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How hydrogen bonding occurs between water molecules, and relate this, and other properties of water, to the
roles of water for living organisms
A range of roles that relate to the properties of water, including solvent, transport medium, coolant and as a
habitat AND roles illustrated using examples of prokaryotes and eukaryotes
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Water has a high latent heat of vaporisation because a large amount of energy is required to
change it from a liquid to a gas
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Water has a high specific heat capacity because a large amount of energy is required to raise the temperature of the water
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When water turns to ice, it becomes less dense and floats
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The water beneath remains liquid and is insulated by the ice so aquatic organisms don’t freeze
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Water has a high surface tension which is a useful habitat for invertebrates such as pond skaters
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The concept of monomers and polymers and the importance of condensation and hydrolysis reactions in a range
of biological molecules
The chemical elements that make up biological molecules
Monomers are small molecules which join up to form polymers
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They form polymers using monomers
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They break down polymers into monomers
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It’s a small molecule so can diffuse across cell membranes
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Glucose molecules can also join to form disaccharides, such as
maltose and lactose, and polysaccharides, such as glycogen and cellulose
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Pentose and hexose tend to form ring structures
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The synthesis and breakdown of a disaccharide and polysaccharide by the formation and breakage of glycosidic
bonds
To include the disaccharides sucrose, lactose and maltose
Disaccharides and polysaccharides are formed through condensation reactions
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Disaccharides and polysaccharides are broken down by hydrolysis reactions
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Sucrose = glucose + fructose

Lactose = galactose + glucose
Maltose = glucose + glucose
The structure of starch (amylose and amylopectin), glycogen and cellulose molecules
Amylose
Amylopectin
Glycogen
Structure
Coiled, helix
Fewer and longer
Short and highly
branches
branched, slightly
coiled
Monosaccharide
α-glucose
α-glucose
α-glucose
Formation
Condensation
Condensation
Condensation
Bonds
α-1,4-glycosidic bonds α-1,4-glycosidic bonds
α-1,4- and α-1,6and some α-1,6- at
glycosidic bonds
branches
Hydrogen bonding
H bonds within
Some H bonds between No hydrogen bonding
molecule and none
molecules
between molecules
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How the structures and properties of glucose, starch, glycogen and cellulose molecules relate to their functions in
living organisms
Glycogen and starch make good storage molecules because they are insoluble so won’t change the water potential of the
cell, can be broken down quickly, has lots of branches for enzymes to attach and compact so can store a lot of energy
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Cellulose is suitable for forming cell walls because it is strong, insoluble and has H bonds between adjacent molecules
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Phospholipids contain 2 fatty acids, a glycerol molecule and a phosphate group joined by 2 ester bonds
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Fatty acids consist of a carboxyl group at one end and a hydrocarbon chain
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Monounsaturated fatty acids
have one C=C bonds whilst polyunsaturated fatty acids have more than one C=C bonds
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Water is produced as a by-product
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How the properties of triglyceride, phospholipid and cholesterol molecules relate to their functions in living
organisms
To include hydrophobic and hydrophilic regions and energy content AND illustrated using examples of
prokaryotes and eukaryotes

Triglycerides are used as an energy store because it is non-polar and insoluble in water so it doesn’t affect the water
potential of cells
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They have more H
atoms than O atoms so produce more energy
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Triglycerides are also used to produce steroid hormones such as oestrogen, provide thermal insulation, form part of
membranes, protect organs, source of cholesterol, waterproof the skin, a source of vitamin D and provide electrical
insulation in myelin
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Phospholipids can contain saturated and unsaturated
fatty acids
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Cholesterol is small and thin so can fit into the phospholipid bilayer giving strength and stability by regulating the fluidity of
the bilayer
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The general structure of an amino acid the synthesis and breakdown of dipeptides and polypeptides, by the
formation and breakage of peptide bonds

