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Slide 1

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Biology revision…read more

Slide 2

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Water is a polar molecule with no overall charge.
The 1 oxygen molecule is slightly negative
While the 2 hydrogen molecules are slightly positive
Thus held with HYDROGEN BONDS which make it
liquid at room temp.
The O end is attracted to negative molecules and vice
versa with hydrogen
Solvent-polarity means they attract other polar
molecules, and chemical reactions can take place. ­ for
example it makes a good TRANSPORT MEDIUM in
(This is called intermolecular bonding)
Water itself can be involved in reactions such as
condensation and hydrolysis reactions, which you
should learn too.)…read more

Slide 3

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Adhesion and cohesion
Cohesion: the intermolecular forces water
Adhesion: intermolecular forces between
cellulose and water
This helps water ascend through xylem in
plant stems.
And keep remembering its all about hydrogen
To remember them think -COhesion, the `co'
shows its only water molecules `coexisting' if
you like
-and ADhesion, the `ad' shows the cellulose
has been `added' to the water…read more

Slide 4

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Thermal Info.
The reason that water turns to ice at 0°C is that as the
water is cooling the molecule doesn't have enough
energy to break the hydrogen bonds as it requires a lot
The water becomes locked in a crystalline lattice as the
hydrogen bonds make the molecules more spaced out.
Water cools and warms slowly because it takes a HUGE
amount of energy to increase by a SMALL amount of
This is useful to organisms to help them keep a steady
temperature even if the temperature in their
surroundings is varying
It also helps enzymes to catalyse
When water freezes, the ice is less dense than the
water. This insulates what is beneath it which is why
whole oceans, lakes etc. don't completely freeze all the
way to the bed…read more

Slide 5

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Hydrophobic and hydrophilic
Just in case you find this hard to remember,
hydroPHOBIC; when you have a phobia its because
you are afraid of something, HYDROphobic; hydro
is like water, so substances such as lipids are
`afraid of water' and don't dissolve.
Lipids- for them to be transported in the blood
they combine with proteins to form
Hydrophilic- `water loving' polar molecules
dissolve easier in water. E.g. sugars and amino
acids. If you remember what hydrophobic means
then you should find it easy to remember that
hydroPHYLIC is just the opposite.…read more


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