AS Level Biology Notes for Topic 1 – Unit 1 ; Molecules, Transport & Health
1A Chemistry for Biologists —-
The Chemistry of Life
Water:
➢ Oxygen has 2 pairs of free electrons, opposite to the bonding pairs in the
covalent bonds.
○ This increases the negativity over ½ of the molecule, resulting in an
induced pole; hence, water is dipolar.
➢ Polar → an imbalance in charges.
Features of H2O:
➢ Hydrogen Bonding –
○ Oxygen atoms of water molecules are
slightly negative, this attracts the
slightly positive hydrogen atoms of
another water molecule – this allows
them to “stick” together.
➢ High Specific Heat Capacity –
○ It’s slow to absorb & release heat due to the high required energy needed
to break down the numerous hydrogen bonds.
➢ High Latent Heat of Evaporation –
○ This is the thermal energy needed to change the state of a liquid into gas.
○ Water has a high LHV, preventing us from evaporating and allowing us to
cool down.
➢ Cohesion & Surface Tension –
○ The forces between the molecules stick together as they’re attracted to
each other/different molecules — likewise, it has a high surface tension due
to the attraction between the hydrogen bonds; forming a skin of surface
tension.
Water in Metabolism:
➢ Water is needed in hydrolysis reactions to break down molecules.
➢ Chemical reactions take place in aqueous conditions.
➢ Water is a raw material for photosynthesis.
Water as a Solvent:
➢ Water readily dissolves other substances for transport.
○ e.g. gases, waste products, enzymes, inorganic ions & small hydrophilic
molecules.
,AS Level Biology Notes for Topic 1 – Unit 1 ; Molecules, Transport & Health
Carbohydrates – Monosaccharides & Disaccharides
Monosaccharides:
➢ Soluble monomers of carbohydrates (CH2O)n
○ n can be any number between 3–7.
○ e.g. glucose, galactose, fructose.
Disaccharides:
➢ When combined in pairs, monosaccharides form a disaccharide.
○ Glucose & glucose = maltose.
○ Glucose & fructose = sucrose.
○ Glucose & galactose = lactose.
➢ A water molecule is removed in this condensation reaction when the two
molecules combine.
○ A glycosidic bond is then formed – this can be between 2 C molecules or
between a C, O molecule.
Benedict’s Test for Reducing Sugars:
➢ All monosaccharides & disaccharides are reducing sugars.
○ Reducing sugars are able to donate electrons to one another.
○ Reduction → gain electrons/hydrogen.
➢ Benedict’s reagent is an alkaline solution of copper(II) sulphate – when
heated, an insoluble precipitate is formed.
1) Put 2cm^3 of the sample into a test tube and set a water bath at 90/95C.
2) Add an equal volume of Benedict’s solution.
3) Heat in the water bath for 5 minutes.
a) In low concentrations of RS; blue → green/yellow.
b) In high concentrations of RS; blue → brick-red.
Types of Data:
➢ Qualitative → tells us if it’s present or not.
➢ Semi-qualitative → gives us an indication of a rough value.
➢ Quantitative → gives us an accurate and exact value.
, AS Level Biology Notes for Topic 1 – Unit 1 ; Molecules, Transport & Health
Carbohydrates: Polysaccharides
➢ Polysaccharides → made up of many monosaccharides.
➢ Features of polysaccharides:
○ Insoluble – it doesn’t affect the water potential nor diffuses out of the
cell.
○ Compact – more of the energy source can be stored in a small space.
○ Highly branched – more active sites are available to be readily used so
more energy is given off at once.
Starch (alpha-glucose – found in plants):
➢ Amylose → made up of repeating α-glucose units joined by 1,4 glycosidic
bonds, forming straight chains.
➢ Amylopectin → made up of α-glucose units joined with both 1,4 & 1,6
glycosidic bonds, forming branched chains.
Glycogen (alpha-glucose – found in animals):
➢ It’s shorter and more branched chains (there are more 1,6 bonds than 1,4),
stored as small granules in the muscle tissues and liver but they’re stored in
small amounts. Glycogen molecules are formed by alpha glucose molecules
joined together by a condensation reaction.
Cellulose (beta-glucose – found in cell walls):
➢ Made up of repeating 1-4 β-glucose units which form long, unbranched
chains. A vast number of hydrogen bonds give cellulose its tensile strength.
○ Group of cellulose molecules → microfibrils → fibres.
Lipids
➢ Roles of lipids:
○ Cell membranes and waterproofing
○ Energy sources (when oxidised, it gives off more energy)
○ Insulation and protection.
➢ Fatty acids and glycerol are combined by ester bonds – all fatty acids have a
long hydrocarbon chain (a folded backbone of carbon and hydrogen, with a
carboxyl (-COOH) group attached).
➢ A molecule of water is removed and an ester bond is made via
condensation/esterification reactions.
○ Fatty acids differ by the length of the carbon chain & whether or not it’s
saturated or unsaturated.
