Draw a molecular diagram of alpha-D-glucose.

Outline how carbon compounds are produced in cells using light energy.

Explain the transformations of carbon compounds in the carbon cycle.

a. hexagonal ring structure with O at one point (between C1 and C5);

b. correct orientation of OH groups (on carbons 1 to 4); Hydrogens not required

c. CH₂OH group shown on fifth carbon with correct orientation;
OR
d. 6 carbon chain with oxygen on first C;

e. H and OH groups correctly orientated;

Carbons do not need to be numbered.

Allow boat or chair diagrams.

Allow [2 max] if linear structure drawn.

a. occurs by the process of photosynthesis;

b. occurs in chloroplasts of plant cells/using chlorophyll;

c. chlorophyll absorbs red/blue light AND reflects green light; Both needed for marking point.

d. raw materials/starting products are carbon dioxide and water/shown in an equation;

e. water is split by photolysis;

f. oxygen is produced as waste/by-product/lost;

g. glucose formed/shown in an equation;

h. glucose molecules combine to form starch for storage;

i. light energy transformed to chemical;

a. autotrophs/producers convert carbon dioxide into carbohydrates/carbon compounds in photosynthesis;

b. carbon dioxide diffuses/moves from the atmosphere /water into autotrophs/plants;

c. carbon compounds are transferred through food chains/OWTTE;

d. carbon dioxide produced by respiration diffuses out of organisms into water/atmosphere;

e. decomposers release carbon dioxide during decay/putrefaction;

f. methane is produced from organic matter in anaerobic conditions (by methanogens);

g. some methane diffuses into the atmosphere/accumulates in the ground;

h. methane is oxidized to carbon dioxide (and water) in the atmosphere;

i. peat forms when organic matter is not fully decomposed because of acidic/anaerobic conditions in waterlogged soils;

j. partially decomposed organic matter from past geological eras/fossils was converted into coal/oil/gas that accumulated in rocks;

k. carbon dioxide is produced by the combustion of biomass/fossilized organic matter/fuels;

i. hard parts of some animals/corals/molluscs are composed of calcium carbonate

m. can become fossilized in limestone;

As this is an “explain” question, simply drawing a labelled diagram is not enough for [7]. Diagram would need sufficient annotations to meet the command term.

If carbon compounds are referred to instead of carbon dioxide, penalise once then ecf.

This was the less favourite option question, generally attempted by the better candidates. In part (a) the candidates tended to gain either 3 for a correct structure or zero. A G2 comment asked whether the different forms of glucose were needed; knowledge of the structure of alpha-glucose is stated in the syllabus.

Most gained some marks for what was really a description of photosynthesis in part (b), and the transformations of carbon compounds in the carbon cycle was quite well known. Some students lost marks by continuing to use the term ‘carbon compounds’ instead of carbon dioxide and the specific compounds. Many went off on a tangent to write about carbon dioxide and climate change etc. Many drew some quite detailed flow charts of the carbon cycle from which some marks could be gleaned or ambiguous statements clarified.