Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
1.What are the useful properties of water and why ? - CORRECT ANSWERS 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 ? - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS Breaks a bond between two molecules by the
addition of a molecule of water
,Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
Condensation - CORRECT ANSWERS Joins two molecules together with the
formation of a bond by the removal of a molecule of water
Polymer - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS Glucose and fructose
Maltose - CORRECT ANSWERS Glucose and glucose
Lactose - CORRECT ANSWERS Glucose and galactose
How do monosaccharides join together - CORRECT ANSWERS By condensation
to form a glycosidic bond between two monosaccharides and a disaccharide
and a molecule of water are formed
,Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
Disaccharide - CORRECT ANSWERS 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 -
CORRECT ANSWERS
Test for starch - CORRECT ANSWERS 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 - CORRECT ANSWERS Heat with Benedict's reagent
( blue) and if reducing sugar is present a brick red precipitate will form
Issues with the Benedict's test ? - CORRECT ANSWERS 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? - CORRECT ANSWERS 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 ? - CORRECT ANSWERS 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.
, Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
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 - CORRECT ANSWERS Three main types - starch , glycogen and
cellulose which are chains of many monomers of glucose formed in
condensation reactions.
Starch - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS 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
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
1.What are the useful properties of water and why ? - CORRECT ANSWERS 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 ? - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS Breaks a bond between two molecules by the
addition of a molecule of water
,Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
Condensation - CORRECT ANSWERS Joins two molecules together with the
formation of a bond by the removal of a molecule of water
Polymer - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS Glucose and fructose
Maltose - CORRECT ANSWERS Glucose and glucose
Lactose - CORRECT ANSWERS Glucose and galactose
How do monosaccharides join together - CORRECT ANSWERS By condensation
to form a glycosidic bond between two monosaccharides and a disaccharide
and a molecule of water are formed
,Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
Disaccharide - CORRECT ANSWERS 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 -
CORRECT ANSWERS
Test for starch - CORRECT ANSWERS 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 - CORRECT ANSWERS Heat with Benedict's reagent
( blue) and if reducing sugar is present a brick red precipitate will form
Issues with the Benedict's test ? - CORRECT ANSWERS 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? - CORRECT ANSWERS 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 ? - CORRECT ANSWERS 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.
, Aqa A Level Biology - Paper 3 (Synoptic) Questions And
Correct Detailed Answers 2024/2025 Best Exam Solution
Top Ranked To Score A+ For Success
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 - CORRECT ANSWERS Three main types - starch , glycogen and
cellulose which are chains of many monomers of glucose formed in
condensation reactions.
Starch - CORRECT ANSWERS 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 - CORRECT ANSWERS 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 - CORRECT ANSWERS 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
