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Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
Topic 5 Communities and Ecosystems
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Topic 5 Communities and Ecosystems

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I didn't make this powerpoint, this is from my IB Biology teacher but it's one of the only topics I actually really enjoyed sooo I'm putting it up, ^_^

I didn't make this powerpoint, this is from my IB Biology teacher but it's one of the only topics I actually really enjoyed sooo I'm putting it up, ^_^

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  • 1. Topic 5Communities & ecosystems The greenhouse effect Populations Evolution Classification
  • 2. Communities and ecosystems• Ecology- the study of relationships between living organisms and between organisms and their environment.• Ecosystems- a community and its abiotic(physical &chemical) environment• Population- a group of organisms of the same species who live in the are at one time.• Community- a group of populations living and interacting with each other in an area.• Species- a group of organisms which can interbreed and produce fertile offspring.• Habitat- the environment in which a species normally lives or the location of a living organism.
  • 3. environment• 4 main components:• Hydrosphere- water• Atmosphere- gases• Lithosphere- rocks• Biosphere- all living organismsAbiotic (non living Biotic (living)Light, Plantsheat, Fungiminerals, Animaloxygen, Protctistshumidity bacteria
  • 4. Autotroph• Producer• Synthesises its organic substances from simple inorganic substancesHeterotroph• Consumer- organism that ingests other organic matter that is living or recently killed.• Consume other organism as a source of organic moleculesDetritivore• Consuming dead (non living) remains of other organisms breaking them down into less complex organic moleculesSaprotroph• Organisms that live on or in non living organic matter, secreting digestive enzymes to breakdown organic molecules and absorb the products. Usually a fungi or a bacteria
  • 5. • The Biosphere is part of both both the surface and atmosphere of the earth occupied by living organisms.Biotic Interactions in the biosphere will include:• migration• disease spreading• predationAbiotic Interaction in the biosphere will include• water cycle• carbon cycle• nitrogen cycle
  • 6. Food chain• Which organism eats what!• Use an arrow to point… really means that energy is passing from the one which is being eaten to the one who is doing the eating!• Grassland• Grass  grasshopper  toad  hognose snake  hawk• River• algae mayfyl larva juvenile trout kingfisher• Marine• diatoms  copepods herring seal  great white shark
  • 7. Food Webs• The food web is a diagram that shows how food chains are linked together into more complex feeding relationships – Shows the much more complex interactions between species within a community/ ecosystem – More than one producer supporting a community – A single producer being a food source for a number of primary consumers – consumer may have a number of different food sources on the same or different trophic levels – consumer can be an omnivore, feeding as a primary consumer and as a consumer at higher trophic levels• Autotroph =Producer =Trophic level 1• Heterotroph = Primary Consumer =Trophic level 2• Heterotroph =Secondary Consumer=Trophic level 3• Heterotroph =Tertiary Consumer =Trophic level 4
  • 8. Sunlight• Sunlight is the source of this energy for most communities both aquatic and terrestrial.• The principle trap of sunlight energy is the protein molecule chlorophyll found in the chloroplasts of producers cells but there are other energy sources for deep ocean communities based on geothermal energy.• Consumers feed and pass on energy in the food but not all the energy.• How is energy lost??– Not all solar energy will come into contact with chlorophyll and will therefore not be trapped in the synthesis of organic compounds– Loss of energy as heat from respiration from all living organisms– death and the consumption of dead organisms by detritivores.– food not assimilated because of incomplete digestion-feaces .– energy in undigested food which will then be used by saprophytes/ decomposers– ultimately all energy will be lost has heat
  • 9. Energy Transformations• The transfer of energy from one trophic level to the next is inefficient• Approx 10-20 % of the energy on one trophic level will be assimilated at the next higher trophic level• It is this loss of energy that makes food chains relatively short.• In extreme environments like the arctic the initial trapping of energy by producers is low. Thus the food chains are short.• In a tropic rainforest the trapping of energy is more efficient and therefore food chains are longer, webs are more complex
  • 10. Pyramids of energy• This is a more typical pyramid of energy.• NB- solar energy is not shown.• The narrowing shape illustrates the gradual loss of energy progressing along the links of a food chain to higher tropic levels• Unlike pyramids of number (of organisms) a pyramid of energy cannot invert due to the second law of thermodynamics,energy cannot be created nor destroyed
  • 11. Decomposition by saprophytic bacteria and fungi• biological process• secretion of extra-cellular digestive enzymes produced by the saprophytic bacteria and fungi onto the dead organism• The enzymes hydrolyse the biological molecules of which the dead organism is made• The hydrolysed molecules are soluble and will then be absorbed by the fungi or the bacteria• Organic molecules are oxidised to release carbon dioxide back to the atmosphere, release nitrogen in form of nitrate, nitrite and ammonium.• The oxidation of these organic compounds produces energy for the saprophyte but returns the various forms of matter to the abiotic environmentFunctions• formation of soil• recycling of nutrients stored in the organic materials• reduction of high energy carbon compounds.
