AQA A Level Biology - Paper 3 (synoptic)
question with answers
What are the useful properties of water and why ? - -1) Water is a metabolite - in
many metabolic reactions including condensation and hydrolysis
2) Water is a solvent - medium in which enzyme catalysed reactions take place
(metabolic reactions ) and readily dissolves substances like inorganic ions ( as water
is dipolar so totally surrounds the ions) , excretory products (urea/ammonia) ,
respiratory gases and small hydrophilic molecules ( amino acids , etc)
3) Water has a high latent heat of vaporisation (lots of energy required to break
hydrogen bonds between water molecules so a lot of energy is used up when water
evaporates ) so helps with temperature control as evaporation of sweat cools
humans down
4) Water has a high specific heat capacity ( to separate the many hydrogen bonds
requires a lot of energy) so acts as a buffer and resists temperature changes to
maintain a constant internal body temperature
5) Water has large cohesive forces ( as hydrogen bonds stick together) so allows
transportation of substances( water travelling in columns in xylem) and means
water has a high surface tension when it comes into contact with air ( allowing pond
skaters to walk on its surface)
-Why is water dipolar ? - -As water is made up of two hydrogen atoms and one
oxygen atom , the hydrogen atoms have a slightly positive pole and the oxygen
atom has a slightly negative pole making water dipolar.
-Hydrogen bonds - -Slightly negatively charged oxygen atom is attracted to the
slightly positively charged hydrogen atom of other water molecules. The attraction
between opposite charges is called hydrogen bonding, which are weak bonds but
strong in large numbers. This makes water a major component in cells
-Hydrolysis - -Breaks a bond between two molecules by the addition of a molecule
of water
-Condensation - -Joins two molecules together with the formation of a bond by the
removal of a molecule of water
-Polymer - -A molecule ( carbohydrate, nucleotide or protein) made up of many
monomers ( small repeating units) joined together by condensation reactions and
broken down my hydrolysis
-Monosaccharides - -Are the monomers from which larger carbohydrates are made
and contain the elements C H and O. They are sweet and soluble and there are
three types : fructose , glucose and galactose. Hexose sugars (glucose) have the
formula C6H12O6
-Glucose is the product of photosynthesis and a major substrate of respiration ,
draw the two structural isomers of glucose in long and short hand and state the
,difference between them - -On carbon 1 in beta glucose the hydroxyl group (OH)
points upwards and in alpha glucose the hydroxyl group points down on carbon 1
-Sucrose - -Glucose and fructose
-Maltose - -Glucose and glucose
-Lactose - -Glucose and galactose
-How do monosaccharides join together - -By condensation to form a glycosidic
bond between two monosaccharides and a disaccharide and a molecule of water
are formed
-Disaccharide - -Two monosaccharides joined together by condensation forming a
glycosidic bond. There are three types : maltose, sucrose and lactose. They have
the chemical formula C12H22O11
-Draw the hydrolysis of maltose in structural formula and short hand formula - -
-Test for starch - -Add iodine solution to the test sample , if starch is present colour
changes from yellow to a blue-black colour.
-Test for a reducing sugar - -Heat with Benedict's reagent ( blue) and if reducing
sugar is present a brick red precipitate will form
-Issues with the Benedict's test ? - -1) It is non specific - doesn't tell which reducing
sugar is present , a biosensor can be used to detect for specific sugars
2) It's qualitative so colour change is being measured so can't obtain concentration
of reducing sugar but allows an estimate for how much is present in the strength of
the colour
3) Is subjective
-How to quantify results on the concentration of unknown glucose concentration? - -
Use a colorimeter, as a serial dilution of known glucose concentrations can be
measured producing a set of solutions with known concentrations . The Benedict's
test can be performed with each of these and the colour intensity measured. A
CALIBRATION CURVE can be produced from the results and used to read iff the
concentration of glucose in an unknown solution.
-Test for a non-reducing sugar ? - -Heat the sample with Benedict's reagent and if
there is no colour change a reducing sugar is not present but a non-reducing sugar
could be.
Heat a fresh sample with dilute acid ( which will hydrolyse the non reducing sugar
into its constituent monosaccharides).
Neutralise with alkali and carry out the Benedict's test again
If the test is positive for a non-reducing sugar it will form a brick red precipitate
-Polysaccharide - -Three main types - starch , glycogen and cellulose which are
chains of many monomers of glucose formed in condensation reactions.
