5.4 Nutrient cycles Flashcards
4 stages of the nitrogen cycle
1- Nitrogen fixation
2- Ammonification
3- Nitrification
4- Denitrification
Why can’t organisms use nitrogen directly from the atmosphere?
N2 is very stable due to strong covalent triple bond.
What is nitrogen fixation?
The process of converting nitrogen gas in the atmosphere to ammonia.
What is nitrification?
The process of converting ammonia to nitrites then nitrates.
What is denitrification?
The process of converting nitrites then nitrates to nitrogen gas in the atmosphere.
Nitrogen Cycle Stage: Nitrogen gas in atmosphere to ammonia
Nitrogen Fixation
Nitrogen Cycle Stage: Ammonia to nitrites then nitrates
Nitrification
Nitrogen Cycle Stage: Nitrites then nitrates to nitrogen gas in atmosphere
Denitrification
Nitrogen Cycle Stage: Dead organic matter to amino-acids
Saprobioitc Nutrition
Nitrogen Cycle Stage: Amino-acids to ammonia
ammonification
What is saprobioitic nutrition?
The process of converting dead organic matter to amino acids.
What is ammonification?
The process of converting amino acids to ammonia.
What carries out nitrogen fixation and where?
Nitrogen fixing bacteria in soil and root nodules of legumes.
What carries out nitrification and where?
Nitrifying bacteria in the soil.
What carries out denitrification?
Denitrifying bacteria.
What sort of process is denitrification?
Anaerobic.
What carries out saprobioitic nutrition?
Saprobionts.
What is and the process of ammonification?
Nitrogen compounds in waste products (e.g. urine and faeces) and dead organisms are converted into ammonia by saprobionts
This ammonia forms ammonium ions in the soil
what carrier out ammonifiacation
saprobionts
What is and the process of 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 convert ammonium ions into nitrites
2- nitrifying bacteria then convert these nitrites into nitrates.
What are saprobionts?
A type of decomposer including some fungi and bacteria.
what is and the process of 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 - in waterlogged soil
In what conditions does denitrification occur?
Water-logged soil.
what is and the process of nitrogen fixation
Atmospheric nitrogen gas is converted into nitrogen-containing compounds
carried out by nitrogen-fixing bacteria
- convert nitrogen into ammonia, which forms ammonium ions (in solution) that can then be used by plants
Where are nitrogen fixing bacteria found?
Inside root nodules of leguminous plants such as peas, beans, and clover.
Why are nitrogen fixing bacteria symbiotic?
They have a mutually beneficial relationship with these plants, providing nitrogen-containing compounds to the plants and receiving organic compounds such as carbohydrates in return.
What is the significance of nitrogen to living organisms?
Plant roots uptake nitrates via active transport and use them to make biological compounds such as amino acids, NAD/NADP, and nucleic acids.
What is the recycling of nutrients (phosphorus and nitrogen) dependent on?
Bacteria.
What are saprobionts? (long)
Organisms that decompose dead organic matter by secreting digestive enzymes extracellularly, hydrolyzing polymers into monomers.
What is the role of Mycorrhizae?
Facilitates the uptake of water and inorganic ions by plants.
What is the phosphate ion?
PO4 3-.
What is the nitrate ion?
NO3-.
Why do plants and animals require phosphorus?
For biological molecules such as nucleic acids (DNA and RNA) and ATP.
What is the phosphorus cycle process?
1- Phosphorus in rocks —> released into the soil & water sources–> form of phosphate ions by —> weathering
2- Phosphate ions from soil by plants through roots or absorbed from water by algae
3- Phosphate ions –> consumers (during feeding)
4- Phosphate ions in waste products and dead organisms are released–> soil or water during decomposition by saprobionts
5- phosphate ions taken up and used by producers or trapped in sediments that, over very long geological time periods may turn into phosphorus-containing rock once again
What is weathering?
The slow breaking down and erosion of rocks over time.
How do dissolved phosphate ions in oceans become phosphate ions in plants?
Through absorption.
How do phosphate ions in plants become phosphate ions in animals?
Through feeding and digestion.
How do phosphate ions in animals become dissolved phosphate ions in oceans?
Through excretion.
How do phosphate ions in animals become phosphate ions in waste and remains?
Through excretion and decomposition.
How do phosphate ions in wastes and remains become dissolved phosphate ions?
Through erosion.
