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LGS A-Level OCR Biology - Unit 6 - Ecosystems Part 3

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This flashcard deck covers key concepts from Unit 6 of the OCR Biology A-Level syllabus, focusing on ecosystems. Topics include crop rotation, primary and secondary productivity, the carbon and nitrogen cycles, and human impacts on these cycles.

How does crop rotation increase primary productivity?

Stops reduction in soil levels of inorganic ions e.g. K^+ or NO3^-
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Key Terms

Term
Definition
How does crop rotation increase primary productivity?
Stops reduction in soil levels of inorganic ions e.g. K^+ or NO3^-
Crop rotation
Growing a diff. crop in each field on a rotational cycle
How does use of pesticides increase primary productivity?
Prevents loss of biomass and lowering yield of plant
Why do plants need NH4+?
Maintains pH
Why do plants need NO3-?
Part of the nitrogen cycle
Function of K+ in plants
Improves growth of leaves

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TermDefinition
How does crop rotation increase primary productivity?
Stops reduction in soil levels of inorganic ions e.g. K^+ or NO3^-
Crop rotation
Growing a diff. crop in each field on a rotational cycle
How does use of pesticides increase primary productivity?
Prevents loss of biomass and lowering yield of plant
Why do plants need NH4+?
Maintains pH
Why do plants need NO3-?
Part of the nitrogen cycle
Function of K+ in plants
Improves growth of leaves
Function of PO4 3- in plants
Improves growth of roots
Increasing secondary productivity
Harvesting animals before adulthood; Selective breeding; Animals treated w/ antibiotics; Zero grazing; Keeping environmental temp constant - prevents energy loss through homeostasis
How does harvesting animals before adulthood increase secondary productivity?
Minimises loss of energy as younger animals invest a larger proportion of energy into their growth
How does selective breeding increase secondary productivity?
Produces improved animal breeds w/ faster growth, increased egg production and increased milk production
Zero grazing
Bringing food directly to animals | Maximises energy allocated to developing muscle by reducing need to move
Processes in the carbon cycle
Photosynthesis; Respiration (animals and plants); Anaerobic respiration (dead organic matter and excreta); Fossilisation; Combustion; Diffusion and carbonic acid formation; Diffusion; Decomposition; Feeding; Sedimentation
Processes adding to atmospheric CO2
Respiration; Combustion; Diffusion frm the sea to the air
Processes removing atmospheric CO2
Photosynthesis | Diffusion and carbonic acid formation in the ocean
Sedimentation
CO2 is used by plankton to produce calcium carbonate shells. When these die, their shells sink to the ocean floor and are buried by sediment
Fossilisation
Organic matter is buried and compressed over millions of years forming gas, coal and oil
Human interferences that affect the carbon cycle
Combustion; Population size (respiration and waste); Deforestation; Farming
Effects of human interferences w/ the carbon cycle
Global warming/enhanced greenhouse effect; Ocean acidification from carbonic acid; Warmer sea - less CO2 absorbed; Removing photosynthesisers; Releasing more CO2 through combustion of trees
Processes in the nitrogen cycle
Nitrification; Assimilation; Denitrification; Nitrogen fixation by organic and non-living processes; Ammonification
What is nitrogen fixing?
Conversion of atmospheric nitrogen (N2) into nitrogen containing compounds
Nitrogen fixing
Carried out by denitrifying bacteria (Azobacter) and mutualistic bacteria (Rhizobium) in plant root nodules. Nitrogenase reduces N2 to NH3 to form amino acids; Atmospheric fixation; Haber process to make chemical fertilisers
Atmospheric fixation
Converting nitrogen gas into nitrates by lightning. The energy from lightning breaks the N2 into atoms which combine w/ oxygen and dissolve in rain
Ammonification
Converting nitrogen containing compounds (e.g. urea from urine) to NH3. Carried out by decomposers
Nitrification
Conversion of ammonium ions to nitrites (by Nitrosomonas) and then into nitrates (by Nitrobacter) by nitrifying bacteria (chemoautotrophs)
Assimilation
Nitrates in the soil are absorbed from the soil by plants and algae. Animals then eat plants and assimilate nitrogen compounds too