  • 12. Topic 5Communities & ecosystems The greenhouse effect Populations Evolution Classification
  • 13. Green House Effect • a) Short wave solar radiation (light) • b) light penetrates the atmosphere • c) Absorption by the ground and conversion to long wave infrared radiation (heat) • d)This warms the planet • e) Some infrared is lost to space as heat • f) Atmospheric gases particularly water vapour, carbon dioxide, methane and CFCs absorb infra-red and scatter this rather than letting it escape to space effectively trapping the heat. • h) Some light reflects off the atmosphere and never enters • if this greenhouse effect did not exist the average temperature would be -17oC! • Living things have evolved and adapted to the conditions in part determined by the greenhouse effect. • Human activity however has increased the levels of greenhouse gases • may have increased the global temperatures
  • 14. Enhanced greenhouse effect• Intensifying natural phenomenon known as Global warming• Gases produced by human activity that retain heat are• Carbon dioxide• Methane• Cattle ranching• Waste disposal• Production and distribution of natural gas• Oxides of nitrogen• Burning fossil fuels• Organic/commercial fertilisers• Industrial processes
  • 15. Causes and EffectsGreenhouse effect• Carbon Dioxide and methane and CFCs• Carbon dioxide levels increase with increased levels of combustion of organic matter and with reduction of photosynthesis (deforestation) Predictions• Threat of a 3 degree rise over the next 50 years• The rising of sea levels due to the melting of the polar ice caps combined with an increase in ocean volume due to thermal expansion.• lead to flooding of significant parts of the world where there are large populations.• Changes in climate and ocean currents e.g. Oden feature
  • 16. The precautionary principle• If effects of human induced change are large those responsible for the change must prove that it will do no harm before proceeding.• Reverse of normal situation where those who are concerned have to prove that it will do harm in order to prevent changes.
  • 17. Evaluation;• economic harm of measures taken now to limit global warming could be balanced against the potentially much greater harm for future generations of taking no action now?• ethical questions about whether the health and wealth of future human generations should be jeopardized, and whether it is right to knowingly damage the habitat of, and possibly drive to extinction, species other than humans.• environmental angle here is that the issue of global warming is, by definition, a genuinely global one in terms of causes, consequences and remedies.• international cooperation?• There is an inequality between those in the world who are contributing most to the problem and those who will be most harmed!
  • 18. consequences of a global temperature rise on arctic ecosystems.• increased rates of decomposition of detritus previously trapped in permafrost,• expansion of the range of habitats available to temperate species, – Woody shrubs were once only mosses and lichens• loss of ice habitat, – More and more ice is melting every year – Less snow and more frozen rain in winter• changes in distribution of prey species affecting higher trophic levels, – Birds so foreign to the area that there is no known name in the language• and increased success of pest species,-including pathogens. – Some regions are now populated with mosquitoes
  • 19. Acid rain • (a) CO2(natural and artificially produced )can form acid rain • (b) combustion fossil fuels from power stations -gases like sulphur dioxide /nitrous oxides into the atmosphere • (c) combustion of vehicle fuel =same gases • (d) gases oxidised by UV light the (catalysts -ozone and ammonia) • (e) Wet deposition occurs at a distance from the gases source forming sulphuric, nitric and carbonic acids • (f) Dry deposition occurs without rain water and close to gas source
  • 20. CAUSES AND EFFECTSAcid rain• Can be caused by carbon dioxide from natural processes but also by sulphur dioxide from volcanic activity.• gas levels are increased through the combustion of fossil fuels to which we add nitrous oxides which are also emitted from fossil fuels combustion.• Coal and gas fired power stations are a major source along with vehicle fuel combustion• Dry deposition-Often close to gas source these acidic compounds fall on vegetation causing burning effects. Damages vegetation and produces a characteristic loss of the growth point especially on trees.• Wet deposition -occurs at a distance and down wind from the gas source. In combination with rain water• The acid leaches ions from the soil and increases levels of Al 3+ free in soil solution. The uptake of such ions reduces the growth rate and may be a metabolic poison• The Al 3+ cause an increase in the viscosity of fish gill mucus, reduces the extraction of oxygen from water and ultimately fish death.
