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EDEXCEL A’S BIOLOGY

Topic 1 - lifest
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The useful
properties of water arise from its structure
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Because oxygen is more electronegative than hydrogen, it has a greater pull on
the shared electrons
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Water is therefore called
a Polar Molecule
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Water will form Hydrogen Bonds within
itself
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This property means
that oceans and lakes provide a stable environment in which organisms can live
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As water decreases in temperature, its molecules are less able to break the Hydrogen
bonds, as they have less kinetic energy
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This means that it insulates the water beneath, allowing
organisms in the liquid water to survive
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Water
has a high Cohesion because of Hydrogen bonding
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Cohesion also gives the
water a high surface tension, allowing small organisms, such as Pond Skaters, to walk
along it
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It is also a good solvent for ionic substances,
since the water molecules cluster around the ions and separate them, thus dissolving
the substance
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Water also takes part in some metabolic reactions, for example, in Hydrolysis and
Condensation reactions
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-anti hypertensive drugs
-ACE inhibitors stop the hormone that converts angiotensil to angiotensin II
-angiotensin II causes vasoconstriction
-therefore ACE inhibitors lower blood pressure

side effects
-dry cough
-dizziness
-kidney failure
-abnormal heart rhythm

Diuretics
-increase urine production
-reduce excess fluids and salts in the blood plasma
-less blood plasma means less blood volume so a lower blood pressure

side effects
-dizziness
-nausea

-stomach cramp

Calcium channel blockers
-anti hypertensive drugs
-they block calcium channels in blood vessel walls which prevents muscle
contraction

side effects
-dizziness
-swollen ankles
-flushed face
-abnormal heart rhythm
-constipation
-death (in people with heart conditions)

lowering blood pressure
If lifestyle changes are not enough to lower blood pressure then drugs may be
prescribed
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Bypass surgery

a blood vessel is taken from another part of the body to bypass the blocked vessel
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these are taken as soon
as a heart attack or stroke happens

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