Make solutions that are salty (salt in water), sour (lemon juice), sweet (sugar in water) and bitter (tonic water). Put drops of each one on different parts of the tongue to find out if all parts can detect salt and are equally sensitive.
Extend the KS2 experiment by making salt solutions of decreasing concentration. Find the weakest salt solution a student can detect.
Find out which part of the body sweats the most by sticking cobalt chloride paper to the skin and observing which piece changes colour first.
Read about the way the loops of Henle and the collecting ducts in the kidney help to regulate the salt and water balance of the blood.
Extend this by researching how the adrenal gland and other organs work together to maintain the internal environment of fish such as eel and salmon, which migrate from salty sea water to freshwater rivers.