Energy flow, pyramids and cyclesIB MYP Sciences: Subtopic test

1. 1
   In a lake in Uganda, the algae capture 5000 kJ of energy per square metre each year. Tiny animals called zooplankton eat the algae, and small fish eat the zooplankton.

   (a)

   Where does the energy captured by the algae originally come from?

   [1 mark]

   • AThe water in the lake
   • BThe zooplankton
   • CThe small fish
   • DThe Sun

   (b)

   Which is one way in which energy is lost from a food chain between one trophic level and the next?

   [1 mark]

   • AIt is destroyed when an animal eats its food
   • BIt is released as heat during respiration
   • CIt is turned into carbon dioxide that animals breathe in
   • DIt is stored as light inside the animal

   (c)

   Assume that 10 % of the energy is passed on at each trophic level. Calculate the energy available to the small fish per square metre each year.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A tree in a tropical forest in Costa Rica takes in carbon for decades as it grows. Eventually it dies and falls to the forest floor. Elsewhere in the world, the remains of ancient forests were buried millions of years ago and slowly turned into coal. Some of that coal is now burned in a power station.

   (a)

   Which process removes carbon dioxide from the air and builds the carbon into the tree?

   [1 mark]

   • APhotosynthesis
   • BRespiration
   • CCombustion
   • DDecomposition

   (b)

   Which process returns carbon from the coal to the atmosphere in the power station?

   [1 mark]

   • APhotosynthesis
   • BCondensation
   • CCombustion
   • DEvaporation

   (c)

   Describe how the carbon in the dead tree on the forest floor returns to the atmosphere.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An ecology class in Otago, New Zealand, studies a pasture. They collect all the organisms from several areas of 1 m², dry them and find the mean dry mass (biomass) per square metre. They find 1200 g of grass, 90 g of grasshoppers and 8 g of frogs. The grasshoppers eat the grass and the frogs eat the grasshoppers. The class wants to use the results to show how biomass changes along the food chain.

   (a)

   Calculate the percentage of the biomass of the grass that is found in the grasshoppers, and the percentage of the biomass of the grasshoppers that is found in the frogs. Comment on your answers.

   [3 marks]

   (b)

   Explain why the biomass is smaller at each trophic level and suggest one improvement to make the survey more reliable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A South American country earns much of its income by exporting beef from cattle that graze on grassland. The government is deciding whether to encourage farmers to use some of this land to grow soya and lentils, which people could eat directly. Some of the grassland is too dry or too steep to grow crops. Beef farming employs many people in the countryside and beef is part of the national food culture.

   (a)

   Explain why more people can be fed from an area of land that grows soya and lentils than from the same area used to raise cattle, and why food chains are usually short.

   [6 marks]

   (b)

   Discuss and evaluate the proposal to replace some beef farming with growing crops for people to eat.

   [6 marks]

   Total for question 4: 12 marks

End of questions