, -Starch - -Starch is used for energy storage in plants and is made from
condensation of alpha glucose.
Amylose- compact helical chains so store lots of glucose in a small space
Amylopectin - branched chains which allow many ends to be quickly hydrolysed by
amylase enzymes to release glucose
Insoluble and large so no osmotic effects , inert and cannot diffuse out of the cells
which they are stored in .
-Cellulose - -Major component of plant cell walls made up of beta glucose monomer
in a condensation reaction.
Chains of beta glucose molecules form long straight unbranched chains.
These chains run parallel to each other and hydrogen bonds form cross-linkages
between chains. These many hydrogen bonds provide high tensile strength which
makes the cell wall rigid and prevents osmotic lysis
Hydrogen bonds also form strong fibres called microfibrils which are grouped into
fibres which provide structural support.
-Glycogen - -Energy storage molecule in animals found in liver cells and in muscle
tissue and is made from the condensation of alpha glucose.
Compact so store lots of glucose in a small space
Is quickly hydrolysed to release soluble glucose as many ends for amylase enzymes
to attack
Large and insoluble so no osmotic effects , inert and cannot diffuse out of the cells
which they are stored in .
-Name the 4 inorganic ions and state their role - -Inorganic ions occur in solution in
the cytoplasm and body fluids ( blood , tissue fluid)
Hydrogen ions - affects pH levels, the higher the concentration of H+ ions the lower
the pH( more acid )
Iron ions - important component of haemoglobin which carries oxygen around the
body in the red blood cells
Phosphate ions - component of DNA , ATP , RNA and phospholipids , bonds between
phosphate groups store energy in ATP
Sodium ions - involved in the absorption of glucose and amino acids in co transport
in the small intestine
-Amino acids - -Are the monomers from which polypeptides are made. Proteins are
made up of one or more polypeptide chains. All amino acids contain the elements C
H O and N and are made up of an amino group (NH2) , a carboxylic acid group
(COOH) and a variable group (R)
-What is a conjugated protein ? - -A protein with a non-protein chemical group
attached
-Draw the structure of an amino acid - -
-How many amino acids are there that are shared in all organisms ? - -20 amino
acids that differ by a different variable group.
, -Dipeptide - -Two amino acids join to form a dipeptide and a peptide bong is formed
between the amino acids by a condensation reaction.
-Draw the formation of a dipeptide from two amino acids? - -
-Describe the protein structure ? - -Primary structure - sequence of amino acids in a
polypeptide chain
Secondary structure - folding of polypeptide chain causing hydrogen bonds to form
between amino acids causing the formation of an alpha helix or a beta pleated
sheet
Tertiary structure - the further folding of the secondary structure which is held into
shape by bonds e.g. hydrogen, ionic and disulphide. Bonds form between R groups
of amino acids forming a 3D structure and is the final structure of one polypeptide
chain
Quaternary structure - is the final 3D structure of a protein consisting of more than
one polypeptide chain
-What are the two types of protein ? - -Fibrous- form long chains running parallel to
each other with cross bridges between chains producing very strong and stable
proteins such as collagen and keratin.
Globular - carry out metabolic functions such as enzymes, haemoglobin and
antibodies
-Collagen - -Primary structure - unbranched polypeptide chain
Secondary structure - forms alpha helix lots of amino acid glycine helps close
packaging
Tertiary structure - polypeptide chain is further folded
Quaternary structure - 3 polypeptide chains are wound together with covalent
bonds between amino acids of adjacent chains
This makes collagen strong and stable and is found in tendons which join muscle to
bong. Tendons need to be strong and not elastic.
-Test for proteins - -Add Biuret solution to a sample of solution , if protein is present
a lilac colour is seen from the blue colour of Biuret solution
-What method separates a mixture of monosaccharides or amino acids ? - -
Chromatography as molecules have different sizes so have different solubilities , the
smaller the molecule the further it will travel up the solvent and the more soluble
the molecule the further it will move up. Rf value must be calculated to allow
comparison between different chromatograms run with the same solvent.
-How do you work out the Rf value ? - -Distance from origin to solute (spot) over the
distance from origin to solvent front
-Why are enzymes biological catalysts ? - -As they lower amount of activation
energy needed to make the reaction proceed which increases the rate of the
chemical reaction
-Enzymes - -Are globular proteins in a spherical shape due to tight folding of the
polypeptide chain.
question with answers
What are the useful properties of water and why ? - -1) Water is a metabolite - in
many metabolic reactions including condensation and hydrolysis
2) Water is a solvent - medium in which enzyme catalysed reactions take place
(metabolic reactions ) and readily dissolves substances like inorganic ions ( as water
is dipolar so totally surrounds the ions) , excretory products (urea/ammonia) ,
respiratory gases and small hydrophilic molecules ( amino acids , etc)
3) Water has a high latent heat of vaporisation (lots of energy required to break
hydrogen bonds between water molecules so a lot of energy is used up when water
evaporates ) so helps with temperature control as evaporation of sweat cools
humans down
4) Water has a high specific heat capacity ( to separate the many hydrogen bonds
requires a lot of energy) so acts as a buffer and resists temperature changes to
maintain a constant internal body temperature
5) Water has large cohesive forces ( as hydrogen bonds stick together) so allows
transportation of substances( water travelling in columns in xylem) and means
water has a high surface tension when it comes into contact with air ( allowing pond
skaters to walk on its surface)
-Why is water dipolar ? - -As water is made up of two hydrogen atoms and one
oxygen atom , the hydrogen atoms have a slightly positive pole and the oxygen
atom has a slightly negative pole making water dipolar.
-Hydrogen bonds - -Slightly negatively charged oxygen atom is attracted to the
slightly positively charged hydrogen atom of other water molecules. The attraction
between opposite charges is called hydrogen bonding, which are weak bonds but
strong in large numbers. This makes water a major component in cells
-Hydrolysis - -Breaks a bond between two molecules by the addition of a molecule
of water
-Condensation - -Joins two molecules together with the formation of a bond by the
removal of a molecule of water
-Polymer - -A molecule ( carbohydrate, nucleotide or protein) made up of many
monomers ( small repeating units) joined together by condensation reactions and
broken down my hydrolysis
-Monosaccharides - -Are the monomers from which larger carbohydrates are made
and contain the elements C H and O. They are sweet and soluble and there are
three types : fructose , glucose and galactose. Hexose sugars (glucose) have the
formula C6H12O6
-Glucose is the product of photosynthesis and a major substrate of respiration ,
draw the two structural isomers of glucose in long and short hand and state the
,difference between them - -On carbon 1 in beta glucose the hydroxyl group (OH)
points upwards and in alpha glucose the hydroxyl group points down on carbon 1
-Sucrose - -Glucose and fructose
-Maltose - -Glucose and glucose
-Lactose - -Glucose and galactose
-How do monosaccharides join together - -By condensation to form a glycosidic
bond between two monosaccharides and a disaccharide and a molecule of water
are formed
-Disaccharide - -Two monosaccharides joined together by condensation forming a
glycosidic bond. There are three types : maltose, sucrose and lactose. They have
the chemical formula C12H22O11
-Draw the hydrolysis of maltose in structural formula and short hand formula - -
-Test for starch - -Add iodine solution to the test sample , if starch is present colour
changes from yellow to a blue-black colour.
-Test for a reducing sugar - -Heat with Benedict's reagent ( blue) and if reducing
sugar is present a brick red precipitate will form
-Issues with the Benedict's test ? - -1) It is non specific - doesn't tell which reducing
sugar is present , a biosensor can be used to detect for specific sugars
2) It's qualitative so colour change is being measured so can't obtain concentration
of reducing sugar but allows an estimate for how much is present in the strength of
the colour
3) Is subjective
-How to quantify results on the concentration of unknown glucose concentration? - -
Use a colorimeter, as a serial dilution of known glucose concentrations can be
measured producing a set of solutions with known concentrations . The Benedict's
test can be performed with each of these and the colour intensity measured. A
CALIBRATION CURVE can be produced from the results and used to read iff the
concentration of glucose in an unknown solution.
-Test for a non-reducing sugar ? - -Heat the sample with Benedict's reagent and if
there is no colour change a reducing sugar is not present but a non-reducing sugar
could be.
Heat a fresh sample with dilute acid ( which will hydrolyse the non reducing sugar
into its constituent monosaccharides).
Neutralise with alkali and carry out the Benedict's test again
If the test is positive for a non-reducing sugar it will form a brick red precipitate
-Polysaccharide - -Three main types - starch , glycogen and cellulose which are
chains of many monomers of glucose formed in condensation reactions.
