Planet Earth - Episode 05 (Deserts) (ATOM Study Guide)

Planet Earth is a BBC production with five episodes in the first series (episodes one through five) and six episodes in the second series (episodes six through eleven). Each episode examines a specific environment, focussing on key species or relationships in each habitat; the challenges they face; the behaviours they exhibit and the adaptations that enable them to survive. Recent advances in photography are used to achieve some spectacular 'first sights' – in particular, stabilised aerial photography gives us remarkable views of migrating animals and the techniques used by their predators to hunt them.

As the series examines pristine environments where possible, they are often extreme. These are the parts of the world where few humans have chosen to live as the climate and landscape is too challenging, too difficult and dangerous. The plants and animals that do survive here have made some spectacular adaptations in forms and behaviour to live in these far reaches of the planet.

The series is suitable for middle secondary students studying Science and SOSE, and for senior secondary students of Biology, Environmental Science and Geography.

Deserts cover a third of the world's land surface but they are very different in character. This episode starts in one of the most extreme, the Gobi Desert of Mongolia which lies in the rain shadow of the Himalayas. This is far from the common idea of desert, searing hot in summer and a freezing, dry landscape lightly dusted with snow in winter, it contains the last groups of wild bactrian camels which cruise the frigid slopes in search of food and mates.

From far above, we see the strange effects of the desert winds in the Sahara as the sand scours rocks into unearthly shapes. Old limestone seabeds are carved into isolated white blocks teetering on thin pedestals as huge sandstorms lasting for days chew away at them and blast the single-humped camels and other creatures that survive out there. In the Namib of southern Africa, monster sand dunes have been formed by the winds and elsewhere mountains are reduced to pyramids and spires before being erased completely.

Animals that live in hot and arid environments must adapt. Kangaroos seek shelter in the heat of the day but also must lick themselves to cool down or risk heat death. African fennec foxes come out of their burrows only at night as do many of their nocturnal prey species.

The driest desert is the Atacama region of Chile. No rain falls for up to fifty years but the coastal edge can support life, dependant on fog and dew from the ocean for water. So, unlike further inland, cactii may grow and guanacos graze. In the Sonora Desert of Arizona, the huge saguaro cactus acts as a reservoir for the infrequent rains and we see their pleated stems swell in time-lapse photography as they take up huge quantities of water from an infrequent shower. These cactii are flowering plants but their flowers open only at night as they are pollinated not by insects but by migrating bats that can make the journey using the nectar as fuel.

Nubian ibex, a wild goat with massive horns, fight for the right to breed in awesome head butting contests, the losers condemned to life on the margin as the group wander in search of boughs. Rainbow coloured flat lizards make their home by a watercourse to take advantage of the clouds of black flies that they catch with acrobatic leaps into the air. Elephants trek along dry watercourses in the Namib, digging up grass roots as they are more nutritious than the dry surface stems while small groups of lions survive by hunting the oryx when they come off the dunes to feed.

But it does rain in the desert sometimes. Flash floods fill the dry watercourses and the water soaking into the ground provides enough for flushes of green growth. Arid areas of Death Valley suddenly burst into bloom as short lived plants grow, flower and die in a few weeks – the seeds of these 'ephemerals' may have been waiting for up to a century for rain before they could germinate.

Nature responds to this spurt of growth with the most voracious eating machine on earth, the plague locust. We join the swarm as the hoppers feed up quickly, get their wings and take to the skies. Gliding downwind in a swarm up to forty kilometres wide and consuming every edible green morsel in their inexorable journey.