Human impact and conservationIB MYP Sciences: Subtopic test

1. 1
   In Borneo, a large area of tropical rainforest has been cleared so that palm oil plantations can be planted. Conservation scientists are recording what happens to the local ecosystem over the following ten years.

   (a)

   Which statement describes the effect of clearing the rainforest on the amount of carbon dioxide in the atmosphere?

   [1 mark]

   • ACarbon dioxide removal increases because fewer trees respire
   • BLess carbon dioxide is removed by photosynthesis, so more stays in the atmosphere
   • CCarbon dioxide levels fall because the soil absorbs it
   • DCarbon dioxide levels are not affected by the number of trees

   (b)

   Which is the main reason soil erosion increases after the trees are removed?

   [1 mark]

   • ATree roots grow deeper and loosen the soil
   • BLeaf litter increases and traps nutrients
   • CRainfall increases because trees are no longer present
   • DFewer roots bind the soil, so heavy rain washes it away

   (c)

   Explain why the population of orang-utans in the area is likely to fall after the forest is cleared.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Cane toads were brought to north-eastern Australia in 1935 to eat beetles that damaged sugar cane crops. The toads spread rapidly across the north of the country. They produce a poison, and native predators such as quolls that eat them often die.

   (a)

   What term describes an organism such as the cane toad that is brought into an area where it does not naturally live?

   [1 mark]

   • AIntroduced species
   • BEndangered species
   • CIndicator species
   • DNative species

   (b)

   Which is the most likely reason the cane toad population increased so quickly?

   [1 mark]

   • ANative predators ate large numbers of them
   • BThey competed poorly for food with native frogs
   • CThey had no natural predators or diseases in Australia to control their numbers
   • DThey could not reproduce in the new environment

   (c)

   Explain how the cane toads could cause the numbers of native species such as quolls to fall.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class in a school near Lake Victoria wants to find out how fertiliser run-off from farms affects a pond. They add different amounts of nitrate fertiliser to five identical tanks, each containing 2 dm³ of pond water. The tanks are kept in the same sunny window, and the students measure the percentage of the water surface covered by algae after 14 days.

   (a)

   State the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   The students' hypothesis was: 'As the amount of fertiliser increases, the algae cover increases, because nitrates are a nutrient that algae need to grow.' The algae cover after 14 days was 2% with no fertiliser, 12% with 5 mg, 31% with 10 mg and 58% with 20 mg. Evaluate whether the results support the hypothesis and suggest one improvement to the investigation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Coral reefs around a group of islands in Indonesia support local fishing communities and a growing tourism industry. In recent years fishers have caught more fish than the reef can replace, and the sea temperature has been rising. The government is considering creating a marine protected area where fishing is banned, and using satellites and drones to detect illegal fishing boats.

   (a)

   Explain how overfishing and rising sea temperature together could cause the coral reef ecosystem to decline.

   [6 marks]

   (b)

   Evaluate the government's plan to create a marine protected area and to use satellites and drones to detect illegal fishing. Discuss the benefits and drawbacks for the environment and for local people, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions