The second episode looks at the challenges of hunting in the Arctic, the most seasonal place on Earth. To a predator, seasonal change is a problem. It means that all the parameters of the hunt - the conditions, the strategies, the prey - change too. The only option for the Arctic's top predators, the wolf, the Arctic fox and the polar bear, is to continually adapt to their changing world, exploiting the good times and enduring the bad.

The stunning beauty of an island paradise on a quest to find the perfect wave-riding experience. Nine-time world surfing champion Kelly Slater and Tahitian surfer Raimana Van Bastolaer and a group of friends seek out the best waves breaking on the reef at Tahiti's famed surf site Teahupo'o. As their quest unfolds, the audience is plunged beneath the surface of things, to explore the hidden forces at work shaping ocean waves and the islands that lie in their path. Amidst playful surfing action, we navigate the cosmos and an ocean storm in a search for the source and nature of a wave's energy. Exploring mountainous Tahiti, we are thrust into the turbulent volcanic past of the island and its neighbours and discover the seagoing, wave-riding roots of the islanders themselves -- a culture still rich in the music, dance and lore of the sea. Beneath the ocean, swimming with our surfers, we explore the stunning, fragile beauty of the reef habitat -- a turbulent, wave-shaping interface that envelops the island and nurtures the ocean's multitudes in motion -- fish, dolphins, sharks and whales. When the truly big surf arrives at Teahupo'o, surfing play becomes surfing survival as the riders artfully tackle some of the heaviest surf on the planet -- spectacularly captured for the giant screen in 3D for the first time.

Push the limits of your imagination as astronomers attempt to grasp the mind-boggling extremes of size, distance and speed within our universe by bringing them down to earth. In this episode, our cast uses awesome analogies to bring the biggest objects, farthest distances and fastest speeds down to earth. To truly understand the scale of the cosmos, we jump behind the wheel of monster trucks, scale the Golden Gate Bridge, and race across the desert in a rocket-powered car.

Hunger at Sea follows blue whales, sharks, sea lions, frigatebirds, dolphins and albatrosses to reveal the strategies they use to hunt for prey in the big blue. The open ocean is an immense wilderness that covers more than half the surface of our planet, yet for the most part it's a watery desert, largely devoid of life. Predators face an endless search to find and catch food, yet these great tracts of ocean are home to some of the most remarkable hunters on the planet.

The fifth programme explores the alliances formed between the animal and plant worlds. Attenborough dives into Australia's Great Barrier Reef and contrasts the nocturnal feeding of coral, on microscopic creatures, with its daytime diet of algae. Some acacias are protected by ants, which will defend their refuge from any predator. Besides accommodation, the guards are rewarded with nectar and, from certain species, protein for their larvae as well. Fungi feed on plants but can also provide essential nutriment to saplings (Mycorrhiza). The connection is never broken throughout a tree's life and a quarter of the sugars and starches produced in its leaves is channelled back to its fungal partners. Meanwhile, fungi that feed on dead wood leave a hollow trunk, which also benefits the tree. Orchids enjoy a similar affiliation. Lichens are the product of a relationship between fungi and a photosynthetic associate, usually algae. They are extremely slow-growing, and a graveyard is the perfect location to discover their exact longevity. Mistletoe is a hemiparasite that obtains its moisture from a host tree, while using own leaves to manufacture food. Its seeds are deposited on another by the mistletoe tyrannulet, following digestion of the fruit. The dodder (Cuscuta) is also parasitic, generally favouring nettles, and siphons its nourishment through periodic 'plugs' along its stem. The rafflesia has no stem or leaves and only emerges from its host in order to bloom — and it produces the largest single flower: one metre across.

The Sea of Cortez, also known as the Gulf of California, is a unique corner of the Pacific Ocean. This remarkable young sea is thought to be around five million years old and home to nearly 900 species of fish and the widest variety of whales and dolphins found anywhere on Earth. Some of the greatest changes threatening the world's oceans today can be seen in this stretch of water.