IB Biology HL 4.2.15 Production, climate and ecosystem modelling Question Bank

Practise IB Biology HL 4.2.15 by analysing production equations and experimental evidence for climate effects.

[Maximum number: 6]

Remote sensing satellites are used to monitor the Earth's ecosystems. One measure of ecosystem status is leaf area index (LAI), which is the total area of leaves in square metres per square metre ( $\mathrm{m}^{2} \mathrm{~m}^{-2}$ ) of the Earth's surface. The graph shows LAI estimates, calculated using data from the Global Inventory Monitoring and Modelling System (GIMMS), during the period from 1981 to 2011. The data points are monthly averages in four latitudinal zones in the northern hemisphere.

Figure for Question C4.2.15—Primary production question 1 — IB Biology HL

(a)

The data in the graph show a long-term trend in global LAI.

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(i)

Global ecosystem modelling suggests that most of the change in LAI is due to increases in atmospheric carbon dioxide. Explain how rising atmospheric carbon dioxide ( $\mathrm{CO}_{2}$ ) concentration could cause the observed change in LAI.

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(b)

The 2015 Paris Agreement sets out an international framework for avoiding dangerous climate change. A key aspect is conserving and enhancing sinks of greenhouse gases, including forests.

Free air carbon dioxide enrichment (FACE) experiments are being used to investigate whether increases in atmospheric $\mathrm{CO}_{2}$ concentration will cause biomass increases in existing forests. Three FACE experiments have been running for at least ten years in young, developing forests. Photosynthesis rates are measured in 25 to 30 m diameter plots. In control plots, carbon dioxide concentrations remain at current atmospheric levels (ambient CO2). In treatment plots, the CO2 concentration is raised by 50 % (elevated $\mathrm{CO}_{2}$ ).

The table gives some details of these experiments and the highest annual net primary production recorded during the period of the experiment. Net primary production is the mass of carbon absorbed and fixed by photosynthesis in plants that is not released due to plant respiration.

State the effect of elevated $\mathrm{CO}_{2}$ on net primary production in these young, developing forests.

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(c)

In each forest, there are two or three trial plots per CO2 treatment. The bar chart shows the allocation of carbon from net primary production to different parts of the trees in these trial plots.

Evaluate the evidence from the bar chart that increases in carbon dioxide cause increases in carbon storage in young, developing forests.

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C4.2.15—Primary production question 1

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