Water

• Properties of water

  • metabolite in condensation/hydrolysis/photosynthesis/respiration
  • a solvent so metabolic reactions can occur
  • solvent allowing transport of substances
  • high specific heat capacity so resists changes in temperature
  • large latent heat of vaporisation providing a cooling effect
  • cohesion between water molecules so supports columns of water in plants
  • also provides surface tension for small organisms
• • consists of two hydrogen atoms bonded to one oxygen atom
  • oxygen is slightly negative and hydrogen slightly positive making it polar then dipolar
• water as a solvent

  • good solvent for ions and polar molecules as water molecules are attracted to them then collect and seperate them . This is what happens when chemicals dissolve in water
  • When a chemical is in a solution it’s free to movr about and react with other chemicals as they collide . This is how most chemical processes happen in living organisms
• Non polar molecules like lipids are insoluble in water . meaning when they are surrounded by water they are pushed together due to the water molecules being attracted to eachother

  This is important within hydrophobic interactions in proteins and structures within cell membrane as it makes it more stable
• Thermal properties

  • hydrogen bonds holding molecules together a relatively large amount of energy is needed to raise the temperature of water
  • This means that water in lakes and circulatory systems is slow to change as external environmental temperatures fluctuate. This then means water based habitats are stable
  • Body temperature remains stable
  • Evaporation is a good way of removing heat from body during cooling
• High surface tension and cohesion

  • water molecules stick together allowing water to move in long unbroken columns within vascular tissue in plants and within cells
  • Small organisms like pond skaters use water as their habitat
• Density and freezing properties

  • when water freezes it becomes less dense which means it floats to the surface and acts as an insulating layer preventing the rest of the water from freezing meaning there’s a greater chance organisms survive
  • temperature gaps below 4 it becomes less dense
  • warm water sinks cold water rises creating a current helping to circulate nutrients within the ocean
• water as transport medium

  • solvent properties make it a great transport medium in
  • the blood
  • lymphatic system
  • excretory and digestive system in animals
  • vascular tissue in plants
• inorganic ions

  • occur in solution in cytoplasm and body fluids some in high concentration the others in low
  • hydrogen ions and ph
  • iron ions in haemoglobin sodium ions in transport of glucose and amino acids
  • phosphate ions in DNA and RNA