Junctional epithelium - the epithelium which seals the base of the gingival sulcus against the tooth.

Keratan sulphate - a glycosaminoglycan found in cartilage, with chondroitin sulphate.

Keratin - a fibrous polymer which is notas strong as collagen but less soluble. It forms the strong and water-resistant properties of skin, nails, hair, horn and beaks.

Keratinised - an epithelium in which the superficial cells have lost their nuclei and become filled with intermediate filaments ofkeratin.

Keratinocytes - Cells of the epidermis which secrete the protein keratin. They become progressively flattened as they mature and are eventually are off.

Kreb cycle - the end stage of aerobic respiration. Kreb's cycle is a circular series of reactions taking place in the matrix of mitochondria in which acetyl CoA is broken down into carbon dioxide and hydrogen atoms. The hydrogen atoms are used to produce ATP via the electron transport system.