Adam reveals new research which overturns received wisdom about how sperm swim. More than three centuries after Antonie van Leeuwenhoek peered down his early microscope to observe human sperm or ‘animalcules’ swimming with a ‘snakelike movement, like eels in water’, high-tech observations now reveal that this was, in fact, an optical illusion.

Hermes Gadelha from Bristol University used 3D microscopy, a high-speed camera and mathematics, to reconstruct the true movement of the sperm tail. Much to his amazement, sperm have a highly sophisticated way of rolling as they swim. They do this to counter the numerous irregularities in their morphology which would otherwise send them swimming in circles. In doing so, they are able to propel themselves forwards. This highly complex set of movements, seen in 3D, is obscured in 2D when sperm appear to use a symmetrical eel-like motion to swim.

Also on the programme, Adam gets an update from Mark Miodownik on the Big Compost Experiment, the citizen science project that wants to know what you compost, how you do it and, most importantly, how quickly the stuff breaks down. Mark reveals how confused participants are, about what they can compost, and explains why items marked ‘compostable’ or biodegradable’ won’t compost at home.

PRODUCERS: Beth Eastwood & Fiona Roberts