Cycles within Ecosystems (Edexcel IGCSE Biology: Double Science)

The diagram shows a cycle found in ecosystems.

Give the name of the cycle.

In the image in part (a), which process is represented by the letter W?

In the image in part (a), which process is represented by the letter X?

Name a group of organisms that is responsible for decomposition.

Carbon dioxide is released into the atmosphere by the decomposition of organic material.

The rate of this decomposition depends on a number of factors.

Design an investigation to find out if changing the pH of organic material affects the rate of decomposition.

Include experimental details in your answer and write in full sentences.

The following table shows changes in atmospheric carbon dioxide levels over time.

Calculate the percentage increase in carbon dioxide concentration between 1960 and 2010. Give your answer to one decimal place.

Use the data provided in part (a) to plot a graph that shows the change in atmospheric carbon dioxide levels over time.

Use a ruler to join the points with straight lines.

Use your understanding of the carbon cycle to suggest how human activities are contributing to the trend shown in the data in parts (a) and (b).

'Carbon flux' is a term used to describe the transfer of carbon from one store to another in the carbon cycle.

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 difference between the amount of carbon entering the atmosphere and the amount of carbon leaving the atmosphere over the course of a year in this ecosystem.

(3)

The figure calculated in part (i) is known as the 'net flux' of carbon in the ecosystem; this refers to the overall direction of carbon transfer.

Explain why the net flux of carbon is important at a global level.

(2)

Explain why the combustion of fossil fuels can have a large impact on the carbon balance in the atmosphere.

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

Suggest why it is difficult to make accurate measurements when studying the transfer of carbon.

(2)

Suggest why estimating carbon fluxes is of such interest to scientists.

(2)