Biology section 4

• Evolution


  The gradual and continuous change of organisms from one generation to the next
• Natural selection


  Survival of the fittest
• Natural selection

  1. Individuals in a population show genetic variation due to differences in alleles

  2. Selection pressures (predation, competition, disease) affect organism's chance of surviving and reproducing

  3. Individuals with characteristics better adapted to selection pressures have better chance of survival and reproduction

  4. Beneficial alleles more likely to be passed to next generation

  5. Less well adapted individuals less likely to survive and reproduce
• Bacteria provide evidence for evolution
• Antibiotic resistance in bacteria

  1. Bacteria develop random mutations

  2. Resistant bacteria better able to survive antibiotic treatment

  3. Resistant bacteria reproduce more, passing on resistance allele

  4. Resistance becomes more common in population
• Fossils provide evidence for evolution
• Fossils show gradual changes in organisms over billions of years
• Fossils


  • Trace of an animal or plant that lived a long time ago
  • Generally, the deeper the rock, the older the fossil
• Humans and chimpanzees evolved from a common ancestor around 6 million years ago
• Hominid fossils show characteristics between apes and humans, demonstrating human evolution
• Ardi (4.4 million years old)


  • Feet suggest tree climbing
  • Long arms, short legs, small brain
  • Legs suggest upright walking
• Lucy (3.2 million years old)

  • Arched feet adapted for walking
  • Arm and leg size between apes and humans
  • Brain slightly larger than Ardi's
  • Better adapted for upright walking than Ardi
• Turkana Boy (1.6 million years old)


  • Short arms, long legs more human-like
  • Brain size similar to humans
  • Better adapted for upright walking than Lucy
• Human evolution timeline


  • Ardipithecus species
  • Australopithecus species
  • Homo species
  • Homo sapiens
• Stone tool development by Homo species

  • Homo habilis: simple pebble tools
  • Homo erectus: more complex sculpted tools
  • Homo neanderthalensis: flint tools, pointed tools, wooden spears
  • Homo sapiens: flint tools, pointed tools (arrowheads, fish hooks, needles)
• Dating tools and fossils

  Structural features, stratigraphy (rock layers), carbon-14 dating
• Classification is the organisation of living organisms into groups
• Five kingdom classification system

  • Animals
  • Plants
  • Fungi
  • Prokaryotes
  • Protists
• Classification systems change over time as technology and understanding improves
• Five kingdom classification system

  • Animals
  • Plants
  • Fungi
  • Prokaryotes
  • Protists
• Classification system hierarchy


  1. Kingdom

  2. Phylum

  3. Class

  4. Order

  5. Family

  6. Genus

  7. Species
• Classification systems change over time
• The five kingdom classification system is still used, but it's now a bit out of date
• Technology has developed further and our understanding of things like biochemical processes and genetics has increased
• We are now able to determine the sequence of DNA bases in different organisms' genes and compare them - the more similar the sequence of a gene, the more closely related the organisms
• Three domains of classification

  • Archaea
  • Bacteria
  • Eukarya
• Archaea


  • Organisms look similar to bacteria but are actually quite different - as differences in their genetic sequences show
  • They were first found in extreme places such as hot springs and salt lakes
• Bacteria


  • This domain contains true bacteria like E. coli and Staphylococcus
• Eukarya


  • This domain includes a broad range of organisms including fungi, plants, animals and protists
• Selective breeding


  Artificially selecting the plants or animals that are going to breed so that the genes for particular characteristics remain in the population
• Selective breeding process


  1. Select the ones with the desired characteristics

  2. Breed them with each other

  3. Select the best of the offspring, and breed them together

  4. Continue this process over several generations
• Selective breeding is nothing new - people have been doing it for thousands of years
• Advantages of selective breeding


  • Improve meat yields in cattle
  • Investigate reasons behind alcoholism in rats
• Disadvantages of selective breeding

  • Reduces the gene pool - the number of different alleles (forms of a gene) in a population
  • Inbreeding can cause health problems
  • Less chance of resistance alleles being present if a new disease appears
• Genetic engineering


  Modifying an organism's genome (its DNA) to introduce desirable characteristics
• Genetic engineering process


  1. Cut out the DNA you want to insert using restriction enzymes

  2. Cut open the vector DNA using the same restriction enzyme

  3. Mix the vector DNA and the DNA you're inserting and use ligase enzymes to join them

  4. Insert the recombinant DNA into other cells, e.g. bacteria
• Uses of genetic engineering

  • Make crops resistant to herbicides
  • Produce human proteins in animals for medical use
  • Concerns about effects on organisms and the environment