Why astronauts would have to grow crops for Mars mission

Schoolchildren are beginning an experiment to grow seeds that have flown in space with British astronaut Tim Peake, alongside ones that remained on Earth.

They are attempting to find out whether the seedlings will be affected by the micro-gravity and radiation they encountered.

It is all because a long mission to Mars would entail astronauts growing crops, as BBC correspondent Pallab Ghosh explains.