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Biology > 5.4 - Nutrient cycles > Flashcards

5.4 - Nutrient cycles Flashcards

1
Q

Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions. Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions. (2)

A
  • Less nitrification
    / Fewer/less active nitrifying bacteria
    / Nitrification/nitrifying bacteria require oxygen/aerobic conditions
  • (Less) oxidation/conversion of ammonium (ions) to nitrite (ions) and to nitrate (ions)
  • More denitrification / More active denitrifying bacteria
    / Denitrification/denitrifying bacteria do not require oxygen
    / Denitrification/denitrifying bacteria require anaerobic conditions
  • (So more) nitrate (ions) reduced/converted to nitrogen (gas)
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2
Q

Describe the role of saprobionts in the nitrogen cycle. (2)

A
  • (They use enzymes to) decompose proteins/DNA/RNA/urea
    ‘accept any named molecule containing nitrogen eg enzymes, NAD, ATP, amino acids’
    ‘accept digest/breakdown/hydrolyse for decompose’
  • Producing/releasing ammonia/ammonium compounds/ammonium ions
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3
Q

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 quantitative measurement of their cloudiness. (3)

A
  • Use of colorimeter
  • Measure the absorbance/transmission (of light)
  • Example of how method can be standardised eg same volume of water, zeroing colorimeter, same wavelength of light, shaking the sample
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4
Q

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested. (2)

A
  • Amino acid / protein / polypeptide / peptide
  • Nucleic acid / nucleotide / base
  • DNA
  • RNA
  • ATP / ADP
  • NAD / NADP (reduced or not)
  • Chlorophyll
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5
Q

Leguminous crop plants have nitrogen-fixing bacteria in nodules on their roots. On soils with a low concentration of nitrate ions, leguminous crops often grow better than other types of crop. Explain why. (2)

A
  • (Nitrogen) to ammonia / NH3 / ammonium
  • Produce protein / amino acids / named protein / DNA / RNA
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6
Q

Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your knowledge of water potential to explain why. (2)

A
  • Soil has low(er) water potential / plant / roots have higher water potential
  • Osmosis from plant / diffusion of water from plant
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7
Q

State two roles of nitrogen in living organisms. (2)

A
  • Building proteins
  • Building nucleic acids/RNA/DNA
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8
Q

The process of denitrification involves anaerobic bacteria. Suggest how flooding might impact the availability of nitrates in the soil. (1)

A
  • Nitrates would be lost/removed from the soil / nitrate availability in the soil would be reduced
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9
Q

Describe the process of ammonification. (2)

A
  • The conversion of nitrogen-containing molecules in dead organisms/waste into ammonia/ammonium compounds/ammonium ions
  • By bacteria/fungi/saprobionts/soil microorganisms
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10
Q

Describe the role of microorganisms in the phosphorus cycle. (2)

A
  • Function as decomposers/saprobionts
  • That break down the molecules in dead organisms / waste matter to release phosphate ions (into the ground/soil)
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11
Q

State one role of phosphorus in living organisms. (1)

A
  • Building phospholipids
  • Building nucleic acids/DNA/RNA
  • Building ATP
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12
Q

Define the term saprobiont. (2)

A
  • Bacteria or fungi
  • Organisms that gain their nutrition from dead matter / organic waste (saprobiotic nutrition)
  • Carry out extracellular digestion / secrete enzymes onto their food
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13
Q

Explain why decomposers are an essential part of any ecosystem. (1)

A
  • They release nutrients (from dead or waste matter), making them available again to other organisms
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14
Q

Explain the importance of the mycorrhizal relationship to both the fungus and the plant. (2)

A
  • The fungi increase the surface area of the plant roots / increase the uptake of water/minerals for the plant
  • The fungi gains carbohydrates/sugars/glucose from the plant (produced in photosynthesis)
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15
Q

Fertilisers are essential for most farmers to prevent soils from becoming deficient in minerals. Explain how the problem of eutrophication shown can be reduced while still maintaining soil mineral availability. (2)

A
  • Using natural fertilisers (rather than artificial fertilisers)
  • Natural fertilisers are less soluble in water / must be broken down by microorganisms before they become water-soluble (reducing the amount/rate of leaching)
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16
Q

Explain why phosphates are essential for plants to grow. (3)