  • 21. Reducing Human ImpactGlobal Warming/ Greenhouse effect• Reducing deforestation• Reforestation• Alternative fuels which reduce Carbon dioxide emissions• Reduce energy demandsAcid Rain• Reduce greenhouse gas emissions with alternative clean energy sources• De-sulphurisation (SCRUBBING), washing of fossil fuels prior to combustion• Control CFCs and Ozone emissions• Add calcium to soils and carbonates to water for neutralisation
  • 22. Topic 5Communities & ecosystems The greenhouse effect Populations Evolution Classification
  • 23. Population SizeFactors that increase population size:• Natality is recruitment to a population through reproduction• Immigration from external populations e.g. Bird migrationFactor reducing population size:• Mortality which is the death rate from any source e.g. predation• Emigration, where individuals leave the population for another habitat
  • 24. Sigmoidal population growtha) Exponential Phase of rapid population growth rateb) Transition stage a slowing yet still high growth rate against time or generationsc) Plateau stage in which the population remains stable with time. There maybe slight oscillations in the numbers
  • 25. a) Exponential Phase• low or reduced limiting factors = population expands exponentially into the habitat. – Plentiful resources- food,space,light – Little/no competition, predation – Favourable abiotic conditions• may be increasing at 2n where n= number of generations.• The rate of natality + immigration is greater than Mortality + emigration. does not mean that death/ emigration= 0 – typical of a population of germinating annual plants in a new season. – bacterial population during the initial phases of an infection. – The population of any species occupying a previously unoccupied habitat (succession)
  • 26. b) Transition Stage• Resources are reduced and become limiting in the growth of the population• increased competition between the individuals of that population for the same resources.• some individuals will obtain resources and survive and others will not.• Easy spread of disease• Overall the effect is to produce a lower rate of population increase than during the exponential phase
  • 27. c) The Population plateau• population remains constant over time/ generations• A constant population means that Natality + Immigration = Mortality + Emigration• The population size is determined by the carrying capacity(K)* of the habitat at that point in time*size of the population that can be supported by the habitat at a particular point in time.
  • 28. • With unlimited resources then the population would increase exponentially.• There is however environmental resistance that limits the population growth and determines the carrying capacity of the habitat: – Avaialbility of resources- water,food,sunlight,shelter,space, habitat – Build up of waste-excrement, excess CO2 – Predation – disease
  • 29. Random sampling• -A sample of a population in which every individual has an equal chance of being selected• QUADRATS-50cm by 50cm squares!• Used to compare one area of ground with another or one distribution of plants to another• Map out area and choose random grid references/square numbers• Record 5% of the area using quadrats• Record how many of each plant in each quadrat.• Then work out the mean number of plants in one quadrat.• Times the mean by the total area of the field• Divide by the area of the quadrat
  • 30. Lincoln indexCapture/mark/release/recapture• Population size= (sample 1 x sample 2)/by recapture.• Sample 1= number of organisms caught, marked & released.• Sample 2 = total number of organisms caught in the second sample• Recaptured= the number of organisms in the second sample that are already marked.
  • 31. mmmmmmmmm• Stress? Harm?• Markings?• Time for redistribution?4. Using pasta you are going to perform the Lincoln index5. Put your hand in the bag of pasta6. Mark the pasta with a pen and count them7. Put it back in the bag and shake!8. Take another handful and count them9. Now count how many of them you had previously marked!Do the Lincoln index.
  • 32. Other methods• Line transects- sample organsims along a line in order to show a change from one area to the next• Belt transect- quadrats placed along intervals• Point transects- species touches particular point along a line• Pit fall traps
  • 33. Simpson diversity index• D= diversity index• N= total number of organisms of all species found – Species richness• n= number of individuals within a particular species – Relative abundance of each species
  • 34. Sand dune eg species n (n-1) n(n-1)• Sample using Marram grass 50 quadrats• Fordune milkweed 10 Poison ivy 10 Sand cress 4 Rose 1 Sand cherry 3 totals N=78
  • 35. Mean Calculations• The Mean of a population can be calculated to provide a value that is typical for the population• Normally the data type should be of interval class, that is measured on some type of scale e.g. cm
  • 36. Standard deviation• Biological data always varies- height, blood pressure, number of fruit on a tree, average age of kids in school, number of chicks raised in a year.• Sd- Summaries the spread of values around a mean• Normally distributed data• 68% of values fall within +/- 1 standard deviation of the mean• 95% of values within +/- 2 standard deviationsof the mean.
