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27 Cards in this Set
- Front
- Back
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The level of resources will determine the level of productivity within a community |
As long as there is an increase in productivity in a community from the addition of a particular resources, then that resource is a limiting factor. Examples include elements such as nitrogen and phosphorus, and other resources such as water and light.
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The level of energy available may limit the productivity in a community
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The mass of organic matter in a community is called the biomass
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Explain how resistant strains of bacteria can evolve by natural selection
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-In a bacterial colony there will usually be several mutant cells present. -There is variation between individuals -Each bacterial cell is capable of binary fission in the right circumstances, and any new mutations are passed on to the next generation. |
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Even is the bacterial chromosomes are not altered, the plasmids may be altered. -Plasmids are small loops of DNA in bacteria that are spate from the larger chromosome. |
-Like the chromosome, plasmids contain genetic information that can be replicated and passed on to daughter cells. -In addition, plasmids can be transferred from on bacterium to the other, carrying genes with them. -One class of plasmids, R-plasmids are able to carry genes that enable the host bacterial cell to resist antibiotics -The increased use of antibiotics in agriculture and medicine has caused those populations of bacteria without R plasmids to decrease number and those with R plasmids to increase. -This unfortunately means as a consequence, it has become increasingly difficult to develop new antibiotics that are effective against these resistant strains of bacteria. |
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Q) Describe the terms trophic level and food chain
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Trophic levels describe therelationship of the organisms with other species in a food chain. E.g. At thefirst trophic level are producers. Herbivores are at the second trophic leveletc. Food chains show a seriesof organisms in a community which eat the previous organism in the chain. |
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Q) Describe some of the mechanism that maintain reproductive isolation
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Reproductiveisolation is maintained if courting rituals are not accepted by organismsoutside the population, if gametes are released or ready at different times, ifreproductive structures don't match, if there are different numbers ofchromosomes, if they live in different habitats.
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Q) Why is it unusual to find a community without any producers?
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Producers capturelight energy from the sun and convert it to the chemical energy of theirorganic molecules. This energy is then used to supply the next organism thateats it etc. So all food chains depend on producers at the start.
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Q)A simple food chain may look like this: grass--> insect --> mouse --> lizard -Describe 'lizard' in terms of wether it is an autotroph or heterotroph; a herbivore or carnivore; its position in the food chain and its trophic level |
A) The lizard is aheterotroph: it must take in organic compounds. It eats animals, so it is acarnivore. It is the fourth organism on the food chain, so is at the fourthtrophic level, ei 3rd order consumer
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Q)What position do parasites and decomposers occupy in the food chain? Explain your answer.
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The position ofparasites and decomposers on the food chain varies, E.g. They may be living offplants, in which case they are at the second trophic level, or a carnivore likea lion which may be at the third, fourth or fifth trophic level, depending onthe specific food chainwhat they eat etc.
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Q)Why is it possible for one organism to occupy many different trophic levels in a community? Give two examples
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A) Many animals eat a varietyof things, so could be at a number of different trophic levels. E.g. Bears mayeat flowers or fish. -So may be 2nd trophic level or 3-5th level depending whatthe fish have eaten etc. Eagles may eat galahs – so are at the third level, orlizards which ate snails – so are at the 4th level. |
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5.a)Opportunistic species are also called r-selected species. What does the r refer to ? explain the term r-selected
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r-selection refersto "r" the rate of reproduction, which is also the rate at which thepopulation grows in a disturbed area with plenty of resources.
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c)K-selected species are equilibrium species, what does the k refer to? explain them mother truckers |
K refers to thecarrying capacity of a community for a population. This is because thesepopulations are not able to expand past this capacity.
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d)The population size of k-selected species is often influenced by density dependent factors. Explain what these factors are and give an example.
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Density dependentfactors include amount of food, shelters for breeding, light reaching groundlevel, water available in soil. As population size increases, all these canbecome limiting factors for population growth.
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6. a) 'Energy flows through a community'. Explain what this statement means
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Energy from the sun istrapped as chemical energy by producers of a community. It may then be used bythe producer and converted eventually to heat energy, or it may flow through aschemical energy to consumers or decomposers when it is eaten. At some pointalong the food chains it will all be converted to heat energy and will thenleave the community. It cannot be recycled, so basically it "flowsthrough" the community. |
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b)Energy is neither created nor destroyed. In what form does energy initially enter a community, in what form does it flows from organism to organism and in what form is it lost from the community?
