Which is the largest terrestrial biome on the earth?

The correct answer is A, the north eastern coast of Australia. The Great Barrier Reef stretches for well over two thousand kilometres along the Queensland coast in the Coral Sea, off the north eastern shore of Australia, and is the largest structure on earth built by living organisms. It lies there because the conditions a reef needs are all present together: shallow water on a wide continental shelf, sea temperature that stays warm through the year, clear water that lets sunlight reach the algae living inside the coral polyps, and normal salinity undisturbed by a great river. Option B is wrong because the western coast faces the cool waters of the Indian Ocean and carries only small fringing reefs. Option C is wrong because the northern coast is muddied by river discharge into the Arafura Sea. Option D is wrong because the southern coast lies in cooler temperate latitudes where reef building corals cannot grow. Remember also that reefs are called the rainforests of the sea.

The correct answer is D, Kyushu Island of Japan. Kyushu is one of the four main islands of the Japanese archipelago and is of volcanic origin, built by the eruptions of an island arc where one plate dives beneath another; Mount Aso on it has one of the largest volcanic calderas in the world. It is not a coral reef island at all. Option A is wrong as a choice because the Great Barrier Reef off the Queensland coast is the classic coral structure, the largest in the world. Option B is wrong because the Rainbow Reef of Fiji, in the Somosomo Strait, is a well known coral reef in the tropical Pacific. Option C is wrong because Swaraj Island, formerly called Havelock Island, lies in the Andaman group, where the islands are ringed by fringing coral reefs. The lesson to carry away is that tropical islands are built in two very different ways, by volcanic activity and by the slow growth of coral, and the question tests whether you can tell them apart.

The correct answer is D, the tropical savanna region. The savanna is a tropical grassland with tall coarse grass and scattered flat topped trees, and its wet season produces an enormous crop of grass. That grass supports the largest herds of grazing animals on earth, the zebra, the wildebeest, the giraffe and the antelope, and those herds in turn support the lion, the leopard and the cheetah. Because so many large mammals live there together, the savanna, especially in East Africa, is called the land of big game. Option A is wrong because the temperate grassland has short grass and has been ploughed for wheat so widely that it is called the granary of the world, and its large wild herds are long gone. Option B is wrong because the tropical monsoon region is known for deciduous forest and for rice cultivation under a seasonal rainfall regime. Option C is wrong because the hot desert has too little vegetation to feed large herds, and its animals are small and mostly nocturnal.

The correct answer is C, the Prairies. The temperate grassland is the same biome the world over, short nutritious grass with almost no tree, but each continent gives it a local name, and the pairs are asked directly in examinations. In North America, across the central United States and the Canadian plains, it is called the Prairies, and so much of it has been ploughed for wheat that the region is known as the granary of the world. Option A is wrong because the Pampas is the temperate grassland of Argentina and Uruguay in South America, famous for cattle ranching. Option B is wrong because the Steppes form the vast grassland belt of Eurasia, running from Ukraine across Central Asia. Option D is wrong because the Veld is the grassland of the plateau of South Africa. Complete the set with the Downs of Australia and the Canterbury of New Zealand, and keep the tropical grasslands separate: the Savanna of Africa, the Llanos and Campos of South America.

The correct answer is B, lichens. A bare rock offers no soil, almost no water and no shelter, and only an organism that can survive long spells of drying and can hold on to bare stone can settle there. A lichen is exactly that, a partnership of an alga and a fungus in which the fungus grips the rock and holds water while the alga makes food. Lichens also release weak acids that eat into the rock and, with their own dead remains, form the first thin film of soil. Option A is wrong because mosses follow the lichens; they need that first film of soil and more moisture than bare rock can give. Option C is wrong because grasses come later still, after the soil is deep enough to hold roots and water. Option D is wrong because shrubs belong to a late seral stage, shortly before the tree climax. The full xerarch sequence to remember is lichen, moss, herb and grass, shrub and finally forest, and the parallel hydrarch sequence begins with phytoplankton in water.