In an experiment two potted plants, labeled Plant 1 and Plant 2, are placed in transparent plastic bags and left in the open. Sodium hydrogen carbonate is added to the bag covering Plant 1. This compound decomposes slowly to produce carbon dioxide. Soda lime is added to the bag covering Plant 2. This compound absorbs carbon dioxide. Both plants are watered regularly with the same amount of water. After several days, starch test results indicate starch in leaf 1 but an absence of starch in leaf 2. This experimental data confirms the