OCR biology - ecosystems
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| Define ecosystem | Dynamic, relatively self-contained system containing abiotic and biotic factors that interact with each other, consisting of: habitat (place), populations, community
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| Distinguish between population and community | Population - group of organisms of the saem species living in the same habitat at the same time. Community - all the living organisms of all species living in the same habtiat at the same time
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| What is a niche? | The specific, unique role that a species plays in an ecosystem e.g. what it eats, excretes
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| Distinguish between biotic and abiotic component | Biotic - living component of an ecosystem that affects the organisms living there e.g. predators, pathogens, competition. Abiotic - non-living component of an ecosystem that affects the organisms living there e.g. soil pH, precipitation, temperature
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| Why are ecosystems described as dynamic? | Population sizes are always fluctuating, which affects competition, predation, food availability for other species, interconnected
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| Define: trophic level | The stage at which a species feeds in a food chain
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| Define: producer | Autotroph, 1st trophic level, uses simple inorganic molecules + energy source to synthesise complex organic molecules, e.g. photoautotrophs (green plants, algae, photosynthetic bacteria), chemoautotrophs (nitrifying bacteria)
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| Define: consumer | Heterotroph, ingests organic matter and digests it into small soluble molecules, then synthesises complex organic molecules form it - primary (herbivore/ omnivore), secondary (carnivore/ omnivore)
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| Why is there a maximum of 4/5 trophic levels in a food chain? | Around 90% of energy is lost at each trophic level, so there is less energy to sustain life at the higher trophic levels, fewer high level consumers
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| What proportion of sun light energy is converted chemical energy in plants? | < 3%
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| Why is primary productivity so low? | Some light misses leaf, some light is reflected off surface of leaf, some light misses chloroplasts so is transmitted directly through leaf, some wavelengths of light (green) are reflected by chlorophyll, some energy lost in photosynthesis?
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| Why is energy lost between the producer and the primary consumer? | Some energy is lost in respiration, some energy is lost in the dead parts of the plant that drop off and are only available to decomposers, not all plant is eaten e.g. roots, poor digestibility e.g. cellulose
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| Why is energy lost between the primary and secondary consumer? | Some energy is lost in respiration (particularly in endotherms/ animals with a high level of movement), some energy is lost as heat e.g. digestion, energy lost in excreta/ dead bits, not all organism is eaten, poor digestibility
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| List the methods of measuring energy transfer | Pyramid of numbers, biomass and energy, and productivity
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| What is a pyramid of numbers? | Area of bar is proportional to number of individuals at that trophic level
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| What is a pyramid of biomass? How can you measure biomass at a trophic level? | Area of bar is proportional to total dry mass at that trophic level, more accurate estimate of quantity of living tissue. Method: heat organisms in oven, or measure wet mass then calculate dry mass using published data
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| What is a pyramid of energy? | Area of bar proportional to amount of energy available to the next TL per unit area+time (biomass + how much energy is released from species per unit mass). Pyramid. Method: temperature rise in calorimeter. Destructive, time consuming, 1 point in time
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| What is productivity? | The rate of energy flow through a trophic level in a food chain, shows how much energy is available to the next trophic level, energy per unit of area and time
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| What is primary productivity? | The rate at which plants convert light energy from sun into their own biomass, by photosynthesis, that is available to the next trophic level
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| What is GPP and NPP? | GPP: rate at which plants convert light energy from sun into chemical energy by photosynthesis. NPP: rate at which plants convert chemical energy left behind after respiration into their own biomass, available to the next trophic level
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| What is secondary productivity? | The rate at which primary consumer converts the chemical energy from its food into its own biomass that is available to the next trophic level
