In an experiment to investigate whether carbon dioxide is essential for photosynthesis, two potted plants were destarched in a dark area/ cupboard for 2 to 3 days. They were then tested to see if they were completely destarched. The two destarched plants were then placed in separate bell jars. They were provided with all the requirements necessary for photosynthesis to take place. However, whereas a beaker with sodium hydroxide was placed next to the plant in bell jar A and the filter funnel was packed with soda lime, a beaker of water was placed next to the plant in bell jar B and the funnel was not packed with the soda lime. Both the pots were covered with polythene bag. What is the purpose of the sodium hydroxide?