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  • Reactant, Including hydrolysis reactions
  • Solvent

Substances can dissolve in it.

Most biological reactions take place in solution, for example in the cytoplasm of eukaryotic and prokaryotic cells.

  • Transport

As it is a liquid and solvent, it can easily transport a variety of materials such as glucose and oxygen around plants and animals. 

  • Temperature Control

Due to it's high specific heat capacity and hihg latent heat of evaporation.

  • Habitat

Its properties that help with temperature control, and the fact that it is a solvent and becomes less dense when frozen means that many organisms can survive and reproduce in it. 

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One molecule of water contains two hydrogen atoms and one atom of oxygen joined by covalent bonds. 

The shared negative hydrogen electrons are pulled towards the oxygen atom meaning the other side of the atom is left with a slightly positive charge. 

The unshared negative electrons on the opposite side of the oxygen atom result in a slightly negative charge.

This results in water being a polar molecule

  • It has a partial negative charge on one side and a partial positive charge on the other

The slightly negative side of the oxygen atom attracts the slightly positive sides of the neighbouring hydrogen atoms. 

  • This attraction is known as hydrogen bonding and is responsible for some of water's useful properties. 
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High Specific Heat Capacity

The energy needed to raise the temperature of one gram of a substance by one degree celcius.

The hydrogen bonds between the molecules absorb a lot of energy meaning a lot of energy is needed to heat the water up.

This means that water does not experience rapid temperature changes making it a good habitat.

  • The temperature under water is likely to be more stable than it is on land. 
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High Latent Heat of Evaporation

A lot of heat energy is required to break the hydrogen bonds between the water molecules.

This is useful for living organisms as it means that water is able to cool things down. 

  • This is why some mammals sweat when they are hot. The sweat evaporates, cooling the surface of the skin as it does so. 
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The attraction between molecules of the same type.

Water molecules are very cohesive and so tend to stick together due to their polarity.

This helps water to flow making it excellent for transporting substances.

It also helps water to be transported up plant stems in the transpiration stream. 

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As water is polar,

  • The slightly positive end of the molecule will be attracted to the negative ion
  • The slightly negative end of the molecule will be attracted to the positive ion

This means that the ions will become surrounded by the water molecules. I.e. they'll dissolve

The polarity of water makes it useful as a solvent in living organisms

  • For example, in humans, important ions can dissolve in the water in the blood and then be transported around the body.  
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Less Dense When Solid

Water molecules are held further apart in ice form than they are in liquid as the water moelcules form four hydrogen bonds with the other water molecules meaning a lattice shape is formed. 

  • This makes ice less dense than liquid water making it able to float.

This is useful for living organisms.

  • In cold temperatures, ice forms an insulating layer on top of the water while the water below does nto freeze. 
  • Organisms like fish do not freeze under the ice meaning they can still move around.
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