Nutrient cyclesIB MYP Biology: Mind map

Exam questions on Nutrient cycles

1. A pine forest in Finland takes in carbon dioxide from the air all summer. In autumn the needles and branches fall to the forest floor, where fungi and bacteria slowly break them down. Not far away, a power station burns coal to generate electricity.
   Explain how carbon in the carbon dioxide of the air can become part of a deer that feeds on the plants in the forest.2 marks
2. A farmer in Kenya grows maize for several years in the same field, and the yields fall each year because the soil runs short of nitrates. A neighbour grows beans (a legume) in the field every third year. Bean roots have small swellings called nodules that contain bacteria.
   Explain why growing beans in the field every third year helps the maize crop that follows.2 marks
3. A student investigates how temperature affects the speed at which decomposers break down dead leaves. She places 20 g of dried leaf litter and 100 g of moist soil in each of four sealed jars. She keeps the jars at 5 °C, 15 °C, 25 °C and 35 °C for four weeks, then measures the mass of leaf litter that remains. The percentage of the leaf mass lost was 2% at 5 °C, 9% at 15 °C, 21% at 25 °C and 12% at 35 °C.
   Identify the independent variable, the dependent variable and two control variables in this investigation.3 marks