Topic 5 - Nutrient Cycles Flashcards
What is a nutrient cycle?
Ensure that essential elements like nitrogen and phosphorus are recycled within natural ecosystems. These cycles maintain the availability of nutrients for living organisms.
What is the nitrogen cycle for?
Nitrogen is essential for biological molecules such as proteins and nucleic acids. Although nitrogen gas (N₂) makes up ~78% of the atmosphere, it is inert and cannot be used directly by most organisms. The nitrogen cycle ensures nitrogen is recycled and made biologically available.
What is nitrogen fixation?
Nitrogen-fixing bacteria in the soil (e.g., Rhizobium) or root nodules of legumes convert nitrogen gas into ammonia (NH₃), which dissolves in water to form ammonium ions (NH₄⁺).
What is ammonification?
Saprobionts break down organic matter from dead organisms and waste products (e.g., urea) into ammonium ions.
What is nitrification?
Nitrifying bacteria convert ammonium ions into nitrites (NO₂⁻) and then into nitrates (NO₃⁻), which plants can absorb.
What is assimilation?
Plants absorb nitrates from the soil and use them to synthesise biological molecules such as amino acids.
What is denitrification?
In anaerobic conditions (e.g., waterlogged soils), denitrifying bacteria convert nitrates back into nitrogen gas (N₂), reducing soil fertility.
What is the phosphorus cycle for?
Phosphorus is an essential component of molecules like ATP, DNA, and phospholipids. Unlike nitrogen, phosphorus does not have a gaseous phase and relies on the movement between land, water, and organisms.
What is the phosphorus cycle in order?
- Weathering rocks: phosphate ions are released form rocks through weathering and enter soils and water bodies.
- Absorption by plants: plants absorb phosphate ions from the soil and incorporate them into biological molecules.
- Feeding and digestion: animals obtain phosphorus by consuming plants or other animals and use it to synthesise molecules like ATP and nucelic acids.
- Decomposition: when plants and animals die, saprobionts break down organic matter, returning phosphate ions to the soil or water.
Sedimentation: phosphate ions in water bodies can form sediments and eventually reform rocks, completing the cycle.
What are the human impacts on nutrient cycles?
Fertiliser use: excess nitrates and phosphates from fertilisers can leach into water bodies, causing eutrophication.
Deforestation: reduced plant uptake of nutrients, leading to nutrient loss from soil.
Animal farming: produces waste in ammonium, altering the nitrogen cycle.
Why are nitrates needed in plants?
Needed for the syntheses of proteins, DNA, and chlorophyll.
Why are phosphates needed in plants?
Required for the production of ATP, DNA and cell membranes.
Why are potassium ions needed in plants?
Regulates stomatal opening and enzyme activation.
Why are magnesium ions needed in plants?
Essential for chlorophyll production and enzyme activity.
What will nitrate deficiency look like in plants?
Stunted growth and yellow leaves.
What will potassium deficiency look like in plants?
Yellowing leaf edges and brown spots.
What will phosphate deficiency look like in plants?
Poor root development and purple discolouration of leaves.
What will magnesium deficiency look like in plants?
Interveinal chlorosis (yellowing between veins.
What is the role of nitrogen fixing bacteria?
Convert atmospheric nitrogen into ammonia.
What is the symbiotic relationship plant and nitrogen fixing bacteria?
In legumes, Rhizobium receives carbohydrates from the plant and supplies nitrogen compounds in return.
What is the importance of microorganisms on maintaining nutrient cycles?
- Recycling nutrients allows ecosystems to remain productive.
- Decomposition prevents the build-up of organic matter and releases essential minerals.
- Symbiosis (e.g., Rhizobium in legumes) boosts agricultural productivity naturally.
What is a natural fertiliser?
Composed of dead and decaying organic matter, such as manure, compost, or sewage sludge.
Release nutrients slowly as organic material decomposes.
What is an artificial fertiliser?
- Manufactured chemicals containing specific minerals, such as nitrates, phosphates, and potassium compounds (NPK fertilisers).
- Provide nutrients in a soluble form that plants can absorb immediately.
What are the advantages of natural fertilisers?
- improves soil structure by increasing organic matter.
- Encourages the activity of soil microorganisms.
- Slow nutrient release reduces the risk of leaching.
What are the disadvantages of natural fertilisers?
– Nutrient content is variable and less concentrated.
- May take time to decompose and become available to plants.
What are the advantages of artificial fertilisers?
- Provide nutrients in a readily available and concentrated form.
- Can be targeted to specific nutrient deficiencies.
What are the disadvantages of artificial fertilisers?
- Overuse can lead to soil acidification and leaching.
- Can cause eutrophication if nutrients run-off into water bodies.
What is leaching?
Nitrates and phosphate are soluble and can be washed out of the soil into rivers and lakes, particularly after rainfall.
What is eutrophication?
Leached nutrients cause algal blooms, blocking light and reducing oxygen levels in water bodies.
Leads to the death of aquatic organisms due to hypoxia (low oxygen levels).
How can fertilisers cause reduction in biodiversity?
Excess nutrients encouraged the growth of fast-growing plants, out competing and reducing slower-growing species.
