State the IUPAC name for leucine.

A mixture of amino acids is separated by gel electrophoresis at pH 6.0. The amino acids are then stained with ninhydrin.

(i) On the diagram below draw the relative positions of the following amino acids at the end of the process: Val, Asp, Lys and Thr.

(ii) Suggest why glycine and isoleucine separate slightly at pH 6.5.

Determine the number of different tripeptides that can be made from twenty different amino acids.

The fibrous protein keratin has a secondary structure with a helical arrangement.

(i) State the type of interaction responsible for holding the protein in this arrangement.

(ii) Identify the functional groups responsible for these interactions.

2-amino-4-methylpentanoic acid

Accept 4-methyl-2-aminopentanoic acid.

i

Lys on cathode side AND Asp on anode side
Val at origin AND Thr on anode side but closer to origin than Asp

Val and Thr need not overlap.
Accept any (reasonable) size and demarcation of position so long as position relative to origin is correct.
Accept crosses for spots.
Award [1 max] for any two correct.
Award [1 max] if net direction of spots is reversed.
Award [1 max] if the four points are in the correct order but not in a straight line.

ii

different sizes/molar masses/chain lengths «so move with different speeds»

«20³ =» 8000

i

hydrogen bonds

ii

carboxamide/amide/amido
OR
C=O AND N–H

Accept peptide.

State the raw materials and source of energy used in the process described above.

The structures of two molecules, X and Y, are shown below.

(i) Justify why both these molecules are carbohydrates.

(ii) Distinguish between these molecules in terms of their functional groups.

Amylose is an unbranched polysaccharide composed of repeating units of glucose.

(i) Draw the structure of the repeating unit of amylose. Use section 34 of the data booklet.

(ii) Amylose is a major component of starch. Corn starch can be used to make replacements for plastics derived from oil, especially for packaging. Discuss one potential advantage and one disadvantage of this use of starch.

CO₂ AND H₂O AND sun

Accept names.
Accept “sunlight/light/photons” instead of “sun”.

i

both have formula C_x(H₂O)_y
OR
both contain several OH/hydroxyl «groups» AND a C=O/carbonyl «group»

Accept “both have the formula C_nH_2nO_n /empirical formula CH₂O” but do not accept “both have same molecular formula/have formula C₃H₆O₃”.

Accept “aldehyde or ketone” for “carbonyl”.

ii

Accept “alkyl” for “R”.
Accept “X: aldose/aldehyde AND Y: ketose/ketone”.
Accept “CO” for “C=O”.

i

continuation bonds AND open O on either but not both ends

Brackets are not necessary for the mark.
Do not accept β-isomer.
Mark may be awarded if a polymer is shown but with the repeating unit clearly identified.
3-D representation is not required.

ii

Advantage:
Any one of:

biodegradable / break down naturally/by bacteria

Do not accept just “decompose easily”.

compostable

does not contribute to land-fill

renewable/sustainable resource

starch grains swell AND help break up plastic

lower greenhouse gas emissions

uses less fossil fuels than traditional plastics

less energy needed for production

Disadvantage:
Any one of:

land use «affects biodiversity/loss of habitat»

growing corn for plastics instead of food

«starch» breakdown can increase acidity of soil/compost

«starch» breakdown can produce methane «especially when buried»

sensitive to moisture/bacteria/acidic foods

«bioplastics sometimes» degrade quickly/before end of use

cannot be reused

poor mechanical strength

eutrophication

increased use of fertilizers/pesticides/phosphorus/nitrogen «has negative environmental effects»

Ignore any reference to cost.

Accept “prone to site explosions/fires” or “low heat resistance” for disadvantage.

Only award [1 max] if the same example is used for the advantage and disadvantage.

Fatty acids react with glycerol to form fats and oils. State the name of the chemical link formed in this reaction and the name of the other product.

The table below shows average figures for the percentage fatty acid composition of some common fats and oils.

(i) Deduce, with a reason, which fat or oil from the table above has the lowest iodine number.

(ii) Deduce, with a reason, which fat or oil from the table above is most likely to become rancid when exposed to the air.

(iii) The P/S index of a fat or oil is the ratio of polyunsaturated fat to saturated fat present. It is sometimes used to compare the relative health benefits of different lipids in the diet. Calculate the P/S index of beef fat and soybean oil.

(iv) Suggest why a P/S index of greater than 1 is considered beneficial to health.

(v) Cotton seed oil and corn oil have similar iodine numbers but the melting point of cotton seed oil is higher than that of corn oil. Suggest an explanation in terms of the structure and bonding in these two oils.

Name of the chemical link: ester/ethoxycarbonyl
AND
Name of the other product: water

Do not accept formulas.
Do not accept “esterification”

i
coconut oil AND lowest «percentage of» unsaturated fatty acids
OR
coconut oil AND smallest number of C=C bonds
OR
coconut oil AND highest «percentage of» saturated fatty acids
Accept “fats” for “fatty acids”.

ii
soybean oil AND highest «percentage of» polyunsaturated fatty acids
OR
soybean oil AND greatest number of C=C bonds
OR
soybean oil AND lowest «percentage of» saturated fatty acids
Accept “fats” for “fatty acids”.

iii
Beef fat: «P/S = $\frac{3}{59}$ = » 0.05
AND
Soybean oil: «P/S = $\frac{50+8}{14}$ =» 4.1

iv
«higher proportion of» polyunsaturated fatty acids decrease risk of atherosclerosis/heart disease/cardiovascular disease/CVD
OR
«higher proportion of» polyunsaturated fatty acids which are less likely to be deposited on the walls of arteries «than saturated fatty acids»

Accept converse arguments.

Accept correct arguments in terms of HDL and LDL but not in terms of “good” and “bad” cholesterol.

Accept “fats” for “fatty acids”.

v

Any two of:
cotton seed oil has «a higher proportion of» longer chain/greater molar mass fatty acids

molecules of cotton seed oil have greater surface area/have higher electron density

Accept “molecules of cotton seed oil are packed more closely/have more regular structure” for M2.

stronger London/dispersion/instantaneous induced dipole-induced dipole forces between chains in cotton seed oil

Accept converse arguments.

Accept “fats” for “fatty acids”.

Calculate the BMF if a $120 \mathrm{kg}$ shark consumes $1000$ mackerel in one year. Each mackerel weighs $1 \mathrm{kg}$ on average. The ${\left[\mathrm{X}\right]}_{\mathrm{mackerel}}=0.3 \mathrm{\mu g} \mathrm{X}$ per $\mathrm{kg}$ body weight. Assume chemical $\mathrm{X}$ remains in the shark’s body for two years.

Suggest, with a reason, if fat-soluble or water-soluble xenobiotics would have a larger BMF.

$«0.3 \mathrm{\mu g}\times 2000=»600«\mathrm{\mu g} \mathrm{X}»$ ✔

$«\frac{{\displaystyle \frac{600 \mathrm{\mu g}}{120 \mathrm{kg}}}}{0.3 \mathrm{\mu g} {\mathrm{kg}}^{-1}}=»17$ ✔

Award [2] for correct final answer.

M2 may also be correctly expressed to $1$ SF.

fat-soluble AND pass through lipid membranes/accumulate in cells/fatty tissues
OR
fat-soluble AND less easily excreted/metabolized ✔

Accept “water-soluble” only if an organometallic–protein interaction is mentioned.