  • 37. • Populations A and B have the same mean• Population B has a smaller Standard Deviation than A• The values for B are spread closer to the mean than those of population A• Population B shows less variation than population A
  • 38. Topic 5Communities & ecosystems The greenhouse effect Populations Evolution Classification
  • 39. Charles Darwin• HMS beagle to Galapagos Islands• Finches on different Islands developed differently.• Theory of evolution was born…..
  • 40. Evolution• Evolution is the cumulative change in the heritable characteristics of a population.• If we accept not only that species can evolve, but also that new species arise by evolution from preexisting ones,• then the whole of life can be seen as unified by its common origins.• Variation within our species is the result of different selection pressures operating in different parts of the world,• yet this variation is not so vast to justify a construct such as race having a biological or scientific basis. or an increase in allele frequency for a population
  • 41. Evidence for evolution• Fossil record• Fish fossils only been found in rocks 500 million years old or younger• Most of todays top predators did not exist at the time of the dinosaurs, or before• Apart from- sharks/cockroaches/ferns- many living organisms today do not have an identical fossil record.• Observation=earth is constantly changing, over 100’s/1000’s/1000000 of years.
  • 42. Evidence for evolution• Artificial selection• Fossil record far from complete• Science of breeding gives modern record• Lots of characteristics gained/lost.• Evidence evolution occurs but in this instance= human choice
  • 43. Homologous anatomical structures• Similar in form and function but found in seemingly dissimlar species.• Five fingered limb!• Human, whale, bat.• According to Darwin- not just a coincidence but evidence of common ancestory.
  • 44. Mechanism for evolutionReproduction• Reproductive success is when an offspring reaches a sexually mature stage such that it has reproduced itself.• A population will tend to reproduce more offspring than the environment will support• In a sexually reproducing community the individual reproducing needs only to replace itself to keep the population constant.• Producing more individuals than required for replacement reflects the likely mortality of offspringOver-population• more offspring than the carrying capacity of the environment can support• compete for limited resources (Intraspecific competition)• individuals have characteristic (or combination ) that give them a competitive advantage.• consequently fitter in terms of freedom from disease, food availability etc.• more likely to successfully reproduce (offspring survive)• the frequency of these characteristics become greater in the next generation.• The gene for the advantageous characteristic becomes more frequent in the population
  • 45. Sexual Reproduction and Variation• Discontinuous • Continuous• There are distinct • no distinct classes but classes of individual a complete range of• e.g. Blood groups the characteristic • e.g. Height of a tree
  • 46. Natural Selection and Variation• population becomes subject to selection pressures due to changes in the population or environment• population will show some genetic variation, particularly so in sexually reproducing species• selection pressures lead to differential survival of some individual over others• Surviving individuals have an advantageous characteristic• These individual obtain a greater share of some limited resource• This improves their ability to reproduce viable offspring• These offspring will carry the genes for the characteristic into the next generation• Useful genes will increase in frequency in the population less useful genes will decrease in frequency
  • 47. Reminder IGCSE• Peppered moth • Industrial tree bark• 2 variants light & dark darkened by soot• Pre industrial trees • Light moth eaten by light so dark stands birds out • Dark moth reproduce• Dark moth eaten by • Less light moths birds• Light moth reproduce• Less dark moths
  • 48. Evolution of Species• species = group of organisms which can interbreed and produce fertile offspring• process of natural selection produces sufficient genetic differences between two groups such that they can no longer produce fertile offspring.• It is thought that in the process of evolution of a species, part of a population must become separated/ isolated from the rest.• That this separation allows for the accumulation of different gene frequencies• When the genetic differences are significant enough that cross fertilisation of individuals from the two populations produces infertile offspring or no offspring then there is said to have a new species evolvedIsolation: how different populations may become separated has been identified as• Geographic isolation e.g. mountain,water barriers• Behavioural isolation : adapt to its new environment and the selection pressures that exist in this new locality
  • 49. Examples of Evolution in response to environmental change• Staphylococcus aureus• bacteria associated with a variety of conditions including skin and lung infections.• evolution of a new antibiotic resistant form of the species (eMRSA-16 or MRSA252).• The bacteria is in two forms;• Methicillin-resistant Staphylococcus aureus (MRSA) also known as the epidemic MRSA against which Methicillin antibiotic has no effect.• Methicillin Susceptible Staphylococcus aureus (MSSA). This form is still contained by the use of the antibiotic Methicillin.
