IB Biology SL 1.3.8 CO2 enrichment experiments Question Bank

Practise IB Biology SL 1.3.8 by interpreting CO2 enrichment data and separating carbon-dioxide effects from temperature when assessing plant growth.

[Maximum number: 2]

C1. Global atmospheric carbon dioxide levels are rising. A study was carried out to test if the temperature dependence of photosynthesis was altered by elevated atmospheric $\mathrm{CO}_{2}$ . Maize plants were grown in natural sunlight in controlled environmental chambers at different temperatures using current atmospheric and doubled $\mathrm{CO}_{2}$ levels.

The graph below shows daily patterns of $\mathrm{CO}_{2}$ exchange at three different temperatures. Open shapes ( $\mathrm{o}, \Delta, \mathrm{v}$ ) represent current atmospheric $\mathrm{CO}_{2}$ levels and closed shapes ( $\bullet, \mathbf{\Delta}, \mathbf{m}$ ) represent elevated $\mathrm{CO}_{2}$ levels.

Figure for Question C1.3.8—CO₂ enrichment experiments question 1 — IB Biology SL

Using the data in the graph, discuss whether rising carbon dioxide levels in the atmosphere will increase growth rates in maize.

data does not support idea that rising $\mathrm{CO}_{2}$ levels will increase growth rates in maize;
(at all temperatures) there appears to be no difference between exchange rate at current or elevated $\mathrm{CO}_{2}$ levels;
temperature has larger effect on growth of maize;
so if rising $\mathrm{CO}_{2}$ levels causes more of a greenhouse effect/larger temperature increase, this will affect growth of maize;

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C1.3.8—CO₂ enrichment experiments question 1