Biological Compounds

These are needed in SMALL amounts! E.g.:

MAGNESIUM: in chlorophyll in leaves!

IRON: in haemoglobin in blood!

PHOPHATE: in plasma membrane, nucleic acids, ATP

CALCIUM: in bones and teeth

is essential as a medium for metabolic reactions.

It is a constituent of cells;

key elements are found in aqueous solution;

it provides a habitat for aquatic organisms.