3.5.4 Nutrient Cycles Flashcards
What happens to nutrients in an ecosystem
They are recycled
Examples of two nutrient cycles
Nitrogen cycle
Phosphorus cycle
What’s the role of saprobionts in decomposition
Extracellular digestion, occurs in nitrogen and phosphorus cycle
Enzymes are released onto dead material, urine, faeces
Digestion, large insoluble molecules are hydrolysed into smaller soluble ones outside the body
Absorption of these products eg amino acids, glucose
Saprobionts release ammonium ions (N cycle), phosphate ions (P cycle)
What’s mycorrhizae
Fungus, facilitates uptake of water and inorganic ions by plants
Role of mycorrhizae in nutrient cycles
microscopic threads (hyphae) acting as extensions of the plants root system, increase surface area for absorption of water and minerals
Acts as a sponge holding water and minerals around the roots, plants can resist drought and take up scarce ions readily
Mutualistic relationship, plant has better water uptake, fungus recurve organic compounds like sugar from plant
What’s the importance of the nitrogen cycle
Plants and animals can obtain nitrogen gas from gas exchange
Microorganisms needed to convert N2 into nitrogen containing substances they can absorb
Which biological molecules contain nitrogen
ATP, adenine is a nitrogenous base
Proteins, amino acids are made of 3 nitrogenous based
DNA, nitrogenous bases
How to plants take up nitrogen
Nitrate ions from soil are absorbed via active transport
How do animals take up nitrogen
Through food
Steps in the nitrogen cycle
- Ammonification
- Nitrification
- Nitrogen fixation
- Denitrification
What happens in nitrogen fixation
N2 in atmosphere converted to nitrogen containing compounds
Root nodules in some plants contain nitrogen fixing bacteria
Nitrogen fixing bacteria in soil reduce nitrogen to ammonia
Artificially lightening produces nitrogen oxides which are taken up as nitrates by plants
What happens in ammonification
Urea, proteins, nucleus acids are digested by saprobionts, forming ammonia then ammonium ions in soil
What happens in nitrification
Ammonium ions oxidised to nitrite ions then oxidised again to nitrate ions
Both reactions require nitrifying bacteria
What happens in denitrification
Waterlogged soil contains less aerobic nitrifying and nitrogen fixing bacteria and more anaerobic denitrifying bacteria, nitrates in soil are converted to N2 gas, this reduced nitrogen containing compounds for plants,
What are sources natural fertilisers
Dead and decaying remains of plants and animals
Manure
Slurry
What are sources of artificial fertilisers
Mined from rocks, converted into different forms, blended to create an appropriate balance of minerals
Chemicals contain nitrogen phosphorus and potassium (NPK)
Why are fertilisers used
In agriculture crops are harvested, soil is depleted of nitrates and phosphates, these ions are replaced by the use of fertilisers
How are fertilisers causing environmental issues
Excessive use of them
How do fertilisers cause leaching
Leaching, nutrients are removed from soil
Rainwater dissolves soluble nutrients like nitrate and phosphate ions, carried deep into soil so plant roots can’t reach them, nitrates move into water sources like lakes
This can further cause eutrophication
How do both fertilisers cause eutrophication
Low conc of nitrate ions in lakes, limiting factor for plant growth
Due to leaching nitrate ion conc increases, algae and plant populations grow
Upper surface of water becomes densely populated with algae
This layer of algae absorbs light, cannot penetrate lower, it becomes a limiting factor for algae at the bottom of the lake causing it to die
There is enough dead matter for saprobionts to use as food causing their population to grow
Saprobionts require oxygen for respiration increasing the demand of oxygen
There is a reduced oxygen conc causing nitrates to be released from dead organisms
Oxygen becomes a limiting factor for aerobic organisms, these organisms then die
Less competition for anaerobic organisms, they decompose dead material releasing nitrates and toxic waste making water putrid
Artificial and natural fertilisers cause leaching and eutrophication but artificial ones are the main cause
Why is phosphorus important
Used in ATP, phospholipids, nucleic acids to make DNA
Explain the phosphorus cycle
Phosphate ions exist in rock deposits, weathering and erosion allows them to dissolve into water
Plants absorb these, become part of their biomass, pass into animals through feeding, excess ions are excreted
Bacteria and fungi break down dead plants and animals releasing ions into water and soil. Phosphate ions in excreta are released by decomposition and transported by lakes to form rocks
