Revision Biology - Water

Revision for biology - water. Spec: OCR

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  • Created by: Sheila
  • Created on: 17-05-10 17:34
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Revision ­ Water
Water is vital to living organisms
Water acts as a reactant in important chemical reactions such as hydrolysis.
Water transports substances.
Water is a good solvent, it can dissolve ions.
Helps with temperature control, carries away heat energy when it evaporates, so it cools the
surface.
Water molecule structure
Water molecule is polar, the oxygen atom is more electronegative
then the hydrogen atom causing the bonding pair of electrons to be
attracted by the oxygen atom leaving a slight positive charge on the
hydrogen atom. The hydrogen atom is then attracted by the negative
oxygen atom and from a hydrogen bond with the lone pair of
electrons on the oxygen atom.
Water's structure related to its property
Water has a high specific heat capacity
Specific heat capacity is the energy it takes to raise the temperature of 1g of substance by 1oc.
The hydrogen bonds between water molecules can absorb a lot of energy, so water has a high
specific heat capacity ­ it takes a lot of energy to heat it up. This is useful in organisms as it stops
rapid temperature change and helps to keep the temperature stable.
Water has a high latent heat of evaporation.
It takes a lot of heat energy to break the hydrogen bonds between water molecules. So, water
has a high latent heat of evaporation ­ a lot of energy is used up when water evaporates. This is
useful in living organisms as it acts as a coolant.
Water is cohesive.
Cohesion is the attraction between molecules of the same type. Water is cohesive because it is
polar. This allows water to flow and transport substances around organisms.
Water's polarity makes it a good solvent.
Many important substances in biological reactions are ionic. The positive end of the water
molecule will be attracted to negative ions and the negative end of the water molecule will be
attracted to positive ions. The ion will become totally surrounded by water molecules and
dissolve.

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