Nutrient Cycles 3.5.4 ( Energy transfers in and between organisms 3.5) Flashcards
Explain the role of saprobionts in recycling chemical elements
- Decompose organic compound- proteins in organic matter
- By secreting enzymes for extracellular digestion
- Absorb soluble needed nutrients and release mineral ions
Explain the role of mycorrhizae
- Fungi act as an extension of plant roots to increase surface area of root system
- To increase rate of absorption of water and inorganic ions
- In return , fungi receive organic compounds e.g. carbohydrates
Describe the role of bacteria in nitrogen fixation
- Nitrogen gas (N2) converted into ammonia which forms ammonium ions in soil
- By nitrogen - fixing bacteria
Describe the role of bacteria in ammonification
- Nitrogen containing compounds e.g. proteins from dead organisms / waste are decomposed
- Converted to ammonia which forms ammonium ions in soil
- By saprobionts
describe the role of bacteria in nitrification
- ammonium ions in soil converted into nitrites then nitrates , via a two step oxidation reaction
• for uptake by plant root hair cells by active transport - By nitrifying bacteria in aerobic conditions
describe the role of bacteria in denitrification
- Nitrates in soil converted into nitrogen gas
- By denitrifying bacteria in anaerobic conditions
suggest why ploughing (aerating ) soil increases its fertility
- More nitrification
- Less denitrification
give examples of biological molecules that contain phosphorus
Phospholipids
DNA or RNA
ATP or ADP
NADP
Describe the phosphorus cycle
1) phosphate ions in rocks released into soils by erosion
2) Phosphate ions taken up by producers e.g. plants and incorporated into their biomass
• rate of absorption increased by mycorrhizae
3) Phosphate ions transferred through food chain
4) some phosphate ions lost from animals in waste products
5) Saprobionts decompose organic compounds releasing phosphate ions
Explain why fertilisers are used
- To replace nitrates / phosphates lost when plants are harvested and livestock 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 artificial and natural fertilisers
Natural :
• Organic e.g. manure , compost
• Ions released during decomposition by saprobionts
Artificial :
• Contain inorganic compounds of nitrogen , phosphoric and potassium
Explain the key environmental issue arising from use of fertilisers
• Phosphates / nitrates dissolve in water , leading to leaching of nutrients into lakes / rivers etc
• This leads to eutrophication :
1) Rapid growth of algae in pond / river (algae bloom) 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
• Less water soluble so less leaching -> eutrophication less likely
• Organic molecules require breaking down by saprobionts ~> slow release of nitrates / phosphate etc
EQ : suggest one source of phosphate in the lake (1)
fertilisers
EQ : Name the type of bacteria which convert
(i) nitrogen in the air into ammonium compounds
(ii) nitrites into nitrates (2)
(i) nitrogen - fixation bacteria
(ii) nitrifying bacteria
EQ: Other than spreading fertilisers , describe and explain how one farming practice results in addition of nitrogen - containing compounds to a field (2)
- Growing leguminous plants
- They have nitrogen fixing bacteria
EQ) Describe and explain how one farming practice results in the removal of nitrogen - containing compounds from a field (2)
- Harvesting the crop
- This removed nitrogen containing compounds
EQ : explain how including leguminous plants in a crop rotation reduced the need to use artificial fertilisers (2)
- They contain nitrogen fixing bacteria
- They can still add nitrogen even when crop has been harvested
EQ: Application of very high concentrations of fertilisers to the soil causes plants to wilt . Explain why (2)
Changed water potential ( more negative )
Plants lose water by osmosis
EQ : In autumn when there is no crop , farm land may be used to grow mustard . The mustard absorbs nitrates which otherwise can leach out of the soil at this time of year . The mustard is ploughed back into the soil just before sowing of the main crop in spring .
Nitrogen compounds in the mustard plants are made available for the main crop after ploughing in the spring . Describe the role of microorganisms in this process . (5)
• Mustard plant would contain amino acids
• Amino acids get broken down by saprobionts into ammonium ions
• Nitrifying bacteria converts ammonium ions to nitrate ions
• Nitrates can be absorbed by roots of plants to be used
EQ : Explain why it is important for the farmer to reducing leaching of nitrates (2)
- Can cause health problems
- Leads to eutrophication
EQ : Plants absorb a number of other nutrients from the soil including phosphates . Describe why phosphates are needed by a growing plant . (4)
To produce phosphate containing compounds such as :
- ATP
- DNA
- RNA
- FAD
-NAD
- phospholipids
- cell membrane
EQ : A large lake is surrounded by fields . These fields are separated from each other by hedges . 100 years ago the lake was a habitat for many plants , invertebrate and fish . Today the lake has no fish and few plants or invertebrate. Explain how increased use of inorganic fertilisers on the fields may have led to these changes (5)
- Leaching in the lake will occur
- Causing algae bloom
- Sunlight is blocked
- Plants can’t photosynthesise
- Plants die
- Decomposed by sapbrobionts using oxygen in respiration
- Less conc of oxygen for fish to aerobically respire
- Fish + invertebrate die
EQ : Famers who grow wheat sometimes have a field fallow for a year by not growing a crop in it . The concentration of nitrate ions in the soil decreases when a field is left fallow .
When grass is grown in a field , fewer nitrate ions are lost than when the field is left with bare soil . Explain why (1)
- Nitrate ions can be leached off in soil , so less leaching in a field
EQ : A crop of leguminous plants such as clover may be grown in the field and then ploughed in . Explain why less fertiliser would be needed for the wheat crop in the following year (2)
- Clover contains nitrogen fixing bacteria
- When added , decomposed nitrate ions released into the soil
EQ : 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 quantitive measurement of their cloudiness (3)
•Use of calorimeter
• measure absorbance of light
• Same volume of water
• Same wavelength of light
give examples of biological molecules that contain nitrogen
amino acids / proteins or enzymes / urea / DNA and RNA / chlorophyll / ATP or ADP / NAD or NADP
