Worried about your maternal effect or biological clock? Need to know a rhizoid from a rhizome? Think you're going to fail your zoology or botany exam? The Penguin Dictionary of Biology is your saviour, defining some 6000 terms relating to this rich, complex and constantly expanding subject - from amino acids, bacteria and the cell cycle to X-ray diffraction, Y chromosome and zygotes. Long established as the definitive single-volume source, this dictionary has sold over 200,000 copies and is extensively updated for its eleventh edition.