Edexcel GCSE Biology - Topic 4: Natural Selection and Evolution

• (4.1B) Who were the two main scientists that proposed the theory of evolution by Natural Selection?

  Alfred Wallace and Charles Darwin

  
• (4.3)

  Explain how the emergence ofresistant organismssupports Darwin's theory of evolution includingantibiotic resistance in bacteria:Antibiotics (eg. Penicillin) target structures found in bacterial cells,thus do not generally harm animal cells, such asrupturing the cell wall.

  However, since their discovery and widespread use, antibiotics have beenoverusedandantibioticresistancehas developed in many different types of bacterial species

  • Bacteria, like all organisms, haverandommutationsin their DNA

  • One of these mutations may give themresistance to an antibiotic

  • If an organism is infected with bacteria and some of them have resistance, they arelikely to survive treatment with antibiotics

  •The population of the resistant bacteria will increase, Natural Selection.

  • If the resistant strain is causing a serious infection thenanother antibiotic will be needed

  • A strain ofStaphylococcus aureushas developed resistance to a powerful antibiotic methicillin, this is known as MRSA (Methicillin resistantStaphylococcus aureus)

  • MRSA can infect wounds and is difficult to treat without antibiotics

  
• Explain

  Darwin's theory of Evolution by Natural Selection:(4.2)1) Individuals of apopulationshowgenetic variation-differences in characteristics caused by differentalleles.New alleles arise throughmutations.

  2) Conditions in the area change, and there ismore competition(for food, water, mates etc.) which causesselection pressure.

  3) Those individuals with characteristics better adapted to theselection pressuresare more likely to survive (Survival of the Fittest).

  4)Inheritance- the survivors breed and pass on theirfavourable characteristic / alleleto their offspring. So the next generation containsmore individuals with the 'better-adapted' variation.

  5)Evolution- this process repeats asmore beneficial characteristics become more common in the population over time.

  Frequency of alleles of advantageous characteristics suited for species' environment increases over generations.

  
• (4.2)What is Evolution?

  Evolution is the slow and continuous change of organisms 'inherited characteristics from one generation to the next.

  
• What are the two types of Variation?

  Genetic- born with, depends on parents and genes, result of mutations.

  Environmental- can acquire during lifetime.

  
• (4.4)

  Describe theevidence for human evolution based on fossils:1)'Ardi'Ardipithecus ramidus• 4.4million years ago• Mixture of human and ape• Ape-like toe to grasp branches• Long arms and short legs• Brain size: 350cm^3• Walked upright

  2)'Lucy'Austrolopithecus afarensis• 3.2million years ago•Arched feet adapted to walking• Shorter arms and longer legs• Brain Size: 400cm^3• Upright

  3)'Turkana Boy'- Homo erectus• 1.6million years ago• Brain size: 800-1100cm^3• Discovered by Richard Leakey• Arms and Legs more like human• Walked upright

  4)'Wise Man' -Homo sapiens• 200,000 years ago to present• Brain size: 1200cm^3• Complex tools• Shortest arms and legs• Flatter face

  
• How does

  Genetic Variationoccur?(4.1)•Crossover during Meiosisproduces genetically different gametes.

  •At fertilization, any one sperm can fuse with the egg (many different diploid combinations)

  •Incorrect copying of DNA during replication(Interphase)

  These are calledMutations.

  
• Describe the

  gradual change of characteristicsof early humans to present day:• Bigger skull / cranium size

  • Less prominent / flatter face

  • Taller, shorter arms, longer legs

  • More upright

  • Increased complexity of tools

  
• (4.6B)

  Describe how the anatomy of thepentadactyl limbprovides scientists with evidence for evolution:•Pentadactyl limbhas5 digits• Visible inmammals, reptiles, amphibians• Similar bone structure,different function

  • Providesevidence that all species with pentadactyl limb have all evolved from a common ancestor(with a pentadactyl limb). As the odds of multiple different ancestors all with pentadactyl limbs is too low.