How do phosphate ions in wastes and remains become phosphates in rocks?
Through deposition.
How do phosphates in rocks become dissolved ions in oceans?
Through erosion and use of fertilizers.
How do dissolved phosphate ions in oceans become phosphates in rocks?
Through sedimentation.
What is the purpose of fertilizers?
Replace minerals lost (nitrates and phosphates) from the soil
By harvesting plants and removing livestock
What is a point of comparison for natural vs artificial fertilizers?
Natural fertilizers need to be decomposed by saprobionts, making them longer lasting, while artificial fertilizers are absorbed quicker.
What is leaching?
When mineral ions dissolve in water from rain and run off into watercourses.
Describe how farmers could increase the productivity of crops
Fertilisers
Selective breeding
Crop rotation, for pest reduction
Plough the soil to aerate it, reducing denitrification and increasing nitrification
Describe the process of eutrophication
1- Higher concentration of mineral ions in the water due to leaching
2- Rapid algal growth occurs, and an algal bloom, covering the surface of the water
3- Algae blocks sunlight, so aquatic plants cannot photosynthesise
4- Aquatic plants die
5- Saprobionts decompose dead aquatic plants
6- This increases the bacterial poppulation, that are respiring aerobically
7- Oxygen concentration in water falls
8- Causes death of aquatic animals
What are three benefits of planting a different crop on the same field each year?
1- Nitrogen-fixing crops like legumes increase soil nitrate content.
2- Different crops have different pathogens.
3- Different crops use different proportions of certain ions.
What are the two categories of fertilizers and their purposes?
Organic - decaying organic matter and animal waste.
Inorganic - minerals from rocks, usually containing nitrogen, phosphorus, potassium.
The purpose –> increase gross productivity for higher yield.
Why does using more fertilizer no longer increase crop yield at a certain point?
A factor unrelated to the concentration of mineral ions limits the rate of photosynthesis, so the rate of growth cannot increase further.
outline 2 main environmental issues caused by the use of fertilisers
Leaching - nitrates dissolve in rainwater and runoff into water sources. Eutrophication - water sources become putrid due to algal bloom.
How can the rise of eutrophication be reduced?
By using sewage treatment marshes on farms, pumping nutrient-enriched sediment out of water, and using phosphate-free detergent.
(b) Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.
Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions. (2)
less nitrification
less active nitrifying bacteria
as nitrifying bacteria require oxygen
less conversion of ammonium ions to nitrite and nitrate ions.
more denitrification
more active denitrifying bacteria
doesn’t require oxygen
more nitrates covered to nitrogen gas
(a) Describe the role of saprobionts in the nitrogen cycle. (2)
They use enzymes to decompose proteins, producing ammonia.
(b) One environmental issue arising from the use of fertilisers is eutrophication. Eutrophication can cause water to become cloudy.
You are given samples of water from three different rivers.
Describe how you would obtain a quantitative measurement of their cloudiness. (3)
Use a colorimeter to measure absorbance with the same volume of water, zero the colorimeter, and use the same wavelength of light.
Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.
- Amino acids
- Nucleic acids
- ATP
- NAD/NADP
Explain why the scientists sterilised the surfaces of the seeds and grew them in soil that had been heated to 85 °C for 2 days.
to kill any fungus
so only the added fungus has any effect
after harvesting, the remians of crop plants are often ploughed into the soil. Explain how microorganisms in the soil produce a source of nitrates from these remains (5)
AA into Ammonium
by saprobionts
Ammonium into nitrite
Nitrite to nitrates
by nitrifying bacteria
In natural ecosystem, most of the light falling on producers is not used in photosynthesis. Suggest 2 reasons why
light is reflected
wrong wavelength
co2 conc or temp is the limiting factor
misses chlorophyill
the tomato seeds were planted into sterilised soil. suggest 2 reasons why
removes other fungi
no pathogens
no pests
no competitors
the soil used in this investigation has the recommended conc of fertilisers. Suggest 2 reasons why
so mycorrhizae is the only variable
So fertilisers is a controlled variable
affects growth
conc of fertilisers would affect WP of soil
doesn’t affect PH of soil
To provide usual farming conditions
lake malwin has more species of fish that any other lake in the world. Suggest and explain how this speciation has occurred
difference due to mutation
allopatric speciation
different lakes have different environmental conditions
reproductive separation
gene pool remains separate
different alleles passed on
