Outline the thermal, cohesive and solvent properties of water.

Explain the role of the kidney in maintaining water balance in humans.

water has a high specific heat capacity;

a large amount of heat causes a small increase in temperature;

water has a high latent heat of vaporization;

a large amount of heat energy is needed to vaporize/evaporate water;

hydrogen bonds between water molecules make them cohesive/stick together;

this gives water a high surface tension / explains how water rises up xylem;

water molecules are polar;

this makes water a good solvent;

Award [4 max] if thermal, cohesive and solvent properties are not all mentioned.

process of water balance is called osmoregulation;

water passes into the kidney tubules by ultrafiltration;

water is reabsorbed in the proximal convoluted tubule;

water reabsorbed into blood from the (descending limb) of the loop of Henle;

process by osmosis;

transport of salts into the medulla of kidney;

changes salt concentration so water is reabsorbed;

ADH released into blood when water is required;

ADH causes concentrated urine / no/low ADH causes dilute urine;

this causes more reabsorption of water from the collecting duct;

excess water is released as urine;

urine concentration depends on the body’s need for water;

drinking a lot gives dilute urine;

Many candidates missed out on one of the thermal marks as they omitted the large specific heat capacity. Very few students failed to gain a mark in this section.

Only very few candidates scored full marks in this section. There were few correct mentions of ultrafiltration, and many some candidates who described it correctly were more determined to describe the reabsorption of glucose and salts rather than water. The role of ADH was well understood, although weaker candidates were confused as to its actual site of action.