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| How does temperature affect primary productivity, and how can it be manipulated to improve primary productivity? | Too low = slow. Too high = LDS limiting, less CO2, photorespiration, denature. Plant crops early for longer growing season+ so fruit ripening isn't affected by cold weather. Keep in greenhouse - shelters from wind + retains long -wave IR radiation
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| How does CO2 concentration affect primary productivity, and how can it be manipulated to improve primary productivity? | Substrate for photosynthesis. Burn a methane fired heater/ pipe in CO2 from power plant
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| How does water availability affect primary productivity, and how can it be manipulated to improve primary productivity? | Substrate for photosynthesis, if in short supply stomata close = less CO2, photorespiration. Irrigate crops, use drought-resistant crops
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| How does light intensity affect primary productivity, and how can it be manipulated to improve primary productivity? | Limiting factor for LDS (photolysis, excitation) and LIS (stomata). Plant crops earlier for a longer growing season. Grow long day plants under light banks
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| How does soil fertility/ nutrient status affect primary productivity, and how can it be manipulated to improve primary productivity? | Nutrients are removed by plants/ denitrifying bacteria, NO3- -> photosynthetic enzymes, Mg2+ ->chlorophyll. Fertiliser (manure/artificial), selective breeding for good response, crop rotation with leguminous plant, aeriate, drain, lime with CaCO3
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| How do pests and pathogens affect primary productivity, and how can it be manipulated to improve primary productivity? | Reduce biomass available to next TL, pests decrease leaf size so rate of photosynthesis decreases. Pests: pesticides, natural predators, GM/ selective breeding for pest resistance. Disease: fungicides, GM/ selective breeding for disease resistance
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| How does competition affect primary productivity, and how can it be manipulated to improve primary productivity? | Weeds compete for space/ nutrients/ water, reducing growth rate. GM crop plants for resistance to herbicides, then apply herbicides
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| How can secondary productivity be improved? | Farm herbivores (less energy losses), harvest young animals (allocate larger proportion of energy to growth), keep in sheds (0grazing/ same temperature, allocate more energy to growth), antibiotics as a prophylactic (reduce losses to pathogens)...
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| Continued | Selective breeding for high yield, efficient energy transfer, high growth rate. Castrate bulls (less energy invested in making gametes), steroids (increase biomass + proportion of energy allocated to growth)
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| What is succession? | Predictable sequence of directional changes in a community of organisms over time that leads to the development of a climax community
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| What are pioneer species +egs? | First colonise bare ground to form a pioneer community, resilient to abiotic stresses, opportunistic species e.g. cyanobacteria, lichens, moss. Make environment more habitable for other species so replaced by waves of more competitive successors
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| How do pioneer species change the environment | Make it more habitable: root stabilise soil, shelter for germinating seeds/ animals, increase nutrient status of soil (plant matter decomposes -> humus, leguminous plants), humus increases water-carrying capacity of soil
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| What is a climax community? | Stable community that has succeeded previous communities, final seral stage
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| What happens over the course of succession to species number, biodiversity, biomass, productivity? | Species number increases, biomass increases until space is limited, GPP increases with biomass, NPP decreases relative to GPP, biodiversity increases then decreases again
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| What is primary succession? | Pioneer species colonise bare ground that has never previously been inhabited e.g. land exposed by retreating glaciers/ erosion
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| What is secondary succession? | Colonisation of land that has previously been inhabited by vegetation that was since cleared by humans/ natural disaster, fast succession, no pioneer community
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| What is a plagioclimax? | Succession doesn't reach a climax community due to grazing/ mowing/ burning ground
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| Give an example of a primary succession resulting in a climax community | Sand dunes show all seres of succession at 1 time. Beach: little vegetation, pioneer species (sea rocket) are resilient to abiotic stress. Sand accumulates around plants. Foredune: xerophytic plants-sea couch grass. Roots stabilise soil, dunes grow...