  • 50. Evolution of MRSA resistance• Antibiotics selectively kill susceptible forms of the bacteria.• The antibiotic is the selection pressure on the population of Staphylococcus aureus.• Random mutation with the species produces a resistance gene at low frequency in the population• The gene can be transferred via plasmids to other bacteria• Frequent use of the antibiotic puts MRSA at a selective advantage to survive and MSSA at a selective disadvantage• MRSA therefore survives to reproduce.• The descendants of MRSA will also carry the resistance gene• The resistance gene increases in frequency or there is a process of cumulative change in the heritable characteristics (resistance gene) in the population• The species has evolved into two new forms• Continued mutants= continued resistance to many antibiotics.
  • 51. New Zealand Kaka• a parrot-like bird of New Zealand.• two species known as North I Island and South Island forms.• The mechanism for speciation involved both geographic isolation and climate change.• The ancestor of the New Zealand birds came from the Australian continent and the isolation began 100my ago with the break up of Gondwanaland and the formation of the Tazmin sea.• 50 my ago New Zealand saw the formation of the Southern Alps and the development of an alpine environment.• The proto-kaka ancestor then diverged into an alpine Kea and the lower altitude Kaka. At this time the Kaka was restricted to the North Island• 0.5 my ago the ice age created bridges from north to south island which allowed the Kaka to spread it s distribution.• However, the ice age ended and the two islands became isolated. Thus the North Island Kaka and South Island Kaka diverged as they adapted to local pressures.
  • 52. • Industrialisation and moths• Galapagus finches!• Tweezers and seeds.
  • 53. Topic 5Communities & ecosystems The greenhouse effect Populations Evolution Classification
  • 54. Binomial nomenclature• Hierarchy of Taxa• Kingdom- King• Phylum Philip• Class Classified• Order Over• Family Fifty• Genus Green• Species Spiders
  • 55. Species• A species is a group of organisms which can interbreed and produce fertile offspringThe purpose of classification is to• clearly identify an organism with a name that is unique to the species and avoids confusion with local naming.• studying the similarities of one group with another establishes the evolutionary relationship between groups• knowing a species classification allows us to predict anatomical, physiological and genetic characteristics it may share with other organisms
  • 56. Binomial System of nomenclature• Each species has two names.• Genus – given first and is always written with an upper case letter. e.g. Homo• Species – follows the genus and is written in lower case e.g. sapiens• humans =Homo sapiensConventions: written by hand = underlined If typed = in italics
  • 57. Hierarchy of TaxaSeven taxa: • Saccharomyces• Kingdom cerevisiae• Phylum • Kingdom: Fungi• Class • Phylum: Ascomycetes• Order • Class: Hemiascomycetes.• Family • Order:• Genus Saccharomycetales. • Family:Saccharomycetac• Species eae • Genus:Saccharomyces • Species :cerevisiae
  • 58. • Rattus rattus• Kingdom Animalia• Phylum: Chordata• Class: Mammalia• Order; Rodenta• Family: Muridae• Genus: Rattus• Species: rattus
  • 59. The 5 Kingdom Classification
  • 60. Plant PhylaBryophyta- mosses & Liverworts• No roots, non-vascular, or cuticle, no flowers, Seedless, no true leaves / stems,Filicinophyta- Ferns• Leave fronds , roots, non woody stems. divided leaves. (20m)• sporangia (sori) hollow contain reproductive sporesConiferophyta- Conifers• trees (100m), shrubs, woody (lignin) stems, waxy narrow needle like leaves. vascular system (tracheads)Angiospermophyta- flowering• plantsroots, stems and leaves. complex tissue structures, vascular bundles (xylem/ phloem ), waxy cuticle,• annual or perennial up to 100m fruits
  • 61. Animal PhylaPorifera- sponges Annelida-segmented worm• No mouth/digestive tract • Body segment divided by rings • Bristles• No muscle/nerve • Gastric tract-mouth &intestines tissue/distinct organs Mollusca- snail/clam/octopusCnidaria- jellis/corals • No segmnets, most aquatic,• All have stinging cells- many produce shell, have nematocysts muscular foot• Some swim some float • Have gastric tract• Digestive pouch Arthropoda-Plathelminthes-flatworms insects,spiders,crustracteanc,m yriapods• One body cavity • Hard exoskeleton, segmented• No heart/lungs bodied,limbs that can bend
  • 62. Dichotomous Key• Each question divides the group of organisms into two smaller groups based on a pair of alternative characteristics• Subsequent groups may focus on more minor detail• In most cases the characteristic will be readily observed or measurable• It is better to choose characteristics that are uninfluenced by environmental variation• Shape and number are often good characteristics on which to base alternative pairings• A complete key will have each type of organism being classified separated with a final identifying name.• Aliens!
  • 63. • See keys from bio for you.

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