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Water summary notes - A Level biology OCR A
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Summary notes on ‘water’ for OCR A A level biology.
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wateruses of water for living organisms
- water is a reactant in a vast amount of chemical reactions in and out of the body such as hydrolysis reactions
- it is a solvent, this means that most substances dissolve in it.
—> most biological reactions take place in the cytoplasms of cells which means that water is needed
- water is found in plasma which is needed to transport important substances around our bodies psych as
oxygen and glucose.
- water is a habitat, this means that many organisms can dwell there. this is due to the fact that it is a solvent
and becomes less dense when it freezes.
structure of water
- a molecule of water (h2O) is one atom of oxygen, conjoined to two hydrogen
atoms by shared electrons (covalent bonding).
-because the shared negative hydrogen electrons are pulled towards the oxygen
atom, the other side of each hydrogen atom is left with a positive charge
- the unshared negative electrons on the oxygen atoms give it a slight negative
charge
- this makes water a polar molecule because it has a partial negative charge on one
side and a partial positive charge on the other.
- the negatively charged oxygen atoms attract the slightly positively
charged hydrogen atoms of other water molecules.
this attraction is called hydrogen bonding and gives water a lot of its
properties.
the properties and functions of water
hydrogen bonds give water a high latent heat of evaporation and a high specific heat capacity.
- hydrogen bonds between water molecules absorb a lot of energy, thus giving water a high specific heat
capacity.
-this means water doesn’t experience rapid temperature changes, so it is a good habitat - the temperature
underwater is likely to be more stable than on land.
- water has a high latent heat of evaporation because it takes a lot of energy (heat) to break the hydrogen bonds
between molecules.
- a lot of energy is used up when water evaporates, which is useful for living organisms because water can cool
things down - eg. Some mammals sweat, when this evaporates it cools the surface of the skin.
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