Many candidates produced the correct answer for M1 but not as many fully scored. Students did not appear to understand the concept, and many missed the idea of 2 years in the calculation. Students should always clearly show their calculations so examiners can award marks throughout the question and potentially award ECF if possible. It is very difficult to do this when students do not show work clearly.

A well answered question although some did not give a reason.

Proteins are polymers of amino acids. A paper chromatogram of two amino acids, A1 and A2, is obtained using a non-polar solvent.

© International Baccalaureate Organization 2020.

Determine the ${\mathrm{R}}_{\mathrm{f}}$ value of A1.

Proteins are polymers of amino acids.

The mixture is composed of glycine, $\mathrm{Gly}$, and isoleucine, $\mathrm{Ile}$. Their structures can be found in section 33 of the data booklet.

Deduce, referring to relative affinities and ${\mathrm{R}}_{\mathrm{f}}$, the identity of A1.

Proteins are polymers of amino acids.

Glycine is one of the amino acids in the primary structure of hemoglobin.

State the type of bonding responsible for the α-helix in the secondary structure.

Proteins are polymers of amino acids.

Describe how the tertiary structure differs from the quaternary structure in hemoglobin.

$0.70$ ✔

Accept any value within the range “$\mathit{0}\mathit{.}\mathit{67}\mathit{-}\mathit{0}\mathit{.}\mathit{73}$”.

Ile AND larger R_f ✔

more soluble in non-polar solvent «mobile phase»
OR
not as attracted to polar «stationary» phase ✔

Only award M2 if Ile is identified in M1.

hydrogen/$\mathrm{H}$ bonding «between amido hydrogen and carboxyl oxygen atoms» ✔

tertiary: folding/shape of a single «polypeptide/protein» chain ✔

quaternary: arrangement/folding of four/several chains/proteins/polypeptides «held together by $\mathrm{IMF}$» ✔

Accept “two or more polypeptides” for M2.

Many students scored this mark. The students who missed this mark that were close either measured from the top or bottom of the spot rather than the middle. A few students had answers that were greater than 1 which indicated a clear lack of understanding of this concept.

Not well answered. Many candidates referred to glycine even when they had obtained the correct R_f value in 5a. Answers referring to Molar mass and isoelectric point were quite common. Some candidates that identified Ile correctly lost the first mark as didn't make any reference to the R_f. There was a clear lack of understanding that the Rf value was related to polarity not molar mass.

A well answered question.

Many candidates didn't understand the question and provided long answers referring to the interactions but failing to identify those took place within the same/one chain. More candidates were able to score the second mark referring to multiple chains.

The diverse functions of biological molecules depend on their structure and shape.

Classify vitamins A, C and D as either mainly fat- or water-soluble, using section 35 of the data booklet.

The diverse functions of biological molecules depend on their structure and shape.

Deduce the straight chain structure of deoxyribose from its ring structure drawn in section 34 of the data booklet.

The diverse functions of biological molecules depend on their structure and shape.

Sucrose is a disaccharide formed in the reaction of glucose with fructose.
Identify the reaction type and the newly formed functional group that joins the monosaccharide units in the product.

all three correct ✔

$–\mathrm{CH}2–$ must be placed next to $\mathrm{CHO}$ AND $2\mathrm{OH}$s on central carbons must be on same side (LHS or RHS) ✔

Accept crosses in place of $C$ on three middle carbons.

Reaction type:
condensation ✔

Accept “nucleophilic substitution/$S_N$” for M1.

Functional group:
acetal/ether/glycosidic «linkage» ✔

Accept “glycoside” for M2.

Only a few very weak candidates answered this one wrongly.

Very disappointing. I had only a few correct answers and the wrong ones very often showed no understanding at all. Some candidates drew ring structures even though a straight chain was requested.

Many candidates scored both marks here. Ether was the most common answer for M2 with some responding glycosidic.

Deduce the products of the hydrolysis of a non-substituted phospholipid, where ${\mathrm{R}}^1$ and ${\mathrm{R}}^2$ represent long alkyl chains.

A representation of a phospholipid bilayer cell membrane is shown:

© International Baccalaureate Organization 2020.

Identify the components of the phospholipid labelled A and B.

State the most significant intermolecular forces in the phospholipid in b(i).

Phospholipids help maintain cellular environments while fatty acid lipids have important roles in energy storage and electrical insulation. Discuss the structural properties of saturated fats needed for these roles.

glycerol ✔

both fatty acids AND phosphoric acid ✔

Accept either names OR structures.
Accept “long chain carboxylic acid” for “fatty acid”.

Penalize once only if an incorrect name is given for a correct structure or vice-versa.

A: phosphate/ionic group
AND
B: alkyl/hydrocarbon «chain» ✔

Accept "glycerol «fragment»" OR "glycerophosphate" OR “ester” for A.

Accept “fatty acid «tail»” for B.

Do not accept terms such as “polar head”, “non-polar tail”, “hydrophilic” OR “hydrophobic” for components alone.

Forces occurring between components labelled A:
hydrogen/$\mathrm{H}$ bonding
OR
ion–dipole
OR
ionic/electrostatic «repulsion and/or attraction» ✔

Accept “dipole-dipole” for M1.
Do not accept “van der Waals/vdW” for M1.

Forces occurring between components labelled B:
dispersion/London/instantaneous dipoles/temporary dipoles ✔

Accept “van der Waals/vdW” for M2.

Energy storage:
not water-soluble/no hydrogen/$\mathrm{H}$ bonding
OR
less oxidized/more reduced
OR
high energy stored in bonds
OR
high «negative» enthalpy of combustion/oxidation ✔

Accept “potential energy” for “stored energy”.

Electrical insulator:
no delocalized electrons/conjugation ✔

Not as well answered as expected. However, many candidates managed to score at least one point. Quite a few lost the only mark due to wrong linkage. Some students drew fatty acid structures with aldehydes or phosphoric acid with incorrect bond linkages in the structure (OH^-).

Mostly well answered. Weaker candidates used the terms hydrophobic (non-polar) tail and/or hydrophilic (polar) head and therefore lost the mark. Students are expected to know the names of these structures.

Many good answers. Those that failed to score often provided the inverted answer. Dipole-dipole was fairly common for M1 but VdW forces less so for M2.

Not well answered. In particular the first mark seemed particularly challenging for students. Even when at times wording wasn't enough to allow BOD for M2 it was evident the candidate had some idea but none for the first one. Non-polar allowed many students to score the second mark.

Deduce the straight chain structure of ribose from its ring structure drawn in section 34 of the data booklet.

Using the partial structure given, complete the structural formula of the molecule formed from the condensation of two cyclic $\alpha$-glucose molecules.

Constructing models that allow visualizations of the stereochemistry of carbohydrates is essential to understand their structural roles in cells.

Describe how Haworth projections help focus on the position of attached groups.

State one advantage of starch based polymers besides being biodegradable.

Biodegradable boxes made from polylactic acid, PLA, disintegrate when exposed to water.

State the formula of the product formed when water reacts with PLA.

All OH groups must be on the same side.

Accept structures with chiral carbon atoms shown as C or C* instead of crosses.

[1 mark]

Accept –O– in a straight line provided both H’s are above the plane.

