Cambridge International AS and A Level Biology Coursebook with CD-ROM
This document has only the key information that you MUST know for your exams, everything biological molecules- from water to lipids to protein folding. You won't find any confusing and unnecessary details here!
The Cell Cycle and Mitosis with precise notes and mnemonics.
HUMAN HEART STRUCTURE WORK
cell and nuclear division mitosis and dna replication
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Written for
A/AS Level
CIE
Biology
Unit 2 - B Biological Molecules
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WATER
In awater molecule the
oxygen is sharing a pair of
electrons with each of the hydrogen atoms However
the sharing is not equal
The electrons are often associated more will
the oxygen ratherthan the hydrogens
PARTIAL
www pe
thisawyresultqjguedthe oxygen iming the walled
anabteenpond Since electrons are now missingfrom hydrogen because they
are
atoms it becomespartiallypositively charged temporary
So the water molecule has positive and negative poles similar to
a magnet
We say that it is a polar molecule
Furthermore
hydrogen bonds ioccur in water molecules between
the negatively charged oxygen and a positively charged hydrogen
atom of a different molecule
This bond is relatively weak however it holds
the structure of water in a matn's
hydrogenbond
O Q
or op
Biological Importance Of Water o O
Properties
Cohesion
The sticking of water molecules to
other water molecules
bonds is what makes wate
Hydrogen cohesive
so that it forms water drops
Causes ace tension allowing insects
to run along the water
Adhesion Hate sticking to other poler surfaces
Cohesive
Sadhesive propeties allow water to
move as a column
, move column
Solvent Properties
Many substances can form hydrogen bonds
withtheir oppositelycharged ions in waterCHT o
Eg NatScl o SH som H bonds
Thermal Properties
The hydrogen bonds near that
water has a high heat
capacityHigh amounts of energyare
needed to break hydrogen bonds
and then escite the atoms
kinetic
Energy
It is also difficult to break
hydrogen bonds to separate
them vaporize molecules
High Latent heat capacity
freezes at 0 C
Ice is less dense than liquid
water because as it cools
it forms more bonds in regularly
spaced intervals
mm
Biological Importance
Coolant
In order for water to evaporate alot
of energy is used
This energy is then lost to its surroundings allowing
the organism to be cooled
g sweating plants respiringetc
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