2.4 Climate and biomesIB Environmental Systems and Societies HL: Subtopic test

1. 1
   A student compares climate records from two places at low altitude. Place P lies on the equator in the Congo Basin, with a mean temperature of about 25 °C in every month and rainfall of more than 1,500 mm per year. Place Q lies at about 25° N in the Sahara Desert, with a large daily temperature range and rainfall of under 100 mm per year.

   (a)

   In the tricellular model of atmospheric circulation, what happens to air at the equator?

   [1 mark]

   • AIt descends and warms, causing high pressure
   • BIt moves horizontally towards the poles at the surface
   • CIt cools and sinks after meeting cold polar air
   • DIt rises, cools and loses water vapour as rain, causing low pressure

   (b)

   Which is the main abiotic limiting factor for plants in the biome at Place Q?

   [1 mark]

   • AWater availability
   • BLight intensity
   • CNitrate concentration in the air
   • DMinimum winter temperature

   (c)

   Using the tricellular model, explain why Place Q receives much less rainfall than Place P.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In northern Alaska and Siberia, long-term records show that mean annual temperature has risen by more than the global average over recent decades. Shrubs and trees are growing in areas that were once treeless tundra, and the northern limit of the boreal forest, the treeline, is moving northwards. Tundra soils lie over permafrost and the growing season is short.

   (a)

   Which statement describes climate rather than weather?

   [1 mark]

   • AIt snowed heavily in a Siberian town on 3 October
   • BA cold front crossed Alaska last night
   • CThe mean July temperature of a town over 30 years is 12 °C
   • DWinds reached 80 km/h this afternoon

   (b)

   What is a biome?

   [1 mark]

   • AA single ecosystem in one place
   • BA group of comparable ecosystems that developed under similar climatic conditions, wherever they occur
   • CAll the organisms of one species in a region
   • DA region defined by political boundaries

   (c)

   Explain how global warming could cause the treeline to move northwards.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The Humboldt Current system off the coast of Peru is one of the most productive marine ecosystems and supports the anchoveta, the basis of one of the world's largest fisheries. In a normal year, trade winds blow from east to west across the tropical Pacific and cold, nutrient-rich water wells up near the coast. A fisheries agency reports that landings of anchoveta are about 5 million tonnes in a normal year but fall to about 1 million tonnes in a strong El Niño year (rounded, simplified figures for this question).

   (a)

   [HL] Calculate the percentage fall in anchoveta landings in the El Niño year and state one reason for the fall.

   [3 marks]

   (b)

   [HL] Explain how El Niño develops and why La Niña has the opposite effect on upwelling.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The Philippines is an archipelago between about 5° N and 19° N in the western Pacific. Its warm, wet climate would be expected to support tropical rainforest across most of the islands, yet only a small fraction of the original forest remains; much of the land has been cleared for rice, coconut plantations and settlements. Each year the islands are crossed by tropical cyclones that form over warm ocean to the east. In November 2013 Typhoon Haiyan, one of the strongest tropical cyclones recorded at landfall, struck the central Philippines.

   (a)

   [HL] Explain how tropical cyclones form and why global warming is expected to affect them.

   [6 marks]

   (b)

   [HL] Evaluate the extent to which climate alone determines the biome found in the Philippines.

   [6 marks]

   Total for question 4: 12 marks

End of questions