B14 & B15

• Extinction

  A species that once existed has completely died out
• Causes of extinction

  • A new disease may kill all members of a species
  • The environment changes over geological time
  • New diseases may be introduced
  • A new predator may evolve or be introduced to an area that kills and eats all of a species
  • A new competitor may evolve or be introduced into an area. The original species may be left with too little to eat
  • A single catastrophic event may occur that destroys a habitat (e.g. a massive volcanic eruption)
  • Natural changes in species occur over time
• Variation

  The differences in the characteristics of individuals in a population
• Causes of variation

  • Differences in the genes they have inherited
  • The conditions in which they have developed
  • A combination of both genetic and environmental causes
• Genetic engineering

  1. A gene for a desired characteristic is 'cut out' of the chromosome of an organism using an enzyme

  2. The gene is then inserted into the chromosome of another organism

  3. A vector (carrier) such as a plasmid or virus may be used to transfer the gene
• In genetic engineering, the new gene is often inserted into an organism of the same species to give it a 'desired' characteristic
• New genes can be transferred to crop plants
• Crops with genes are called genetically modified (GM) crop plants
• GM crops may make their own pesticide, or be herbicide-resistant, and usually have increased yields
• Adult cell cloning


  1. The nucleus of an adult cell, such as a skin cell, replaces the nucleus of an egg cell

  2. The new cell is given an electric shock that causes it to start to divide

  3. The ball of cells is called an embryo

  4. The embryo is genetically identical to the adult skin cell

  5. Once the embryo has developed into a ball of cells, it is inserted into the womb of a host mother