6.1. CHARACTERISTICS OF LIVING THINGS

All living things have the following characteristics:

• A similar CHEMICAL COMPOSITION:
  • Chemical elements
    95% --> C: carbon; H: hydrogen; O: oxygen; N: nitrogen.
  • Molecules (biomolecules):
    INORGANIC BIOMOLECULES - Water and mineral salts.
    ORGANIC BIOMOLECULES - carbohydrates, lipids, proteins and nucleic acids.
• They are made up of 1 CELL (unicellular) or MANY CELLS (multicellular).
• They carry out the LIFE FUNCTIONS:
  • NUTRITION is an essential life function because it involves all the processes to obtain ENERGY and MATTER that living things need to stay alive.
    • Autotrophs combine inorganic matter (water, mineral salts and CO2) with energy from the Sun (photosynthesis) or from chemical reactions (chemosynthesis) to produce their own organic compounds. Plants, algae and some bacteria are autotrophs.
    • Heterotrophs take organic matter made by other living things. Animals, fungi, protozoa and some bacteria are heterotrophs. According to the type of food they eat, the heterotrophic organisms are classified into: herbivores, carnivores, omnivores, saprophytes.
  • INTERACTION enables living things to interact with other living things and with the environment. Interaction is an essential life function because it makes it possible for living things to react to and respond to changes in their environment. In addition, it enables them to maintain stable internal conditions even though external conditions may change.
  • REPRODUCTION allows living things to produce new individuals. The variety in new individuals depends on the type of reproduction: there is more variety with sexual reproduction than with asexual one.