[1 mark]

«allow» 3-D perspective of structures «of cyclic monosaccharide molecules»
OR
«show» cis/same side arrangement of «attached» groups
OR
«show» trans/opposite side arrangement of «attached» groups
OR
«make» carbon and hydrogen implicit

[1 mark]

abundant/renewable/allows use of «local» vegetation
OR
less use of fossil fuel/oil based plastics
OR
air permeable/better breathing of products
OR
«can be» mixed/blended with synthetic polymers

Do not accept answers related to biodegradable examples.

Ignore any reference to cost.

Accept “carbon neutral/do not contribute to global warming”.

Accept “require less energy to produce”.

Accept “do not produce toxic products”.

[1 mark]

HO–CH(CH₃)–COOH/CH₃CH(OH)COOH

Do not accept C₃H₆O₃.

Do not accept OH–CH(CH₃)–COOH.

[1 mark]

List the building blocks of triglycerides and carbohydrates.

The drain pipe of a kitchen sink can become clogged by fatty acids, such as linoleic acid, C₁₈H₃₂O₂, but not by the trisaccharide, raffinose, C₁₈H₃₂O₁₆, containing the same number of carbon atoms.

Explain why raffinose is far more water soluble than linoleic acid.

Solid fat triglycerides can also clog kitchen sink drains.

Explain how sodium hydroxide unblocks the drain.

The amount of proteins, fats and carbohydrates determine the energy content of foods.

Explain why linoleic acid, C₁₈H₃₂O₂, is a more efficient energy storage molecule than raffinose, C₁₈H₃₂O₁₆.

Triglycerides:
organic acid/fatty acid and glycerol/propane-1,2,3-triol

AND

Carbohydrates:
monosaccharides

Accept simple sugars.

[1 mark]

«water/aqueous solubility depends on forming many» H-bonds with water

raffinose has many hydroxyl/O–H/oxygen atoms/O «and forms many H-bonds» AND linoleic acid has few/one hydroxyl/O–H/oxygen atom/O/carboxyl group/ COOH/is largely non-polar «and cannot form many H-bonds»

Accept statement which implies comparison.

[2 marks]

«base» hydrolysis/saponification
OR
«produces glycerol and» soap/salt of the «fatty» acid

«products are» water soluble «and drain away»

Accept condensed formulas.

Accept non-balanced equation.

Accept “RCOONa”.

[2 marks]

linoleic acid/C₁₈H₃₂O₂ combustion/oxidation more exothermic «per mol»

linoleic acid/C₁₈H₃₂O₂ has lower proportion/number of O atoms
OR
linoleic acid/C₁₈H₃₂O₂ is less oxidized

Accept converse arguments.

[2 marks]

Identify the type of metabolic process that occurs in the hydrolysis of the peptide during digestion.

Identify the name of the amino acid that does not move under the influence of the applied voltage.

Deduce, giving a reason, which amino acid will develop closest to the negative electrode.

The breakdown of a dipeptide in the presence of peptidase was investigated between 18 °C and 43 °C. The results are shown below.

Comment on the rate of reaction at temperature X in terms of the enzyme’s active site.

The solubility of a vitamin depends on its structure.

Identify the vitamin given in section 35 of the data booklet that is the most soluble in water.

Pollution from heavy metal ions has become a health concern.

Outline how the presence of heavy metal ions decreases the action of enzymes.

Outline how lead ions could be removed from an individual suffering from lead poisoning.

catabolism/catabolic

[1 mark]

alanine

Do not accept ala.

[1 mark]

Lys/lysine

pH «buffer» < pI «Lys»
OR
buffer more acidic than Lys «at isoelectric point»
OR
«Lys» exists as 

OR

«Lys» charged positively/has +1/1+ «overall» charge «and moves to negative electrode»

Do not apply ECF from M1.

Accept converse argument.

Do not accept just “has H₃N⁺ group” for M2 (as H₃N⁺ is also present in zwitterion).

Do not penalize if COOH is given in the structure of lysine at pH 6 instead of COO^–.

[2 marks]

highest frequency of successful collisions between active site and substrate
OR
highest frequency of collisions between active site and substrate with sufficient energy/$E⩾E_{\text{a}}$ AND correct orientation/conformation
OR
optimal shape/conformation of the active site «that matches the substrate»
OR
best ability of the active site to bind «to the substrate»

Accept “number of collisions per unit time” for “frequency”.

Do not accept “all active sites are occupied”.

[1 mark]

ascorbic acid/vitamin C

[1 mark]

react/bind/chelate with enzyme
OR
disrupt ionic salt bridges
OR
affect shape of tertiary/quaternary structures
OR
precipitate enzymes
OR
break/disrupt disulfide bridges/bonds

Do not accept “changes shape of active site” by itself.

[1 mark]

«use of» host-guest chemistry
OR
chelation «therapy»

Accept specific medication/chelating agent such as EDTA, CaNa₂ EDTA, succimer, D-penicillamine, dimercaprol.

[1 mark]

Deduce the structural formula of the dipeptide Cys-Lys.

Identify the type of bond between two cysteine residues in the tertiary structure of a protein.

Deduce the structural formula of the predominant form of cysteine at pH 1.0.

A mixture of the three amino acids, cysteine, glutamine and lysine, was placed in the centre of a square plate covered in polyacrylamide gel. The gel was saturated with a buffer solution of pH 6.0. Electrodes were connected to opposite sides of the gel and a potential difference was applied.

Sketch lines on the diagram to show the relative positions of the three amino acids after electrophoresis.

correct order 

amide link

Accept CO–NH but not CO–HN for amide link.

Penalize incorrect bond linkages or missing hydrogens once only in 7 (a) and 7 (c).

[2 marks]

covalent

Accept “S-S/disulfide”.

[1 mark]

Penalize incorrect bond linkages or missing hydrogens once only in 7 (a) and 7 (c).

[1 mark]

Cys and Gln move to positive electrode AND Lys to negative electrode

Cys further to positive electrode than Gln

Do not penalize if lines are omitted or if different markings are given (eg, spots etc.), as long as relative positions are correctly indicated.

Accept Gln on original position indicated.

Award [1 max] for reverse order of amino acids.

[2 marks]

Glycerol is one product of the reaction. Identify the two other organic products.

Identify the type of reaction which occurs.

C₁₇H₃₁COONa 

[(CH₃)₃NCH₂CH₂OH]OH

Accept “NaC₁₇H₃₁COO”.

Accept “(CH₃)₃N⁺CH₂CH₂OH OR [(CH₃)₃NCH₂CH₂OH]⁺” if positive charge is shown.

Accept suitable names (eg, sodium linoleate, choline hydroxide etc.) OR correct molecular formulas.

[2 marks]

hydrolysis

Accept “nucleophilic substitution/displacement / S_N/S_N2 /saponification”.

Do not accept “acid hydrolysis”.

[1 mark]

Explain which one of these fatty acids has the highest boiling point.

10.0 g of sunflower oil reacts completely with 123 cm³ of 0.500 mol$$dm^–3 iodine solution. Calculate the iodine number of sunflower oil to the nearest whole number.

stearic acid AND chain has no kinks/more regular structure
OR
stearic acid AND it has straight chain
OR
stearic acid AND no C=C/carbon to carbon double bonds
OR
stearic acid AND saturated
OR
stearic acid AND chains pack more closely together

stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules»

Accept “stearic acid AND greater surface area/electron density”.

