosphorus ions into the soil
- Plants absorb phosphate via the roots and mycorrhizae increase the rate of assimilation of phosphorus
- Phosphate ions are transferred through the food chain as animals consume plants
- Phosphate ions are lost by animals through waste
- Saprobionts decompose dead animal material and this releases phosphate ions into the soil and these are taken up by plants by assimilation
- Weathering of rocks releases phosphate ions into lakes, rivers and seas and this is taken up by aquatic producers such as algae and this is passed along the food chain by consumers
State the role of magnesium in plants
Needed to make chlorophyll
State the two types of fertilisers
-Organic (natural)
-Inorganic (artificial)
Explain why fertilisers are added to the soil
-Replace phosphate and nitrate ions
-lost when plants are harvested and removed from nutrient cycles
-to be used as crops
What are organic fertilisers?
-Dead and decaying plant and animal matter
-includes manure, composted vegetables and crop residues
What are inorganic fertilisers?
-Mined from rocks
-Converted to a suitable form
-Blended to suit a particular crop
-Creates pollution to mine from rock and is artificial so people may disagree / not want it on crops
Compare organic and inorganic fertilisers
Organic
+ Often cheaper (free if the farmer owns animals)
- Exact mineral proportions cannot be controlled
Inorganic
+ Exact proportions of minerals can be measured
+ More water-soluble, so more ions dissolve in water surrounding the soil and therefore more nitrates and phosphates are absorbed by plants
- As they are more water soluble, larger quantities are washed away by rainfall, which creates environmental impacts
What is meant by the term ‘leaching’?
When water-soluble compounds found in the soil are washed away by rain into nearby ponds or rivers
Describe the process of eutrophication
- Mineral ions leached from fertilised soils stimulate the growth of algae on ponds or rivers
- Excessive growth of algae on the surface blocks out light energy from reaching aquatic plants below the surface
- The plants are unable to photosynthesise and they decompose
- Bacteria feed on decaying plant matter and the increased number of bacteria reduce the oxygen concentration by aerobic respiration
- Fish and aquatic organisms die due to a lack of dissolved oxygen
Leguminous crop plants have nitrogen-fixing bacteria in nodules on their roots. On soils with a low concentration of nitrate ions, leguminous crops often grow better than other types of crop. State two reasons why.
-Nitrogen-fixing bacteria can fix atmospheric nitrogen into ammonium (NH4+) ions
-used to make proteins and amino acids
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. Nitrogen gas is the usual substrate for this enzyme. Name the product.
Ammonium ions (NH4+)
When fertilisers are applied to fields next to a lake, nitrogen-containing substances from the fertilisers get into the lake. State how the nitrogen-containing substances get into the lake.
-Surface runoff when there is excess rainfall
- Leaching
Name the type of bacteria which convert:
a) nitrogen in the air into ammonium compounds
b) nitrites into nitrates
a) Nitrogen-fixing bacteria
b) Nitrifying bacteria
State two reasons why it is important for a farmer to reduce the leaching of nitrates
-Can result in eutrophication causing death of aquatic plants and animals
-Leaching into water sources can lead to health concerns with drinking water
-Can result in nitrate deficiencies in the soil which will affect crop yields
-Costs money to add more fertilisers which have been leached
What conditions are anaerobic denitrifying bacteria present in great numbers?
When soils become waterlogged
State why farmers use good drainage systems
-Anaerobic denitrifying bacteria are present in great numbers in waterlogged soils
-without drainage systems more nitrates in the soil would be converted back to atmospheric nitrogen
-less would be available for crops
-yield would decrease
Explain why farmers plough the soil
-Increases O2 concentration in the soil
-Less anaerobic denitrifying bacteria present in the soil (less anaerobic respiration)
-Less denitrification
-Less nitrates converted back to atmospheric nitrogen
-More nitrates available in soil so more plant growth
State two ways in which farmers increase the efficiency of energy transfers
-Shorten the food chain -> less energy lost between tropic levels
-Crop rotation -> replenished concentration of nutrients in the soil
