Defining Life

Life is the characteristic that distinguishes objects that are organisms (have signalling and self-sustaining processes) from those that are not.

All life depends on a series of complex chemical exchanges.

Fundamental Characteristics (Exhibit all/most)

  • Reproduction
    • Creating offspring
  • Growth
  • Adaptation
    • Changing over time in response to the environment
  • Metabolism
    • Converting chemicals and energy into cellular components (i.e. they have anabolism and also catabolism - they decompose things).
  • Response to Stimuli
    • Any kind of reaction brought on by an external change - sunlight or a chemical change in the environment. The reaction can be movement, contraction, releasing a toxin, etc.
  • Organisation
    • Being structurally composed of cell(s).
  • Homeostasis
    • Regulating the internal environment to maintain a constant state. (E.g sweating for temperature regulation).

Possess Chemicals of Life

  • Usually due to having cells (hence explained over there), but viruses have these without them)
  • Carbohydrates
    • Store and transport energy and structural components
    • Composed of Carbon chains with water molecules
    • Monosaccharides are the basic unit, but they can combine
  • Proteins
    • Polymers formed from linked amino acids
    • Joined with peptide bonds
  • Lipids
    • Different kinds of fats. E.g.
      • Fat-soluble Vitamins
      • Waxes
      • Cholesterol
      • Monoglycerides
    • Hydrophobic
    • Energy Storage and Structural composition of the cell membrane
  • Nucleic Acids
    • Genetic Material
    • Storage and transfer of genetic information
    • DNA Nucleotides:
      • Purines: Adenine, Guanine
      • Pyrimidines: Cytose, Thymine
      • 3 components to nucleotide:
        • pentose sugar
        • phosphate grou
        • nitrogenous base
    • Polymers = links of various nucleotides