M2 can only be scored if stearic acid is correctly identified.

Accept “stronger intermolecular/van der Waals’/vdW forces”.

[2 marks]

«n(I₂) = 0.123 dm³ x 0.500 mol$$dm^–3 =» 0.0615 «mol»

«m(I₂) = 0.0615 mol x 253.8 g$$mol^–1 =» 15.6 «g»

«iodine number $=\frac{15.6\text{ g}\times 100}{10.0\text{ g}}$» = 156

Award [3] for correct final answer.

Iodine number must be a whole number.

Award [2 max] for 78.

[3 marks]

Identify the functional groups which are present in only one structure of glucose.

Sucrose is a disaccharide formed from $\alpha$-glucose and β-fructose.

Deduce the structural formula of sucrose.

Starch is a constituent of many plastics. Suggest one reason for including starch in plastics.

Suggest one of the challenges scientists face when scaling up the synthesis of a new compound.

Only in straight chain form:
carbonyl
OR
aldehyde

Only in ring structure:
hemiacetal

Accept functional group abbreviations (eg, CHO etc.). 

Accept “ether”.

[2 marks]

correct link between the two monosaccharides

Correct 1,4 beta link AND all bonds on the 2 carbons in the link required for mark.

Ignore any errors in the rest of the structure.

Penalize extra atoms on carbons in link.

[1 mark]

plastic «more» biodegradable/degrades into nontoxic products
OR
plastic can be produced using green technology/renewable resource
OR
reduces fossil fuel use/petrochemicals
OR
easily plasticized
OR
used to form thermoplasts

[1 mark]

minimize «negative» impact on environment
OR
minimize waste produced
OR
consider atom economy
OR
efficiency of synthetic process
OR
problems of side reactions/lower yields
OR
control temperature «inside large reactors»
OR
availability of starting/raw materials
OR
minimize energy costs
OR
value for money/cost effectiveness/cost of production

[1 mark]

Determine the empirical formula of linoleic acid.

The empirical formula of fructose is CH₂O. Suggest why linoleic acid releases more energy per gram than fructose.

State the type of reaction occurring during the titration.

Calculate the volume of iodine solution used to reach the end-point. 

Outline the importance of linoleic acid for human health.

C₉H₁₆O

ratio of oxygen to carbon in linoleic acid lower

OR

linoleic acid less oxidized

OR

linoleic acid more reduced

Accept “«average» oxidation state of carbon in linoleic acid is lower”.

«electrophilic» addition/A_E

OR

oxidation–reduction/redox

«$\frac{1.24\text{g}}{280.50\text{g}\text{mo}{\text{l}}^{-1}}$ =» 0.00442 «mol»

0.00884 mol of C=C

OR

ratio of linoleic acid : iodine = 1:2

«volume of I₂ solution = $\frac{0.00884\text{mol}}{0.300\text{mol}\text{d}{\text{m}}^{-3}}$ =» 0.0295 «dm³» / 29.5 «cm³»

Award [3] for correct final answer.

Any two of:

increases «ratio of» HDL «to LDL» cholesterol

OR

decreases LDL cholesterol «level»

removes plaque from/unblocks arteries

OR

decreases risk of heart disease

decreases risk of stroke «in the brain»

Accept "essential fatty acid".

Do not accept “bad cholesterol” for “LDL cholesterol” OR “good cholesterol” for “HDL cholesterol”.

Do not accept general answers such as “source of energy” OR “forms triglycerides” OR “regulates permeability of cell membranes” etc.

[Max 2 Marks]

Describe what is meant by a condensation reaction.

Draw the structure of galactose on the skeleton provided.

Explain how the inclusion of carbohydrates in plastics makes them biodegradable.

«reaction in which» two reactants/molecules/functional groups bond/react «to form a larger molecule/single main product»

small/tiny molecule

OR

H₂O formed

Accept formula or name of a specified small molecule other than water such as ammonia, ethanoic/acetic acid,
ethanol, hydrogen sulfide etc. for M2.

Do not accept just “molecule formed”.

Award [1 max] for an example giving an equation of a condensation reaction such as the formation of a disaccharide.

Accept “alpha” or “beta” form of galactose.

Any two of:

makes the plastic more hydrophilic/water soluble

carbohydrates are broken down/hydrolysed by bacteria/microorganisms

makes plastic more accessible to bacteria as holes/channels are created

OR

plastic of lower density is more permeable/susceptible to water/oxygen/heat/pressure

weakens intermolecular/London/dispersion/instantaneous induced dipole-induced dipole forces «between polymer chains in the plastic»

Accept “van der Waals/vdW” for “London” forces.

[Max 2 Marks]

Explain, at the molecular level, why vitamin D is soluble in fats. Use section 35 of the data booklet.

State one function of vitamin D in the body.

«mainly» hydrocarbon/non-polar «structure»

forms London/dispersion/instantaneous induced dipole-induced dipole forces «with fats»

Accept “forms van der Waals’/vdW forces”.

Award [1 max] for “contains only one OH/hydroxyl AND cannot form «enough» H-bonds”.

helps absorb calcium
OR
helps build bones
OR
helps keep bones healthy
OR
helps block the release of parathyroid hormone
OR
helps in muscle function
OR
helps immune system function
OR
cell growth
OR
reduction of inflammation
OR
protection from osteoporosis
OR
prevents rickets

Accept helps prevent colon/breast/prostate cancer.

Accept treat/prevent diabetes/heart disease/high blood pressure/multiple sclerosis.

Accept other correct answers.

State the specific type of linkage formed between α-glucose fragments in both maltose and amylose.

A person with diabetes suffering very low blood sugar (hypoglycaemia) may be advised to consume glucose immediately and then eat a small amount of starchy food such as a sandwich. Explain this advice in terms of the properties of glucose and starch.

«α-1,4-»glycosidic

Accept «α-1,4-»glycoside.

Accept “ether”.

[1 mark]

Glucose:

readily passes through intestine wall/dissolves in blood

OR

is immediately available for energy/respiration

OR

transported rapidly around body

Starch:

must be hydrolysed/broken down «into smaller molecules» first

[2 marks]

Explain the solubility of vitamins A and C using section 35 of the data booklet.

Vitamin A:

fat soluble/soluble in non-polar solvents AND non-polar/long hydrocarbon backbone/chain

Vitamin C:

water soluble AND contains 4 hydroxyl groups/contains many hydroxyl groups/forms «many» H-bonds with water

Accept “Vitamin A: fat soluble/soluble in non-polar solvents as it contains only one hydroxyl group whose H-bonds with water are not strong enough to overcome London/dispersion/vdW forces between Vitamin A molecules”.

Accept “lipid” for “fats”.

Accept “alcohol” OR “hydroxy” OR “OH groups” for “hydroxyl” but not “hydroxide”.

Award [1 max] for “Vitamin A: fat soluble AND Vitamin C: water soluble” with no or incomplete explanation.

[2 marks]

Identify the type of chemical reaction that occurs between fatty acids and glycerol to form lipids and the by-product of the reaction.

Arachidonic acid is a polyunsaturated omega-6 fatty acid found in peanut oil.

Determine the number of carbon–carbon double bonds present if the iodine number for the compound is 334. (Arachidonic acid M_r = 304.5)

Deduce the structure of the lipid formed by the reaction between lauric acid and glycerol (propane-1,2,3-triol) using section 34 of the data booklet.

