OCR Biology A - 6.3.2 - Ecosystems Part 2
Pioneer species such as algae and lichens are the first to colonise bare rock, as they can survive without soil and begin the process of soil formation through weathering and organic matter accumulation.
Pioneer species on bare rock
Algae and lichens as they don't need to be anchored into the soil
Key Terms
Pioneer species on bare rock
Algae and lichens as they don't need to be anchored into the soil
Increasing primary productivity
Some crops are planted early
Irrigating crops
Drought resistant crops
Using greenhouses
Crop rotation
Fertilisers (pr...
How does planting some crops early increase primary productivity
Provides a longer growing season to harvest more light
How does irrigating crops increase primary productiviy
Water is readily available for the light dependent stage of photosynthesis even when rainfall is below average
How does growing crops in a greenhouse increases primary productivity
Provides a warmer temp ---> increases the rate of photosynthesis
How does crop rotation increase primary productivity
Stops reduction in soil levels of inorganic ions e.g. K^+ or NO3^-
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| Term | Definition |
|---|---|
Pioneer species on bare rock | Algae and lichens as they don't need to be anchored into the soil |
Increasing primary productivity | Some crops are planted early Irrigating crops Drought resistant crops Using greenhouses Crop rotation Fertilisers (provides inorganic ions) Pesticides/ pest resistant crops |
How does planting some crops early increase primary productivity | Provides a longer growing season to harvest more light |
How does irrigating crops increase primary productiviy | Water is readily available for the light dependent stage of photosynthesis even when rainfall is below average |
How does growing crops in a greenhouse increases primary productivity | Provides a warmer temp ---> increases the rate of photosynthesis |
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 productibity | 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 pants | Improves growth of roots |
Increasing secondary productivity | Harvesting animals before adulthood Selctive 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 copressed 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 interences w/ the carbon cycle | Global warming/enhanced greenhuse effect Ocean acidification from carbonic acid Warmer sea - less CO2 absrbed 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 mtualistic 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 containg 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 |
Denitrification | Conversion of soil nitrates to atmospheric nitrogen. Carried out by denitrifying bacteria in anaerobic conditions (e.g. waterlogged soil) who use the nitrates as the final e- acceptor in respiration instead of O2 |
Human activities affecting the nitrogen cycle | Use of fertiliser - neutrification, algae use up all the oxygen |
Processes removing atmospheric nitrogen | Nitrogen fixation by bacteria Atmospheric fixation Haber process |
Processes adding to atmospheric nitrogen | Denitrification |
Similarities in nitrogen and carbon cycles | Involves plants and animals Involves anaerobic respiration (decomposers) Both cycles involve atmospheric chemicals |
Differences in nitrogen and carbon cycles | Involves sea in cc No fixation of CO2 Only uses organic processes in cc N is fixed by bacteria vs on plants |
Use of transects | Look for changes in vegetation across a habitat |
Types of transects | Line | Belt |
Line transect | At reg. intervals | Note of which species are touching the tape |
Belt transect | At reg. intervals Place a quadrat next to the line (interrupted belt transect) or move the quadrat along the line (continuous) Used to sample succession |
Estimating pop. size | Mean number of a species in a quadrat/ faction of the total habitat area covered by a single quadrat |
Deciding how many samples to take | In a pilot study take random samples looking at species distribution Plot quadrat number against cumulative frequency When curve levels off use that number of quadrats |
Units to measure primary productivity on land | gm-2 yr-1 |
Units to measure primaary productivity in water | gm-3 yr-1 |
Decomposes in the nitrogen cycle | Pass urea to next stage |