Why do we need to keep replacing our cells?

John writes in wondering whether the 10,000 steps rule applies eqully to everyone, given the range of body types and fitness among the population. James Tytko wondered where the 10,000 number came from in the first place, and sought an answer to John's question with the help of Dr Raj Amarnani, Consultant in Sport, Exercise and Muscoskeletel Medicine... Like this podcast? Please help us by supporting the Naked Scientists

This time on Question of the Week, James Tytko is being given a mental work-out thanks to this listener question on muscle fatigue. We learn about the biological reactions which govern intense exercise from Andy Jones, Professor of Applied Physiology at the University of Exeter... Like this podcast? Please help us by supporting the Naked Scientists

Listener Krzysztof has written in to ask how skin is protected from potentially harmful UV radiation by sun cream products. To help him with the answer, James Tytko put in a call to Antony Young, Emeritus Professor of Experimental Photobiology at King's College London... Like this podcast? Please help us by supporting the Naked Scientists

Ian from Stockport has had a thought. If heat pumps transfer thermal energy from outside into our homes, will they counteract the relative heat of urban areas compared to the countryside? To get to the bottom of this energy enquiry, James Tytko asked for the expertise of Professor Bob Critoph, from the University of Warwick's School of Engineering. Like this podcast? Please help us by supporting the Naked Scientists

Bhavesh wants to know how guided missiles find their target. James Tytko took on his question with help from Dr David Galvao Wall, Head of the Air Platforms and Weapons Group at Cranfield University... Like this podcast? Please help us by supporting the Naked Scientists

In response to our programme celebrating 10 years since the first detection of gravitational waves, listeners got in touch with fascinating questions. Here, James Tytko takes on a couple, with help from Ben Allanach, Professor of Theoretical Physics at the University of Cambridge... Like this podcast? Please help us by supporting the Naked Scientists

Trent wants to know why trees of the same species, in the same geography, seem to change the colour of their leaves at different rates. He's even noticed differences on branches of the same tree! James Tytko sought to provide an answer, with help from Charles Shi, botanical horticulturalist at the Royal Botanic Gardens, Kew. Like this podcast? Please help us by supporting the Naked Scientists

Sva writes in, asking whether stories of snakes being tamed by human milk have any grounding in science. James Tytko took on the question with the help of herpetologist Fortunate Mafeta Phaka, and Angela Julian of the Amphibian and Reptiles Group of the UK. Like this podcast? Please help us by supporting the Naked Scientists

In some parts of the world, some groups will fire guns directly into the air in celebration. Mike wants to know what happens to these bullets, and if they have the potential to be dangerous. To help answer this question, James Tytko spoke with neurologists Yousef Hayder and Luis Rafael Moscote-Salazar... Like this podcast? Please help us by supporting the Naked Scientists

Maddie wants to know what a daring adventurer might find if they journeyed to the centre of one of our Solar System's gas giants: Juptier and Saturn. James Tytko took on her question, with the help of University of Cambridge astrophysicist, Xander Byrne. Like this podcast? Please help us by supporting the Naked Scientists