Outline one impact food labelling has had on the consumption of foods containing different types of lipids.

Determine, to the correct number of significant figures, the energy produced by the respiration of 29.9 g of C₅H₁₀O₅.

ΔH_c (C₅H₁₀O₅) = 205.9 kJ mol⁻¹

Explain why lipids provide more energy than carbohydrates and proteins.

Type of reaction:

condensation

OR

esterification/triesterification

OR

nucleophilic substitution/nucleophilic displacement/S_N2

By-product:

water/H₂O

Do not accept just “substitution/displacement”.

[2 marks]

ALTERNATIVE 1

«$\frac{334}{253.8}$ =» 1.32 AND «$\frac{100}{304.5}$ =» 0.328

«$\frac{1.32}{0.328}$ ≈» 4

ALTERNATIVE 2

«334 × $\frac{304.5}{100}$ ≈» 1017

«$\frac{1017}{253.8}$ ≈» 4

Award [2] for correct final answer.

[2 marks]

glycerol backbone

ester formula AND linkage

Accept a skeletal structure.

Penalize missing hydrogens or incorrect bond connectivities once only in Option B.

Accept condensed formula for ester.

[2 marks]

has affected consumption of trans-fats/cis-fats/saturated fats/unsaturated fats/hydrogenated/artificially altered fats

OR

reduce/eliminate trans-fats/increase in cis-fats

OR

reduce/eliminate saturated fats

OR

increase unsaturated fats

Do not accept “decrease in fat” alone.

Accept “lipid” for “fats”.

[1 mark]

«$\frac{29.9\text{ g}}{150.15\text{ g mo}{\text{l}}^{-1}}$ =» 0.199 «mol»

«0.199 mol × 205.9 kJ mol^–1 =» 41.0 «kJ»

Ignore significant figures in M1.

Award [2] for correct final answer.

Award [1 max] for incorrect significant figures in final answer.

[2 marks]

ratio of oxygen to carbon in lipids lower

OR

lipids less oxidized

OR

lipids more reduced

more energy per mass/g released when lipids are oxidized

Accept “«average» oxidation number of carbon in linoleic acid is lower” for M1.

[2 marks]

Identify the type of rancidity occurring in saturated lipids and the structural feature that causes it.

State one factor that increases the rate at which saturated lipids become rancid.

Butter contains varying proportions of oleic, myristic, palmitic and stearic acids. Explain in terms of their structures why stearic acid has a higher melting point than oleic acid, using section 34 of the data booklet.

Fish oil is an excellent dietary source of omega-3 fatty acids. Outline one impact on health of consuming omega-3 fatty acids.

Predict the solubility of retinol (vitamin A) in body fat, giving a reason. Use section 35 of the data booklet.

Explain why sharks and swordfish sometimes contain high concentrations of mercury and polychlorinated biphenyls (PCBs).

Plastics are another source of marine pollution. Outline one way in which plastics can be made more biodegradable.

hydrolytic «rancidity»

ester group

Accept a formula for ester group.

[2 marks]

«presence of» moisture/water

OR

«increase in» temperature

OR

«presence of» enzymes/bacteria/fungi/mould

OR

low pH/«presence of» acid

Accept “heat”.

[1 mark]

«stearic acid» straight chain/chain has no kinks/more regular structure

OR

«stearic acid» saturated/no «carbon–carbon» double bonds

«stearic acid» chains pack more closely together

stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules»

Accept “«stearic acid» greater surface area/electron density”.

[3 marks]

lowers risk of heart disease/atherosclerosis

OR

lowers LDL cholesterol

OR

increases HDL cholesterol

OR

aids brain/neurological development «in children»

OR

relieves rheumatoid arthritis

[1 mark]

soluble AND non-polar hydrocarbon chain

Accept as reasons “«predominantly» non-polar” OR “long hydrocarbon chain”.

[1 mark]

not biodegradable

OR

stored/accumulate in fat

biomagnification occurs

OR

concentration increases along food chain

Accept “stored/accumulate in bodies of prey/animals eaten”.

Accept “not excreted”.

[2 marks]

add starch/cellulose/carbohydrates/additives/catalysts «to plastic during manufacture to allow digestion by micro-organisms»

OR

replace traditional plastics with polylactic acid/PLA-based ones

OR

blend traditional and polylactic acid/PLA-based plastics

Accept reference to biodegradable plastics other than PLA; for example polyhydroxyalkanoates (PHA), poly(butylene succinate) (PBS), polybutylene adipate terephthalate (PBAT) and polycaprolactone (PCL).

[1 mark]

Draw the structural formula of a dipeptide containing the residues of valine, Val, and asparagine, Asn, using section 33 of the data booklet.

Deduce the strongest intermolecular forces that would occur between the following amino acid residues in a protein chain.

State the name of the process used to break down the insulin protein into its constituent amino acids.

Outline how the amino acids may be identified from a paper chromatogram.

correct structures of Val AND Asn

correct amide link

[2 marks]

Phenylalanine and valine:

London/dispersion/instantaneous induced dipole-induced dipole forces

OR

permanent dipole-induced dipole «interactions»

Glutamine and asparagine:

hydrogen bonds

Do not accept dipole-dipole interactions.

[2 marks]

hydrolysis

[1 mark]

compare R_f with known amino acids

OR

compare distance moved with known amino acids

Accept “from R_f”.

[1 mark]

A phospholipid generally consists of two hydrophobic fatty acids and a hydrophilic group.

Fatty acids are products of the acidic hydrolysis of phospholipids. Deduce the names of the other two products.

The iodine number is the maximum mass of iodine that reacts with 100 g of an unsaturated compound.

Determine the iodine number of stearidonic acid, C₁₇H₂₇COOH.

State two functions of lipids in the body.

Outline one effect of increased levels of low-density lipoproteins in the blood.

phosphoric acid ✔

glycerol/propane-1,2,3-triol ✔

Do not accept formulas.

ALTERNATIVE 1:

4 C=C bonds/4 carbon to carbon double bonds ✔

mass of iodine per mole of acid = «4 × 253.80 g mol^–1 =» 1015.2 «g mol^–1» ✔

iodine number «= $\frac{1015.2\text{g}\text{mo}{\text{l}}^{-1}}{276.46\text{g}\text{mo}{\text{l}}^{-1}}\times 100$» = 367 ✔

ALTERNATIVE 2:

4 C=C bonds/4 carbon to carbon double bonds ✔

«$\frac{100\text{g}}{276.46\text{g}\text{mo}{\text{l}}^{-1}}\times 4$ =» 1.447 mol of I₂ «reacts with 100 g» ✔

iodine number «= 1.447 mol × 253.80 g mol^–1» = 367 ✔

Award [3] for correct final answer.

Any two of:

«structural» components of cell membranes ✔

energy storage/utilization ✔

«thermal/electrical» insulation ✔

transport «of lipid-soluble molecules» ✔

hormones/chemical messengers ✔

Accept other specific functions, such as “prostaglandin/cytokine/bile acid synthesis”, “cell differentiation/growth”, “myelination”, “storage of vitamins/biomolecules”, “signal transmission”, “protection/padding of organs”, “precursors/starting materials for the biosynthesis of other lipid”.

