Water

Water

• Water is a polar molecule

• form hydrogen bonds

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Roles of water

• Solvent

  • many substances dissolve in water

• Temperature control

  • water can buffer sudden temperature changes

• Cooling mechanism

  • mammals use the evaporation of water as sweat to cool the skin

• Habitat

  • many organisms can survive and reproduce in water

• Metabolite

  • many chemical reactions involve water

• Transport

  • organisms can use water to move substances

Water as a solvent

• other polar molecules can dissolve in water

• the positive and negative ends of water molecules attract ions and allow them to dissolve

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Water as a temperature buffer

• high specific heat capacity

• hydrogen bonds can absorb a lot of energy before breaking so water takes a lot of energy to heat

• high specific heat capacity means water is resistant to rapid changes in temperature

• allows organisms to keep a steady body temp as mainly made up of water

Water as a cooling mechanism

• high latent heat of vaporisation (high bp)

• organisms can use evaporation of water as a cooling method without losing too much water

• when water evaporates from the surface of the skin it takes heat energy away from the surface thus cooling the organism

Water as a habitat

• high specific heat capacity and high latent heat gives a stable environment

• ice is less dense than water as an open lattice structure is formed

• floating ice forms an insulating layer on the surface of a water body

• water below does not freeze allowing organisms underneath to go undisturbed

Water as a metabolite

• Hydrolysis

  • use of water to break down complex molecules

• Condensation reactions

  • release water to join molecules

• photosynthesis

  • uses water as a raw material

Water as a transport medium

• The tendency of molecules to stick together via hydrogen bonds is cohesion

• also has a tendency to stick to other molecules known as adhesion

• strong cohesion and adhesion helps water flow through organisms and carry substances with it

• when water molecules meet air they create high surface tension - forms a skin like structure on the surface of the water which is strong enough to support small organisms like pond skaters

• xylem example

  • cohesion and adhesion allow plants to transport water through the xylem in a continuous column

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