Author: Philip Colls
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Biological molecules Booklet revision questions   NAME:
Q1. The diagram represents a triglyceride.

(a)     Name the molecules represented in the diagram by:
Box P _____________________________________________________________
Box Q ___________________________________________________________(2)
(b)     Name the type of bond between P and Q in he diagram.
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(1)
(c)     Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result.
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(Total 5 marks)
Q2. (a)     Describe how a peptide bond is formed between two amino acids to form a dipeptide.
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(b)     The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how.
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(c)     Two proteins have the same number and type of amino acids but different tertiary structures. Explain why.
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(Total 6 marks)
Q3.  (a)     Describe how you would use a biochemical test to show that a solution contained protein.
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The diagram shows the structure of two amino acid molecules, tyrosine and phenylalanine.
 
(b)     Copy from the diagram the R group in the phenylalanine molecule.

 
(1)
(c)     (i)      In the space below, draw the chemical bond formed when these two amino acids are joined by condensation. You need only draw the parts of the molecules shown in the box.

 

 
(2)
(ii)     Name this bond.
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(1)
(d)     Tyrosine can be made in the body by hydroxylating phenylalanine. Use the diagram to explain the meaning of hydroxylating.
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(Total 7 marks)
Q4. (a)     Name the monomers from which a maltose molecule is made.
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(b)     Name the type of chemical bond that joins the two monomers to form maltose.
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A student wanted to produce a dilution series of a maltose solution so he could plot a calibration curve. He had a stock solution of maltose of concentration 0.6 mol dm^−3 and distilled water. He made a series of dilutions from 0.1 to 0.6 mol dm^−3.
(c)     Complete the table below by giving all headings, units and the concentration of the maltose solution produced.

Concentration of maltose solution
/ ____________

Volume of 0.6 mol dm^−3 maltose solution / cm^3

_______________
______ / _______

____________ | 5 | 10
(2)
The student performed the Benedict’s test on six maltose solutions ranging from 0.1 mol dm^−3 to 0.6 mol dm^−3. He placed a sample of each solution in a colorimeter and recorded the light absorbance. His results are shown in the graph below.
 
(d)     Explain how you would use the graph to determine the maltose concentration with a light absorbance of 0.45 arbitrary units.
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(Total 6 marks)
Q5. (a)     The table shows some substances found in cells. Complete the table to show the properties of these substances. Put a tick in the box if the statement is correct.
 
| Substance
Statement | Starch | Glycogen | Deoxyribose | DNA helicase
Substance contains only the elements carbon, hydrogen and oxygen | | | |
Substance is made from amino acid monomers | | | |
Substance is found in both animal cells and plant cells | | | |
(4)
(b)     The diagram shows two molecules of β-glucose.
 
On the diagram, draw a box around the atoms that are removed when the two β-glucose molecules are joined by condensation.
(2)
(c)     (i)      Hydrogen bonds are important in cellulose molecules. Explain why.
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(ii)     A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.
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(Total 9 marks)
Q6.  (a)     Glycogen and cellulose are both carbohydrates. Describe two differences between the structure of a cellulose molecule and a glycogen molecule.
1. _________________________________________________________________
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2. _________________________________________________________________
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(b)     Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage molecule.
1. _________________________________________________________________
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2. _________________________________________________________________
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(c)     Tick (✔) the box that identifies the test which would be used to show the presence of starch.
 
Acid hydrolysis test |
Benedict’s test |
Emulsion test |
Iodine/potassium iodide test |
(1)
(d)     The diagram shows a section through a plant tissue at a magnification of ×500.
 
Calculate the actual diameter of the starch grain between points A and B.

Answer = ____________________ μm
(2)
(e)     What type of microscope was used to obtain the image shown in the diagram above?
Give one piece of evidence to support your answer.
Type of microscope _______________________________________________
Evidence ________________________________________________________
(2)
(Total 9 marks)

Q7. The diagram shows four biological molecules.
 
(a)     Give the full name of:
Molecule A _____________________________________________________
Molecule B ____________________________________________________(2)
(b)     What type of molecule is molecule C?
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(2)
(c)     Glycine, shown in the diagram, is an amino acid.
In the space below, draw a diagram to show the dipeptide produced when two molecules of glycine are joined together.
(2)
(d)     Name the other molecule formed when two molecules of glycine are joined together.
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(1)
(Total 7 marks)
Q8. Apple farmers want to harvest their fruit when it is ripe enough for eating but also when it can be stored to sell later.
One method apple farmers use to decide when to harvest their fruit is to determine the starch content. As apples ripen, starch in the apple is converted into soluble sugars that make them taste sweet.
Scientists investigated the best time to harvest apples for storage before being sold.
To determine the starch content, they picked samples of apples. They cut each apple in half and covered the cut surface with iodine solution. They left it for 1 minute and then compared it with the diagram below to give it a starch index score between 1 and 10.
 
They collected samples of apples at 5 different days during the ripening period and tested them for starch content. These results are shown in the table below.
 
When apples were collected / day during ripening period | Mean starch index
117 | 3.7
124 | 4.4
131 | 6.3
138 | 7.7
145 | 8.2
The scientists stored samples of apples from each collection day for 180 days. They then determined the percentage of apples that were rotten. These results are shown in the graph below.
 
