19.1 Principles of genetic technology19.2 Genetic technology applied to medicine19.3 Genetically modified organisms in agricultureThe discovery of the structure of DNA by Watson and Crick in the early 1950s and discoveries since have led to many applications of gene technology in areas of medicine, agriculture and forensic...

18.1 Biodiversity18.2 Classification18.3 ConservationThe biodiversity of the Earth is threatened by human activities and climate change. Classification systems attempt to put order on the chaos of all the organisms that exist on Earth. Field work is an important part of a biological education to appreciate this diversity...

17.1 Variation17.2 Natural and artificial selection17.3 EvolutionCharles Darwin and Alfred Russel Wallace proposed a theory of natural selection to account for the evolution of species in 1858. A year later, Darwin published On the Origin of Species providing evidence for the way in which aspects of the environment act...

15.1  Control and co-ordination in mammals15.2  Control and co-ordination in plantsAll the activities  of multicellular organisms require  co-ordinating, some very rapidly and some more slowly. The nervous system and the endocrine system provide co-ordination in mammals. Similar co-ordination systems...

14.1  Homeostasis in mammals14.2  Homeostasis in plantsCells function  most efficiently if they  are kept  in near  constant conditions. Cells in multicellular animals are surrounded by tissue fluid. The composition, pH and temperature of tissue fluid are kept  constant by exchanges with...