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AS/A LEVEL NOTES SECTION 1
Exam answers made as notes for section 1 of the A level biology
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1.1 Introduction to biological moleculesMoles
A mole is the SI unit for measuring the amount of a substance (mol) – the molecular mass
(molecular weight) expressed in 1 gram
Molar solution = contains 1 mole of solute in each litre of solution.
Example – Na= 23 + Cl= 35.5 is NaCl= 58.5 so 1M solution of NaCl contains 58.5 grams of NaCl in 1
litre of solution
Bonding and formation of molecules
Covalent bonding –
atoms share pairs of electrons (from outershell) filling their outershell = more stable
compound, molecule formed, occurs between two non-metals
Ionic bonding –
ions of opposite charges attract one another, they form an electrostatic attraction = ionic
bond, occurs between a metal and a non-metal
Hydrogen bonding –
the electrons within a molecule are not evenly distributed, 1 region is more negatively
charged than the rest of the molecule, negative region of 1 polarised molecule and the
positively charged region attract each other = weak electrostatic bond
Polarised – a molecule with uneven distribution of charge (polar molecule)
Polymerisation and macromolecules
Monomers can be linked together to form long chains called polymers through the process
of polymerisation
Made of carbon, oxygen and hydrogen – biological molecules
Polymers like polythene and polyester are industrially produced
However others like polysaccharides, polypeptides and polynucleotides are naturally made
by living organisms
Condensation and hydrolysis reactions
Condensation reaction – formation of polymers, 2 molecules combine to form a more
complex one, water is formed as a condensation
Hydrolysis reaction – polymers are broken down with the addition of water breaks the
bonds that link the monomers in the polymer
Metabolism – all the chemical processes that take place in living organisms
, 1.2 Carbohydrates – monosaccharides
Carbohydrates are made up of carbon, hydrogen and oxygen, they can be small while others are
large.
Number of carbon atoms Type of monosaccharide
in monosaccharide
3 triose
4 tetrose
5 pentose
6 hexose
7 heptose
Monosaccharides
A single monomer is called a monosaccharide, a pair of monosaccharides can be combines
to form a disaccharide or many combined make a
polysaccharide.
Carbon can readily link to one another to form a
chain
Sweet tasting + Soluble
(CH2O)n, N is any number between 3 and 7
Crystalline
Examples – glucose, fructose and galactose
glucose has 2 isomers: alpha α-glucose and beta β-
glucose
Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.
isomers = 2 or more compunds with the same formula but different arrangement of atoms
Testing reducing sugars
All monosaccharides and some disaccharides
(maltose) are reducing sugars
Reduction is gain of electrons, reducing sugar
can donate electron (reduce) another
chemical = benedict reagent
Benedicts test = blue alkaline copper II sulfate
solution reduces to form insoluble red
paticipate copper I oxide
1. Add 2cm3 of food sample to test tube
2. Add equal volume of benedicts reagent
3. Heat mixture in water bath for 5 minutes
Differences in colour = semi quantative, can
be used to estimate the approximate amount
of reducing suagr in a sample
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