1A Chemistry for Biologists —-
The Chemistry of Life
Water:
➢ Oxygen has 2 pairs of free electrons, opposite to the bonding pairs in the
covalent bonds.
○ This increases the negativity over ½ of the molecule, resulting in an
induced pole; hence, water is dipolar.
➢ Polar → an imbalance in charges.
Features of H2O:
➢ Hydrogen Bonding –
○ Oxygen atoms of water molecules are
slightly negative, this attracts the
slightly positive hydrogen atoms of
another water molecule – this allows
them to “stick” together.
➢ High Specific Heat Capacity –
○ It’s slow to absorb & release heat due to the high required energy needed
to break down the numerous hydrogen bonds.
➢ High Latent Heat of Evaporation –
○ This is the thermal energy needed to change the state of a liquid into gas.
○ Water has a high LHV, preventing us from evaporating and allowing us to
cool down.
➢ Cohesion & Surface Tension –
○ The forces between the molecules stick together as they’re attracted to
each other/different molecules — likewise, it has a high surface tension due
to the attraction between the hydrogen bonds; forming a skin of surface
tension.
Water in Metabolism:
➢ Water is needed in hydrolysis reactions to break down molecules.
➢ Chemical reactions take place in aqueous conditions.
➢ Water is a raw material for photosynthesis.
Water as a Solvent:
➢ Water readily dissolves other substances for transport.
○ e.g. gases, waste products, enzymes, inorganic ions & small hydrophilic
molecules.
,AS Level Biology Notes for Topic 1 – Unit 1 ; Molecules, Transport & Health
Carbohydrates – Monosaccharides & Disaccharides
Monosaccharides:
➢ Soluble monomers of carbohydrates (CH2O)n
○ n can be any number between 3–7.
○ e.g. glucose, galactose, fructose.
Disaccharides:
➢ When combined in pairs, monosaccharides form a disaccharide.
○ Glucose & glucose = maltose.
○ Glucose & fructose = sucrose.
○ Glucose & galactose = lactose.
➢ A water molecule is removed in this condensation reaction when the two
molecules combine.
○ A glycosidic bond is then formed – this can be between 2 C molecules or
between a C, O molecule.
Benedict’s Test for Reducing Sugars:
➢ All monosaccharides & disaccharides are reducing sugars.
○ Reducing sugars are able to donate electrons to one another.
○ Reduction → gain electrons/hydrogen.
➢ Benedict’s reagent is an alkaline solution of copper(II) sulphate – when
heated, an insoluble precipitate is formed.
1) Put 2cm^3 of the sample into a test tube and set a water bath at 90/95C.
2) Add an equal volume of Benedict’s solution.
3) Heat in the water bath for 5 minutes.
a) In low concentrations of RS; blue → green/yellow.
b) In high concentrations of RS; blue → brick-red.
Types of Data:
➢ Qualitative → tells us if it’s present or not.
➢ Semi-qualitative → gives us an indication of a rough value.
➢ Quantitative → gives us an accurate and exact value.
, AS Level Biology Notes for Topic 1 – Unit 1 ; Molecules, Transport & Health
Carbohydrates: Polysaccharides
➢ Polysaccharides → made up of many monosaccharides.
➢ Features of polysaccharides:
○ Insoluble – it doesn’t affect the water potential nor diffuses out of the
cell.
○ Compact – more of the energy source can be stored in a small space.
○ Highly branched – more active sites are available to be readily used so
more energy is given off at once.
Starch (alpha-glucose – found in plants):
➢ Amylose → made up of repeating α-glucose units joined by 1,4 glycosidic
bonds, forming straight chains.
➢ Amylopectin → made up of α-glucose units joined with both 1,4 & 1,6
glycosidic bonds, forming branched chains.
Glycogen (alpha-glucose – found in animals):
➢ It’s shorter and more branched chains (there are more 1,6 bonds than 1,4),
stored as small granules in the muscle tissues and liver but they’re stored in
small amounts. Glycogen molecules are formed by alpha glucose molecules
joined together by a condensation reaction.
Cellulose (beta-glucose – found in cell walls):
➢ Made up of repeating 1-4 β-glucose units which form long, unbranched
chains. A vast number of hydrogen bonds give cellulose its tensile strength.
○ Group of cellulose molecules → microfibrils → fibres.
Lipids
➢ Roles of lipids:
○ Cell membranes and waterproofing
○ Energy sources (when oxidised, it gives off more energy)
○ Insulation and protection.
➢ Fatty acids and glycerol are combined by ester bonds – all fatty acids have a
long hydrocarbon chain (a folded backbone of carbon and hydrogen, with a
carboxyl (-COOH) group attached).
➢ A molecule of water is removed and an ester bond is made via
condensation/esterification reactions.
○ Fatty acids differ by the length of the carbon chain & whether or not it’s
saturated or unsaturated.
