AQA AS Unit 2 from Classification onwards

AQA AS Unit 2 from Classification onwards

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Concept of a species...

  • Very similar genes and therefore closely resemble one another physicaly and biochemicaly.
  • They are capable of breeding to produce living, fertile offspring.
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Naming species - the binomial system

Binomial system where organisms are are identified by two names(both in italics or underlined)

It's universal and so ensures no confusion when scientists are referring to the same organism.

Generic name first, Capital first.

Specific name, all in lower case.

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The prinicples of classification

Classification- grouping of orgainisms, allows better communication between scientists and avoids confusion.

Taxonomy- theory and practice of biological classification

2 types

Artificial classification- divides organisms according to differences that are useful at the time. Eg, colour, size, number of  legs .

Natural Classificaion- based on evolutionary relationships between organisms and their ancestors

...Arranges groups into a heirarchy- The hierachical order of taxonomic ranks is based upon the evolutionary line of descent of the group members.

Groups are contained within larger composite groups with no overlap.

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  • The hierachical order of taxonomic ranks is based upon the evolutionary line of descent of the group members.
  • This evolutionary relationship between organisms is known as phylogeny.
  • The term is derived from the work 'ohylum' which, in classification, is a group of related or similar organisms.
  • The phylogeny of an organism reflects the evolutionary branch that led to it.
  • The phylogenetic relationships of different species are usueally represented by a tree-like diagram called phylogenetic tree.
  • In these diagrams, the oldest species is at the base of the tree while the most recent ones are represented by the ends of the branches
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  • Kingdom
  • phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

King phillip came over for good sex.

Phylogeny- evolutionary relationship between organisma.

In some diagrams..... the closer the branches, the closer the the evolutionary relationship.

Difficulties... species evolve over time; many species extinxt with no fossil records; some rarely, if ever, repoduce sexually; some are sterile; considerable variation within a species, eg dogs and artificial selection of diff breeds.

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Evidence for relationships using DNA and proteins.

Comparing the DNA and proteinsof different species helps scientists to determine the evolutionary relationships between them.

Due to mutations, the sequence of nucleotides bases in the DNA of the new species will change. Overtime, the new species will accumulate more and more differences in its DNA. Therefore, expect that species that are more closely related to show similarity in their DNA base sequences than species that are more distantly related.

  • DNA hybridisation......
  • heat breaks hydrogen bonds and seperates strands from 2 diff species DNA.
  • Mixing and cooling of strands allows hydrogen bonds to reform
  • (complementary bases join by hydrogen bonds, non-complementary bases can't join together)
  • Hybrid strands where 2 species closely related = most bases pair up - higher temperature needed to seperate the 2 strands
  • Hybrid strands where the 2 species are distantly related = few bases are paired - lower temp. is sufficient to seperate the 2 bonds.
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Courtship behaviour

Each individual tries to ensure that their DNA is passed on, through the reproductive process, to the next generation. Females only produce eggs at specific times= important mating is successful and that the offspring have a max. chance of survival.

Courtship enables,,

  • recognise members of their own species - ensures mating only between same species for fertile young
  • identify a mate capable of breeding - both partners sexualy mature, fertile and receptive to mating.
  • form a bond pair
  • synchronise mating.

Courtship is used by males to determine whether female is at reproductive stage.Typicaly, male carries out action, a stimulus to the female, females responds with specific action, her respnse is then a stimulus to the male to carry out futher action.. Ritual proceeds = "stimulus-response chain".         Chain of actions is same for same species but diff.for diff. species therefore individuals recognise whether partner is of the same species.

Longer the chain continues, more likely mating will result. If at any point one responds inappropriately, courtship sequence ends.

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Genetic variation in bacteria

Adaption- organisms, through the process of natural selection, adjust to suit the changing environment in which they live. It increases the long term reproductive success of a speces by helping its members to survive long enough to breed= significant contribution to the diversity of living organisms.

Diversity in organisms arises from changes in DNA...

  • by quantity or structure of the DNA of an organism= mutation
  • sexual reproduction - recpmbining the existing DNA of two individuals.

Conjugating- recombines DNA of two individuals, not strictly sexual reproduction.

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Mutaions are changes in the DNA that result in diff. characteristics. E.g one or more bases in a DNA sequence may  be added,deleted or replaces by others during replication.

