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AQA A Level Biology > Section 5 - Unit 13: Energy and Ecosystems > Flashcards

Section 5 - Unit 13: Energy and Ecosystems Flashcards

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1
Q

After harvesting, the remains of crop plants are often ploughed into the soil. Explain how microorganisms in the soil produce a source of nitrates from these remains (5 marks)

A
  • Protein/DNA converted into ammonium compounds/ammonia
  • By saprobionts
  • Ammonium/ammonia converted into nitrite
  • Nitrite converted into nitrate
  • By nitrifying bacteria/microorganisms
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2
Q

Describe a process carried out by microorganisms which adds ammonium ions to soil (2 marks)

A
  • Protein/amino acids broken down into ammonium ions/ammonia

- By saprobionts

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3
Q

Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil (2 marks)

A
  • Fertility increased as more nitrate formed

- Less/no denitrification as there are fewer denitrifying bacteria

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4
Q

One farming practice used to maintain high crop yields is crop rotation. This involves growing a different crop each year in the same field. Suggest two ways in which crop rotation may lead to high crop yields (2 marks)

A
  • Grow crops / plants with nitrogen-fixing bacteria
  • Different crops use different minerals / salts / nutrients / ions
  • Different pests
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5
Q

Give two biological molecules that contain:
- nitrogen
- phosphorus
(2 marks)

A 
Nitrogen:
- Amino acid/protein/enzyme
- DNA/RNA/ATP/ADP
Phosphorus:
- DNA/RNA/ATP/ADP / 
- Phospholipids/nucleic acids
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6
Q

Describe the role of microorganisms in producing nitrates from the remains of dead organisms (3 marks)

A
  • Saprobiotic microorganisms break down remains/dead material/proteins into ammonia/ammonium
  • Ammonia/ammonium ions into nitrite and then into nitrate
  • By nitrification/nitrifying bacteria
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7
Q

Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water (5 marks)

A
  • Growth of algae/surface plants/algal bloom blocks light
  • Reduced/no photosynthesis so (submerged) plants die
  • Saprobiotic microorganisms/bacteria
  • Aerobically respire
  • So less oxygen for fish to respire/aerobic organisms die
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8
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 marks)

A
  • Nitrogen converted into ammonia/ammonium

- To produce proteins/amino acids/DNA

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9
Q

Explain how farming practices increase the productivity of agricultural crops (5 marks)

A
  • Fertilisers/minerals added to soil
  • Role of named nutrient or element e.g. nitrate/nitrogen for proteins or phosphate for ATP/DNA
  • Selective breeding/genetic modification of crops
  • Ploughing/aeration allows nitrification/decreases denitrification
  • Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction
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10
Q

Name the process by which some bacteria oxidise ammonia to nitrate (1 mark)

A
  • Nitrification
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11
Q

Explain how an increase in nitrate concentration in the water entering the lake could affect algae and fish in the lake (3 marks)

A
  • Increase in algae blocks light/ plants/algae die
  • Decomposers/saprobionts break down dead plant materials
  • Decomposers/saprobionts use up oxygen in respiration causing fish to die
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12
Q

Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen-containing compounds to a field (2 marks)

A
  • Growing legumes
  • Nitrogen fixing bacteria in the nodules
    OR
  • Cattle to graze
  • Add dung/urine
    OR
  • Add manure
  • Decomposed to release nitrates
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13
Q

Describe and explain how one farming practice results in the removal of nitrogen containing compounds from a field (2 marks)

A
  • Bare soil
  • Leaching of nitrates
    OR
  • Uptake of nitrates
  • Harvesting crops
    OR
  • Animals eat plants
  • Then the animals are removed
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14
Q

Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants (5 marks)

A
  • Saprobionts
  • Digest proteins / DNA / nitrogen-containing substances
  • Extracellular digestion / release of enzymes
  • Ammonia / ammonium produced
  • Ammonia converted to nitrite to nitrate
  • Nitrification
  • Oxidation
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15
Q

Steps in the Nitrogen Cycle (4)

A
  • Nitrogen fixation
  • Ammonification
  • Nitrification
  • Denitrification
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16
Q

Nitrogen fixation (2)

A
  • Rhizobium contains an enzyme called nitrogenase that converts nitrogen and hydrogen to ammonia
  • Which is used to make amino acids which the legume can use to make proteins in return for supplying the bacteria with carbohydrates
17
Q

Ammonification (1)

A
  • Saprobionts break down proteins in dead organisms to make ammonia
18
Q

Nitrification (1)

A
  • Nitrifying bacteria convert ammonia into nitrites (NO2-) and nitrates (NO3-)
19
Q

Denitrification (2)

A
  • Occurs in waterlogged anaerobic conditions

- Nitrates are converted into nitrogen gas, thus replenishing the atmosphere

20
Q

Describe how waterlogged soil can cause nitrate to be removed from the soil (4)

A
  • Flooded wetlands give an opportunity for denitrification to take place
  • As there are anaerobic conditions
  • Nitrate is converted into nitrogen gas
  • By denitrifying bacteria which is released into the atmosphere
21
Q

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

A
  • Soil has lower water potential

- So osmosis from plant into soil

22
Q

Azotobacter has a very high rate of aerobic respiration compared with bacteria that do not fix nitrogen. Suggest two advantages of the very high rate of aerobic respiration (2 marks)

A
  • Provides ATP for the reaction / nitrogen fixation
  • Nitrogenase produced quicker / more enzyme produced
  • Removes oxygen (so nitrogenase works)
23
Q

Explain why it is important for farmers to reduce the leaching of nitrates (2 marks)

A
  • Leaching decreases nitrates in the soil for the next crop
  • Therefore more fertiliser is required as growth is limited
    OR
  • Nitrates leach into water and eutrophication may occur
24
Q

Explain what limits the size of populations in a climax community (5 marks)

A
  • Named nutrient availability
  • Numbers of producers providing energy / light intensity affecting the rate of photosynthesis
  • Disease killing members of species / predation described
  • Space for niches
  • Competition for a named limited resource (intra/interspecific competition)
25
Q

Give the equation that links gross productivity and net productivity (1 mark)

A

Gross productivity = net productivity + respiratory loss

26
Q

Suggest how you could determine the dry mass of a sample of plant material (2 marks)

A
  • Heat at 100°C

- Weigh and heat until no further change in mass

27
Q

What is the advantage of using dry mass and not fresh mass to compare the yield of plants (2 marks)

A
  • Amount of water present will vary

- This will affect fresh mass / will not affect dry mass

28
Q

Explain how including leguminous plants in a crop rotation reduces the need to use artificial fertilisers (2 marks)

A
  • Nitrogen-fixing bacteria in the root nodules

- So nitrogen containing compounds added to the soil when a plant dies

29
Q

After harvesting a crop, the farmer digs the unwanted stems and roots into the soil. Explain how the nutrients contained in these plant parts become available for use by other organisms (6 marks)

A
  • Decomposers feed on proteins
  • Excreting ammonia
  • Nitrifying bacteria convert these into nitrate
  • Nitrates taken up by plants
  • Phosphates released
  • Organisms respire and produce CO₂ which is then used by plants in photosynthesis
30
Q

Explain the role of saprobionts (2 marks)

A
  • Convert proteins to amino acids

- And then ammonium compounds

31
Q

Explain how an increase in temperature over time could decrease the dry mass of a plant (4 marks)

A
  • Enzyme activity reduced / enzymes denatured
  • Less photosynthesis, so fewer sugars formed
  • Less respiration / less energy / ATP for growth
  • Less energy for named function associated with growth, e.g. mitosis

AQA A Level Biology (14 decks)

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