Section 5 - Unit 13: Energy and Ecosystems Flashcards
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)
- Protein/DNA converted into ammonium compounds/ammonia
- By saprobionts
- Ammonium/ammonia converted into nitrite
- Nitrite converted into nitrate
- By nitrifying bacteria/microorganisms
Describe a process carried out by microorganisms which adds ammonium ions to soil (2 marks)
- Protein/amino acids broken down into ammonium ions/ammonia
- By saprobionts
Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil (2 marks)
- Fertility increased as more nitrate formed
- Less/no denitrification as there are fewer denitrifying bacteria
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)
- Grow crops / plants with nitrogen-fixing bacteria
- Different crops use different minerals / salts / nutrients / ions
- Different pests
Give two biological molecules that contain:
- nitrogen
- phosphorus
(2 marks)
Nitrogen: - Amino acid/protein/enzyme - DNA/RNA/ATP/ADP Phosphorus: - DNA/RNA/ATP/ADP / - Phospholipids/nucleic acids
Describe the role of microorganisms in producing nitrates from the remains of dead organisms (3 marks)
- Saprobiotic microorganisms break down remains/dead material/proteins into ammonia/ammonium
- Ammonia/ammonium ions into nitrite and then into nitrate
- By nitrification/nitrifying bacteria
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)
- 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
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)
- Nitrogen converted into ammonia/ammonium
- To produce proteins/amino acids/DNA
Explain how farming practices increase the productivity of agricultural crops (5 marks)
- 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
Name the process by which some bacteria oxidise ammonia to nitrate (1 mark)
- Nitrification
Explain how an increase in nitrate concentration in the water entering the lake could affect algae and fish in the lake (3 marks)
- 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
Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen-containing compounds to a field (2 marks)
- Growing legumes
- Nitrogen fixing bacteria in the nodules
OR - Cattle to graze
- Add dung/urine
OR - Add manure
- Decomposed to release nitrates
Describe and explain how one farming practice results in the removal of nitrogen containing compounds from a field (2 marks)
- Bare soil
- Leaching of nitrates
OR - Uptake of nitrates
- Harvesting crops
OR - Animals eat plants
- Then the animals are removed
Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants (5 marks)
- Saprobionts
- Digest proteins / DNA / nitrogen-containing substances
- Extracellular digestion / release of enzymes
- Ammonia / ammonium produced
- Ammonia converted to nitrite to nitrate
- Nitrification
- Oxidation
Steps in the Nitrogen Cycle (4)
- Nitrogen fixation
- Ammonification
- Nitrification
- Denitrification
Nitrogen fixation (2)
- 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
Ammonification (1)
- Saprobionts break down proteins in dead organisms to make ammonia
Nitrification (1)
- Nitrifying bacteria convert ammonia into nitrites (NO2-) and nitrates (NO3-)
Denitrification (2)
- Occurs in waterlogged anaerobic conditions
- Nitrates are converted into nitrogen gas, thus replenishing the atmosphere
Describe how waterlogged soil can cause nitrate to be removed from the soil (4)
- 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
Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your
knowledge of water potential to explain why (2 marks)
- Soil has lower water potential
- So osmosis from plant into soil
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)
- Provides ATP for the reaction / nitrogen fixation
- Nitrogenase produced quicker / more enzyme produced
- Removes oxygen (so nitrogenase works)
Explain why it is important for farmers to reduce the leaching of nitrates (2 marks)
- 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
Explain what limits the size of populations in a climax community (5 marks)
- 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)
Give the equation that links gross productivity and net productivity (1 mark)
Gross productivity = net productivity + respiratory loss
Suggest how you could determine the dry mass of a sample of plant material (2 marks)
- Heat at 100°C
- Weigh and heat until no further change in mass
What is the advantage of using dry mass and not fresh mass to compare the yield of plants (2 marks)
- Amount of water present will vary
- This will affect fresh mass / will not affect dry mass
Explain how including leguminous plants in a crop rotation reduces the need to use artificial fertilisers (2 marks)
- Nitrogen-fixing bacteria in the root nodules
- So nitrogen containing compounds added to the soil when a plant dies
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)
- 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
Explain the role of saprobionts (2 marks)
- Convert proteins to amino acids
- And then ammonium compounds
Explain how an increase in temperature over time could decrease the dry mass of a plant (4 marks)
- 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