A
  • The production of phospholipids (which are an essential component of) cell membranes
  • The synthesis of ATP
  • The production of DNA
  • The production of RNA
  • The production of NADP
17
Q

Once phosphorus (in the form of phosphates) has been absorbed and used by animals, how does the phosphorus get recycled back into the ecosystem. (3)

A
  • Animals produce faeces / animals die
  • The phosphorus-containing substances in their faeces or tissues are digested by saprobiotic bacteria
  • This releases phosphate ions
  • Phosphate ions can then be taken up again by plants
18
Q

Describe how the saprobionts obtain their nutrients from dead organisms and animal waste products. (2)

A
  • Extracellular digestion
  • Secreting enzymes onto food/dead organisms/animal waste products
  • Absorbing the nutrients / products of digestion
19
Q

Saprobionts release nitrogen into the soil in the form of ammonia/ammonium ions but another key process must occur before the crops can use this nitrogen. Name and describe this process. (5)

A
  • Nitrification
  • Nitrifying bacteria
  • Convert ammonium ions to nitrites
  • (Other nitrifying bacteria) convert nitrites to nitrates
  • Oxidation occurs
20
Q

Adding inorganic fertilisers to a field, is a farming practice that can increase the amount of nitrogen-containing compounds in the soil. Describe and explain one other farming practice that can increase the amount of nitrogen-containing compounds in the soil. (2)

A
  • Adding organic fertiliser/manure/slurry
  • This decomposes to release ammonia/nitrites/nitrates
21
Q

Otherthan their importance in the production of ATP, state and explain two reasons why phosphate ions are important forthe growth of plants. (4)

A
  • (Phosphate ions are required to) make nucleotides for DNA/mRNA/tRNA
  • (Which are required) for cell division / production of protein (for growth)
  • (Phosphate ions are required to) make RuBP / NADP
  • (Which are required) to fix CO2 / reduce CO2 into sugar
  • (Phosphate ions are required to) make phospholipids
  • (Which are required) for membranes
22
Q

Outline four ways in which nitrogen and its compounds are introduced into soil as a mineral nutrient for plants. (4)

A
  • The fixing of nitrogen by nitrogen fixing bacteria
  • The application of artificial fertilisers by farmers
  • Urination / defecation of animals onto soil
  • Lightning causes oxidation of atmospheric nitrogen to nitrogen oxides, carried to the soil by rain as nitrous or nitric acid
  • Decay of organic matter by saprobionts / decomposer microorganisms
23
Q

Farmers regularly plough their arable fields. Use your knowledge of the nitrogen cycle to explain the benefits of this practice. (3)

A
  • To prevent soil waterlogging / to aerate the soil / introduce oxygen
  • To prevent build-up of denitrifying bacteria
  • So that soil nitrates are not converted to gaseous nitrogen
24
Q

Describe the nature of mycorrhizae and their role in facilitating the uptake of water and inorganic ions by plants. (3)

A
  • Mycorrhizae are associations between fungi and roots of certain plants
  • Mycorrhizae form mutualistic / symbiotic relationships with host plants
  • Fungus receives sugars (for respiration) / amino acids in return (for water and minerals)
25
Q

In the phosphorus cycle, outline three ways in which phosphorus is introduced into soil and into water in oceans, lakes and rivers. (3)

A
  • Excretion by animals
  • Erosion of dead animal material such as bones / shells
  • Use of sedimentary rock minerals in fertilisers
  • Weathering / erosion of sedimentary rocks
26
Q

Describe and explain how two different farming practices result in the removal of nitrogen-containing compounds from a field. (4)

A
  • Leaving bare soil / fallow fields
  • Nitrates leach away
    or
  • Removal of hedges
    Soil erosion
    or
  • Growing a high-protein crop
  • Nitrogen is taken up by the crop (and removed at harvest)
    or
  • Grazing animals in the field
  • Nitrogen is taken up by the animals (and removed for slaughter)
27
Q

Describe the importance to ecosystems of the role played by nitrogen-fixing bacteria in the nitrogen cycle. (3)

A
  • They convert nitrogen (gas) into ammonium / ammonia / amino acids
  • They provide nitrogen in usable forms
  • To other organisms on all trophic levels
  • For protein/DNA synthesis

Biology (40 decks)

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