1.1. There are two types of chlorophyll in chloroplasts; chlorophyll a and chlorophyll b. Researchers created a genetically-modified (GM) vine plant with an allele that caused them to synthesise higher levels of chlorophyll b than wild-type vine plants. They investigated the effect of this new allele on the rate of photosynthesis.

The researchers grew wild-type and GM vines in both low and high light intensity. They extracted chloroplasts from mature plants of both types. Finally, they measured oxygen production by the chloroplasts at increasing light intensities.

Figure 1 shows the researchers’ results.

Figure 1

Explain why oxygen production is measured here.

1.2. Calculate the percentage increase in oxygen production in GM vines compared to wild-type vines grown at high light intensity, at an experimental light intensity of 20 mmol photons m^-2 min^-1. Give your answer to 3 significant figures. 

1.3. Explain how this increase in growth rate in GM vines could have occurred.

1.4. In a woodland, the concentrations of carbon dioxide in the air at different heights above ground change during a 24-hour period. 

Use your knowledge of photosynthesis to explain these changes. Assume that there is no air movement caused by wind throughout the 24-hour period.