Any one of:

atherosclerosis/cholesterol deposition «in artery walls» ✔

heart/cardiovascular disease ✔

stroke ✔

Accept “arteries become blocked/walls become thicker”.

The formation of proteins from amino acids is an example of an anabolic reaction in the human body.

State the source of energy for such a synthetic reaction.

Suggest why it is advisable for those living in northerly or southerly latitudes (that is away from the equator) to take vitamin D supplements during the winter.

Explain how a xenobiotic is biomagnified.

catabolism «of food/nutrients»

OR

«cellular» respiration ✔

Accept “ATP” but not “burning of food/nutrients”.

not enough sunlight/UV light «for synthesis of vitamin D in the skin» ✔

cannot be metabolized/broken down

OR

not biodegradable

OR

accumulates in lipid/fat tissues ✔

increased concentration as one species feeds on another «in the food chain» ✔

Name the type of link between the two monosaccharide residues.

Outline how the two monomer structures, galactose and glucose, differ.

«1,4-»glycosidic ✔

Do not accept “glucosidic”.

H and OH are reversed/in different positions on C-4 ✔

C-4 must be specified.

Do not penalize if reference is made to H and OH above and below ring/in alpha and beta positions on C-4 incorrectly.

Suggest, in terms of its structure, why vitamin D is fat-soluble using section 35 of the data booklet.

«mostly» non-polar
OR
hydrocarbon backbone
OR
only 1 hydroxyl «group so mostly non-polar»

Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.

[1 mark]

Enzyme activity depends on many factors. Explain how pH change causes loss of activity of an enzyme.

conformation/shape altered

OR

active site altered

OR

tertiary structure altered

acidic/basic/ionizable/COOH/carboxyl/NH₂/amino groups in the R groups/side chains «react»

exchange/lose/gain protons/H⁺

ionic/H-bonds altered

Accept “substrate doesn't fit/fits poorly into active site” OR “enzyme denatures” for M1 but not “affects potential of
enzyme to form complex with substrate”.

Draw the dipeptide represented by the formula Ala-Gly using section 33 of the data booklet.

Deduce the number of ¹H NMR signals produced by the zwitterion form of alanine.

Outline why amino acids have high melting points.

peptide bond

order of amino acids

Accept zwitterion form of dipeptide.

Accept a condensed structural formula or a skeletal structure.

Penalize missing hydrogens or incorrect bond connectivities once only in Option B.

[2 marks]

3

[1 mark]

form zwitterions

«strong» ionic bonding

OR

«strong» ionic lattice

OR

«strong» electrostatic attraction/forces

Do not accept hydrogen bonding or IMFs for M2.

[2 mark]

Draw the structure of the repeating unit of starch and state the type of linkage formed between these units.

Type of linkage:

Formulate the equation for the complete hydrolysis of a starch molecule, (C₆H₁₀O₅)_n.

Calculate the energy released, in kJ g⁻¹, when 3.49 g of starch are completely combusted in a calorimeter, increasing the temperature of 975 g of water from 21.0 °C to 36.0 °C. Use section 1 of the data booklet.

Explain how the inclusion of starch in plastics makes them biodegradable.

continuation bonds AND -O- attached to just one end AND both H-atoms on end carbons must be on the same side  [✔]

Note: Square brackets not required.
Ignore “n” if given.
Mark may be awarded if a polymer is shown but with the repeating unit clearly identified.

Type of linkage:
glycosidic  [✔]

Note: Accept “ether”.

(C₆H₁₀O₅)_n(s) + nH₂O (l) → nC₆H₁₂O₆ (aq)  [✔]

Note: Accept “(n-1)H₂O”.

Do not award mark if “n” not included.

q = «mcΔT = 975 g × 4.18 J g^–1 K^–1 × 15.0 K =» 61 100 «J» / 61.1 «kJ»   [✔]

«heat per gram= $\frac{61.1\text{ kJ}}{\text{3}\text{.49 g}}$ =» 17.5 «kJ g^–1»  [✔]

Note: Award [2] for correct final answer.

Any two of:
carbohydrate grains swell/break plastic into smaller pieces  [✔]

inclusion of carbohydrate makes the plastic more hydrophilic/water soluble [✔]

carbohydrates are broken down/hydrolysed/digested by bacteria/micro-organisms [✔]

plastic becomes more accessible to bacteria as holes/channels are created in it [✔]

«presence of» carbohydrate weakens intermolecular/London/dispersion forces between polymer chains in the plastic [✔]

Note: Accept “starch” for “carbohydrate” throughout. Do not accept carbohydrates are broken down/hydrolyzed.

Hardly any students were able to draw the required repeating unit, but in contrast almost all knew that the monomers were joined by a glycosidic linkage.

It was very unusual to find a candidate who could give a correct equation for starch hydrolysis.

Nearly half the students correctly calculated the enthalpy change and some of these went on to find the value in kJ g^-1. The most common mistakes were to use the mass of starch rather than the mass of water and adding 273 to the temperature change.

Whilst many could quote from 7b, that starch undergoes hydrolysis, very few linked this to a biochemical mechanism. Other factors, relating to the reduction of intermolecular forces between the polymer chains were also rarely encountered.

The melting points of cocoa butter and coconut oil are 34 °C and 25 °C respectively.

Explain this in terms of their saturated fatty acid composition.

Fats contain triglycerides that are esters of glycerol and fatty acids. Deduce an equation for the acid hydrolysis of the following triglyceride.

The addition of partially hydrogenated cocoa butter to chocolate increases its melting point and the content of trans-fatty acids (trans-fats).

Outline two effects of trans-fatty acids on health.

coconut oil has higher content of lauric/short-chain «saturated» fatty acids
OR
cocoa butter has higher content of stearic/palmitic/longer chain «saturated» fatty acids [✔]

longer chain fatty acids have greater surface area/larger electron cloud  [✔]

stronger London/dispersion/instantaneous dipole-induced dipole forces «between triglycerides of longer chain saturated fatty acids»  [✔]

Note: Do not accept arguments that relate to the melting points of saturated and unsaturated fats.

correct products  [✔]

correctly balanced  [✔]

Any two of:
«increased risk of» coronary/heart disease  [✔]

«increased risk of» stroke [✔]

«increased risk of» atherosclerosis [✔]

«increased risk of type-2» diabetes [✔]

increase in LDL cholesterol [✔]

decrease in HDL cholesterol [✔]

«increased risk of» obesity [✔]

A classic instance of candidates answering the question they thought (or hoped?) they had been asked rather than the one that was asked. Almost all answers referred to the differing amounts of saturated and unsaturated fatty acids present, totally ignoring the fact that the question clearly stated “their saturated fatty acid composition”, where the relative lengths of the chains was the key point. Nevertheless some who went on to discuss the nature of the intermolecular forces between the chains gained some credit.

A disappointingly small number of candidates gained any marks for deducing the equation for the hydrolysis of the given lipid.

Almost all students were aware of negative health effects of trans-fats, though quite a few lost marks by just stating “cholesterol” without specifying HDL or LDL.

Draw a circle around the functional group formed between the amino acids and state its name.

Name: 

A mixture of phenylalanine and aspartic acid is separated by gel electrophoresis with a buffer of pH = 5.5.

Deduce their relative positions after electrophoresis, annotating them on the diagram. Use section 33 of the data booklet.

Name:
amide/amido/carboxamide  [✔]

Note: Accept “peptide bond/linkage”.