  • Any diff. in the base sequence of a DNA molecule may result in a diff. sequence of amino acids being coded for.
  • Diff. amino acids sequence lead to diff, polypeptide and hence diff protein, or none at all, produced.
  • If protein is an enzyme, likely to disrupt the metabolic pathway leading to the production to other substances, including proteins
  • Since proteins are responsible for the characteristics of an organism, it follows that changes to DNA are likely to alter an organism's characteristics.
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Conjugation- one bacterial cell transfers DNA to another bacterial cell.

bleh,bleh, bleh.

Horizontal gene transmission- genes passed from one species to another species

Vertical gene transmission- genes are passed down from one generation of a species to the next generation of the same species.

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Antibiotics are substances produced by living organisms that can destroy or inhibit the growth of microorganisms. Eg. preveneting bacteria from making normal cell walls. Certain antibiotices kill bacteria by preventing them forming cell walls. They inhibit the synthesis and assemble of important peptide cross-linkages in bacteria cell walls= weakens walls and therefore unable to withstand pressure.

= unable to prevent water entering and so osmotic lysis occurs, killing the bacterium.

Inhibit the formation of cell walls =  they are only effective when bacteria are growing, eg , Penicillin.

Viruses have a different covering from bacteria and so arent killed by antibiotics.

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Antibiotic Resistance

Chance mutation within the bacteria. (As earlier a mutation is a change in DNA that results in diff characteristics, usally resulting from a change to some protein)

Eg. Penivillion, mutation=able to make new protein which was an enzyme that was able to break down the antibiotic penicillin before it was able to kill the bacteria.. enzyme=penicillinase.


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Antibiotic resistance continued...

Total no. mutations is large, some with no advantage, some may be harmful.

  • Leads to an increased antibiotic resistance...
  • only the mutant will be able to survive as eg. it is resistant to penicillian.
  • hence it is passed on to future generations by vertical gene transmission
  • Therefore the resistant form is selected for rather than the non-mutant when exposed to penicilin therefore penincilin-resistant forms gradually predominate in the population.
  • THe frequency of the allelt for penicillin resistance increases in the population.

ALSO.. the allele for antibiotic resistance is carries on the small circular loops of DNA called plasmids. Plasmids transferred from cell to cell by conjugation = horizontal gene transmission. Bacteria accumulate DNA that gives them resistance to a range of antibiotics. SUPERBUGS


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Antibiotics continued...

New mutations that give bacteria resistance to antibiotics arise randomly all the time. HOwever, the more we use antibiotics, the greater chance that the mutant bacterium will gain an advantage over the normal variety.

In time, and with continued use of an antibiotic, the greater chance that the mutant will out-compete and replace the normal variety.

WHEN SOME PEOPLE TAKE AN ANTIBIOTIC COURSE..temptation for patients to cndier themselves cured and to stop taking antibiotics after serval months. But, worse course of action as few remaining bacteria are the resistant ones to the antibiotic.. These resistant strains then multiply  and spread the genes for antibiotic reisistance to other strains by conjugation(i.e. horizontal gene transmission)

Overcome this problem- a "cocktail" of 3/4 antibiotic strains are usedto ensue 1 will be effective.

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Species Diversity

Biodiversity-general term used to describe variety in the living world

Species diversity- the number of diffferent species and the number of individuals of each species within any one community.

Genetic diversity- the variety of genes possessed by the individuals that make up any one species.

Ecosustem diversity - the range of different habitats within a particular area.

Measuring species diversity-- d=N(N-1) / En(n-1)        d= species diversity index

N=total number of organisms of all species

n= total number of organisms of each species

E=the sum of... Cal.speciesdiversity=easier to compare the variety in diff.habitats. would be much harder and less precise if we had to rely on descriptions of different habitats to make these comparisons.

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Biodiversity reflects how well an ecosystem functions... The higher the species diveristy, the more stable an ecosystem usually is and the less it it affected by climate change.Argriculture and deforestations have reduced species diversity..

Argriculture- natural ecosystems develop over time and they become more complex communities with a high species diversity. But farmers select species for particular quality that make them more productive. So only grows this species and the genetic variety of alleles they pocess is reduced to those with desired features. To be economic, numbers must be large. Certain amount of area has limited biomass therefore less available area for all other speces- compete for and resources=many will not survive. Also, pesticides are used to exclude species cause compete for light, .mineral ionswater and food required by the farmed species = overall reduced species diversity

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Forests=many layers between ground and tops of trees= numerous habitats available. Therefore many different species are adapted to living in these different habitats andd species diversity is high.

Deliberate human actions... deforestaion-permanent clearing of forests and the conversion of the land to other uses, such as agriculture, graxing, houseing and reservoirs. Also, some forests destroyed as a result of man-made products pollutants producing acid rain.


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