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Topic B: Biochemistry
For both SL and HL students
1a. [2 marks]
Proteins are polymers of amino acids.
The mixture is composed of glycine, Gly, and isoleucine, Ile. Their structures can be found in section 33 of the data booklet.
Deduce, referring to relative affinities and Rf, the identity of A1.

1b. [1 mark]
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.

1c. [2 marks]
Proteins are polymers of amino acids.
Describe how the tertiary structure differs from the quaternary structure in hemoglobin.


2a. [2 marks]
Biomagnification factor, BMF, can be defined as the concentration of a chemical, X, in a predator, relative to the concentration found in its prey.
BMF=XpredatorXprey, where X=(μg X per kg body weight)
[Franklin, J., 2015. How reliable are field-derived biomagnification factors and trophic magnification factors as
indicators of bioaccumulation potential? Conclusions from a case study on per- and polyfluoroalkyl substances.
Available at: https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.1642.]
 
Calculate the BMF if a 120 kg shark consumes 1000 mackerel in one year. Each mackerel weighs 1 kg on average. The Xmackerel=0.3 μg X per kg body weight. Assume chemical X remains in the shark’s body for two years.

2b. [1 mark]
Suggest, with a reason, if fat-soluble or water-soluble xenobiotics would have a larger BMF.

3a. [1 mark]
Vitamins are organic compounds essential in small amounts.
State the name of one functional group common to all three vitamins shown in section 35 of the data booklet.

3b. [2 marks]
Explain the biomagnification of the pesticide DDT.

3c. [2 marks]
Explain why maltose, C12H22O11, is soluble in water.
4a [2 marks]
Explain why a change in pH affects the tertiary structure of an enzyme in solution.

4b. [1 mark]
State one use of enzymes in reducing environmental problems.

5a. [1 mark]
Stearic acid (Mr = 284.47) and oleic acid (Mr = 282.46) have the same number of carbon atoms. The structures of both lipids are shown in section 34 of the data booklet.
The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.

5b. [1 mark]
State one impact on health of the increase in LDL cholesterol concentration in blood.

5c. [2 marks]
Explain why stearic acid has a higher melting point than oleic acid.

5d. [2 marks]
State one similarity and one difference in composition between phospholipids and triglycerides.
Similarity:
Difference:

5e. [1 mark]
Identify a reagent that hydrolyses triglycerides.

6. [2 marks]
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.

7a. [1 mark]
Formulate the equation for the complete hydrolysis of a starch molecule, (C6H10O5)n.

7b. [2 marks]
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.

7c. [2 marks]
Explain how the inclusion of starch in plastics makes them biodegradable.

7d. [1 mark]
Proteins have structural or enzyme functions.
Some proteins form an α-helix. State the name of another secondary protein structure.

8a. [2 marks]
Compare and contrast the bonding responsible for the two secondary structures.
One similarity:
One difference:


8b. [2 marks]
Explain why an increase in temperature reduces the rate of an enzyme-catalyzed reaction.

8c. [2 marks]
Oil spills are a major environmental problem.
Suggest two reasons why oil decomposes faster at the surface of the ocean than at greater depth.

8d. [1 mark]
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.

9a. [1 mark]
Dietary recommendations are made by scientists.
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.

9b. [1 mark]
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.

9c. [2 marks]
Explain how a xenobiotic is biomagnified.

10a. [2 marks]
Enzymes are mainly globular proteins.
Describe the interaction responsible for the secondary structure of a protein.

10b. [3 marks]
Explain the action of an enzyme and state one of its limitations.

10c. [1 mark]
Enzymes are widely used in washing detergents. Outline how they improve the efficiency of the process.

11a. [2 marks]
Saturated lipids found in butter and unsaturated lipids found in fish oil readily become rancid.
Identify the type of rancidity occurring in saturated lipids and the structural feature that causes it.

11b. [1 mark]
State one factor that increases the rate at which saturated lipids become rancid.

11c. [3 marks]
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.

11d. [1 mark]
Fish oil is an excellent dietary source of omega-3 fatty acids. Outline one impact on health of consuming omega-3 fatty acids.

11e. [1 mark]
Predict the solubility of retinol (vitamin A) in body fat, giving a reason. Use section 35 of the data booklet.
11f. [2 marks]
Explain why sharks and swordfish sometimes contain high concentrations of mercury and polychlorinated biphenyls (PCBs).
11g. [1 mark]
Plastics are another source of marine pollution. Outline one way in which plastics can be made more biodegradable.​​​​​​​
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page
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