1.2 SystemsIB Environmental Systems and Societies HL: Subtopic test

1. 1
   A student seals a small garden of mosses, ferns and soil with its resident bacteria and fungi inside a large glass jar and places it on a windowsill. The jar is never opened or watered. Several years later the plants are still alive. Water evaporates from the soil, condenses on the glass and drips back down.

   (a)

   Which description of the sealed jar as a system is correct?

   [1 mark]

   • AOpen, because it exchanges energy and matter with its surroundings
   • BOpen, because it receives light
   • CClosed, because it exchanges energy but not matter with its surroundings
   • DClosed, because it exchanges neither energy nor matter with its surroundings

   (b)

   Which flow in the jar is a transformation rather than a transfer?

   [1 mark]

   • AWater dripping from the glass to the soil
   • BLight energy being converted to chemical energy in sugars by the plants
   • CHeat flowing out through the glass
   • DWater moving upwards through the roots of a fern

   (c)

   Explain why the plants in the sealed jar can survive for years without added nutrients.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Scientists studying the Arctic Ocean report that melting sea ice exposes dark open water. White ice reflects most incoming sunlight, but dark water absorbs most of it. The water warms, and the warmer water melts more ice. Some scientists warn that if ice cover falls below a certain level, the Arctic could shift quickly to a state with ice-free summers.

   (a)

   The effect of melting ice exposing dark water, which then leads to more melting, is an example of:

   [1 mark]

   • AA positive feedback loop
   • BA negative feedback loop
   • CA steady state
   • DAn emergent property

   (b)

   The level of ice cover at which the Arctic would shift quickly to a new state is best described as:

   [1 mark]

   • AA storage
   • BA resilience threshold in a closed system
   • CA model
   • DA tipping point

   (c)

   Distinguish between the sea-ice feedback loop and a negative feedback loop.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The Aral Sea in Central Asia was once one of the world's largest lakes. From the 1960s the rivers Amu Darya and Syr Darya, which fed it, were diverted to irrigate cotton fields. The lake's area fell from about 68 000 km² in 1960 to about 7 000 km² in 2015. Salinity rose sharply, the commercial fish species disappeared and the fishing industry collapsed. Exposed seabed became a salty, dusty desert.

   (a)

   Calculate the percentage decrease in the area of the Aral Sea between 1960 and 2015. Show your working.

   [3 marks]

   (b)

   Explain how human actions affected the resilience of the Aral Sea system.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Scientists studying the Amazon rainforest warn that it may be nearing a tipping point. Trees release water vapour by transpiration, and this helps to form the rain that falls on the forest. Large areas have been cleared for cattle ranching and soya. Some computer models predict that if deforestation passes a threshold, widespread parts of the forest could shift to a drier savanna.

   (a)

   Explain how positive feedback and a tipping point could lead to the loss of Amazon rainforest.

   [6 marks]

   (b)

   Evaluate the usefulness of computer models in predicting how the Amazon rainforest will respond to deforestation.

   [6 marks]

   Total for question 4: 12 marks

End of questions