Photosynthesis as an energy transfer process — practice question

An investigation was done to find out how light of different colours affects photosynthesis. Fifteen leaf discs from one plant were taken. Five sealed test-tubes were prepared, each with three leaf discs in hydrogencarbonate indicator solution. Hydrogencarbonate indicator solution changes colour at different $\text{pH}$ values. At the beginning of the investigation the indicator solution in all five test-tubes was orange-red. Four of the test-tubes were exposed to light of a particular colour. The test-tubes were exposed for the same time period. The fifth test-tube was wrapped in black paper and acted as a control. The outcomes are shown in Table 7.1. As the $\text{pH}$ rises, the indicator turns purple and as the $\text{pH}$ falls, the indicator becomes yellow.