O-LevelChemistryChemistry of the Environment5070/22 · Oct/Nov 2018 · Q710 Marks

Plants remove carbon dioxide from the air during photosynthesis.

(a)(i)Complete the equation for photosynthesis. .......... + .......... → C₆H₁₂O₆ + ........O₂[2]
(a)(ii)State two conditions required for photosynthesis to happen. 1. .......... 2. ..........[2]
(a)(iii)Explain how photosynthesis can provide a renewable energy source.[1]
(b)The structure of a simple sugar is shown. HO -[Square]- OH Starch is made by the polymerisation of simple sugars. During this polymerisation, water is formed.
(b)(i)What type of polymerisation occurs?[1]
(b)(ii)Draw the partial structure of starch. You must show at least two repeat units.[2]
(b)(iii)Name the process by which starch is converted into simple sugars.[1]
(c)The partial structure of poly(lactic acid) is shown. [Figure 7.1: A polymer chain showing repeating units of lactic acid linked by ester bonds: -O-CH(CH₃)-C(=O)-O-CH(CH₃)-C(=O)-O-CH(CH₃)-C(=O)-O-CH(CH₃)-C(=O)-] On the diagram, draw a ring around all of the atoms in one ester linkage.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[2] (a)(i) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (2)
[1] (a)(i) If 2 marks not scored, award one mark for correct formulae (1)
[1] (a)(ii) (sun)light (1)
[1] (a)(ii) chlorophyll (1)
[1] (a)(iii) glucose can be used to make a fuel / glucose (can be fermented) to make ethanol
[1] (b)(i) condensation
[2] (b)(ii) 2 or more units polymerised e.g. -O-[square]-O-[square]-O- (2)
[1] (b)(ii) If two marks not scored, award 1 mark for: -O – linking two squares / rectangles but no extension bonds
[1] (b)(iii) hydrolysis
[1] (c) ring around the COO group

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