Topic 5.4 - Nutrient Cycles Flashcards
Explain the role of saprobionts in recycling chemical elements (3)
1) Decompose organic compounds e.g. proteins / urea / DNA in dead matter / organic waste
2) By secreting enzymes for extracellular digestion
3) Absorb soluble needed nutrients and release mineral ions e.g. phosphate ions
What are mycorrhizae?
Symbiotic association between fungi and plant roots
Explain the role of mycorrhizae (3)
1) Fungi act as an extension of plant roots to increase surface area of root system
2) To increase rate of uptake / absorption of water and inorganic ions
3) In return, fungi receive organic compounds e.g. carbohydrates
Give examples of biological molecules that contain nitrogen (7)
- Amino acids
- Proteins / enzymes
- Urea
- DNA / RNA
- Chlorophyll
- ATP / ADP
- NAD / NADP
Describe the role of bacteria in nitrogen fixation (2)
1) Nitrogen gas (N2) converted into ammonia (NH3) which forms ammonium ions (NH4+) in soil
2) By nitrogen fixing bacteria
Describe the role of bacteria in ammonification (3)
1) Nitrogen containing compounds e.g. proteins / urea from dead organisms / waste are broken down / decomposed
2) Converted to ammonia, which forms ammonium ions in soil
3) By saprobionts -> secrete enzymes for extracellular digestion
Describe the role of bacteria in nitrification (2)
1) Ammonium ions in soil converted into nitrites then nitrates, via a 2-step oxidation reaction
(For uptake by plant root hair cells by active transport)
2) By nitrifying bacteria in aerobic conditions
Describe the role of bacteria in denitrification (2)
1) Nitrates in soil converted into nitrogen gas (reduction)
2) By denitrifying bacteria in anaerobic conditions
Explain why ploughing soil increases its fertility (2)
1) More ammonium converted into nitrite and nitrate (more nitrification)
2) Less nitrate converted to nitrogen gas (less denitrification)
Give examples of biological molecules that contain phosphorus (6)
- Phospholipids
- DNA / RNA
- ATP / ADP
- NADP
- TP / GP
- RuBP
Describe the phosphorus cycle (5)
1) Phosphate ions in rocks released by erosion / weathering
2) Phosphate ions taken up by producers / plants / algae and incorporated into their biomass
- Rate of absorption increased by mycorrhizae
3) Phosphate ions transferred through food chain e.g. as herbivores not producers
4) Some phosphate ions lost from animals in waster products (excretion)
5) Saprobionts decompose organic compounds e.g. DNA in dead matter / organic waste, releasing phosphate ions
Explain why fertilisers are used (2)
1) To replace nitrates / phosphates 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
2) So improve efficiency of energy transfer -> increase productivity / yield
Describe the difference between artificial and natural fertilisers
Natural:
- Organic e.g. manure, compost, sewage
- Ions released during decomposition by saprobionts
Artificial:
- Contain inorganic compounds of nitrogen, phosphorus and potassium
Explain the key environmental issue arising from use of fertilisers (2+4)
- Phosphates / nitrates dissolve in water, leading to leaching of nutrients into lakes / rivers / oceans
- This leads to eutrophication
1) Rapid growth of algae in pond / river so light is blocked
2) So submerged plants die as they cannot photosynthesise
3) So saprobionts decompose dead plant matter, using oxygen in aerobic respiration
4) So less oxygen for fish to aerobically respire, leading to their death
Explain the key advantage of using natural fertiliser over artificial fertiliser (2)
1) Less water soluble so less leaching -> eutrophication less likely
2) Organic molecules require breaking down by saprobionts -> slow release of nitrate / phosphate etc…