Phe: must be on the origin  [✔]

Asp: any position on the left/anode/+ side  [✔]

Many candidates correctly circled the bond between the amino acid residues, though in some cases their circle missed out key atoms. Many correctly identified it as a peptide or amide linkage.

Most candidates seemed to realise that phenylalanine would be neutral and hence unaffected by the field, but many failed to realise that the negative charge of the aspartic acid anion would cause it to move to the left, not the right.

Some proteins form an α-helix. State the name of another secondary protein structure.

Compare and contrast the bonding responsible for the two secondary structures.

One similarity:

One difference:

Explain why an increase in temperature reduces the rate of an enzyme-catalyzed reaction.

Suggest two reasons why oil decomposes faster at the surface of the ocean than at greater depth.

Oil spills can be treated with an enzyme mixture to speed up decomposition.

Outline one factor to be considered when assessing the greenness of an enzyme mixture.

β/beta pleated/sheet  [✔]

One similarity:
hydrogen bonding
OR
attractions between C=O and N–H  [✔]

One difference:
α-helix has hydrogen bonds between amino acid residues that are closer than β-pleated sheet
OR
H-bonds in α-helix parallel to helix axis AND perpendicular to sheet in β-pleated sheet
OR
α-helix has one strand AND β-pleated sheet has two «or more» strands
OR
α-helix is more elastic «since H-bonds can be broken easily» AND β-pleated sheet is less elastic «since H-bonds are difficult to break»  [✔]

Note: Accept a diagram which shows hydrogen bonding between O of C=O and H of NH groups for M1.

Accept “between carbonyl/amido/amide/carboxamide” but not “between amino/amine” for M1.

enzyme denatured/loss of 3-D structure/conformational change
OR
«interactions responsible for» tertiary/quaternary structures altered [✔]

shape of active site changes
OR
fewer substrate molecules fit into active sites  [✔]

Any two of:
surface water is warmer «so faster reaction rate»/more light/energy from the sun [✔]

more oxygen «for aerobic bacteria/oxidation of oil» [✔]

greater surface area [✔]

Any one of:
non-hazardous/toxic to the environment/living organisms [✔]

energy requirements «during production» [✔]

quantity/type of waste produced «during production»
OR
atom economy  [✔]

safety of process  [✔]

Note: Accept “use of solvents/toxic materials «during production»”.

Do not accept “more steps involved”.

This question was quite well answered with many scoring the mark although there were quite a few incorrect responses that answered “beta-helix” rather than “beta-pleated sheet”.

The similarity in bonding between the 2 types of secondary structures was answered well but the difference was not. Most students were not descriptive enough to receive the second mark or simply repeated the idea of proteins containing an alpha-helix and beta-pleated sheets rather than describing something different about them.

This was another question where most candidates received one mark for identifying that the enzyme will denature with an increase in temperature. However, many candidates did not continue with the explanation of the active site shape changing or substrate molecules not longer fitting into the active site.

While many candidates did receive two marks for this question some candidates only suggested one reason or repeated the same reason (for example - heat and energy from the sun) even though the question clearly asked for two reasons.

Students tend to struggle with these questions and end up giving journalistic or vague answers that cannot be awarded marks. It is important for teachers to instruct students to give more specific answers directly related to the topics presented.

Deduce the structural formula of phosphatidylcholine.

Identify the type of reaction in (a).

Lecithin is a major component of cell membranes. Describe the structure of a cell membrane.

Predict, giving a reason, the relative energy density of a carbohydrate and a lipid of similar molar mass.

Lecithin aids the body’s absorption of vitamin E.

Suggest why vitamin E is fat-soluble.

Phospholipids are also found in lipoprotein structures.

Describe two effects of increased levels of low-density lipoprotein (LDL) on health.

phosphodiester correctly drawn  [✔]

both ester groups correctly drawn [✔]

Note: Accept protonated phosphate.

Accept phosphodiester in centre position.

condensation [✔]

Note: Accept “esterification”.

Accept “nucleophilic substitution/S_N”.

phospholipid bilayer/double layer
OR
two layers of phospholipids  [✔]

polar/hydrophilic heads facing aqueous environment AND non-polar/hydrophobic tails facing away from aqueous environment  [✔]

Note: Award [2] for a suitably labelled diagram.

Award [1 max] for a correct but unlabelled diagram.

Accept “polar/hydrophilic heads on outside AND non-polar/hydrophobic tails on inside for M2.

carbohydrates less energy dense AND carbohydrates higher ratio of oxygen to carbon/more oxidized/less reduced  [✔]

long non-polar/hydrocarbon chain «and only one hydroxyl group»
OR
forms London/dispersion/van der Waals/vdW interactions with fat  [✔]

Note: Accept “alcohol/hydroxy/OH” for “hydroxyl” but not “hydroxide”.

atherosclerosis/cholesterol deposition «in artery walls»  [✔]

increases risk of heart attack/stroke/cardiovascular disease/CHD  [✔]

Note: Accept “arteries become blocked/walls become thicker”, “increases blood pressure”, or “blood clots”.

Do not accept “high cholesterol”.

This was very poorly answered. Although the phosphodiester was a challenging mark it could be awarded in both the protonated and deprotonated form. The two esters should have been much more straight forward mark, and both were required to receive the second mark. Students struggled with proper structural drawings for both marks and many students simply left this question blank. The functional groups did need to be drawn out in their full structural form to receive the mark as indicated in the question.

This question was well answered.

This question was another one where the first mark was fairly well answered but the explanation or second mark was often not correct or complete.

This question was not well answered even though it has appeared on previous tests. In any cases the students did not give the relative energy density or the reason. It is important that candidates read question carefully and responds completely to each question as asked.

This question was also not answered well even though it has appeared on previous tests. Many students missed the idea of a long or large non-polar chain when describing the structure.

Students were required to state two effects of increased LDL. High cholesterol is not an accepted answer but still frequently seen. Many students also repeated similar answers that could not receive the same mark.

State the name of the functional group forming part of the ring structure of each monosaccharide unit.

Sketch the cyclic structures of the two monosaccharides which combine to form sucrose.

acetal
OR
ether  [✔]

Note: Accept “glycosidic bond/linkage” but not “glucosidic”.

Do not accept “hemiacetal”.

  [✔]

   [✔]

This was reasonably answered although there were some students who responded with ester or hemiacetal which is incorrect.

This question was very poorly answered. Many students lost marks due to sloppy drawing and incorrect bond linkages. Some students did not separate the two saccharides as instructed.

The graph shows the relationship between the temperature and the rate of an enzyme-catalysed reaction.

State one reason for the decrease in rate above the optimum temperature.

Explain why a change in pH affects the tertiary structure of an enzyme in solution.

State one use of enzymes in reducing environmental problems.

enzyme denatures
OR
change of conformation/shape of active site
OR
substrate cannot bind to active site/binds less efficiently ✔

NOTE: Accept “change in structure” or “substrate doesn't fit/fits poorly into active site”

Any two of:
acidic/basic/ionizable/COOH/carboxyl/NH₂/amino groups in the R groups/side chains «react» ✔
exchange/lose/gain protons/H⁺ ✔
change in H-bonds/ionic interactions/intermolecular forces/London dispersion forces ✔

NOTE: Do not accept “enzyme denatures” OR “change of conformation/tertiary structure” OR “substrate cannot bind to active site/binds less efficiently” as this was the answer to 8(a).

breakdown of oil spills/industrial/sewage waste/plastics
OR
production of alternate sources of energy «such as bio diesel»
OR
involve less toxic chemical pathway «in industry» ✔

NOTE: Accept “«enzymes in» biological detergents can improve energy efficiency”.

