[3.5.4] Nutrient Cycles Flashcards
Explain the role of saprobionts in recycling chemical elements.
- Decompose (break down) organic compounds e.g. proteins / urea / DNA in dead matter / organic waste.
- By secreting enzymes for extracellular digestion (saprobiotic nutrition).
- Absorb soluble needed nutrients and release mineral ions e.g. phosphate ions.
Explain the role of mycorrhizae.
Mycorrhizae = symbiotic association between fungi and plant roots.
- Fungi (hyphae) act as an extension of plant roots to increase surface area of root system.
- To increase rate of uptake / absorption of water and inorganic ions .
- In return, fungi receive organic compounds e.g. carbohydrates.
Give examples of biological molecules that contain nitrogen.
- Amino acids / proteins or enzymes / urea / DNA or RNA / chlorophyll / ATP or ADP / NAD or NADP.
Draw a diaram to show the key stages of the nitrogen cycle.
Describe the role of bacteria in nitrogen fixation.
- Nitrogen gas (N₂) converted into ammonia (NH₃), which forms ammonium ions (NH₄⁺) in soil.
- By nitrogen-fixing bacteria (may be found in root nodules).
Describe the role of bacteria in ammonification.
- Nitrogen-containing compounds e.g. proteins / urea from dead organisms / waste are broken down / decomposed.
- Converted to ammonia, which forms ammonium ions in soil.
- By saprobionts - secrete enzymes for extracellular digestion.
Describe the role of bacteria in nitrification.
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Ammonium ions in soil converted into nitrites then nitrates, via a two-step oxidiation reaction.
- For uptake by plant root hair cells by active transport.
- By nitrifying bacteria in aerobic conditions (oxygen).
Describe the role of bacteria in denitrification.
- Nitrates in soil converted into nitrogen gas (reduction).
- By denitrifying bacteria in anaerobic conditions (no oxygen, e.g. waterlogged soil).
Suggest why ploughing (aerating) soil increases its fertility.
- More ammonium converted into nitrite and nitrate / more nitrification / more (active) nitrifying bacteria.
- Less nitrate converted to nitrogen gas / less dentrification / fewer (active) denitrifying bacteria.
Give examples of biological molecules that contain phosphorus.
- Phospholipids / DNA or RNA / ATP or ADP / NADP / TP or GP / RuBP.
Describe the phosphorus cycle.
- Phosphate ions in rocks released (into soils/oceans) by erosions / weathering.
- Phosphate ions taken up by producers / plants / algae and incorporated into their biomass.
- Rate of absorption increased by mycorrhizae.
- Phosphate ions transferred through food chain e.g. as herbivores eat producers.
- Some phosphate ions lost from animals in waste products (excretion).
- Saprobionts decompose organic compounds e.g. DNA in dead matter / organic waste, releasing phosphate ions.
Explain why fertilisers are used.
- To replace nitrates / phosphate lost when plants are harvested and livestock are removed.
- Those removed from soil and incorporated into biomass can’t be released back into the soil through decomposition by saprobionts.
- So improve efficiency of energy transfer -> increase productivity / yield.
Describe the difference between artifical and natural fertilisers.
NATURAL
- Organic, e.g. manure, compost, sewage.
- Ions released during decomposition by saprobionts.
ARTIFICAL
- Contain inorganic compounds of nitrogen, phosphorous and potassium.
Explain the key environmental issue arising from use of fertilisers.
- Phosphates / nitrates dissolve in water, leading to leaching of nutritents into lakes / rivers / oceans.
- This leads to eutrophication.
- Rapid growth of algae in pond / river (algal bloom) so light blocked.
- So submerged plants die as they cannot photosynthesis.
- So saprobionts decompose dead plant matter, using oxygen in aerobic respiration.
- So less oxygen for fish to aerobically respire, leading to their death.
Explain the key advantages of using natural fetiliser over artifical fertiliser.
- Less water soluble so less leaching -> eutrophiciation less likely.
- Organic molecules require breaking down by sapriobionts -> slow release nirate / phosphate etc.
