Transfer of Energy & Matter (HL IB Biology)

Scientists investigated the production of high nutrient compost made from organic household waste.

The method they used was as follows:

1. Place waste in a large container for 125 days
2. Rotate the container each day
3. Record the temperature of the waste every 25 days
4. Remove samples of waste and test nutrient content

The temperature changes that they recorded were as follows:

Describe and explain what these data show about the processes occurring in the composter.

Explain the reason for step 2. in the method described in part a).

Nutrient content of the compost was measured at the start and the end of the process.

The results can be seen in the chart below.

Suggest reasons for the changes in carbon and nitrogen shown in the graph.

Tundra soils are mainly composed of peat that forms in the extreme cold conditions found within this ecosystem. Peat contains large amounts of carbon which is released when the tundra soils thaw during warmer seasons. Scientists investigated the amount of carbon released from tundra soils at one location, that were thawed to different extents over the course of three years. The results from this investigation can be seen in the graph below.

Explain why tundra soils act as a carbon store.

Calculate the difference in the mean carbon loss that occurred in tundra soils that were thawed considerably and those that were thawed slightly. Show your working.

Compare the rate of carbon release in moderately thawed soils with those in soils that were considerably thawed.

Evaluate this statement based on the investigation that was done.

The following data show fluxes in carbon between different storage reserves in an ecosystem, measured in gigatonnes per year (GT yr^-1). A gigatonne equals 1 billion tonnes.

Calculate the net flux of carbon. Show your working.

[2]

State the direction of this movement with regards to the atmosphere.

[1]

Explain how the combustion of fossil fuels can affect the carbon balance in the atmosphere.

Estimating global carbon fluxes are of great interest to scientists, even though it may be challenging to make accurate measurements.

Discuss the scientific importance of estimating carbon fluxes.

The amount of carbon in the atmosphere is constantly changing over time. Carbon dioxide and methane gases contribute to carbon levels in the atmosphere and have important impacts on the planet.

Discuss the importance of obtaining reliable data on the atmospheric concentration of these gases over time.

The diagram below shows a soil food web.

State the specific mode of nutrition used by the following organisms:

Draw a food chain that includes bacteria from the food web shown above

The longest food chain in the food web above contains 7 organisms. Explain why it is unusual to see food chains of this length.

One mark is available for clarity of communication throughout this question.

Outline the processes by which energy flows through ecosystems.

Some plants are parasitic, gaining their carbon compounds by tapping into the roots of other plants, for example. 

Explain how this mode of plant nutrition is unusual.

The graph below shows changes in atmospheric carbon dioxide levels between 1960-2010, recorded at Mauna Loa observatory, Hawaii.

Estimate the increase in average atmospheric carbon dioxide concentration between 1960 and 2000.

Suggest why yearly fluctuations occur in actual atmospheric carbon dioxide concentration, as seen in the graph in part (a) above.

In addition to collecting data on atmospheric carbon dioxide levels, scientists also collect data on average global temperatures. Both sets of data between the years 1000 and 2000 are shown together in the graph below.

Evaluate the claim that rising global temperatures are caused by rising atmospheric carbon dioxide levels.

State what the graph shows about the impact of human activities on atmospheric carbon dioxide levels and average global temperatures.  Note that the Industrial Revolution began in the mid-1700s.

One mark is available for clarity of communication throughout this question.

Draw a labelled diagram of the carbon cycle.