, -Starch - -Starch is used for energy storage in plants and is made from
condensation of alpha glucose.
Amylose- compact helical chains so store lots of glucose in a small space
Amylopectin - branched chains which allow many ends to be quickly hydrolysed by
amylase enzymes to release glucose
Insoluble and large so no osmotic effects , inert and cannot diffuse out of the cells
which they are stored in .
-Cellulose - -Major component of plant cell walls made up of beta glucose monomer
in a condensation reaction.
Chains of beta glucose molecules form long straight unbranched chains.
These chains run parallel to each other and hydrogen bonds form cross-linkages
between chains. These many hydrogen bonds provide high tensile strength which
makes the cell wall rigid and prevents osmotic lysis
Hydrogen bonds also form strong fibres called microfibrils which are grouped into
fibres which provide structural support.
-Glycogen - -Energy storage molecule in animals found in liver cells and in muscle
tissue and is made from the condensation of alpha glucose.
Compact so store lots of glucose in a small space
Is quickly hydrolysed to release soluble glucose as many ends for amylase enzymes
to attack
Large and insoluble so no osmotic effects , inert and cannot diffuse out of the cells
which they are stored in .
-Name the 4 inorganic ions and state their role - -Inorganic ions occur in solution in
the cytoplasm and body fluids ( blood , tissue fluid)
Hydrogen ions - affects pH levels, the higher the concentration of H+ ions the lower
the pH( more acid )
Iron ions - important component of haemoglobin which carries oxygen around the
body in the red blood cells
Phosphate ions - component of DNA , ATP , RNA and phospholipids , bonds between
phosphate groups store energy in ATP
Sodium ions - involved in the absorption of glucose and amino acids in co transport
in the small intestine
-Amino acids - -Are the monomers from which polypeptides are made. Proteins are
made up of one or more polypeptide chains. All amino acids contain the elements C
H O and N and are made up of an amino group (NH2) , a carboxylic acid group
(COOH) and a variable group (R)
-What is a conjugated protein ? - -A protein with a non-protein chemical group
attached
-Draw the structure of an amino acid - -
-How many amino acids are there that are shared in all organisms ? - -20 amino
acids that differ by a different variable group.
, -Dipeptide - -Two amino acids join to form a dipeptide and a peptide bong is formed
between the amino acids by a condensation reaction.
-Draw the formation of a dipeptide from two amino acids? - -
-Describe the protein structure ? - -Primary structure - sequence of amino acids in a
polypeptide chain
Secondary structure - folding of polypeptide chain causing hydrogen bonds to form
between amino acids causing the formation of an alpha helix or a beta pleated
sheet
Tertiary structure - the further folding of the secondary structure which is held into
shape by bonds e.g. hydrogen, ionic and disulphide. Bonds form between R groups
of amino acids forming a 3D structure and is the final structure of one polypeptide
chain
Quaternary structure - is the final 3D structure of a protein consisting of more than
one polypeptide chain
-What are the two types of protein ? - -Fibrous- form long chains running parallel to
each other with cross bridges between chains producing very strong and stable
proteins such as collagen and keratin.
Globular - carry out metabolic functions such as enzymes, haemoglobin and
antibodies
-Collagen - -Primary structure - unbranched polypeptide chain
Secondary structure - forms alpha helix lots of amino acid glycine helps close
packaging
Tertiary structure - polypeptide chain is further folded
Quaternary structure - 3 polypeptide chains are wound together with covalent
bonds between amino acids of adjacent chains
This makes collagen strong and stable and is found in tendons which join muscle to
bong. Tendons need to be strong and not elastic.
-Test for proteins - -Add Biuret solution to a sample of solution , if protein is present
a lilac colour is seen from the blue colour of Biuret solution
-What method separates a mixture of monosaccharides or amino acids ? - -
Chromatography as molecules have different sizes so have different solubilities , the
smaller the molecule the further it will travel up the solvent and the more soluble
the molecule the further it will move up. Rf value must be calculated to allow
comparison between different chromatograms run with the same solvent.
-How do you work out the Rf value ? - -Distance from origin to solute (spot) over the
distance from origin to solvent front
-Why are enzymes biological catalysts ? - -As they lower amount of activation
energy needed to make the reaction proceed which increases the rate of the
chemical reaction
-Enzymes - -Are globular proteins in a spherical shape due to tight folding of the
polypeptide chain.
