Neutrophils - members of the family of white blood cells which are involved in non-specific phagocytosis of bacteria and foreign material. Neutrophils are also called polymorphonuclear leucocytes (PMN) because of their multi-lobed nucleus. Neutrophils also release toxic enzymes, stored safely in their cy lasm as lysosomes and released in the presence of foreign proteins. These toxic enzymes may do more harm to the host tissues than the bacteria they were released to kill.

Niche - an opportunity which can be exploited in order to make a living or survive in an ecosystem.

Noma - a highly destructive and usually fatal infection of the teeth and jaws which is a progression of ANUG Only found in malnourished children. - also called cancrum oris.

Nucleic acids - occur as chains of nucleotides, either asDNA (two chains) or RNA(one chain) and make up the genetic material of a cell.

Nucleotides - are made up of three components, a pentose sugar (ribose or deoxyribose), a phosphate group and an organic base which may either be a purine ( adenine or guanine) or a pyrimidine ( cytosine thymine or uracil).This basic structure is found in many important cell molecules such as in ADP, ATP and coenzymes. Nucleotides also form the subunits from which nucleic acids (DNA and RNA)are built.

Nucleus a cell organelle which contains the chromosomes whose genes control the structure of proteins within the cell. The nucleus is also a term used to refer to the mass of nerve cell bodies connected by tracts of nerve fibres, which occur in the brain.