Water is vital to life in animals and plants:

  • Good solvent - allowing transport and cell reactions to occur
    • Transports dissolved substances through the body of animals (blood, lymph, tissue fluid) and plants (xylem/phloem)
    • Transports substances into and out of cells through osmosis process e.g. in lungs and digestive system
    • Cell reactions, acting as a medium to bring chemicals into contact and it is involved in some reactions e.g.:
      • hydrolysis: water is used to hydrolyse (split) many substances e.g. proteins into amino acids; fats to fatty acids and glycerol; and polysaccharides to monosaccharides
      • condensation reactions through which smaller molecules combine to form one larger molecule, with the elimination of water (e.g. glu + glu - water -> maltose)
      • photosynthesis (water is broken down to supply hydrogens) and respiration, where water is a necessary product
    • Medium for dispersal e.g. gametes, pollen, spores, fruits and seeds
  • Good energy absorber - helping to stabilise temperatures
    • A large increase in heat results in a small rise in temperature. Water usually maintains its temperature irrespective of fluctuations to the surrounding environmental temperature. This facilitates enzymes because they have a limited temperature range for activity. Also, aquatic environments show less seasonal and diurnal temperature changes than on land, so growth of aquatic plants is more constant
  • Lubricant

    • Mucus – used in intestines
    • Synovial fluid – lubricates joints
    • Pleural fluid – friction-free movement of lungs against ribs
    • Pericardial fluid - friction-free movement of heart against ribs
  • Support
    • Water is not easily compressed, making it useful in supporting organisms
    • Skeleton e.g. earthworms supported by the pressure of water within
    • Water has a high density therefore supporting the weight of aquatic plants and animals e.g. whales
    • Maintains turgidity in plant cells - water is present in vacuoles.
    • Eye - eye shape is due to watery humour in it
    • Foetus – Amniotic fluid supports and protects foetus
  • Large latent heat of vaporisation - Regulates temperature
    • It absorbs heat to evaporate and so sweating cools animals and transpiration cools plants
  • High surface tension
    • Resulting from the inward cohesive forces of attraction between molecules causing the surface to have the smallest possible area. Organisms can therefore walk or float on “skin”
  • Ice floats on freezing water
    • Because water volume increases and therefore density decreases when it freezes it insulates aquatic organisms below the ice from extreme cold
  • Neutral pH (7)
    • Suitable for most enzymes
  • High cohesion
    • Water molecules attach to each other and lower adhesion. Water molecules attach to other surfaces, contributing to capillarity in plants (water rising up the stems - against gravity) and soil (causes water to disperse in soil)
  • Colourless
    • Allows submerged plants to photosynthesise
  • Hearing and balance in ear
    • Watery liquid in cochlea and semi-circular canals

previousPrevious - Vitamins
Next - Scientific Methodnext