(a)     The cut surface of the apple covered with iodine solution is left for 1 minute before being compared to Figure 1.
Explain why each apple must be left for the same length of time.
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(b)     Describe and explain the change in appearance of the cut surface of the apple when treated with iodine solution from underripe (starch index 1) to overripe (starch index 10).
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____________________________________________________(3) (Total 5 marks)

Mark schemes
Q1.
(a)     P – glycerol
Q – fatty acid (chains)
Accept phonetic spelling
2
(b)     Ester (bond);
1
(c)     1.      (Mix / shake sample) with ethanol, then water;
Sequence is important
2.      White / milky (emulsion);
Ignore cloudy
Reject precipitate
2
[5]
Q2.
(a)     1.      Condensation (reaction) / loss of water;
Accept each marking point if shown clearly in diagram.
2.      Between amine / NH_2 and carboxyl / COOH;
Accept between amino (group) and carboxylic / acid (group)
2
(b)     1.      Hydrogen bonds;
Accept as a diagram
Reject N - - - C / ionic / disulfide bridge / peptide bond
2.      Between NH (group of one amino acid) and C=O (group);
OR
Forming β pleated sheets / α helix;
2
(c)     1.      Different sequence of amino acids
OR
Different primary structure;
If candidate assumes proteins are the same, accept effect of different pH/ temperature
2.      Forms ionic / hydrogen / disulfide bonds in different places;
2
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Q3.
(a)     (i)      Biuret / alkali + copper sulphate;
Lilac / purple / mauve / violet;
Do not give credit for blue or pink. Ignore references to heating.
2
(b)     R group of phenylalanine copied accurately;
1
(c)     (i)      Bond shown linking carbon and nitrogen;
OH and H removed, =O and –H remaining;
2
(ii)     Peptide bond;
1
(d)     Addition of hydroxyl / OH group;
Candidate must distinguish clearly between hydroxylation and hydrolysis
1
[7]
Q4.
(a)     Glucose (and glucose);
1
(b)     (α1,4) Glycosidic;
1
(c)     1.      Headings correct – mol dm^–3 and volume of water / cm^3;
2.      Concentration correct. ie 0.2;
2
(d)     Line of best fit drawn;
Read off value at 0.45.
2
[6]
Q5.
(a)
One mark for each correct column
Mark ticks only and ignore crosses
4
(b)     1.      Two marks for box round two hydrogens and one of the oxygens from OH groups on carbons 1 and 4;;
2.      One mark from incorrect answer involving any two hydrogens and an oxygen from carbons 1 and 4;
Do not award marks if all atoms concerned are on same carbon atom or are on carbon atoms other than 1 and 4 or where the answer does not have two hydrogen and one oxygen
2
(c)     (i)      1.      Holds chains / cellulose molecules together / forms cross links between chains / cellulose molecules / forms microfibrils, providing strength / rigidity (to cellulose / cell wall);
2.      Hydrogen bonds strong in large numbers;x
Principles here are first mark for where hydrogen bonds are formed and second for a consequence of this.
Accept microfibres
2
(ii)     Compact / occupies small space / tightly packed;
Answer indicates depth required. Answers such as “good for storage”, “easily stored” or “small” are insufficient.
1
[9]
Q6.
(a)     1.      Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers);
2.      Cellulose molecule has straight chain and glycogen is branched;
3.      Cellulose molecule has straight chain and glycogen is coiled;
4.      glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds;
Ignore ref. to H bonds / microfibrils
2 max
(b)    Any two from:
1.      Insoluble (in water), so doesn’t affect water potential;
2.      Branched / coiled / (α-)helix, so makes molecule compact;
OR
Branched / coiled / (α-)helix so can fit many (molecules) in small area;
3.      Polymer of (α-)glucose so provides glucose for respiration;
4.      Branched / more ends for fast breakdown / enzyme action;
5.      Large (molecule), so can’t cross the cell membrane
Require feature and explanation for 1 mark
1.      Accept Ψ or WP
1.      Accept Insoluble so doesn’t affect osmosis
1.      Do not allow ref to ‘doesn’t affect water leaving cells
4.      Ignore ‘surface area’
4.      Accept ‘branched so glucose readily released’
2 max
(c)     Iodine/potassium iodide;
1
(d)     For correct answer of 40 (μm) award 2 marks;
Evidence of division by 500: award 1 mark
Allow tolerance of 0.5mm i.e. 20±0.5mm
2
(e)     1.      Scanning electron (microscope);
2.      3D (image);
Accept SE(M)
2.      Ignore any other correct features
2
[9]
Q7.
(a)     1.      A = β glucose;
B = Adenosine triphosphate;
do not accept ATP
2
(b)     1.      Saturated;
1
2.      Fatty acid;
1
(c)     1.      Peptide bond shown correctly;
2.      Rest of dipeptide structure shown correctly;
2
(d)      Water;
1
[7]
Q8.
(a)     1.      Allow equal (time for) diffusion of iodine into apple cells;
2.      For comparison between apples / between harvest dates;
1. Accept equal time for reaction / colour change to occur
2. For comparison alone is insufficient.
Ignore unqualified references to fair test, controlling a variable, standardising the method.
2
(b)     1.      Starch lost from the centre first / area with no starch gets bigger as it ripens;
2.      (Less starch / blue / black as the) starch is converted to sugars / maltose;
3.      (Less starch) as it is hydrolysed;
4.      By amylase;
Less starch as it is hydrolysed into sugars scores MP2 and MP3.
3. For ‘hydrolysed’ accept ‘as a result of hydrolysis’ or ‘broken down by hydrolysis’.
3 max
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