| Date | November 2016 | Marks available | 3 | Reference code | 16N.3.sl.TZ0.9 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Discuss and Draw | Question number | 9 | Adapted from | N/A |
Question
Carbohydrates are energy-rich molecules which can be synthesized in some plant cells from inorganic compounds.
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.
Markscheme
CO2 AND H2O AND sun
Accept names.
Accept “sunlight/light/photons” instead of “sun”.
i
both have formula Cx(H2O)y
OR
both contain several OH/hydroxyl «groups» AND a C=O/carbonyl «group»
Accept “both have the formula CnH2nOn /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.
