There is no greater test for life than winter, as temperatures plummet to 70 below and winds reach 200kph. Darkness and ice extend across the polar regions and only a few remarkable survivors gamble on remaining. We join a female polar bear trekking into the Arctic mountains to give birth as the first blizzards arrive. Out on the frozen ocean, the entire world's population of spectacled eider ducks brave the winter in a giant ice hole kept open by ferocious currents. Arctic forests transform into a wonderland of frost and snow - the scene of a desperate and bloody battle between wolf and bison, but also where a remarkable alliance between raven and wolverine is made. Beneath the snow lies a magical world of winter survivors. Here tiny voles dodge the clutches of the great grey owl, but cannot escape the ultimate under-show predator - the least weasel. Midwinter and a male polar bear wanders alone across the dark, empty icescape. Below the snow, polar bear cubs begin life in an icy den while fantastical auroras light the night skies above. In Antarctica, we join male emperor penguins in their darkest hour, battling to protect precious eggs from fierce polar storms. Weddell seals escape to a hidden world of jewel-coloured corals and alien-looking creatures but frozen devastation follows as sinister ice stalactites reach down with deadly effect.

George Harrison first became known to the world as 'The Quiet Beatle', but there was far more to his life than simply being a part of The Beatles. This film explores the life and career of this seminal musician, philanthropist, film producer and amateur race car driver who grew to make his own mark on the world. Through his music, archival footage and the memories of friends and family, Harrison's deep spirituality and humanity are explored in his singular life as he took on artistic challenges and important causes as only he could. Directed by Martin Scorsese.

In the second episode, filmmaker Martin Scorsese examines the life of musician George Harrison, weaving together interviews, concert footage, home movies and photographs.

Schwalmstadt Maximum Security Prison in Germany. Locked up behind the walls of this 12th-century castle are 188 of Germany's worst offenders. The prison is a fortress surrounded by a moat, and houses dangerous criminals, many of whom attend intense therapy sessions.

A deconstruction of the Church of Scientology's claims through a combination of presenting a condensed history of Scientology and its founder, L. Ron Hubbard, how celebrities interact with the church, the stories of a number of ex-members, and the abuse and exploitation the ex-members described seeing and experiencing". The Church responded vehemently to the film, complaining to film critics about their reviews and denouncing the filmmakers and their interviewees. Directed by Alex Gibney, it is based on Lawrence Wright's book Going Clear: Scientology, Hollywood and the Prison of Belief (2013). Produced by HBO, the film premiered at the 2015 Sundance Film Festival

The second episode is about how plants gain their sustenance. Sunlight is one of the essential requirements if a seed is to germinate, and Attenborough highlights the cheese plant as an example whose young shoots head for the nearest tree trunk and then climb to the top of the forest canopy, developing its leaves en route. Using sunshine, air, water and a few minerals, the leaves are, in effect, the "factories" that produce food. However, some, such as the begonia, can thrive without much light. To gain moisture, plants typically use their roots to probe underground. Trees pump water up pipes that run inside their trunks, and Attenborough observes that a sycamore can do this at the rate of 450 litres an hour — in total silence. Too much rainfall can clog up a leaf's pores, and many have specially designed 'gutters' to cope with it. However, their biggest threat is from animals, and some require extreme methods of defence, such as spines, camouflage, or poison. Some can move quickly to deter predators: the mimosa can fold its leaves instantly when touched, and the Venus flytrap eats insects by closing its leaves around its prey when triggered. Another carnivorous plant is the trumpet pitcher that snares insects when they fall into its tubular leaves. Attenborough visits Borneo to see the largest pitcher of them all, Nepenthes rajah, whose traps contain up to two litres of water and have been known to kill small rodents.