  
• What are the

  4 main evidence for evolution?• Comparative Anatomy (EG. Pentadactyl Limb)

  • Embryology

  • DNA Analysis

  • Fossils (Records)

  
• Explain

  selective breeding and its impact on food plants and domesticated animals(4.8)To select organismswith desirable characteristics to breed together. Choosingoffspring that show these favourable characteristics and repeating the breeding process. Theprocess must be repeated over several generations so that favourable characteristics show reliably in all offspring. A newbreedis formed.

  Reasons for Selective Breeding:• Taste / Appearance• Disease Resistance• High Yield• Speed of Growth• Resilience to Climate• Usefulness (in working animals)

  Problem with Selective Breeding•Limits the gene pool(i.e. number of alleles present). Population has less variation,due to inbreeding.

  •Less variation leads to less chance of resistant alleles being present. Increases likelihood of disease wiping out population.

  •Greater chance of also inheriting harmful defectsor unfavourable characteristics.

  Examples:domestic dog breeds originate from wolvescauliflower, cabbage, broccoli from brassica

  
• Describe the


  evidence for human evolution based on stone tools(4.5)As different species within the genusHomoevolved, they started using stone tools thatgradually became more complex over evolutionary time(as theirbrainswere also evolving to belarger and larger)

  These stone tools, as well as the hominid fossils, can bedated(i.e. have their age determined) in a few ways:

  •Bylooking at thestructural featuresof the tool or fossil(e.g.simpler toolsare probablyolderthan more complex tools)

  •By usingstratigraphy(the study ofrock layers). Older rock layers are usually found below younger rock layers, meaning that tools or fossils found indeeper layersare probablyolder)

  •By usingCarbon-14 dating(fossils contain carbon and stone tools are sometimes found along with carbon-containing materials e.g. a wooden tool handle)

  
• Describe how genetic analysis has led to the suggestion of

  the three domains rather than the five kingdoms classification method(4.7)Traditionally, living things were classified byLinnaeus' system of Classification-beginning with 5 Kingdoms.

  Thissorted organisms based on what was visible, morphology (form and shape) or anatomy (body).

  Asgenetic analysis improved,newer microscope technology was introducedand understanding of genetics improved,the three domain system was introduced.

  Shows that after studying the RNA and DNA sequences of different species,the similarity of the base sequences reflect the species similarity, the more closely related the species are, and the closer in time the common ancestor was.

  The three domains are:Archaea(primitive bacteria living in extreme conditions)Bacteria(true bacteria such as E.coli)Eukaryota(includes protists, plants, animals)

  
• What is tissue culture

  ?(4.9)•Tissue cultureis a process in which very small pieces of organisms (‘tissues’) are grown (‘cultured’)using nutrient media(i.e. in some kind ofartificial growth medium)

  • This allows scientists to produce alarge amount of tissuefrom just asingle individual organism

  • This tissue can then be used for a variety of different purposes

  
• Describe

  the process of plant tissue culture(4.9)• Aparent plantis chosen with thedesired characteristics(eg. high yield, better taste)

  • Small amount of tissue scraped from parent plant - known asexplant,from a fast growing region of plant,such as root or shoot tip

  • The explant is transferred to asterile petri dishcontainingnutrient agarusingaseptic techniques, to prevent the growth of microbes that might harm the plant.

  •Growth hormonesare added to stimulatemitosis.

  • Stem cellsdifferentiateand grow into aplantlet, which can grow into a new plant once transferred into compost.

  
• What are the

  advantages of plant tissue culture?(4.9)• Producesmany offspring all with specific desirable characteristics

  •Increasing number of crops resistant to bad weather(or disease etc.)can greatly improve yields for farmers.

  •Can help endangered plant species

  
• What is

  the binomial naming system?(4.7)Based on the genus and speciesSuch asHomo sapiensWritten in all italicsGenus has capital, species lowercase
• What are the

  disadvantages of plant tissue culture?(4.9)• Reduced gene poolreduces chance of population surviving if a disease arises

  •Clones have low survival rates
• What is the name of the

  technique used to estimate when a fossil was formed?(4.4)Carbon dating

  
• What is

  Genetic Engineering?(4.10)Modifying the genome of an organism to introduce desirable characteristics.

  
• Describe the

  stages of Genetic Engineering:(4.11)• The gene that is to be inserted islocated in the original organism

  •Restriction enzymesare used to isolate the required gene, leaving it with‘sticky ends’(a short section of unpaired bases)

  • Same restriction enzymes are used to cut thevector(such as a virus or bacterial plasmid) into which the genes will be placed, leaving it with corresponding sticky ends to the isolated gene.

  •Ligase enzymeis used to attach thesticky ends of the geneand the vector together , to produce arecombinant gene product.

  • The vectoris placed in another organismat an early stage in development so thedesired gene moves into its cells and cause the organism to grow with the desired characteristics.

  • In plants, thevector is put into meristematic cells(unspecialised) which can then produce identical copes of the modified plant.

  
• Give 3 examples of


  Genetically Modified Organisms:(4.10)• Thegene forhuman insulinhas beeninserted intobacteria, which then produce human insulin that can becollected and purified for medical use for diabetics

  •Crop plants,such as wheat and maize, have beengenetically modified to contain a gene from a bacteriumthatproduces a poison that kills insects, making themresistant to insect pestssuch as caterpillars

  •Some crops have been genetically modified toproduce additional vitamins, e.g.‘golden rice’contains genes from another plant and a bacterium which make the rice grains produce a chemical that is turned intovitamin Ain the human body.
• What are the

  advantages of Genetic Engineering?(4.12)• Can be used in medicine to mass-produce certain hormones (eg. Insulin using bacteria)

  
  

  • Can be used to genetically modify crops to be resistant to harsher climates or resistance to herbicides to increase yields.

  
  

  • Can genetically modify crops to produce their own pesticides (eg. Bt corn)

  
• What are the

  disadvantages of Genetic Engineering?(4.12)•May lead to Genetic Engineering in humans, which has many ethical implications

  •Genes from GM crops can move into environment(pollination + wind etc.) creating 'superweeds' reducing yield.

  • GM crops with their own pesticide cause selection pressures whichcould lead pesticide resistance in evolving pest species.

  
• What are

  Bt crops?(4.12)Bt cropsare crops that have beengenetically modified with a gene for a toxinthatkills insect larvaewhich are damaging for the crops.

  The toxin is called Bt toxin, taken from the bacteriumBacillus thuringiensis

  The crops with theBt geneproduce the toxin in their stems and leaves

  The significance of genetically engineering crops to beinsect resistantis that there is anincrease in yieldandfewer pesticides are usedwhich could haveecological benefits(e.g. non-targeted invertebrates are not harmed)

  
• What are

  Fertilisers (as Agricultural Solutions)?(4.13)Fertilisers:Plants require arangeofmineral ionsin order togrow well.As crop plants take up these mineral ions from the soil, the mineral ions need to bereplacedif crops are grown repeatedly in the same field.

  Fertilisersare used to replace these mineral ions.

  They can make crops growfasterandbiggerso thatyields are increased.

  Fertilisers can be in the form oforganic fertiliserorchemical fertiliser.

  They mainly provide crop plants withnitrogen,phosphorusandpotassium. (NPK)

  However, a majordisadvantageis thatexcessfertilisersnot taken up by crops can getwashed into lakes and riversandcause problems, such aseutrophication

  
• What is the name of the

  process where excess fertilisers are washed into lakes and rivers?(4.13)Eutrophication

  
• What is

  Biological Control (as an Agricultural Solution)?(4.13)The use of certain species to control the population of others. However, thisreduces biodiversityand has aknock on effect on the entire ecosystem(less food = death = less food for predators etc.)

  
• What is the

  difference between discontinuous and continuous variation?DiscontinuousSet, can either be one of many valuesEG. Blood group, Ear lobe

  ContinuousCan take any value within a rangeEG. Height, mass, circumference