Medulla (oblongata): The part of the lower brain which controls involuntary activities, such as control of breathing and heart rate.

Meiosis: Cell division that shuffles the genes on the chromosomes so that no two gametes are the same. Has two divisions, so a diploid cell gives rise to four haploid cells.

Messenger RNA [mRNA]: A mobile copy of a gene, a single strand of nucleotides which directs protein synthesis. Made in transcription, used in translation.

Mitosis: Normal cell division. One diploid cell gives rise to two identical diploid cells 

Monoculture: Growing the same crop on a large scale over several years.

Mutagen: An agent which causes mutation. e.g. ionising radiation, mustard gas

Myocardium: posh word for heart muscle.

Myogenic: the ability of heart muscle to beat on its own, without the stimulation of nerves. The word means ‘muscle originating’

Myoglobin: red pigment found in muscles. Essentially one quarter of a haemoglobin molecule. It has a higher affinity for oxygen than haemoglobin, so the curve is to the left. Its function is to store oxygen in the muscles, to allow aerobic respiration to continue for longer. More myoglobin = more stamina.