Amino acids contain an amine group (H₂N), an acid/carboxyl group (COOH) and a carbon in the middle which bonds a
hydrogen atom and an R group
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The H from the amine combines with the OH from the carboxyl group through a condensation
reaction where water is produced
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The levels of protein structure
To include primary, secondary, tertiary and quaternary structure AND hydrogen bonding, hydrophobic and
hydrophilic interactions, disulphide bonds and ionic bonds
Primary structure - The unique sequence of amino acids held together by peptide bonds in a protein molecule/polypeptide
chain
Secondary structure – The initial folding of the polypeptide chains to form alpha helixes and beta pleated sheets which are
held together by hydrogen bonds
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Quaternary structure – The structure formed when the alpha and beta subunits of the polypeptide chains join together,
sometimes with an inorganic component, to form a protein
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After synthesis, the polypeptide chains are folded or pleated into different
shapes called their secondary structure
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The
final 3D structure is the tertiary structure which involves pleating or coiling with straight amino acids in between
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Ionic bonds – Oppositely charged ‘R’ groups (+ve and –ve) found close to each other
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The hydrophilic and hydrophobic interaction, ionic bonds and hydrogen bonds break and the
protein denatures
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They are roughly spherical in shape
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Insulin is a globular protein
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It’s soluble so it can
be transported in the bloodstream and have precise shapes to fit into specific receptors on cell-surface membranes and
work
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A simple protein doesn’t have prosthetic groups
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Each subunit contains a prosthetic haem group
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It is soluble in water so can travel around in the blood
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The Fe²⁺ ions in the
prosthetic groups allow it to interact with hydrogen peroxide and speed up its breakdown
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The properties and functions of fibrous proteins
To include collagen, keratin and elastin (no details of structure are required)
Fibrous proteins are strong, long molecules which aren’t folded into complex 3D shapes like globular proteins
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Collagen is a fibrous protein which is strong and insoluble so is a useful component of blood vessel walls and forming the
structure of bones
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Keratin is strong, inflexible and insoluble due to the many strong disulphide bonds from the sulphur-containing amino acid,
cysteine
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Hair contains less disulphide bonds making it more flexible than nails
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The key inorganic ions that are involved in biological processes
To include the correct chemical symbols for the following cations and anions
Cations: calcium ions (Ca²⁺), sodium ions (Na⁺), potassium ions (K⁺), hydrogen ions (H⁺), ammonium ions (NH₄ ⁺)
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How to carry out and interpret the results of the following chemical tests:
• Biuret test for proteins
• Benedict’s test for reducing and non-reducing sugars
• Reagent test strips for reducing sugars
• Iodine test for starch
• Emulsion test for lipids
You can test for the presence of proteins by adding biuret reagent to a sample
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For reducing sugars, add Benedict’s solution and heat to 80°C in a water bath
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Green = low concentration, yellow/orange = medium, red = high
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The solution is then cooled
and neutralised by adding sodium hydrogen carbonate solution or sodium carbonate
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Non-reducing sugars would give a negative result for the reducing sugar test
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The colour-coded chart can
determine the concentration of the sugar
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Pour the solution into water in
a clean test tube
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Quantitative methods to determine the concentration of a chemical substance in a solution
To include colorimetry and the use of biosensors (an outline only of the mechanism is required)
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The more concentrated a
solution is the more light it will absorb and the less light it will transmit
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The solutions are first filtered to remove precipitate and placed in cuvettes
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A calibration curve can be plotted to show the results
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presence

and

Molecular recognition – A protein or DNA is
immobilised to a surface
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Transduction – This interaction causes a change in
the transducer
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Display – A visible, qualitative or quantitive signal is
produced
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Chromatography allows us to separate substances in complex mixtures
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The mobile phase may either be an aqueous (water-based) liquid
or a non-aqueous organic (carbon-based) solvent
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g
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g
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TLC tends to produce more useful chromatograms than paper chromatography, which show greater separation of the
components in the mixture - and are therefore easier to analyse
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Practical investigations to analyse biological solutions using paper or thin layer chromatography
For example the separation of proteins, carbohydrates, vitamins or nucleic acids
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The solution is spotted using a
capillary tube and allowed to dry before being spotted again (If it is unknown, the other known solutions are also spotted at
a distance from the unknown spot)
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It is left in the solvent until the solvent has reached about 2cm from the top
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Colours may be used to make colourless solutions clearer e
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Ninhydrin spray reacts with amino acids turning them a
purple/brown colour

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