Guest presented by Liz Bonnin.

We all instinctively know that sleep is incredibly important but science doesn’t actually have a satisfying answer for why we need to sleep. There are multiple theories, but now, new research from Imperial College London has suggested that the leading idea might actually be incorrect. Science journalist Ginny Smith explains.

Nearly 80 years ago, one of the rarest elements in the world, promethium, was first discovered, but it’s properties have only now been revealed. Andrea Sella, Professor of Chemistry at University College London, tells us what this means.

What’s the scariest animal on the planet? Lions, crocodiles, or maybe tigers might come to mind. Yet a recent study has found that animals around the globe fear our voices far more than sounds of any other predators. Professor Liana Zanette explains how her research could help conservation efforts.

Finally, we answer one of your questions. Listener Mary Evans got in touch to ask: ‘do you think it's likely that people who are widely travelled and used to eating local food and drinking tap water would have more diverse bacteria in their gut?’ Expert on all things microbiome, Megan Rossi, joins us in the studio to answer Mary’s query. If you have any questions you think we can tackle, you can always email us at insidescience@bbc.co.uk.

Presenter: Liz BonninProducers: Hannah Robins, Ella Hubber, Sophie OrmistonResearcher: Caitlin KennedyEditor: Martin Smith