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Enters the community aslight energy. Flows from organism to organism as chemical energy. Leavescommunity as heat energy. |
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7.Q)Define the terms productivity and biomass of a community.
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a)Biomass is the mass ofliving matter (organisms) in an ecosystem. Productivity is the rate ofproduction of new biomass in an ecosystem. |
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b) How is productivity measured? |
in mass per hectare per year
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c) Why is the term primary productivity more accurate (than productivity) for describing biomass production?
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Primary productivityis the total conversion of light energy to chemical energy in producers. Thisis difficult to measure as members of community are continually respiringand turning food to gaseous products that are being lost from the community,and are not measured easily.
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geographical isolation |
geographical isolationmeans that if selective pressures are different in 2 locations, such as 2islands where finches need to eat different foods, or if there are differentrandom mutations occurring, two populations may begin to evolve differently.They may get to the point where they no longer recognize each other as relatedand will not mate. |
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gene flow
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If genes are flowingbetween population, than any trends towards evolution in a certain direction inone of the populations will be watered down by the continued influx of genesfrom the others. If Galapagos finches can easily reach several islands so thereis gene flow between populations on those islands, they will not evolve intodifferent species.
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mutations
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Mutations in onegeographically isolated population may be selected for, causing the populationto change in ways that are not available to other isolated populations.
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selection pressures - abiotic and biotic
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Selection pressures will bedifferent on the different islands where the physical environment and the otherspecies. present vary. (ie. Different abiotic and biotic factors contributingto selection pressure.) This will mean that different features of finches givethem a survival advantage on different islands, and evolution will continue indifferent directions provided there is geographical isolation. |
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natural selection
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Natural selection is thehigher chance of survival of some individuals in a population due togenetically caused characteristics that they have. This results in individualswhich are surviving in a population being very well suited to the ecosystemthey are in. |
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reproductive isolation |
Reproductive isolation –the inability for a population to reproduce healthy, fertile offspring withanother population. (May be the result of prezygotic or post-zygotic factors.)This ensures that there is no gene flow between the population and others, andchanges that evolve in that group make them different from other groups.Eventually they are different enough to be called different species. |
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Q) Human activity can alter the physical environment of an area and the nature of the communities living there. a) List some of the impacts which humans/ human activities can have on an environment |
Human impacts on anenvironment include: overgrazing leading to erosion of topsoil, clearingnatural communities of trees leading to increased salinity as salt table rises,cropping leading to loss of soil nutrients that are taken away when crop isharvested, damming rivers causing drowning of the valley communities along muchof the waterway, increased use of fossil fuels resulting in excess CO2 inatmosphere , greenhouse effect, increased global temperatures, climate change, risingsea levels.
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b)List some of the impacts which humans/ human activities can have on populations of plants and animals living in an area
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Human impacts on plants andanimals in an area include: - clearing of naturalcommunities resulting in extinction of species or replacement withmonocultures, over hunting, fishing etc leading to extinction, introduction ofexotic species, (deliberately or when they go feral,) leading to over predationor over grazing of native species, or outcompeting native species, fossil fuel burning resulting in acidrain which kills natural forests and river communities, fertilizer useresulting in blue-green algae blooms killing aquatic animals, or eutrophicationof lakes or waterways, use of non-biodegradable pesticides or toxic chemicalsreleased into waterways or oceans, resulting in accumulation of poisons inanimals, increasing up the food chain till birds of prey lay easily broken eggsand are threatened with extinction. |
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c) what is the greenhouse effect and why are coastal areas likely to be significantly effected by it?
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The greenhouse effectrefers to the warming of the Earth's atmosphere caused by rising levels ofgases like CO2 and methane, as a result of human activities. (Burning of fossilfuels for transport and industry and huge increase in numbers of ruminantanimals for human food.) As it increases, global temperatures are rising,climate changes are occurring, and sea levels will rise as ice caps melt andsea water expands. This will flood coastal areas, including many big cities andheavily populated areas. |
