State one role in living organisms for each of the following: sulfur, calcium, phosphorus and iron.

Outline the role of condensation and hydrolysis in the relationship between fatty acids, glycerol and triglycerides.

Explain the relationship between the properties of water and its uses in living organisms as a coolant, a medium for metabolic reactions and a transport medium.

sulfur: (structural element in some) amino acids/proteins/enzymes;
calcium: (structural element in) bones/teeth/shells / signal for cellular processes/ neurotransmitter release/muscle contraction/electrical conduction system of the heart/blood clotting;
phosphorus: (structural element in) ATP/DNA/RNA/phospholipids/bones;
iron: carries oxygen / formation of hemoglobin/myoglobin/cytochrome / cofactor of enzymes;

hydrolysis: [3 max]
when larger molecules are broken to smaller molecules/subunits;
with the addition of water;
fatty acids produced by the hydrolysis of fats/triglycerides;
breaking of ester bonds;
with release of glycerol;

condensation: [3 max]
when molecules/subunits are joined to form a larger molecule;
water formed/removed;
fatty acids linked to glycerol;
up to three fatty acids can be linked to each glycerol;
through formation of ester bonds;

water is a polar molecule;
oxygen has a partial negative charge / hydrogen has a partial positive charge;
hydrogen bonds form between adjacent water molecules;
water remains liquid over wide range of temperatures/0 to 100 °C ;
moderates temperature fluctuation / stable environment;
accurate reference to specific heat;
sweating/evaporation cools organisms;
accurate reference to high heat of vaporization;
polarity makes water a good/universal solvent for polar/ionic substances;
(all) metabolic reactions of cells take place in (aqueous) solutions;
blood/xylem/phloem transport solutes in water;
cohesive properties allow capillary action/transpiration stream/water column in xylem;

Stating a role for sulphur, calcium, phosphorus, and iron (A.S. 3.1.1) allowed candidates to easily gain four marks. Sulphur was slightly problematic because its structural role in amino acids or proteins or enzymes is somewhat abstract.  

The question required an outline of condensation and hydrolysis with reference to fatty acids, glycerol and triglycerides (A.S. 3.2.5). This was often done quite well. Some answers were accompanied by carefully annotated diagrams.  
 

This part had the poorest achievement among candidates. The polarity of water molecules with hydrogen bonding as the basis for many of its properties (A.S. 3.1.4, 3.1.5, 3.1.6) was either overlooked or inadequately explained. The concept of water providing a stable environment over a broad temperature range also challenged candidate understanding. However, as always, some candidates were totally competent in their answers which even integrated accurate reference to specific heat. Ideas about water as a solvent and transport medium, water as a medium for metabolic reactions and how cohesion properties in water relate to transpiration were scattered among candidate answers.