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| Continued | Yellow dune: marram grass, shoots trap sand, sand accumulates, shoots grow taller. Roots stabilise sand, dunes grow, humus increases nutrient status + water-carrying capacity. Grey dunes: climax community, biodiverse, bird's foot trefoil
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| What are dune slacks and what lives there? | The pools of water in the hollows between dunes - natterjack toads
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| What harsh abiotic conditions are presented to sea rocket and how is it adapted to deal with them? | Salt water spray - high salt tolerance. Unstable sand, lack of freshwater - long roots. Poor nutrient status of soil. Windy - low to ground
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| What is sampling? | Studying a small part of a habitat to estimate the distribution and abundance of species in the entire habitat
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| Define distribution | The position of organisms in an ecosystem, record the presence/ absence of a species in quadrats along a transect
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| What are examples of distributions? | Uniform: individuals evenly spaced +distance is maximised to reduce competition for scarce resource e.g. allelopathic chemicals. Random: uniform environment, little/no competition. Aggregated: unevenly spaced, aggregated around resources e.g. prey
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| Define abundance | The number of individuals of each species present in an ecosystem
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| How can abundance be measured? | Density - number of individuals of species per unit area. Frequency - percentage of quadrats that species occurs in. Percentage cover - point frame (number of touches proportional to %cover), quadrat with a grid -> 100 squares, ACFOR estimate
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| Describe random sampling | Each point in area has equal chance of being sampled. Tape measures along side of habitat =axis. Computer generates random pairs of numbers as coordinates to position the quadrats. Unbiased
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| Describe systematic sampling | Line transect: record which species touch tape measure continuously/ at regular intervals (interputed) along transect. Belt transect: sample quadrat continuously/ at regular intervals along trasnect. Measure distribution/changes caused by environment
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| How do you know how many quadrats to use? | Take random samples from an ecosystem in a pilot study: plot graph of cumulative number of new species found against number of quadrats used, point at which graph plateaus = ?
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| Why is it important to use the right number of quadrats? | Too few - species may be missed out, not representative. Too many - effort is wasted.
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| How do you know what size quadrat to use? | Take random samples from an ecosystem in a pilot study: plot graph of cumulative number of new species found against area covered by quadrat, point at which graph plateaus = ?
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| How would you estimate population size? | (Mean number of individuals of a species in a quadrat) divided by (fraction of total area of habitat covered by a quadrat)
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| What is the role of decomposers? | Decomposers (saprotrophs-bacteria, fungi) secrete enzymes onto detritus (excreta, dead organisms) to digest it into small, soluble molecules, some of which are absorbed by the organism, forming humus. Detritivores (small animals e.g. woodlice) form humus
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| Continued | Recycles carbon and nitrogen that would otherwise remain trapped in the detritus, increases productivity
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| What are the methods of nitrogen-fixation? | Nitrogen-fixing bacteria (rhizobium in root nodules, azobacter in soil, cyanobacteria in water) use nitrogenase enzyme to reduce N2-> NH3. Haber process uses N2/H2 to form artificial fertiliser(NH4+, NO3-). Lightning: N2 -> NO -> NO3- in soil
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| How are leguminous plants and nitrogen fixing bacteria mutualistic? | Rhizobium supplies plants with fixed nitrogen. Plants supplies rhizobium with carbon compounds e.g. glucose, and leghaemoglobin creates anaerobic conditions for nitrogenase to work in by absorbing O2 in root nodules
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| What is nitrification? | Nitrifying, chemoautotrophic bacteria in well aeriated soils: Nitrosomonas oxidises NH4+ -> NO2- , nitrobacter oxidises NO2- -> NO3-
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| What is denitrification and when does it occur? | Denitrifying bacteria e.g. Pseudomonas denitrificans respires NO3- to N2 and NO in air in anaerobic conditions. Thrives in waterlogged soils as less competition
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| Why should several trnsects be done? | species may not be evenly distributed, this is more reliable + can identify/ ignore anomalies
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| How do you sample animals? | longworth trap (small mammals), sweep net, pond net, light trap, pitfall trap, tullgren funnel (animals in leaf litter), hit a tree with a stick
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| What should be taken with while sampling? | dichotomous key to identify species
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| What is a pyramid used for? | to represent the amount of energy stored in a trophic level of a food chain
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