State the name of one functional group common to all three vitamins shown in section 35 of the data booklet.

Explain the biomagnification of the pesticide DDT.

Explain why maltose, C₁₂H₂₂O₁₁, is soluble in water.

hydroxyl ✔

NOTE: Accept “hydroxy” but not “hydroxide”.
Accept “alkenyl”.
Do not accept formula.

accumulates in fat/tissues/living organisms
OR
cannot be metabolized/does not break down «in living organisms»
OR
not excreted / excreted «very» slowly ✔

passes «unchanged» up the food chain
OR
increased concentration as one species feeds on another «up the food chain» ✔

NOTE: Accept “lipids” for “fat”.

«solubility depends on forming many» H-bonds with water ✔
maltose has many hydroxyl/OH/oxygen atom/O «and forms many H-bonds» ✔

NOTE: Reference to “with water” required.
Accept “hydroxy” for “hydroxyl” but not “hydroxide/OH^–”.
Reference to many/several OH groups/O atoms required for M2.

Draw the structure of the dipeptide Asp–Phe using section 33 of the data booklet.

The isoelectric point of amino acids is the intermediate pH at which an amino acid is electrically neutral.

Suggest why Asp and Phe have different isoelectric points.

amide link (eg, CONH) ✔

correct order and structures of amino acids ✔

NOTE: Accept a skeletal formula or a full or condensed structural formula.
Accept zwitterion form of dipeptide.
Accept CO–NH but not CO–HN for amide link.

«Asp isoelectric point lower than Phe and » Phe has a neutral/hydrocarbon side chain ✔
Asp side chain contains −COOH/carboxyl ✔

NOTE: Award [1 max] for “Asp has two carboxyl/−COOH groups and Phe has one carboxyl/−COOH group”.
Accept “Asp has an acidic side chain” for M2

The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.

State one impact on health of the increase in LDL cholesterol concentration in blood.

Explain why stearic acid has a higher melting point than oleic acid.

State one similarity and one difference in composition between phospholipids and triglycerides.

Similarity:

Difference:

Identify a reagent that hydrolyses triglycerides.

«one C=C bond»
«1 mole iodine : 1 mole oleic acid»

« $\frac{100\times 253.80}{282.46}$ =» 89.85 «g of I₂» ✔

NOTE: Accept “90 «g of I₂»”.

atherosclerosis/cholesterol deposition «in artery walls»/increases risk of heart attack/stroke/cardiovascular disease/CHD ✔

NOTE: Accept “arteries become blocked/walls become thicker”, “increases blood pressure”, OR “blood clots”.
Do not accept “high cholesterol” OR "obesity"

no kinks in chain/more regular structure
OR
straight chain
OR
no C=C/carbon to carbon double bonds
OR
saturated
OR
chains pack more closely together ✔

NOTE: Accept “greater surface area/electron density” for M1.

stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules» ✔

NOTE: Accept “stronger intermolecular/van der Waals’/vdW forces” for M2.

Similarity:

«derived from» propane-1,2,3-triol/glycerol/glycerin/glycerine

OR
«derived from» at least two fatty acids
OR
contains ester linkages
OR
long carbon chains ✔

NOTE: Do not accept “two fatty acids as both a similarity and a difference”.
Do not accept just “hydrocarbon/carbon chains”.

Difference:

phospholipids contain two fatty acids «condensed onto glycerol» AND triglycerides three
OR
phospholipids contain phosphate/phosphato «group»/residue of phosphoric acid AND triglycerides do not ✔

NOTE: Accept “phospholipids contain phosphorus AND triglycerides do not".
Accept “phospholipids are amphiphilic AND triglycerides are not” OR “phospholipids have hydrophobic tails and hydrophilic heads AND triglycerides do not”.

«concentrated» NaOH (aq)/sodium hydroxide
OR
«concentrated» HCl (aq)/hydrochloric acid
OR
enzymes/lipases ✔

NOTE: Accept other strong acids or bases.

Ascorbic acid and retinol are two important vitamins.

Explain why ascorbic acid is soluble in water and retinol is not. Use section 35 of the data booklet.

ascorbic acid: many hydroxyl/OH groups AND retinol: few/one hydroxyl/OH group
OR
ascorbic acid: many hydroxyl/OH groups AND retinol: long hydrocarbon chain  [✔]

ascorbic acid: «many» H-bond with water
OR
retinol: cannot «sufficiently» H-bond with water  [✔]

Note: Do not accept “OH⁻/hydroxide”.

Another instance where candidates insist on discussing water solubility in terms of polarity or hydrophilicity rather than its fundamental dependence on the presence of sufficient groups that can form hydrogen bonds to water. A few however gained a mark through pointing out the significance of the –OH groups in ascorbic acid and the long hydrocarbon chain in retinol.

Describe the interaction responsible for the secondary structure of a protein.

Explain the action of an enzyme and state one of its limitations.

Enzymes are widely used in washing detergents. Outline how they improve the efficiency of the process.

hydrogen bonding ✔

between C=O and H–N «groups» ✔

Accept a diagram which shows hydrogen bonding for M1 and which shows the interaction between O of C=O and H of NH groups for M2.

Accept “between amido/amide/carboxamide” but not “between amino/amine” for M2.

Enzyme action:

Any two of:

substrate binds to active site ✔

weakens bonds in substrate ✔

lowers activation energy

OR

provides alternate pathway ✔

increases rate of reaction

OR

acts as catalyst ✔

substrate specific ✔

Limitation:

Any one of:

temperature dependent ✔

pH dependent ✔

can be sensitive to heavy metal ions ✔

sensitive to denaturation ✔

can be inhibited ✔

substrate specific ✔

Accept “favourable orientation/conformation of the substrate «enforced by enzyme»” for M1.

Do not accept “substrate specific” as both an enzyme action and a limitation.

Any one of:

«increase rate of» hydrolyse/break down lipids/oils/fats/proteins ✔

«wash at» lower temperature/consume less energy ✔

Green Chemistry reduces the production of hazardous materials and chemical waste.

Outline two specific examples or technological processes of how Green Chemistry has accomplished this environmental impact.

Any two of:

replaces plastics with biodegradable/starch/cellulose based plastics

use enzymes instead of polluting detergents/phosphates

OR

use of enzymes means lower temperatures can be used

OR

use enzymes instead of emulsifiers to treat oil spills

OR

use enzymes to produce esters at lower temperatures/without sulfuric acid

replace organic/toxic solvents with carbon dioxide

replace polymers from fossil fuel with bamboo/renewable resources

develop paint resins reducing production of volatile compounds «when paint is applied»

industrial synthesis of ethanoic/acetic acid from methanol and carbon monoxide has 100% atom economy

energy recovery

Accept formulas for names.

Award mark for any other reasonable specific green chemistry example that prevents the release of pollutants/toxic chemicals into the environment by changing the method or the materials used.

Do not award mark for methods that involve clean-up of pollutants from the environment such as host-guest chemistry or alternative energy sources.

[2 marks]