Evolution - Unit 2 OCR

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  • Evolution
    • Variation
      • What Is It? - differences that exist between individuals, each individual organism is unique, even clones show some variation
        • Within a species is called intraspecific variation
        • Between different species is called interspecific variation
      • Continuous - individuals in a population vary within a range so there are no distinct categories
        • E.g. Animals height or mass, Plants number of leaves or mass, Microorganisms width or length
      • Discontinuous - two or more distinct categories that each individual fits into, no intermediates
        • E.g. Animals sex or blood group, Plants colour or seed shape, Microorganisms antibiotic resistance or pigment production
      • Causes of Variation
        • Genetic Factors - different species have different genes, individuals of same species have the same genes but different versions of them (alleles) , these make a genotype and the difference in these result in variation in phenotype (characteristics displayed)
          • E.g. Eye colour in humans, blood type in humans and antibiotic resistance in bacteria
        • Environmental Factors - differences in environment cause variation (climate food lifestyle), characteristics controlled by environment can change over an organisms life
          • E.g. Accents and pierced ears
        • Both Genetic and Environmental - genetic determines characteristics born with but environmental influence how some are developed
          • E.g. Height and Flagellum
    • Adaptations
      • What Are They? - all variations mean some organisms are better adapted to environment than others, being adapted means an organism has features that increase its chances of survival and reproduction as well as successful offspring reproduction
        • They develop because of evolution by natural selection, each generations best adapted individual is more likely to survive and reproduce to pass on their adaptations to offspring, less well adapted individuals are more likely to die before reproducing
      • Types of Adaptation
        • 1. Behavioural Adaptations - ways an organism acts that increases its chance of survival
          • E.g. Possums sometimes 'play dead' if threatened by predator, Scorpions dance before mating to ensure same species mate
        • 2. Physiological Adaptations - processes inside an organism's body that increase its chance of survival
          • E.g. Brown bears hibernate to lower metabolism over winter conserving energy so no need to look for food
        • 3. Anatomical Adaptations - structural features of an organisms body that increase chance of survival
          • E.g. Otters have streamlined shape so easier to glide through water and catch prey of escape predators, Whales have thick blubber layer to help keep them warm in cold sea
    • Evolution
      • Darwin's Theory
        • Made four key observations about the world around him
          • 3. Some of the characteristics can be passed on from one generation to the next
          • 2. There's variation in characteristics of members of same specie
          • 4. Individuals that are best adapted to environment are more likely to survivs
          • 1. Organisms produce more offspring than survive
        • Natural Selection
          • Individuals within a population show variation in their phenotypes due to differences in alleles
          • Predation, disease and competition create struggle for survival
          • Individuals with better adaptations are more likely to survive reproduce and pass on alleles that cause the advantageous adaptation to offspring
          • Over time, the number of individuals with advantageous adaptations increases
          • Over generations this leads to evolution as the alleles causing advantageous adaptations become more common in population
        • Reactions To Theory - at first there was opposition as it conflicted with religious beliefs but over time it has become increasingly accepted as more evidence found to support it and no evidence to disprove it
      • Evidence To Support
        • Fossil Record Evidence - fossils are remains of organisms preserved in rocks, by arranging them in chronological order we can observe gradual changes in organisms, provides evidence for evolution
        • Molecular DNA Evidence - theory suggests all organisms evolved from shared common ancestors, closely related species diverged more recently
          • Evolution caused by gradual changes in base sequence of organisms DNA, organisms that diverge away from each other more recently should have similar DNA as less time passed for DNA sequence changes
        • Molecular Proteins and Other Molecules Evidence - as well as DNA similarities in other molecules provides evidence, compare sequence of amino acids in proteins and antibodies, diverged organisms have more similar molecules as less time parred for changes to occur
      • Speciation - evolution can lead to this, the formation of a new species, a species if defined as a group of similar organisms that can reproduce to produce fertile offspring, speciation happens when populations of same species are isolated in a way and evolve to become so different that they can breed with one another to produce fertile offspring
        • E.g. Darwin observed 14 finch species on Galapagos Island, each was unique to single island where although similar in size the shape of beak differed as an adaptation to food source
      • Evolution of Antibiotic Resistance
        • Antibiotics are drugs that kill or inhibit growth of bacteria, scientists have observed evolution of resistance of many bacteria species - MRSA is a strain of bacteria that's resistant to methicilin
          • This evolution of resistance can be explained by natural selection : variation in population of bacteria where genetic mutation make some of them naturally resistant, if population is exposed to antibiotic only individuals that are resistant will survive, alleles that cause resistance will be passed on to next generation and over time the population will evolve to resist drug
        • Testing for Resistance
          • Spread a sample of bacteria onto agar plate, place paper discs soaked in same concentration of different antibiotics on plate and allow to gros
            • Anywhere it can't grow will be seen as a clear patch and the size of this will tell you how well a particular antibiotic works, the larger the patch the more bacteria has inhibited growth
              • Hospitals and clinicians use tests like these to choose most suitable antibiotic for treatment, tests are cheap quick and easy so most suitable antibiotic can be prescribed in time
        • Implications for Resistance in Humans
          • Infections caused by resistance are hard to treat as some species are resistant to lots of different antibiotics
            • May take doctors a while to find a cure and in that time patient may become very ill or die, could come a point where bacterium has developed resistance to all known antibiotic so to prevent this new ones must be developed taking time and costing lots of money
      • Evolution of Pesticide Resistance
        • Pesticides are chemicals that kill pests and scientists have observed evolution of resistance in many insect species
          • E.g. Some populations of mosquito have evolved to resist DDT, some populations of pollen beetles are resistant to pyrethroid pesticides
          • Can be explained by natural selection : variation in population of insects so genetic mutations make some resistant, if population exposed to it then only resistant individuals will survive, alleles causing resistance will be passed on to next generation and over time population will evolve to be resistant
        • Implications for Resistance in Humans
          • Similar to those of antibiotic resistance, crop infestation is harder to control as some insects resistant to a lot of pesticides, takes farmers a while to figure out which kills insects in time that all crops could be destroyed
            • If insects resistant to specific pesticides farmers may have to use broader ones which could kill beneficial insects and if disease carrying insects become resistant the spread of disease could increase
              • Population of insects could evolve to resist all pesticides in use and to prevent this new ones would need to be produces taking time and costing lots of money

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